Understanding Velocity in Vibration Analysis
Portable balancer & Vibration analyzer Balanset-1A
Balanset-1A is a portable, USB-powered vibration analyzer and balancer for one- and two-plane balancing of rotors in their own bearings. The Full Kit includes the interface unit, two vibration sensors, optical laser tachometer, reflective tape, Windows balancing software on a USB drive, magnetic stand, digital scale and transport case. Requires a compatible Windows computer with a free USB port; computer …
Vibration sensor
Vibration sensor for Balanset balancing devices, based on the ADXL335 accelerometer. Supplied with a 5 m cable as standard for measuring vibration during rotor balancing and analysis. A 10 m cable option is available.
Optical Sensor (Laser Tachometer)
Optical laser sensor for Balanset balancing devices, based on the modified HS2234 tachometer. Measures rotational speed without contact using a reflective mark on the rotor. Supplied with a 5 m cable as standard; a 10 m cable option is available.
Balanset-4
Balanset-4 is a four-channel vibration analyzer and balancing system for correction in one to four planes. Designed for cardan shafts and rotors supported on four bearings, it can also serve as the measuring system for a balancing machine. The kit includes four vibration sensors, an optical laser tachometer, USB interface, software, magnetic stand, scale and transport case.
Magnetic Stand Insize-60-kgf
Adjustable magnetic stand for positioning the laser RPM sensor in Balanset balancing kits. The switchable magnetic base provides up to 60 kgf of holding force on suitable ferromagnetic surfaces. Adjustable arms and joints help align the sensor with the reflective mark on the rotor.
Reflective tape
Silver self-adhesive reflective tape for the optical laser tachometer in Balanset balancing kits. Apply a small piece to the rotor to provide a reflective reference mark for rotational speed measurement. Supplied as a 1 m length for multiple setups.
Dynamic balancer “Balanset-1A” OEM
Balanset-1A OEM is the core measuring kit for one- and two-plane rotor balancing and vibration analysis. It includes the USB interface unit, two vibration sensors, optical laser tachometer, reflective tape and Windows balancing software on a USB drive. Compared with the Full Kit, the magnetic stand, digital scale and transport case are not included. Requires a compatible Windows computer with …
Velocity is the rate of change of displacement with respect to time — in plain terms, a measure of how fast a vibrating component is moving. Of the three primary vibration parameters — displacement, velocity and acceleration — velocity is the one most widely used to judge the overall health and vibration severity of general rotating machinery across the most common diagnostic frequency range. It sits in the middle of the trio both literally and practically: one mathematical step away from displacement and one from acceleration.
1. Why Velocity is the Standard for Severity
Velocity has become the default parameter for general-purpose vibration monitoring for several connected reasons:
- Best indicator of destructive energy: the energy that fatigues a machine is most directly related to velocity. A given velocity level corresponds to a fairly consistent level of severity across a wide span of machine speeds and types, which is why velocity limits transfer well between similar machines — though the standards still tabulate them by machine group and support conditions rather than as one universal number.
- “Flat” frequency response: across the most critical band for machine diagnostics — roughly 10 Hz to 1,000 Hz, or 600 to 60,000 CPM — velocity gives the most balanced view. It is almost equally sensitive to low-frequency faults such as unbalance and to higher-frequency faults such as misalignment, making it an excellent all-round single number.
- Basis for international standards: the global machinery-vibration standards — chiefly ISO 20816, which superseded the long-serving ISO 10816 — use RMS velocity as the primary metric for acceptance limits and alarm levels. The familiar zone A/B/C/D boundaries in ISO 20816-3 are quoted in mm/s RMS, with the numeric values depending on machine group and support conditions rather than being one universal set.
2. Units and Measurement
Common Units
Vibration velocity is normally expressed in one of two units:
- mm/s (millimetres per second): the SI unit, used in most of the world.
- in/s (inches per second): the imperial unit, common in the United States.
Velocity is almost always measured and trended as an RMS value, because RMS best represents the energy content of the signal. Where a peak figure is quoted instead, it should be labelled clearly, since converting between the two assumes a sinusoid; a vibration unit converter handles the arithmetic and keeps mm/s, in/s and dB consistent.
How is it Measured?
Velocity can be obtained in two principal ways:
- Directly, with a velocity transducer: an electrodynamic velocity sensor generates a voltage in direct proportion to vibration velocity. These rugged moving-coil pickups were once common but have largely been superseded by accelerometers.
- By integrating an accelerometer signal: the dominant method today. A robust accelerometer measures acceleration, and the data collector or monitoring system electronically performs the integration that converts it to velocity. This combines the wide frequency range and durability of an accelerometer with the diagnostic advantages of the velocity parameter.
3. Velocity’s Role in Diagnostics
A high overall velocity level tells you a machine has a problem, but not what the problem is. The diagnostic step is to examine the velocity spectrum and see which frequencies are feeding the high overall value:
- High velocity at 1× RPM (running speed) points to unbalance.
- High velocity at 2× RPM points to misalignment.
- A series of velocity peaks at running-speed harmonics indicates mechanical looseness.
This is precisely the workflow a field instrument follows. A portable two-channel analyser such as the Balanset-1A measures the overall velocity at each bearing, then breaks it into a spectrum so the engineer can read off the 1×, 2× and harmonic content — and, where the culprit is unbalance, proceed directly to correcting it in the machine’s own bearings.
4. Velocity Compared with Displacement and Acceleration
No single parameter is best everywhere; each dominates a different part of the frequency range:
- Displacement is best for very low-frequency motion — shaft orbits, structural movement and clearances — and is the natural choice for proximity-probe measurements on journal bearings.
- Velocity owns the broad mid-band where most rotating-machinery faults live, making it the everyday parameter for overall severity.
- Acceleration is best at very high frequencies, where it emphasises early bearing and gear faults that velocity would under-weight.
You can move between the three by integration (acceleration → velocity → displacement) and differentiation in the other direction. Even so, for a “big-picture” view of a machine’s dynamic health in its normal operating range, velocity remains the single most valuable parameter — and a quick way to benchmark a reading against ISO zones is the vibration severity chart.
