ISO 1940-1 \u2014 Balance Quality Requirements for Rigid Rotors \u2014 Vibromera<\/title>\n<meta name=\"description\" content=\"Complete guide to ISO 1940-1 (ISO 21940-11): G-grade balance quality system for rigid rotors. Interactive tolerance calculator, full G0.4\u2013G4000 table, allocation to correction planes, worked examples, and field balancing procedures.\">\n<meta name=\"keywords\" content=\"ISO 1940-1, ISO 21940-11, balance quality grade, G-grade, rigid rotor balancing, permissible residual unbalance, balancing tolerance, G 6.3, G 2.5, G 1.0, rotor balancing, dynamic balancing, specific unbalance, Balanset\">\n<meta name=\"author\" content=\"Vibromera\">\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large\">\n\n\n\n\n\n\n\n<meta property=\"og:type\" content=\"article\">\n<meta property=\"og:title\" content=\"ISO 1940-1 \u2014 Balance Quality Requirements for Rigid Rotors (G-Grades)\">\n<meta property=\"og:description\" content=\"G-grade system (G 0.4\u2013G 4000), tolerance calculator, allocation to correction planes, worked examples. 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Covers tolerance calculation, allocation to correction planes, types of unbalance, verification procedures, and practical field balancing.\",\n \"author\": {\"@type\": \"Organization\", \"name\": \"Vibromera\", \"url\": \"https:\/\/vibromera.eu\/\"},\n \"publisher\": {\"@type\": \"Organization\", \"name\": \"Vibromera\", \"url\": \"https:\/\/vibromera.eu\/\", \"logo\": {\"@type\": \"ImageObject\", \"url\": \"https:\/\/vibromera.eu\/wp-content\/uploads\/vibromera-logo.png\"}},\n \"mainEntityOfPage\": \"https:\/\/vibromera.eu\/glossary\/iso-1940-1\/\",\n \"datePublished\": \"2024-03-10\",\n \"dateModified\": \"2026-02-07\",\n \"inLanguage\": \"en\",\n \"about\": [\n {\"@type\": \"Thing\", \"name\": \"ISO 1940-1\"},\n {\"@type\": \"Thing\", \"name\": \"ISO 21940-11\"},\n {\"@type\": \"Thing\", \"name\": \"Balance Quality Grade\"},\n {\"@type\": \"Thing\", \"name\": \"Rigid Rotor Balancing\"},\n {\"@type\": \"Thing\", \"name\": \"Residual Unbalance\"}\n ],\n \"isPartOf\": {\"@type\": \"WebPage\", \"url\": \"https:\/\/vibromera.eu\/glossary\/\"}\n },\n {\n \"@type\": \"FAQPage\",\n \"@id\": \"https:\/\/vibromera.eu\/glossary\/iso-1940-1\/#faq\",\n \"mainEntity\": [\n {\"@type\": \"Question\", \"name\": \"What is ISO 1940-1?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"ISO 1940-1 is an international standard that defines balance quality requirements for rigid rotors using a system of G-grades. It provides the formula U_per = (9549 x G x M) \/ n to calculate permissible residual unbalance, and a table mapping G-grades to rotor types. It has been superseded by ISO 21940-11, but the G-grade values and methodology remain identical.\"}},\n {\"@type\": \"Question\", \"name\": \"What is the difference between ISO 1940-1 and ISO 21940-11?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"ISO 21940-11:2016 supersedes ISO 1940-1:2003 as part of the comprehensive ISO 21940 series. The G-grade system, tolerance values, and application recommendations are identical. ISO 21940-11 incorporates minor editorial improvements but no technical changes.\"}},\n {\"@type\": \"Question\", \"name\": \"How do you calculate permissible residual unbalance from a G-grade?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Use the formula: U_per (g-mm) = (9549 x G x M) \/ n, where G is the grade number in mm\/s, M is rotor mass in kg, and n is maximum service speed in RPM. For example, a 50 kg rotor at 3000 RPM with G 6.3: U_per = (9549 x 6.3 x 50) \/ 3000 = 1003 g-mm.\"}},\n {\"@type\": \"Question\", \"name\": \"What is a rigid rotor?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"A rigid rotor is one whose elastic deformations under centrifugal forces are negligibly small compared to the specified unbalance tolerances across its entire operating speed range. A rotor balanced at low speed remains balanced at operating speed. Rotors above their first bending critical speed are flexible.\"}},\n {\"@type\": \"Question\", \"name\": \"What G-grade should I use for a pump, fan, or motor?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"G 6.3 for most industrial fans, pumps, and general electric motors. G 2.5 for high-speed or critical-service pumps (API 610), gas turbines, and turbo-compressors. G 1.0 for precision grinding spindles. G 16 for non-critical agricultural or crushing equipment.\"}},\n {\"@type\": \"Question\", \"name\": \"How do you allocate tolerance between two correction planes?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"For symmetric rotors: split 50\/50. For asymmetric between-bearing rotors: U_left = U_per x (b\/L), U_right = U_per x (a\/L), where a and b are distances from centre of mass to left and right bearings, L = a + b. For overhung rotors, moment-based recalculation with tighter tolerances is required.\"}},\n {\"@type\": \"Question\", \"name\": \"What types of unbalance does ISO 1940-1 define?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Three types: Static unbalance (mass axis parallel but displaced, corrected in one plane), Couple unbalance (mass axis through centre of mass but tilted, corrected in two planes), and Dynamic unbalance (general case combining both, corrected in two planes).\"}},\n {\"@type\": \"Question\", \"name\": \"Can I verify ISO 1940-1 compliance with a portable balancer?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Yes. The Balanset-1A includes a built-in ISO 1940 tolerance calculator. 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vibromera.eu<\/div>\n <p class=\"subtitle\">The foundational international standard defining the G-grade balance quality system \u2014 from G 0.4 (gyroscopes) to G 4000 (marine diesels). Now incorporated into ISO 21940-11, with identical G-grade values and methodology.<\/p>\n <\/div>\n<\/header>\n\n<nav class=\"quick-nav\">\n <div class=\"quick-nav-inner\">\n <a href=\"#calculator\">\u2699 Calculator<\/a>\n <a href=\"#g-grade-table\">\ud83d\udcca G-Grade Table<\/a>\n <a href=\"#definition\">\ud83d\udcd0 Overview<\/a>\n <a href=\"#rigid-rotor\">\ud83d\udd29 Rigid Rotor<\/a>\n <a href=\"#unbalance-types\">\u2696 Unbalance Types<\/a>\n <a href=\"#g-grades\">\ud83d\udd22 G-Grades<\/a>\n <a href=\"#tolerance-calc\">\ud83d\udccf Tolerance<\/a>\n <a href=\"#allocation\">\ud83d\udcd0 Allocation<\/a>\n <a href=\"#verification\">\ud83d\udee0 Verification<\/a>\n <a href=\"#case-studies\">\ud83d\udcdd Cases<\/a>\n <a href=\"#faq\">\u2753 FAQ<\/a>\n <\/div>\n<\/nav>\n\n<section class=\"summary-dashboard\" id=\"calculator\">\n <div class=\"container\">\n <div class=\"dashboard-grid\">\n <div class=\"calc-panel\">\n <h2 class=\"panel-title\">Permissible Residual Unbalance<\/h2>\n <p class=\"panel-subtitle\">ISO 1940-1 \/ ISO 21940-11 \u2014 enter rotor data, get U<sub>per<\/sub><\/p>\n <div class=\"calc-form\">\n <div class=\"form-group full-width\">\n <label>G-Grade (Balance Quality)<\/label>\n <select id=\"gGrade\">\n <option value=\"0.4\">G 0.4 \u2014 Gyroscopes, precision spindles<\/option>\n <option value=\"1.0\">G 1.0 \u2014 Grinding spindles, precision armatures<\/option>\n <option value=\"2.5\">G 2.5 \u2014 Turbines, turbo-compressors, high-speed motors<\/option>\n <option value=\"6.3\" selected>G 6.3 \u2014 Fans, pumps, motors, flywheels (standard)<\/option>\n <option value=\"16\">G 16 \u2014 Agricultural machinery, crushers<\/option>\n <option value=\"40\">G 40 \u2014 Car wheels, low-speed<\/option>\n <option value=\"100\">G 100 \u2014 Complete IC engines<\/option>\n <option value=\"250\">G 250 \u2014 Diesel crankshafts (high-speed)<\/option>\n <option value=\"630\">G 630 \u2014 Large 4-stroke crankshafts<\/option>\n <option value=\"1600\">G 1600 \u2014 2-stroke crankshafts<\/option>\n <option value=\"4000\">G 4000 \u2014 Marine diesel crankshafts<\/option>\n <\/select>\n <\/div>\n <div class=\"form-group\"><label>Rotor Mass <span class=\"unit\">(kg)<\/span><\/label><input type=\"number\" id=\"rotorMass\" value=\"50\" min=\"0.001\" step=\"0.1\"><\/div>\n <div class=\"form-group\"><label>Max Speed <span class=\"unit\">(RPM)<\/span><\/label><input type=\"number\" id=\"rotorRPM\" value=\"1500\" min=\"1\" step=\"1\"><\/div>\n <div class=\"form-group\"><label>Correction Planes<\/label><select id=\"rotorPlanes\"><option value=\"1\">1 plane (L\/D < 0.5)<\/option><option value=\"2\" selected>2 planes (elongated rotor)<\/option><\/select><\/div>\n <div class=\"form-group\"><label>Correction Radius <span class=\"unit\">(mm, optional)<\/span><\/label><input type=\"number\" id=\"rotorRadius\" value=\"\" min=\"0.1\" step=\"0.1\" placeholder=\"e.g. 150\"><\/div>\n <button class=\"calc-btn\" onclick=\"calcG()\">Calculate Tolerance \u2192<\/button>\n <\/div>\n <\/div>\n <div class=\"results-panel\">\n <h2 class=\"panel-title\">Results \u2014 ISO 1940-1<\/h2>\n <p class=\"panel-subtitle\">Permissible residual unbalance<\/p>\n <div id=\"resultsArea\"><div class=\"results-empty\"><span class=\"icon\">\u2696\ufe0f<\/span>Enter rotor parameters<br>to calculate tolerance<\/div><\/div>\n <\/div>\n <\/div>\n <\/div>\n<\/section>\n\n<section class=\"section-bg alt\" id=\"g-grade-table\">\n <div class=\"container\">\n <div class=\"section-header\">\n <h2>G-Grade Balance Quality Grades<\/h2>\n <p>Logarithmic scale with factor 2.5 between adjacent grades \u2014 from ultra-precision G 0.4 to marine G 4000<\/p>\n <\/div>\n <div class=\"grade-cards\">\n <div class=\"grade-card g1\"><div class=\"gc-grade\">G 1.0<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 1.0 mm\/s<\/div><div class=\"gc-desc\">Precision grinding spindles, tape recorders, small high-speed armatures<\/div><\/div>\n <div class=\"grade-card g25\"><div class=\"gc-grade\">G 2.5<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 2.5 mm\/s<\/div><div class=\"gc-desc\">Gas\/steam turbines, turbo-generators, turbo-compressors, high-speed motors<\/div><\/div>\n <div class=\"grade-card g63\"><div class=\"gc-grade\">G 6.3<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 6.3 mm\/s<\/div><div class=\"gc-desc\"><strong>Standard<\/strong> \u2014 fans, pumps, flywheels, motors, machine-tool drives<\/div><\/div>\n <div class=\"grade-card g16\"><div class=\"gc-grade\">G 16<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 16 mm\/s<\/div><div class=\"gc-desc\">Agricultural machinery, crushers, cardan shafts, drive components<\/div><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udccb Complete G-Grade Table \u2014 ISO 1940-1 \/ ISO 21940-11<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>G-Grade<\/th><th>e\u00b7\u03c9 (mm\/s)<\/th><th>Typical Rotor Types<\/th><th>Notes<\/th><\/tr><\/thead>\n <tbody>\n <tr><td class=\"mono\"><span class=\"tag ultra\">G 0.4<\/span><\/td><td class=\"mono\">0.4<\/td><td>Gyroscopes, precision spindles, optical disc drives<\/td><td>Near limit of conventional balancing<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag ultra\">G 1.0<\/span><\/td><td class=\"mono\">1.0<\/td><td>Grinding spindle drives, tape recorders, small precision armatures<\/td><td>Requires ultra-clean conditions<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag precision\">G 2.5<\/span><\/td><td class=\"mono\">2.5<\/td><td>Gas & steam turbines, turbo-generators, turbo-compressors, high-speed motors<\/td><td>Prevents premature bearing damage<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag standard\">G 6.3<\/span><\/td><td class=\"mono\">6.3<\/td><td><strong>Fans, pumps, flywheels, electric motors, machine tools, paper rolls<\/strong><\/td><td>Most common \u2014 default grade<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag general\">G 16<\/span><\/td><td class=\"mono\">16<\/td><td>Cardan shafts (special), agricultural machinery, crushers, mine fans<\/td><td>Heavy-duty, severe conditions<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag general\">G 40<\/span><\/td><td class=\"mono\">40<\/td><td>Car wheels and rims, cardan shafts (standard), slow fans<\/td><td>Tyre variation dominates<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 100<\/span><\/td><td class=\"mono\">100<\/td><td>Complete engines of cars, trucks, locomotives<\/td><td>IC engines as assemblies<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 250<\/span><\/td><td class=\"mono\">250<\/td><td>Crankshafts of high-speed diesel engines<\/td><td>Component-level<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 630<\/span><\/td><td class=\"mono\">630<\/td><td>Crankshafts of large 4-stroke engines, marine diesels on elastic mounts<\/td><td>Large low-speed reciprocating<\/td><\/tr>\n <tr><td class=\"mono\">G 1600<\/td><td class=\"mono\">1600<\/td><td>Crankshafts of large 2-stroke engines<\/td><td>Very slow, massive foundations<\/td><\/tr>\n <tr><td class=\"mono\">G 4000<\/td><td class=\"mono\">4000<\/td><td>Crankshafts of low-speed marine diesels on rigid foundations<\/td><td>Loosest requirements<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udcca Pre-Calculated Tolerances for Common Industrial Rotors<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>Rotor Type<\/th><th>Mass (kg)<\/th><th>RPM<\/th><th>G<\/th><th>U<sub>per<\/sub> (g\u00b7mm)<\/th><th>Per Plane<\/th><th>e<sub>per<\/sub> (\u00b5m)<\/th><\/tr><\/thead>\n <tbody>\n <tr><td>Small motor<\/td><td class=\"mono\">8<\/td><td class=\"mono\">2 900<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">166<\/td><td class=\"mono\">83<\/td><td class=\"mono\">20.7<\/td><\/tr>\n <tr><td>HVAC fan<\/td><td class=\"mono\">45<\/td><td class=\"mono\">1 480<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">1 835<\/td><td class=\"mono\">918<\/td><td class=\"mono\">40.8<\/td><\/tr>\n <tr><td>Pump impeller<\/td><td class=\"mono\">25<\/td><td class=\"mono\">2 950<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">510<\/td><td class=\"mono\">255<\/td><td class=\"mono\">20.4<\/td><\/tr>\n <tr><td>Turbo-compressor<\/td><td class=\"mono\">120<\/td><td class=\"mono\">8 000<\/td><td class=\"mono\">G 2.5<\/td><td class=\"mono\">358<\/td><td class=\"mono\">179<\/td><td class=\"mono\">3.0<\/td><\/tr>\n <tr><td>Paper roll<\/td><td class=\"mono\">2 000<\/td><td class=\"mono\">300<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">401 000<\/td><td class=\"mono\">200 500<\/td><td class=\"mono\">200.5<\/td><\/tr>\n <tr><td>Power-plant fan<\/td><td class=\"mono\">350<\/td><td class=\"mono\">990<\/td><td class=\"mono\">G 2.5<\/td><td class=\"mono\">8 468<\/td><td class=\"mono\">4 234<\/td><td class=\"mono\">24.2<\/td><\/tr>\n <tr><td>Grinding spindle<\/td><td class=\"mono\">2<\/td><td class=\"mono\">24 000<\/td><td class=\"mono\">G 1.0<\/td><td class=\"mono\">0.80<\/td><td class=\"mono\">0.40<\/td><td class=\"mono\">0.40<\/td><\/tr>\n <tr><td>Car wheel<\/td><td class=\"mono\">12<\/td><td class=\"mono\">800<\/td><td class=\"mono\">G 40<\/td><td class=\"mono\">5 729<\/td><td class=\"mono\">2 865<\/td><td class=\"mono\">477<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udcd0 Tolerance Allocation Methods \u2014 ISO 1940-1 Chapter 7<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>Rotor Type<\/th><th>Allocation<\/th><th>Formula<\/th><th>Notes<\/th><\/tr><\/thead>\n <tbody>\n <tr><td>Symmetric<\/td><td>Equal split<\/td><td class=\"mono\">U<sub>L<\/sub>=U<sub>R<\/sub>=U<sub>per<\/sub>\/2<\/td><td>Simplest case. Motors, some fans.<\/td><\/tr>\n <tr><td>Asymmetric between-bearing<\/td><td>Proportional<\/td><td class=\"mono\">U<sub>L<\/sub>=U<sub>per<\/sub>\u00b7(b\/L)<\/td><td>Most common method.<\/td><\/tr>\n <tr><td>Overhung (cantilever)<\/td><td>Moment-based<\/td><td>Statics eqns<\/td><td>Tighter tolerances on overhung plane.<\/td><\/tr>\n <tr><td>Narrow (planes close)<\/td><td>Separate static+couple<\/td><td>Per ISO 21940-12<\/td><td>Different vibration effects.<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <\/div>\n<\/section>\n\n<main class=\"main-content\" id=\"definition\">\n <div class=\"container\">\n <div class=\"content-layout\">\n <article class=\"article-content\">\n\n <h2>What is ISO 1940-1?<\/h2>\n <div class=\"info-box\" style=\"border-left-color:var(--navy);background:var(--beige-light);\">\n <div class=\"box-title\" style=\"font-size:16px;\">Quick Answer<\/div>\n <p style=\"font-size:15px;\"><strong>ISO 1940-1<\/strong> (<em>Mechanical vibration \u2014 Balance quality requirements of rotors in a constant (rigid) state<\/em>) defines the <a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\">G-grade balance quality system<\/a> for rigid rotors. The formula <strong>U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/strong> calculates permissible residual <a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\">unbalance<\/a>. Superseded by <strong>ISO 21940-11:2016<\/strong> with identical values. Default grade for industrial machinery: <strong>G 6.3<\/strong>.<\/p>\n <\/div>\n <p>ISO 1940-1 is the foundational document for rotor balancing worldwide. Its G-grade system is the de facto language of balancing: \"balance to G 6.3\" is understood by every specialist globally. The standard covers rigid rotors from tiny precision spindles to massive crankshafts, providing a universal framework for specifying, calculating, and verifying balance quality.<\/p>\n <p>The standard applies only to <em>rigid<\/em> rotors \u2014 those whose elastic deformations under centrifugal forces are negligible across the operating speed range. Flexible rotors (operating above the first bending critical speed) are covered by ISO 21940-12.<\/p>\n\n <h2 id=\"rigid-rotor\">The Rigid Rotor Concept<\/h2>\n <p>A rotor is classified as rigid if its mass distribution does not change significantly as speed varies from zero to maximum operating speed. The key consequence: <strong>a rotor balanced at low speed on a balancing machine remains balanced at its operating speed.<\/strong> This allows balancing at 300\u2013600 RPM on a workshop machine while meeting tolerances at 3 000+ RPM in service.<\/p>\n <p>If a rotor operates in the supercritical region (above the first bending <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\">critical speed<\/a>) or near <a href=\"https:\/\/vibromera.eu\/glossary\/resonance\/\">resonance<\/a>, deflections change the effective mass distribution, and low-speed balancing may be ineffective at high speed. Such rotors are classified as flexible.<\/p>\n <div class=\"info-box\">\n <div class=\"box-title\">What ISO 1940-1 Does NOT Cover<\/div>\n <p>Rotors with changing geometry (articulated shafts, helicopter blades). Resonance in rotor\u2013support\u2013foundation systems. Aerodynamic and hydrodynamic forces not related to mass distribution. For fans specifically, see <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> (BV\/FV categories).<\/p>\n <\/div>\n\n <h2 id=\"unbalance-types\">Types of Unbalance<\/h2>\n <p><a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\">Unbalance<\/a> = rotor's inertia axis \u2260 rotation axis. In vector form: <strong>U = m \u00d7 r<\/strong> (g\u00b7mm). ISO 1940-1 classifies three types:<\/p>\n <ul>\n <li><strong>Static unbalance:<\/strong> Inertia axis parallel to rotation axis but displaced. Single unbalanced mass equivalent. Correctable in <strong>one plane<\/strong>. Typical: pulleys, narrow gears, fan impellers (L\/D < 0.5).<\/li>\n <li><strong>Couple unbalance:<\/strong> Inertia axis through centre of mass but tilted. Net force zero, but a couple (pair) rocks the rotor. Requires <strong>two planes<\/strong>.<\/li>\n <li><strong>Dynamic unbalance:<\/strong> General case \u2014 static + couple combined. Inertia axis neither parallel nor intersecting rotation axis. Requires <strong>two planes<\/strong>. Most real rotors have dynamic unbalance.<\/li>\n <\/ul>\n\n <h3>Specific Unbalance (Eccentricity)<\/h3>\n <div class=\"formula-box\">\n <div class=\"formula-label\">Specific Unbalance<\/div>\n <div class=\"formula-main\">e = U \/ M<\/div>\n <div class=\"formula-note\">e in \u00b5m (g\u00b7mm\/kg) | U = unbalance (g\u00b7mm) | M = rotor mass (kg) \u2014 displacement of centre of mass from rotation axis<\/div>\n <\/div>\n <p>The G-grade is defined as the product <strong>e \u00d7 \u03c9<\/strong> (mm\/s) \u2014 the linear velocity of the rotor's centre of mass orbiting the rotation axis. This single number characterises balance quality independently of rotor size and speed.<\/p>\n\n <h2 id=\"g-grades\">The G-Grade System \u2014 Physical Basis<\/h2>\n <h3>Mass Similarity<\/h3>\n <p>For geometrically similar rotors: U<sub>per<\/sub> \u221d M \u2192 specific unbalance e<sub>per<\/sub> should be constant. One standard applies across all sizes.<\/p>\n <h3>Speed Similarity<\/h3>\n <p>Centrifugal force F = M\u00b7e\u00b7\u03c9\u00b2. To maintain acceptable bearing loads at different speeds, e<sub>per<\/sub> must decrease as \u03c9 increases:<\/p>\n <div class=\"formula-box\">\n <div class=\"formula-label\">G-Grade Definition<\/div>\n <div class=\"formula-main\">G = e<sub>per<\/sub> \u00d7 \u03c9 = constant (mm\/s)<\/div>\n <div class=\"formula-note\">G 6.3 = centre of mass orbits at \u2264 6.3 mm\/s | Adjacent grades differ by factor 2.5<\/div>\n <\/div>\n\n <h2 id=\"tolerance-calc\">Calculating Permissible Residual Unbalance<\/h2>\n <div class=\"formula-box\">\n <div class=\"formula-label\">ISO 1940-1 \/ ISO 21940-11 Tolerance Formula<\/div>\n <div class=\"formula-main\">U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/div>\n <div class=\"formula-note\">U<sub>per<\/sub> in g\u00b7mm | G = grade (mm\/s) | M = rotor mass (kg) | n = max service RPM | 9 549 = 60 000\/(2\u03c0)<\/div>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Worked Example: Fan Rotor, G 6.3<\/div>\n <p><strong>Given:<\/strong> Centrifugal fan impeller, M = 200 kg, n = 1 500 RPM, G 6.3.<\/p>\n <p><strong>Total:<\/strong> U<sub>per<\/sub> = 9 549 \u00d7 6.3 \u00d7 200 \/ 1 500 = <strong>8 021 g\u00b7mm<\/strong><\/p>\n <p><strong>Eccentricity:<\/strong> e<sub>per<\/sub> = 8 021 \/ 200 = <strong>40.1 \u00b5m<\/strong><\/p>\n <p><strong>Per plane (symmetric, 2):<\/strong> 8 021 \/ 2 = <strong>4 011 g\u00b7mm<\/strong><\/p>\n <p><strong>At R = 400 mm:<\/strong> 4 011 \/ 400 = <strong>10.0 g per plane<\/strong><\/p>\n <\/div>\n\n <div class=\"info-box warning\">\n <div class=\"box-title\">Always Use Maximum Service Speed<\/div>\n <p>The speed in the formula must be the highest RPM in service \u2014 not balancing machine speed. Many rotors are balanced at 300\u2013600 RPM but tolerance must use actual service speed (e.g. 1 480 RPM). Using balancing machine speed produces dangerously loose tolerances.<\/p>\n <\/div>\n\n <h2 id=\"allocation\">Allocation to Correction Planes<\/h2>\n <p>U<sub>per<\/sub> applies to the rotor's centre of mass. In practice, balance in two planes (near bearings). Chapter 7 rules:<\/p>\n <h3>Symmetric Rotors<\/h3>\n <p>CoM at midpoint \u2192 equal: U<sub>L<\/sub> = U<sub>R<\/sub> = U<sub>per<\/sub> \/ 2.<\/p>\n <h3>Asymmetric Between-Bearing<\/h3>\n <div class=\"formula-box\">\n <div class=\"formula-label\">Asymmetric Allocation<\/div>\n <div class=\"formula-main\">U<sub>left<\/sub> = U<sub>per<\/sub> \u00d7 (b \/ L) | U<sub>right<\/sub> = U<sub>per<\/sub> \u00d7 (a \/ L)<\/div>\n <div class=\"formula-note\">a = CoM to left bearing | b = CoM to right bearing | L = a + b<\/div>\n <\/div>\n <h3>Overhung Rotors<\/h3>\n <p>Overhung mass creates bending moment loading both bearings. Moment-based recalculation needed \u2192 typically much tighter tolerance on overhung plane. Common for pumps, single-stage compressors, cantilevered fan impellers.<\/p>\n\n <h2 id=\"verification\">Errors and Verification<\/h2>\n <h3>Error Sources<\/h3>\n <ul>\n <li><strong>Systematic:<\/strong> Machine calibration drift, eccentric mandrels, keyway effects (ISO 8821), thermal distortion.<\/li>\n <li><strong>Random:<\/strong> Sensor noise, support play, rotor seating variation.<\/li>\n <\/ul>\n <p>Total error must not exceed 10\u201315% of tolerance. If larger, tighten working tolerance accordingly.<\/p>\n <h3>Assembly Effects<\/h3>\n <p>Component balancing \u2260 assembly balance. Coupling eccentricity, radial runout, loose fits can negate component work. Trim balance the assembled rotor.<\/p>\n <h3>Verification Methods<\/h3>\n <ul>\n <li><strong>Index test:<\/strong> Rotate rotor 180\u00b0 on mandrel, remeasure. Change = fixture error.<\/li>\n <li><strong>Trial weight test:<\/strong> Add known mass, verify measured vector change matches expectation.<\/li>\n <li><strong>Field check:<\/strong> Measure vibration on bearings per <a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\">ISO 10816<\/a>.<\/li>\n <\/ul>\n\n <div class=\"info-box success\">\n <div class=\"box-title\">Balanset-1A: Built-In ISO 1940-1 Compliance<\/div>\n <p>The <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> automates ISO 1940-1: enter mass, speed, G-grade \u2192 instant U<sub>per<\/sub> with automatic plane allocation. After balancing, compares residual vs. limit. The F6 Reports function generates a formal protocol documenting the achieved G-grade. Accuracy \u00b15% velocity, \u00b11\u00b0 phase \u2014 sufficient for G 16 through G 2.5. The <a href=\"https:\/\/vibromera.eu\/product\/balanset-4\/\">Balanset-4<\/a> extends to four channels for complex multi-bearing rotors.<\/p>\n <\/div>\n\n <h2 id=\"case-studies\">Worked Examples<\/h2>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 1: Electric Motor \u2014 G 6.3<\/div>\n <p><strong>Rotor:<\/strong> 15 kW, 1 460 RPM, 35 kg, between-bearing symmetric.<\/p>\n <p><strong>Tolerance:<\/strong> U<sub>per<\/sub> = 9 549 \u00d7 6.3 \u00d7 35 \/ 1 460 = <strong>1 442 g\u00b7mm<\/strong> \u2192 721\/plane.<\/p>\n <p><strong>At R = 80 mm:<\/strong> 721 \/ 80 = <strong>9.0 g\/plane<\/strong>. Shop balanced: 180 g\u00b7mm residual. \u2705<\/p>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 2: Pump \u2014 Overhung Impeller, G 6.3<\/div>\n <p><strong>Rotor:<\/strong> Shaft + impeller 18 kg, 2 950 RPM. Impeller 6 kg overhung 120 mm. Bearing span 250 mm.<\/p>\n <p><strong>Total:<\/strong> U<sub>per<\/sub> = <strong>367 g\u00b7mm<\/strong>. Moment allocation: front \u2248 202, rear \u2248 165 g\u00b7mm.<\/p>\n <p><strong>Field balanced<\/strong> with <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> single-plane: 8.5 g at 230\u00b0. Final: 95 g\u00b7mm. \u2705<\/p>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 3: Turbo-Compressor \u2014 G 2.5<\/div>\n <p><strong>Rotor:<\/strong> 3-stage, 65 kg, 12 000 RPM. Slightly asymmetric.<\/p>\n <p><strong>Tolerance:<\/strong> U<sub>per<\/sub> = <strong>129 g\u00b7mm<\/strong> \u2192 65\/plane \u2192 at R = 95 mm: <strong>0.68 g\/plane<\/strong>.<\/p>\n <p>Sub-gram precision \u2192 shop high-speed machine only. Index test: mandrel error < 5 g\u00b7mm. Final: 28 g\u00b7mm\/plane. \u2705<\/p>\n <\/div>\n\n <h2 id=\"iso21940\">ISO 1940-1 \u2192 ISO 21940-11<\/h2>\n <ul>\n <li>G-grade values, formulas, application tables \u2014 <strong>identical<\/strong>. No technical changes.<\/li>\n <li>ISO 21940 series: Part 11 (quality), Part 12 (flexible), Part 14 (procedures), Part 21 (descriptions), Part 31 (susceptibility), Part 32 (keys).<\/li>\n <li>Both designations used interchangeably in practice.<\/li>\n <li><a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> BV categories reference G-grades directly.<\/li>\n <\/ul>\n\n <h2 id=\"related-standards\">Related Standards<\/h2>\n <ul>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\">ISO 21940-11<\/a>:<\/strong> This standard \u2014 G-grade system.<\/li>\n <li><strong>ISO 21940-12:<\/strong> Flexible rotor balancing.<\/li>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\">ISO 10816 \/ ISO 20816<\/a>:<\/strong> Vibration evaluation \u2014 operational result of balance quality.<\/li>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a>:<\/strong> Fan-specific BV\/FV categories \u2192 G-grades.<\/li>\n <li><strong>ISO 8821:<\/strong> Keyway influence (half-key convention).<\/li>\n <li><strong>API 610 \/ API 617:<\/strong> Petroleum pumps\/compressors referencing ISO 1940.<\/li>\n <\/ul>\n\n <hr style=\"margin:48px 0 24px;border:none;border-top:1px solid var(--border-light);\">\n <p><strong>Official standard:<\/strong> <a href=\"https:\/\/www.iso.org\/standard\/27092.html\" rel=\"nofollow noopener\" target=\"_blank\">ISO 1940-1 on ISO Store \u2192<\/a><\/p>\n <p><a href=\"https:\/\/vibromera.eu\/glossary\/\">\u2190 Back to Glossary Index<\/a><\/p>\n <\/article>\n\n <aside class=\"toc-sidebar\">\n <div class=\"toc-box\">\n <h3>On This Page<\/h3>\n <a href=\"#calculator\">Tolerance Calculator<\/a>\n <a href=\"#g-grade-table\">G-Grade Table<\/a>\n <a href=\"#definition\">What is ISO 1940-1?<\/a>\n <a href=\"#rigid-rotor\">Rigid Rotor Concept<\/a>\n <a href=\"#unbalance-types\">Types of Unbalance<\/a>\n <a class=\"sub\" href=\"#unbalance-types\">Static \/ Couple \/ Dynamic<\/a>\n <a class=\"sub\" href=\"#unbalance-types\">Specific unbalance<\/a>\n <a href=\"#g-grades\">G-Grade System<\/a>\n <a class=\"sub\" href=\"#g-grades\">Similarity laws<\/a>\n <a href=\"#tolerance-calc\">Tolerance Formula<\/a>\n <a href=\"#allocation\">Plane Allocation<\/a>\n <a class=\"sub\" href=\"#allocation\">Symmetric \/ Asymmetric<\/a>\n <a class=\"sub\" href=\"#allocation\">Overhung rotors<\/a>\n <a href=\"#verification\">Errors & Verification<\/a>\n <a href=\"#case-studies\">Case Studies (3)<\/a>\n <a href=\"#iso21940\">ISO 21940-11 Transition<\/a>\n <a href=\"#faq\">FAQ (8 Questions)<\/a>\n <\/div>\n <div class=\"toc-box\" style=\"margin-top:24px;background:var(--navy);border-color:var(--navy);\">\n <h3 style=\"color:#fff;\">Balancing Equipment<\/h3>\n <p style=\"color:rgba(255,255,255,.6);font-size:13px;margin-bottom:12px;\">Portable field balancing with built-in ISO 1940 tolerance calculator and G-grade verification.<\/p>\n <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\" style=\"display:block;padding:8px 14px;background:var(--blue);color:white;border-radius:6px;text-align:center;font-weight:600;font-size:14px;text-decoration:none;margin-bottom:8px;border-left:none;\">Balanset-1A \u2192<\/a>\n <a href=\"https:\/\/vibromera.eu\/product\/balanset-4\/\" style=\"display:block;padding:8px 14px;background:rgba(255,255,255,.1);color:white;border-radius:6px;text-align:center;font-weight:600;font-size:14px;text-decoration:none;border:1px solid rgba(255,255,255,.2);border-left:none;\">Balanset-4 \u2192<\/a>\n <\/div>\n <\/aside>\n <\/div>\n <\/div>\n<\/main>\n\n<section class=\"section-bg alt\" id=\"faq\">\n <div class=\"container\" style=\"max-width:1000px;\">\n <div class=\"section-header\"><h2>Frequently Asked Questions \u2014 ISO 1940-1<\/h2><p>G-grade balance quality system for rigid rotors<\/p><\/div>\n <div style=\"display:flex;flex-direction:column;gap:16px;\">\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What is the difference between ISO 1940-1 and ISO 21940-11?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">ISO 21940-11:2016 supersedes ISO 1940-1:2003. The G-grade system, tolerance values, and application tables are <strong>identical<\/strong>. ISO 21940-11 includes minor editorial improvements but no technical changes. Both designations are used interchangeably.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> How do I calculate permissible residual unbalance?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/strong> \u2014 G = grade (mm\/s), M = mass (kg), n = max RPM. Example: 50 kg at 3 000 RPM, G 6.3 \u2192 9 549 \u00d7 6.3 \u00d7 50 \/ 3 000 = <strong>1 003 g\u00b7mm<\/strong>. Divide by planes for per-plane value.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What is a rigid rotor?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">A rotor whose elastic deformations under centrifugal forces are negligibly small across its operating speed range. Balanced at low speed \u2192 stays balanced at operating speed. Rotors above first bending <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\">critical speed<\/a> are flexible and require ISO 21940-12.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What G-grade for pumps, fans, or motors?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>G 6.3<\/strong> \u2014 most fans, pumps, general motors. <strong>G 2.5<\/strong> \u2014 turbines, turbo-compressors, critical pumps (API 610). <strong>G 1.0<\/strong> \u2014 grinding spindles. <strong>G 16<\/strong> \u2014 agricultural\/crushers. For fans: <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> BV categories map to G-grades.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> How to allocate tolerance between planes?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Symmetric: 50\/50. Asymmetric: proportional to bearing reactions \u2014 U<sub>left<\/sub> = U<sub>per<\/sub>\u00d7(b\/L). Overhung: moment-based with tighter overhung-plane tolerance. The <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> handles allocation automatically.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What are the three types of unbalance?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>Static<\/strong> \u2014 displaced but parallel, one-plane fix. <strong>Couple<\/strong> \u2014 tilted through CoM, two-plane fix. <strong>Dynamic<\/strong> \u2014 general (static+couple), two-plane fix. Most real rotors: dynamic unbalance.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> Why are G-grades on a logarithmic scale?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Factor 2.5 between grades covers the full range from gyroscopes (G 0.4) to marine diesels (G 4000). Logarithmic scaling is appropriate because perceived vibration severity and bearing life follow logarithmic relationships. Each step \u2248 same relative change in quality.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> Can I verify compliance with a portable balancer?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Yes. <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a>: built-in ISO 1940 calculator, automatic plane allocation, real-time comparison of residual vs. limit, formal balance report. \u00b15% accuracy sufficient for G 16\u2013G 2.5. For G 1.0, careful preparation needed.<\/div><\/details>\n <\/div>\n <\/div>\n<\/section>\n\n<section style=\"padding:32px 0;background:var(--white);border-top:1px solid var(--border-light);\">\n <div class=\"container\" style=\"max-width:1000px;\">\n <h3 style=\"font-family:'DM Serif Display',serif;font-size:22px;color:var(--navy);margin-bottom:20px;\">Related Glossary Articles<\/h3>\n <div style=\"display:grid;grid-template-columns:repeat(3,1fr);gap:16px;\">\n <a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Balance Quality Grade<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Interactive G-grade calculator with full tolerance tables<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">ISO 14694<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Fan-specific BV\/FV categories mapping to G-grades<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">ISO 10816-1<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Vibration evaluation \u2014 measuring balance quality in service<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Unbalance<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Types, measurement, and correction of mass unbalance<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Natural Frequency<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Critical speeds and the rigid\/flexible rotor boundary<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/rotor-balancing\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Rotor Balancing<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Single-plane and two-plane balancing procedures<\/div><\/a>\n <\/div>\n <\/div>\n<\/section>\n\n<section class=\"shop-cta\">\n <div class=\"container\">\n <h2>Balance to ISO 1940-1 \u2014 In the Field<\/h2>\n <p>Vibromera portable balancers include built-in ISO 1940 tolerance calculators, automatic plane allocation, and formal balance reports documenting the achieved G-grade.<\/p>\n <a href=\"https:\/\/vibromera.eu\/shop\/\" class=\"cta-btn\">Browse Balancing Equipment \u2192<\/a>\n <\/div>\n<\/section>\n\n<footer class=\"page-footer\">\n <div class=\"container\"><p><a href=\"https:\/\/vibromera.eu\/glossary\/\">\u2190 Back to Glossary<\/a> | <a href=\"https:\/\/vibromera.eu\/\">vibromera.eu<\/a><\/p><\/div>\n<\/footer>\n\n<script>\nfunction calcG(){\n const G=parseFloat(document.getElementById('gGrade').value);\n const M=parseFloat(document.getElementById('rotorMass').value);\n const n=parseFloat(document.getElementById('rotorRPM').value);\n const p=parseInt(document.getElementById('rotorPlanes').value);\n const R=parseFloat(document.getElementById('rotorRadius').value)||0;\n if(!M||!n||M<=0||n<=0)return;\n const e=(9549*G)\/n,U=e*M,Up=U\/p,w=2*Math.PI*n\/60,F=(U\/1e6)*w*w;\n const cw=R>0?Up\/R:0;\n const f=v=>v>=1000?Math.round(v).toLocaleString('en'):v>=100?v.toFixed(0):v>=1?v.toFixed(1):v>=0.01?v.toFixed(3):v.toExponential(2);\n document.getElementById('resultsArea').innerHTML=\n '<div class=\"result-primary\"><div class=\"res-label\">Permissible Residual Unbalance (G '+G+')<\/div><div class=\"res-value\">'+f(U)+'<\/div><div class=\"res-unit\">g\u00b7mm \u2014 ISO 1940-1 \/ ISO 21940-11<\/div><\/div>'+\n '<div class=\"results-secondary\">'+\n '<div class=\"res-card\"><div class=\"rc-label\">Specific Eccentricity<\/div><div class=\"rc-value\">'+(e>=10?e.toFixed(1):e>=0.1?e.toFixed(2):e.toFixed(3))+'<\/div><div class=\"rc-unit\">\u00b5m (e<sub>per<\/sub>)<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">Centrifugal Force<\/div><div class=\"rc-value\">'+(F>=10?F.toFixed(1):F>=0.1?F.toFixed(2):F.toFixed(3))+'<\/div><div class=\"rc-unit\">N at '+n+' RPM<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">G-Grade<\/div><div class=\"rc-value\" style=\"font-size:18px\">G '+G+'<\/div><div class=\"rc-unit\">e\u00b7\u03c9 = '+G+' mm\/s<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">Rotor<\/div><div class=\"rc-value\" style=\"font-size:14px;font-family:Source Sans 3,sans-serif\">'+M+' kg @ '+n+' RPM<\/div><div class=\"rc-unit\">'+p+' plane'+(p>1?'s':'')+'<\/div><\/div>'+\n '<\/div>'+\n '<div class=\"plane-note\"><div class=\"pn-label\">Per Plane ('+(p===1?'single plane':'each of '+p+' planes')+')<\/div><div class=\"pn-value\">'+f(Up)+'<\/div><div class=\"pn-unit\">g\u00b7mm'+(cw>0?' = '+f(cw)+' g at R = '+R+' mm':'')+'<\/div><\/div>';\n}\n['gGrade','rotorMass','rotorRPM','rotorPlanes','rotorRadius'].forEach(function(id){\n var el=document.getElementById(id);\n el.addEventListener(el.tagName==='SELECT'?'change':'input',calcG);\n});\ncalcG();\n<\/script>\n<\/body>\n<\/html><\/div><\/div><\/div><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>An overview of ISO 1940-1 (now part of ISO 21940), the key international standard that defines balance quality requirements and tolerance calculations for rigid rotors using G-Grades.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[109,112],"tags":[],"class_list":["post-9","glossary","type-glossary","status-publish","hentry","category-glossary","category-iso-standards"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary"}],"about":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/types\/glossary"}],"version-history":[{"count":7,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9\/revisions"}],"predecessor-version":[{"id":101534,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9\/revisions\/101534"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/media?parent=9"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/categories?post=9"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/tags?post=9"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

\n\n\n\n\nISO 1940-1 \u2014 Balance Quality Requirements for Rigid Rotors \u2014 Vibromera<\/title>\n<meta name=\"description\" content=\"Complete guide to ISO 1940-1 (ISO 21940-11): G-grade balance quality system for rigid rotors. Interactive tolerance calculator, full G0.4\u2013G4000 table, allocation to correction planes, worked examples, and field balancing procedures.\">\n<meta name=\"keywords\" content=\"ISO 1940-1, ISO 21940-11, balance quality grade, G-grade, rigid rotor balancing, permissible residual unbalance, balancing tolerance, G 6.3, G 2.5, G 1.0, rotor balancing, dynamic balancing, specific unbalance, Balanset\">\n<meta name=\"author\" content=\"Vibromera\">\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large\">\n\n\n\n\n\n\n\n<meta property=\"og:type\" content=\"article\">\n<meta property=\"og:title\" content=\"ISO 1940-1 \u2014 Balance Quality Requirements for Rigid Rotors (G-Grades)\">\n<meta property=\"og:description\" content=\"G-grade system (G 0.4\u2013G 4000), tolerance calculator, allocation to correction planes, worked examples. 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Covers tolerance calculation, allocation to correction planes, types of unbalance, verification procedures, and practical field balancing.\",\n \"author\": {\"@type\": \"Organization\", \"name\": \"Vibromera\", \"url\": \"https:\/\/vibromera.eu\/\"},\n \"publisher\": {\"@type\": \"Organization\", \"name\": \"Vibromera\", \"url\": \"https:\/\/vibromera.eu\/\", \"logo\": {\"@type\": \"ImageObject\", \"url\": \"https:\/\/vibromera.eu\/wp-content\/uploads\/vibromera-logo.png\"}},\n \"mainEntityOfPage\": \"https:\/\/vibromera.eu\/glossary\/iso-1940-1\/\",\n \"datePublished\": \"2024-03-10\",\n \"dateModified\": \"2026-02-07\",\n \"inLanguage\": \"en\",\n \"about\": [\n {\"@type\": \"Thing\", \"name\": \"ISO 1940-1\"},\n {\"@type\": \"Thing\", \"name\": \"ISO 21940-11\"},\n {\"@type\": \"Thing\", \"name\": \"Balance Quality Grade\"},\n {\"@type\": \"Thing\", \"name\": \"Rigid Rotor Balancing\"},\n {\"@type\": \"Thing\", \"name\": \"Residual Unbalance\"}\n ],\n \"isPartOf\": {\"@type\": \"WebPage\", \"url\": \"https:\/\/vibromera.eu\/glossary\/\"}\n },\n {\n \"@type\": \"FAQPage\",\n \"@id\": \"https:\/\/vibromera.eu\/glossary\/iso-1940-1\/#faq\",\n \"mainEntity\": [\n {\"@type\": \"Question\", \"name\": \"What is ISO 1940-1?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"ISO 1940-1 is an international standard that defines balance quality requirements for rigid rotors using a system of G-grades. It provides the formula U_per = (9549 x G x M) \/ n to calculate permissible residual unbalance, and a table mapping G-grades to rotor types. It has been superseded by ISO 21940-11, but the G-grade values and methodology remain identical.\"}},\n {\"@type\": \"Question\", \"name\": \"What is the difference between ISO 1940-1 and ISO 21940-11?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"ISO 21940-11:2016 supersedes ISO 1940-1:2003 as part of the comprehensive ISO 21940 series. The G-grade system, tolerance values, and application recommendations are identical. ISO 21940-11 incorporates minor editorial improvements but no technical changes.\"}},\n {\"@type\": \"Question\", \"name\": \"How do you calculate permissible residual unbalance from a G-grade?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Use the formula: U_per (g-mm) = (9549 x G x M) \/ n, where G is the grade number in mm\/s, M is rotor mass in kg, and n is maximum service speed in RPM. For example, a 50 kg rotor at 3000 RPM with G 6.3: U_per = (9549 x 6.3 x 50) \/ 3000 = 1003 g-mm.\"}},\n {\"@type\": \"Question\", \"name\": \"What is a rigid rotor?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"A rigid rotor is one whose elastic deformations under centrifugal forces are negligibly small compared to the specified unbalance tolerances across its entire operating speed range. A rotor balanced at low speed remains balanced at operating speed. Rotors above their first bending critical speed are flexible.\"}},\n {\"@type\": \"Question\", \"name\": \"What G-grade should I use for a pump, fan, or motor?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"G 6.3 for most industrial fans, pumps, and general electric motors. G 2.5 for high-speed or critical-service pumps (API 610), gas turbines, and turbo-compressors. G 1.0 for precision grinding spindles. G 16 for non-critical agricultural or crushing equipment.\"}},\n {\"@type\": \"Question\", \"name\": \"How do you allocate tolerance between two correction planes?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"For symmetric rotors: split 50\/50. For asymmetric between-bearing rotors: U_left = U_per x (b\/L), U_right = U_per x (a\/L), where a and b are distances from centre of mass to left and right bearings, L = a + b. For overhung rotors, moment-based recalculation with tighter tolerances is required.\"}},\n {\"@type\": \"Question\", \"name\": \"What types of unbalance does ISO 1940-1 define?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Three types: Static unbalance (mass axis parallel but displaced, corrected in one plane), Couple unbalance (mass axis through centre of mass but tilted, corrected in two planes), and Dynamic unbalance (general case combining both, corrected in two planes).\"}},\n {\"@type\": \"Question\", \"name\": \"Can I verify ISO 1940-1 compliance with a portable balancer?\", \"acceptedAnswer\": {\"@type\": \"Answer\", \"text\": \"Yes. The Balanset-1A includes a built-in ISO 1940 tolerance calculator. 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.res-value{font-size:28px}.grade-cards{grid-template-columns:1fr 1fr}table{font-size:13px}table th,table td{padding:8px 10px}.calc-panel,.results-panel{padding:20px}.formula-box{padding:18px 20px}.formula-box .formula-main{font-size:16px}.example-block{padding:20px}.info-box{padding:16px 18px}.shop-cta h2{font-size:24px}}\n@media(max-width:480px){.hero h1{font-size:24px}.grade-cards{grid-template-columns:1fr}.quick-nav a{padding:12px 12px;font-size:13px}}\n@media print{.quick-nav,.shop-cta,.toc-sidebar{display:none}}\n<\/style>\n<\/head>\n<body>\n\n<header class=\"hero\">\n <div class=\"hero-inner\">\n <div class=\"breadcrumb\"><a href=\"https:\/\/vibromera.eu\/\">Home<\/a> \u2192 <a href=\"https:\/\/vibromera.eu\/glossary\/\">Glossary<\/a> \u2192 ISO 1940-1<\/div>\n <h1>ISO 1940-1 \u2014 <span>Balance Quality Requirements<\/span> for Rigid Rotors<\/h1>\n <div class=\"canon-badge\"><span style=\"font-size:14px;\">\ud83d\udccc<\/span> Canonical Reference Article \u2014 vibromera.eu<\/div>\n <p class=\"subtitle\">The foundational international standard defining the G-grade balance quality system \u2014 from G 0.4 (gyroscopes) to G 4000 (marine diesels). Now incorporated into ISO 21940-11, with identical G-grade values and methodology.<\/p>\n <\/div>\n<\/header>\n\n<nav class=\"quick-nav\">\n <div class=\"quick-nav-inner\">\n <a href=\"#calculator\">\u2699 Calculator<\/a>\n <a href=\"#g-grade-table\">\ud83d\udcca G-Grade Table<\/a>\n <a href=\"#definition\">\ud83d\udcd0 Overview<\/a>\n <a href=\"#rigid-rotor\">\ud83d\udd29 Rigid Rotor<\/a>\n <a href=\"#unbalance-types\">\u2696 Unbalance Types<\/a>\n <a href=\"#g-grades\">\ud83d\udd22 G-Grades<\/a>\n <a href=\"#tolerance-calc\">\ud83d\udccf Tolerance<\/a>\n <a href=\"#allocation\">\ud83d\udcd0 Allocation<\/a>\n <a href=\"#verification\">\ud83d\udee0 Verification<\/a>\n <a href=\"#case-studies\">\ud83d\udcdd Cases<\/a>\n <a href=\"#faq\">\u2753 FAQ<\/a>\n <\/div>\n<\/nav>\n\n<section class=\"summary-dashboard\" id=\"calculator\">\n <div class=\"container\">\n <div class=\"dashboard-grid\">\n <div class=\"calc-panel\">\n <h2 class=\"panel-title\">Permissible Residual Unbalance<\/h2>\n <p class=\"panel-subtitle\">ISO 1940-1 \/ ISO 21940-11 \u2014 enter rotor data, get U<sub>per<\/sub><\/p>\n <div class=\"calc-form\">\n <div class=\"form-group full-width\">\n <label>G-Grade (Balance Quality)<\/label>\n <select id=\"gGrade\">\n <option value=\"0.4\">G 0.4 \u2014 Gyroscopes, precision spindles<\/option>\n <option value=\"1.0\">G 1.0 \u2014 Grinding spindles, precision armatures<\/option>\n <option value=\"2.5\">G 2.5 \u2014 Turbines, turbo-compressors, high-speed motors<\/option>\n <option value=\"6.3\" selected>G 6.3 \u2014 Fans, pumps, motors, flywheels (standard)<\/option>\n <option value=\"16\">G 16 \u2014 Agricultural machinery, crushers<\/option>\n <option value=\"40\">G 40 \u2014 Car wheels, low-speed<\/option>\n <option value=\"100\">G 100 \u2014 Complete IC engines<\/option>\n <option value=\"250\">G 250 \u2014 Diesel crankshafts (high-speed)<\/option>\n <option value=\"630\">G 630 \u2014 Large 4-stroke crankshafts<\/option>\n <option value=\"1600\">G 1600 \u2014 2-stroke crankshafts<\/option>\n <option value=\"4000\">G 4000 \u2014 Marine diesel crankshafts<\/option>\n <\/select>\n <\/div>\n <div class=\"form-group\"><label>Rotor Mass <span class=\"unit\">(kg)<\/span><\/label><input type=\"number\" id=\"rotorMass\" value=\"50\" min=\"0.001\" step=\"0.1\"><\/div>\n <div class=\"form-group\"><label>Max Speed <span class=\"unit\">(RPM)<\/span><\/label><input type=\"number\" id=\"rotorRPM\" value=\"1500\" min=\"1\" step=\"1\"><\/div>\n <div class=\"form-group\"><label>Correction Planes<\/label><select id=\"rotorPlanes\"><option value=\"1\">1 plane (L\/D < 0.5)<\/option><option value=\"2\" selected>2 planes (elongated rotor)<\/option><\/select><\/div>\n <div class=\"form-group\"><label>Correction Radius <span class=\"unit\">(mm, optional)<\/span><\/label><input type=\"number\" id=\"rotorRadius\" value=\"\" min=\"0.1\" step=\"0.1\" placeholder=\"e.g. 150\"><\/div>\n <button class=\"calc-btn\" onclick=\"calcG()\">Calculate Tolerance \u2192<\/button>\n <\/div>\n <\/div>\n <div class=\"results-panel\">\n <h2 class=\"panel-title\">Results \u2014 ISO 1940-1<\/h2>\n <p class=\"panel-subtitle\">Permissible residual unbalance<\/p>\n <div id=\"resultsArea\"><div class=\"results-empty\"><span class=\"icon\">\u2696\ufe0f<\/span>Enter rotor parameters<br>to calculate tolerance<\/div><\/div>\n <\/div>\n <\/div>\n <\/div>\n<\/section>\n\n<section class=\"section-bg alt\" id=\"g-grade-table\">\n <div class=\"container\">\n <div class=\"section-header\">\n <h2>G-Grade Balance Quality Grades<\/h2>\n <p>Logarithmic scale with factor 2.5 between adjacent grades \u2014 from ultra-precision G 0.4 to marine G 4000<\/p>\n <\/div>\n <div class=\"grade-cards\">\n <div class=\"grade-card g1\"><div class=\"gc-grade\">G 1.0<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 1.0 mm\/s<\/div><div class=\"gc-desc\">Precision grinding spindles, tape recorders, small high-speed armatures<\/div><\/div>\n <div class=\"grade-card g25\"><div class=\"gc-grade\">G 2.5<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 2.5 mm\/s<\/div><div class=\"gc-desc\">Gas\/steam turbines, turbo-generators, turbo-compressors, high-speed motors<\/div><\/div>\n <div class=\"grade-card g63\"><div class=\"gc-grade\">G 6.3<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 6.3 mm\/s<\/div><div class=\"gc-desc\"><strong>Standard<\/strong> \u2014 fans, pumps, flywheels, motors, machine-tool drives<\/div><\/div>\n <div class=\"grade-card g16\"><div class=\"gc-grade\">G 16<\/div><div class=\"gc-vel\">e\u00b7\u03c9 = 16 mm\/s<\/div><div class=\"gc-desc\">Agricultural machinery, crushers, cardan shafts, drive components<\/div><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udccb Complete G-Grade Table \u2014 ISO 1940-1 \/ ISO 21940-11<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>G-Grade<\/th><th>e\u00b7\u03c9 (mm\/s)<\/th><th>Typical Rotor Types<\/th><th>Notes<\/th><\/tr><\/thead>\n <tbody>\n <tr><td class=\"mono\"><span class=\"tag ultra\">G 0.4<\/span><\/td><td class=\"mono\">0.4<\/td><td>Gyroscopes, precision spindles, optical disc drives<\/td><td>Near limit of conventional balancing<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag ultra\">G 1.0<\/span><\/td><td class=\"mono\">1.0<\/td><td>Grinding spindle drives, tape recorders, small precision armatures<\/td><td>Requires ultra-clean conditions<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag precision\">G 2.5<\/span><\/td><td class=\"mono\">2.5<\/td><td>Gas & steam turbines, turbo-generators, turbo-compressors, high-speed motors<\/td><td>Prevents premature bearing damage<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag standard\">G 6.3<\/span><\/td><td class=\"mono\">6.3<\/td><td><strong>Fans, pumps, flywheels, electric motors, machine tools, paper rolls<\/strong><\/td><td>Most common \u2014 default grade<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag general\">G 16<\/span><\/td><td class=\"mono\">16<\/td><td>Cardan shafts (special), agricultural machinery, crushers, mine fans<\/td><td>Heavy-duty, severe conditions<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag general\">G 40<\/span><\/td><td class=\"mono\">40<\/td><td>Car wheels and rims, cardan shafts (standard), slow fans<\/td><td>Tyre variation dominates<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 100<\/span><\/td><td class=\"mono\">100<\/td><td>Complete engines of cars, trucks, locomotives<\/td><td>IC engines as assemblies<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 250<\/span><\/td><td class=\"mono\">250<\/td><td>Crankshafts of high-speed diesel engines<\/td><td>Component-level<\/td><\/tr>\n <tr><td class=\"mono\"><span class=\"tag coarse\">G 630<\/span><\/td><td class=\"mono\">630<\/td><td>Crankshafts of large 4-stroke engines, marine diesels on elastic mounts<\/td><td>Large low-speed reciprocating<\/td><\/tr>\n <tr><td class=\"mono\">G 1600<\/td><td class=\"mono\">1600<\/td><td>Crankshafts of large 2-stroke engines<\/td><td>Very slow, massive foundations<\/td><\/tr>\n <tr><td class=\"mono\">G 4000<\/td><td class=\"mono\">4000<\/td><td>Crankshafts of low-speed marine diesels on rigid foundations<\/td><td>Loosest requirements<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udcca Pre-Calculated Tolerances for Common Industrial Rotors<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>Rotor Type<\/th><th>Mass (kg)<\/th><th>RPM<\/th><th>G<\/th><th>U<sub>per<\/sub> (g\u00b7mm)<\/th><th>Per Plane<\/th><th>e<sub>per<\/sub> (\u00b5m)<\/th><\/tr><\/thead>\n <tbody>\n <tr><td>Small motor<\/td><td class=\"mono\">8<\/td><td class=\"mono\">2 900<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">166<\/td><td class=\"mono\">83<\/td><td class=\"mono\">20.7<\/td><\/tr>\n <tr><td>HVAC fan<\/td><td class=\"mono\">45<\/td><td class=\"mono\">1 480<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">1 835<\/td><td class=\"mono\">918<\/td><td class=\"mono\">40.8<\/td><\/tr>\n <tr><td>Pump impeller<\/td><td class=\"mono\">25<\/td><td class=\"mono\">2 950<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">510<\/td><td class=\"mono\">255<\/td><td class=\"mono\">20.4<\/td><\/tr>\n <tr><td>Turbo-compressor<\/td><td class=\"mono\">120<\/td><td class=\"mono\">8 000<\/td><td class=\"mono\">G 2.5<\/td><td class=\"mono\">358<\/td><td class=\"mono\">179<\/td><td class=\"mono\">3.0<\/td><\/tr>\n <tr><td>Paper roll<\/td><td class=\"mono\">2 000<\/td><td class=\"mono\">300<\/td><td class=\"mono\">G 6.3<\/td><td class=\"mono\">401 000<\/td><td class=\"mono\">200 500<\/td><td class=\"mono\">200.5<\/td><\/tr>\n <tr><td>Power-plant fan<\/td><td class=\"mono\">350<\/td><td class=\"mono\">990<\/td><td class=\"mono\">G 2.5<\/td><td class=\"mono\">8 468<\/td><td class=\"mono\">4 234<\/td><td class=\"mono\">24.2<\/td><\/tr>\n <tr><td>Grinding spindle<\/td><td class=\"mono\">2<\/td><td class=\"mono\">24 000<\/td><td class=\"mono\">G 1.0<\/td><td class=\"mono\">0.80<\/td><td class=\"mono\">0.40<\/td><td class=\"mono\">0.40<\/td><\/tr>\n <tr><td>Car wheel<\/td><td class=\"mono\">12<\/td><td class=\"mono\">800<\/td><td class=\"mono\">G 40<\/td><td class=\"mono\">5 729<\/td><td class=\"mono\">2 865<\/td><td class=\"mono\">477<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <div class=\"table-wrap\">\n <div class=\"table-title\">\ud83d\udcd0 Tolerance Allocation Methods \u2014 ISO 1940-1 Chapter 7<\/div>\n <div class=\"table-scroll\"><table>\n <thead><tr><th>Rotor Type<\/th><th>Allocation<\/th><th>Formula<\/th><th>Notes<\/th><\/tr><\/thead>\n <tbody>\n <tr><td>Symmetric<\/td><td>Equal split<\/td><td class=\"mono\">U<sub>L<\/sub>=U<sub>R<\/sub>=U<sub>per<\/sub>\/2<\/td><td>Simplest case. Motors, some fans.<\/td><\/tr>\n <tr><td>Asymmetric between-bearing<\/td><td>Proportional<\/td><td class=\"mono\">U<sub>L<\/sub>=U<sub>per<\/sub>\u00b7(b\/L)<\/td><td>Most common method.<\/td><\/tr>\n <tr><td>Overhung (cantilever)<\/td><td>Moment-based<\/td><td>Statics eqns<\/td><td>Tighter tolerances on overhung plane.<\/td><\/tr>\n <tr><td>Narrow (planes close)<\/td><td>Separate static+couple<\/td><td>Per ISO 21940-12<\/td><td>Different vibration effects.<\/td><\/tr>\n <\/tbody>\n <\/table><\/div>\n <\/div>\n <\/div>\n<\/section>\n\n<main class=\"main-content\" id=\"definition\">\n <div class=\"container\">\n <div class=\"content-layout\">\n <article class=\"article-content\">\n\n <h2>What is ISO 1940-1?<\/h2>\n <div class=\"info-box\" style=\"border-left-color:var(--navy);background:var(--beige-light);\">\n <div class=\"box-title\" style=\"font-size:16px;\">Quick Answer<\/div>\n <p style=\"font-size:15px;\"><strong>ISO 1940-1<\/strong> (<em>Mechanical vibration \u2014 Balance quality requirements of rotors in a constant (rigid) state<\/em>) defines the <a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\">G-grade balance quality system<\/a> for rigid rotors. The formula <strong>U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/strong> calculates permissible residual <a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\">unbalance<\/a>. Superseded by <strong>ISO 21940-11:2016<\/strong> with identical values. Default grade for industrial machinery: <strong>G 6.3<\/strong>.<\/p>\n <\/div>\n <p>ISO 1940-1 is the foundational document for rotor balancing worldwide. Its G-grade system is the de facto language of balancing: \"balance to G 6.3\" is understood by every specialist globally. The standard covers rigid rotors from tiny precision spindles to massive crankshafts, providing a universal framework for specifying, calculating, and verifying balance quality.<\/p>\n <p>The standard applies only to <em>rigid<\/em> rotors \u2014 those whose elastic deformations under centrifugal forces are negligible across the operating speed range. Flexible rotors (operating above the first bending critical speed) are covered by ISO 21940-12.<\/p>\n\n <h2 id=\"rigid-rotor\">The Rigid Rotor Concept<\/h2>\n <p>A rotor is classified as rigid if its mass distribution does not change significantly as speed varies from zero to maximum operating speed. The key consequence: <strong>a rotor balanced at low speed on a balancing machine remains balanced at its operating speed.<\/strong> This allows balancing at 300\u2013600 RPM on a workshop machine while meeting tolerances at 3 000+ RPM in service.<\/p>\n <p>If a rotor operates in the supercritical region (above the first bending <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\">critical speed<\/a>) or near <a href=\"https:\/\/vibromera.eu\/glossary\/resonance\/\">resonance<\/a>, deflections change the effective mass distribution, and low-speed balancing may be ineffective at high speed. Such rotors are classified as flexible.<\/p>\n <div class=\"info-box\">\n <div class=\"box-title\">What ISO 1940-1 Does NOT Cover<\/div>\n <p>Rotors with changing geometry (articulated shafts, helicopter blades). Resonance in rotor\u2013support\u2013foundation systems. Aerodynamic and hydrodynamic forces not related to mass distribution. For fans specifically, see <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> (BV\/FV categories).<\/p>\n <\/div>\n\n <h2 id=\"unbalance-types\">Types of Unbalance<\/h2>\n <p><a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\">Unbalance<\/a> = rotor's inertia axis \u2260 rotation axis. In vector form: <strong>U = m \u00d7 r<\/strong> (g\u00b7mm). ISO 1940-1 classifies three types:<\/p>\n <ul>\n <li><strong>Static unbalance:<\/strong> Inertia axis parallel to rotation axis but displaced. Single unbalanced mass equivalent. Correctable in <strong>one plane<\/strong>. Typical: pulleys, narrow gears, fan impellers (L\/D < 0.5).<\/li>\n <li><strong>Couple unbalance:<\/strong> Inertia axis through centre of mass but tilted. Net force zero, but a couple (pair) rocks the rotor. Requires <strong>two planes<\/strong>.<\/li>\n <li><strong>Dynamic unbalance:<\/strong> General case \u2014 static + couple combined. Inertia axis neither parallel nor intersecting rotation axis. Requires <strong>two planes<\/strong>. Most real rotors have dynamic unbalance.<\/li>\n <\/ul>\n\n <h3>Specific Unbalance (Eccentricity)<\/h3>\n <div class=\"formula-box\">\n <div class=\"formula-label\">Specific Unbalance<\/div>\n <div class=\"formula-main\">e = U \/ M<\/div>\n <div class=\"formula-note\">e in \u00b5m (g\u00b7mm\/kg) | U = unbalance (g\u00b7mm) | M = rotor mass (kg) \u2014 displacement of centre of mass from rotation axis<\/div>\n <\/div>\n <p>The G-grade is defined as the product <strong>e \u00d7 \u03c9<\/strong> (mm\/s) \u2014 the linear velocity of the rotor's centre of mass orbiting the rotation axis. This single number characterises balance quality independently of rotor size and speed.<\/p>\n\n <h2 id=\"g-grades\">The G-Grade System \u2014 Physical Basis<\/h2>\n <h3>Mass Similarity<\/h3>\n <p>For geometrically similar rotors: U<sub>per<\/sub> \u221d M \u2192 specific unbalance e<sub>per<\/sub> should be constant. One standard applies across all sizes.<\/p>\n <h3>Speed Similarity<\/h3>\n <p>Centrifugal force F = M\u00b7e\u00b7\u03c9\u00b2. To maintain acceptable bearing loads at different speeds, e<sub>per<\/sub> must decrease as \u03c9 increases:<\/p>\n <div class=\"formula-box\">\n <div class=\"formula-label\">G-Grade Definition<\/div>\n <div class=\"formula-main\">G = e<sub>per<\/sub> \u00d7 \u03c9 = constant (mm\/s)<\/div>\n <div class=\"formula-note\">G 6.3 = centre of mass orbits at \u2264 6.3 mm\/s | Adjacent grades differ by factor 2.5<\/div>\n <\/div>\n\n <h2 id=\"tolerance-calc\">Calculating Permissible Residual Unbalance<\/h2>\n <div class=\"formula-box\">\n <div class=\"formula-label\">ISO 1940-1 \/ ISO 21940-11 Tolerance Formula<\/div>\n <div class=\"formula-main\">U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/div>\n <div class=\"formula-note\">U<sub>per<\/sub> in g\u00b7mm | G = grade (mm\/s) | M = rotor mass (kg) | n = max service RPM | 9 549 = 60 000\/(2\u03c0)<\/div>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Worked Example: Fan Rotor, G 6.3<\/div>\n <p><strong>Given:<\/strong> Centrifugal fan impeller, M = 200 kg, n = 1 500 RPM, G 6.3.<\/p>\n <p><strong>Total:<\/strong> U<sub>per<\/sub> = 9 549 \u00d7 6.3 \u00d7 200 \/ 1 500 = <strong>8 021 g\u00b7mm<\/strong><\/p>\n <p><strong>Eccentricity:<\/strong> e<sub>per<\/sub> = 8 021 \/ 200 = <strong>40.1 \u00b5m<\/strong><\/p>\n <p><strong>Per plane (symmetric, 2):<\/strong> 8 021 \/ 2 = <strong>4 011 g\u00b7mm<\/strong><\/p>\n <p><strong>At R = 400 mm:<\/strong> 4 011 \/ 400 = <strong>10.0 g per plane<\/strong><\/p>\n <\/div>\n\n <div class=\"info-box warning\">\n <div class=\"box-title\">Always Use Maximum Service Speed<\/div>\n <p>The speed in the formula must be the highest RPM in service \u2014 not balancing machine speed. Many rotors are balanced at 300\u2013600 RPM but tolerance must use actual service speed (e.g. 1 480 RPM). Using balancing machine speed produces dangerously loose tolerances.<\/p>\n <\/div>\n\n <h2 id=\"allocation\">Allocation to Correction Planes<\/h2>\n <p>U<sub>per<\/sub> applies to the rotor's centre of mass. In practice, balance in two planes (near bearings). Chapter 7 rules:<\/p>\n <h3>Symmetric Rotors<\/h3>\n <p>CoM at midpoint \u2192 equal: U<sub>L<\/sub> = U<sub>R<\/sub> = U<sub>per<\/sub> \/ 2.<\/p>\n <h3>Asymmetric Between-Bearing<\/h3>\n <div class=\"formula-box\">\n <div class=\"formula-label\">Asymmetric Allocation<\/div>\n <div class=\"formula-main\">U<sub>left<\/sub> = U<sub>per<\/sub> \u00d7 (b \/ L) | U<sub>right<\/sub> = U<sub>per<\/sub> \u00d7 (a \/ L)<\/div>\n <div class=\"formula-note\">a = CoM to left bearing | b = CoM to right bearing | L = a + b<\/div>\n <\/div>\n <h3>Overhung Rotors<\/h3>\n <p>Overhung mass creates bending moment loading both bearings. Moment-based recalculation needed \u2192 typically much tighter tolerance on overhung plane. Common for pumps, single-stage compressors, cantilevered fan impellers.<\/p>\n\n <h2 id=\"verification\">Errors and Verification<\/h2>\n <h3>Error Sources<\/h3>\n <ul>\n <li><strong>Systematic:<\/strong> Machine calibration drift, eccentric mandrels, keyway effects (ISO 8821), thermal distortion.<\/li>\n <li><strong>Random:<\/strong> Sensor noise, support play, rotor seating variation.<\/li>\n <\/ul>\n <p>Total error must not exceed 10\u201315% of tolerance. If larger, tighten working tolerance accordingly.<\/p>\n <h3>Assembly Effects<\/h3>\n <p>Component balancing \u2260 assembly balance. Coupling eccentricity, radial runout, loose fits can negate component work. Trim balance the assembled rotor.<\/p>\n <h3>Verification Methods<\/h3>\n <ul>\n <li><strong>Index test:<\/strong> Rotate rotor 180\u00b0 on mandrel, remeasure. Change = fixture error.<\/li>\n <li><strong>Trial weight test:<\/strong> Add known mass, verify measured vector change matches expectation.<\/li>\n <li><strong>Field check:<\/strong> Measure vibration on bearings per <a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\">ISO 10816<\/a>.<\/li>\n <\/ul>\n\n <div class=\"info-box success\">\n <div class=\"box-title\">Balanset-1A: Built-In ISO 1940-1 Compliance<\/div>\n <p>The <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> automates ISO 1940-1: enter mass, speed, G-grade \u2192 instant U<sub>per<\/sub> with automatic plane allocation. After balancing, compares residual vs. limit. The F6 Reports function generates a formal protocol documenting the achieved G-grade. Accuracy \u00b15% velocity, \u00b11\u00b0 phase \u2014 sufficient for G 16 through G 2.5. The <a href=\"https:\/\/vibromera.eu\/product\/balanset-4\/\">Balanset-4<\/a> extends to four channels for complex multi-bearing rotors.<\/p>\n <\/div>\n\n <h2 id=\"case-studies\">Worked Examples<\/h2>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 1: Electric Motor \u2014 G 6.3<\/div>\n <p><strong>Rotor:<\/strong> 15 kW, 1 460 RPM, 35 kg, between-bearing symmetric.<\/p>\n <p><strong>Tolerance:<\/strong> U<sub>per<\/sub> = 9 549 \u00d7 6.3 \u00d7 35 \/ 1 460 = <strong>1 442 g\u00b7mm<\/strong> \u2192 721\/plane.<\/p>\n <p><strong>At R = 80 mm:<\/strong> 721 \/ 80 = <strong>9.0 g\/plane<\/strong>. Shop balanced: 180 g\u00b7mm residual. \u2705<\/p>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 2: Pump \u2014 Overhung Impeller, G 6.3<\/div>\n <p><strong>Rotor:<\/strong> Shaft + impeller 18 kg, 2 950 RPM. Impeller 6 kg overhung 120 mm. Bearing span 250 mm.<\/p>\n <p><strong>Total:<\/strong> U<sub>per<\/sub> = <strong>367 g\u00b7mm<\/strong>. Moment allocation: front \u2248 202, rear \u2248 165 g\u00b7mm.<\/p>\n <p><strong>Field balanced<\/strong> with <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> single-plane: 8.5 g at 230\u00b0. Final: 95 g\u00b7mm. \u2705<\/p>\n <\/div>\n\n <div class=\"example-block\">\n <div class=\"example-title\">Case 3: Turbo-Compressor \u2014 G 2.5<\/div>\n <p><strong>Rotor:<\/strong> 3-stage, 65 kg, 12 000 RPM. Slightly asymmetric.<\/p>\n <p><strong>Tolerance:<\/strong> U<sub>per<\/sub> = <strong>129 g\u00b7mm<\/strong> \u2192 65\/plane \u2192 at R = 95 mm: <strong>0.68 g\/plane<\/strong>.<\/p>\n <p>Sub-gram precision \u2192 shop high-speed machine only. Index test: mandrel error < 5 g\u00b7mm. Final: 28 g\u00b7mm\/plane. \u2705<\/p>\n <\/div>\n\n <h2 id=\"iso21940\">ISO 1940-1 \u2192 ISO 21940-11<\/h2>\n <ul>\n <li>G-grade values, formulas, application tables \u2014 <strong>identical<\/strong>. No technical changes.<\/li>\n <li>ISO 21940 series: Part 11 (quality), Part 12 (flexible), Part 14 (procedures), Part 21 (descriptions), Part 31 (susceptibility), Part 32 (keys).<\/li>\n <li>Both designations used interchangeably in practice.<\/li>\n <li><a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> BV categories reference G-grades directly.<\/li>\n <\/ul>\n\n <h2 id=\"related-standards\">Related Standards<\/h2>\n <ul>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\">ISO 21940-11<\/a>:<\/strong> This standard \u2014 G-grade system.<\/li>\n <li><strong>ISO 21940-12:<\/strong> Flexible rotor balancing.<\/li>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\">ISO 10816 \/ ISO 20816<\/a>:<\/strong> Vibration evaluation \u2014 operational result of balance quality.<\/li>\n <li><strong><a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a>:<\/strong> Fan-specific BV\/FV categories \u2192 G-grades.<\/li>\n <li><strong>ISO 8821:<\/strong> Keyway influence (half-key convention).<\/li>\n <li><strong>API 610 \/ API 617:<\/strong> Petroleum pumps\/compressors referencing ISO 1940.<\/li>\n <\/ul>\n\n <hr style=\"margin:48px 0 24px;border:none;border-top:1px solid var(--border-light);\">\n <p><strong>Official standard:<\/strong> <a href=\"https:\/\/www.iso.org\/standard\/27092.html\" rel=\"nofollow noopener\" target=\"_blank\">ISO 1940-1 on ISO Store \u2192<\/a><\/p>\n <p><a href=\"https:\/\/vibromera.eu\/glossary\/\">\u2190 Back to Glossary Index<\/a><\/p>\n <\/article>\n\n <aside class=\"toc-sidebar\">\n <div class=\"toc-box\">\n <h3>On This Page<\/h3>\n <a href=\"#calculator\">Tolerance Calculator<\/a>\n <a href=\"#g-grade-table\">G-Grade Table<\/a>\n <a href=\"#definition\">What is ISO 1940-1?<\/a>\n <a href=\"#rigid-rotor\">Rigid Rotor Concept<\/a>\n <a href=\"#unbalance-types\">Types of Unbalance<\/a>\n <a class=\"sub\" href=\"#unbalance-types\">Static \/ Couple \/ Dynamic<\/a>\n <a class=\"sub\" href=\"#unbalance-types\">Specific unbalance<\/a>\n <a href=\"#g-grades\">G-Grade System<\/a>\n <a class=\"sub\" href=\"#g-grades\">Similarity laws<\/a>\n <a href=\"#tolerance-calc\">Tolerance Formula<\/a>\n <a href=\"#allocation\">Plane Allocation<\/a>\n <a class=\"sub\" href=\"#allocation\">Symmetric \/ Asymmetric<\/a>\n <a class=\"sub\" href=\"#allocation\">Overhung rotors<\/a>\n <a href=\"#verification\">Errors & Verification<\/a>\n <a href=\"#case-studies\">Case Studies (3)<\/a>\n <a href=\"#iso21940\">ISO 21940-11 Transition<\/a>\n <a href=\"#faq\">FAQ (8 Questions)<\/a>\n <\/div>\n <div class=\"toc-box\" style=\"margin-top:24px;background:var(--navy);border-color:var(--navy);\">\n <h3 style=\"color:#fff;\">Balancing Equipment<\/h3>\n <p style=\"color:rgba(255,255,255,.6);font-size:13px;margin-bottom:12px;\">Portable field balancing with built-in ISO 1940 tolerance calculator and G-grade verification.<\/p>\n <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\" style=\"display:block;padding:8px 14px;background:var(--blue);color:white;border-radius:6px;text-align:center;font-weight:600;font-size:14px;text-decoration:none;margin-bottom:8px;border-left:none;\">Balanset-1A \u2192<\/a>\n <a href=\"https:\/\/vibromera.eu\/product\/balanset-4\/\" style=\"display:block;padding:8px 14px;background:rgba(255,255,255,.1);color:white;border-radius:6px;text-align:center;font-weight:600;font-size:14px;text-decoration:none;border:1px solid rgba(255,255,255,.2);border-left:none;\">Balanset-4 \u2192<\/a>\n <\/div>\n <\/aside>\n <\/div>\n <\/div>\n<\/main>\n\n<section class=\"section-bg alt\" id=\"faq\">\n <div class=\"container\" style=\"max-width:1000px;\">\n <div class=\"section-header\"><h2>Frequently Asked Questions \u2014 ISO 1940-1<\/h2><p>G-grade balance quality system for rigid rotors<\/p><\/div>\n <div style=\"display:flex;flex-direction:column;gap:16px;\">\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What is the difference between ISO 1940-1 and ISO 21940-11?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">ISO 21940-11:2016 supersedes ISO 1940-1:2003. The G-grade system, tolerance values, and application tables are <strong>identical<\/strong>. ISO 21940-11 includes minor editorial improvements but no technical changes. Both designations are used interchangeably.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> How do I calculate permissible residual unbalance?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>U<sub>per<\/sub> = (9 549 \u00d7 G \u00d7 M) \/ n<\/strong> \u2014 G = grade (mm\/s), M = mass (kg), n = max RPM. Example: 50 kg at 3 000 RPM, G 6.3 \u2192 9 549 \u00d7 6.3 \u00d7 50 \/ 3 000 = <strong>1 003 g\u00b7mm<\/strong>. Divide by planes for per-plane value.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What is a rigid rotor?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">A rotor whose elastic deformations under centrifugal forces are negligibly small across its operating speed range. Balanced at low speed \u2192 stays balanced at operating speed. Rotors above first bending <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\">critical speed<\/a> are flexible and require ISO 21940-12.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What G-grade for pumps, fans, or motors?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>G 6.3<\/strong> \u2014 most fans, pumps, general motors. <strong>G 2.5<\/strong> \u2014 turbines, turbo-compressors, critical pumps (API 610). <strong>G 1.0<\/strong> \u2014 grinding spindles. <strong>G 16<\/strong> \u2014 agricultural\/crushers. For fans: <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\">ISO 14694<\/a> BV categories map to G-grades.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> How to allocate tolerance between planes?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Symmetric: 50\/50. Asymmetric: proportional to bearing reactions \u2014 U<sub>left<\/sub> = U<sub>per<\/sub>\u00d7(b\/L). Overhung: moment-based with tighter overhung-plane tolerance. The <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a> handles allocation automatically.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> What are the three types of unbalance?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\"><strong>Static<\/strong> \u2014 displaced but parallel, one-plane fix. <strong>Couple<\/strong> \u2014 tilted through CoM, two-plane fix. <strong>Dynamic<\/strong> \u2014 general (static+couple), two-plane fix. Most real rotors: dynamic unbalance.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> Why are G-grades on a logarithmic scale?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Factor 2.5 between grades covers the full range from gyroscopes (G 0.4) to marine diesels (G 4000). Logarithmic scaling is appropriate because perceived vibration severity and bearing life follow logarithmic relationships. Each step \u2248 same relative change in quality.<\/div><\/details>\n <details style=\"background:var(--white);border:1px solid var(--border-light);border-radius:var(--radius);overflow:hidden;\"><summary style=\"padding:18px 24px;font-weight:700;font-size:16px;cursor:pointer;color:var(--navy);list-style:none;display:flex;align-items:center;gap:10px;\"><span style=\"color:var(--blue);font-size:18px;\">\u25b8<\/span> Can I verify compliance with a portable balancer?<\/summary><div style=\"padding:0 24px 18px 52px;font-size:15px;line-height:1.7;color:var(--text);\">Yes. <a href=\"https:\/\/vibromera.eu\/product\/balanset-1\/\">Balanset-1A<\/a>: built-in ISO 1940 calculator, automatic plane allocation, real-time comparison of residual vs. limit, formal balance report. \u00b15% accuracy sufficient for G 16\u2013G 2.5. For G 1.0, careful preparation needed.<\/div><\/details>\n <\/div>\n <\/div>\n<\/section>\n\n<section style=\"padding:32px 0;background:var(--white);border-top:1px solid var(--border-light);\">\n <div class=\"container\" style=\"max-width:1000px;\">\n <h3 style=\"font-family:'DM Serif Display',serif;font-size:22px;color:var(--navy);margin-bottom:20px;\">Related Glossary Articles<\/h3>\n <div style=\"display:grid;grid-template-columns:repeat(3,1fr);gap:16px;\">\n <a href=\"https:\/\/vibromera.eu\/glossary\/balance-quality-grade\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Balance Quality Grade<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Interactive G-grade calculator with full tolerance tables<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/iso-14694\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">ISO 14694<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Fan-specific BV\/FV categories mapping to G-grades<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/iso-10816-1\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">ISO 10816-1<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Vibration evaluation \u2014 measuring balance quality in service<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/unbalance\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Unbalance<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Types, measurement, and correction of mass unbalance<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/natural-frequency\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Natural Frequency<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Critical speeds and the rigid\/flexible rotor boundary<\/div><\/a>\n <a href=\"https:\/\/vibromera.eu\/glossary\/rotor-balancing\/\" style=\"display:block;padding:18px;background:var(--beige-light);border:1px solid var(--beige-dark);border-radius:var(--radius-sm);text-decoration:none;box-shadow:var(--shadow-sm);\"><div style=\"font-weight:700;color:var(--navy);font-size:15px;margin-bottom:4px;\">Rotor Balancing<\/div><div style=\"font-size:13px;color:var(--text-secondary);\">Single-plane and two-plane balancing procedures<\/div><\/a>\n <\/div>\n <\/div>\n<\/section>\n\n<section class=\"shop-cta\">\n <div class=\"container\">\n <h2>Balance to ISO 1940-1 \u2014 In the Field<\/h2>\n <p>Vibromera portable balancers include built-in ISO 1940 tolerance calculators, automatic plane allocation, and formal balance reports documenting the achieved G-grade.<\/p>\n <a href=\"https:\/\/vibromera.eu\/shop\/\" class=\"cta-btn\">Browse Balancing Equipment \u2192<\/a>\n <\/div>\n<\/section>\n\n<footer class=\"page-footer\">\n <div class=\"container\"><p><a href=\"https:\/\/vibromera.eu\/glossary\/\">\u2190 Back to Glossary<\/a> | <a href=\"https:\/\/vibromera.eu\/\">vibromera.eu<\/a><\/p><\/div>\n<\/footer>\n\n<script>\nfunction calcG(){\n const G=parseFloat(document.getElementById('gGrade').value);\n const M=parseFloat(document.getElementById('rotorMass').value);\n const n=parseFloat(document.getElementById('rotorRPM').value);\n const p=parseInt(document.getElementById('rotorPlanes').value);\n const R=parseFloat(document.getElementById('rotorRadius').value)||0;\n if(!M||!n||M<=0||n<=0)return;\n const e=(9549*G)\/n,U=e*M,Up=U\/p,w=2*Math.PI*n\/60,F=(U\/1e6)*w*w;\n const cw=R>0?Up\/R:0;\n const f=v=>v>=1000?Math.round(v).toLocaleString('en'):v>=100?v.toFixed(0):v>=1?v.toFixed(1):v>=0.01?v.toFixed(3):v.toExponential(2);\n document.getElementById('resultsArea').innerHTML=\n '<div class=\"result-primary\"><div class=\"res-label\">Permissible Residual Unbalance (G '+G+')<\/div><div class=\"res-value\">'+f(U)+'<\/div><div class=\"res-unit\">g\u00b7mm \u2014 ISO 1940-1 \/ ISO 21940-11<\/div><\/div>'+\n '<div class=\"results-secondary\">'+\n '<div class=\"res-card\"><div class=\"rc-label\">Specific Eccentricity<\/div><div class=\"rc-value\">'+(e>=10?e.toFixed(1):e>=0.1?e.toFixed(2):e.toFixed(3))+'<\/div><div class=\"rc-unit\">\u00b5m (e<sub>per<\/sub>)<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">Centrifugal Force<\/div><div class=\"rc-value\">'+(F>=10?F.toFixed(1):F>=0.1?F.toFixed(2):F.toFixed(3))+'<\/div><div class=\"rc-unit\">N at '+n+' RPM<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">G-Grade<\/div><div class=\"rc-value\" style=\"font-size:18px\">G '+G+'<\/div><div class=\"rc-unit\">e\u00b7\u03c9 = '+G+' mm\/s<\/div><\/div>'+\n '<div class=\"res-card\"><div class=\"rc-label\">Rotor<\/div><div class=\"rc-value\" style=\"font-size:14px;font-family:Source Sans 3,sans-serif\">'+M+' kg @ '+n+' RPM<\/div><div class=\"rc-unit\">'+p+' plane'+(p>1?'s':'')+'<\/div><\/div>'+\n '<\/div>'+\n '<div class=\"plane-note\"><div class=\"pn-label\">Per Plane ('+(p===1?'single plane':'each of '+p+' planes')+')<\/div><div class=\"pn-value\">'+f(Up)+'<\/div><div class=\"pn-unit\">g\u00b7mm'+(cw>0?' = '+f(cw)+' g at R = '+R+' mm':'')+'<\/div><\/div>';\n}\n['gGrade','rotorMass','rotorRPM','rotorPlanes','rotorRadius'].forEach(function(id){\n var el=document.getElementById(id);\n el.addEventListener(el.tagName==='SELECT'?'change':'input',calcG);\n});\ncalcG();\n<\/script>\n<\/body>\n<\/html><\/div><\/div><\/div><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>An overview of ISO 1940-1 (now part of ISO 21940), the key international standard that defines balance quality requirements and tolerance calculations for rigid rotors using G-Grades.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[109,112],"tags":[],"class_list":["post-9","glossary","type-glossary","status-publish","hentry","category-glossary","category-iso-standards"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary"}],"about":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/types\/glossary"}],"version-history":[{"count":7,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9\/revisions"}],"predecessor-version":[{"id":101534,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/glossary\/9\/revisions\/101534"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/media?parent=9"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/categories?post=9"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/tags?post=9"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}