What is a Trip Level? Emergency Shutdown Threshold • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors What is a Trip Level? Emergency Shutdown Threshold • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

What is a Trip Level? Emergency Shutdown Threshold

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Understanding Trip Levels

Definition: What is a Trip Level?

Trip level (also called shutdown setpoint, emergency trip, or critical alarm) is the highest vibration or condition threshold in machinery protection systems that, when exceeded, automatically initiates emergency equipment shutdown to prevent catastrophic damage. Trip levels are typically set at vibration amplitudes where continued operation risks rapid, irreversible damage to the machine or creates safety hazards. Unlike lower alarm levels that notify operators, trip levels execute automatic protective action, removing human decision-making from the critical path when every second counts.

Trip levels are mandatory for critical turbomachinery under API 670 and other safety standards, representing the last line of defense preventing catastrophic failures that could destroy equipment worth millions, cause injuries, or create environmental releases.

Setting Trip Levels

Based on Damage Thresholds

  • Set below vibration causing immediate damage
  • Typically 10-20× baseline or top of ISO Zone D
  • Account for clearances (proximity probe trip before contact)
  • Consider bearing load limits
  • Factor in safety margins

API 670 Guidance

For turbomachinery:

  • Shaft vibration trip: typically 25 mils (635 µm) peak-to-peak
  • Bearing housing: typically 0.5-0.6 in/s (12-15 mm/s) velocity
  • Must be 2-voted (two independent sensors agreeing)
  • Time delay typically < 1-5 seconds

Machine-Specific Factors

  • Clearances: Trip before rotor contact with seals or stator
  • Bearing Limits: Below bearing load failure threshold
  • Historical Data: Vibration at previous failures
  • Manufacturer Recommendations: OEM specifications if available

Trip Level vs. Other Alarms

Level Typical Value Action Timeline
Alert 2× baseline Investigate Weeks to months
Warning 4× baseline Plan maintenance 1-4 weeks
Danger 8× baseline Urgent repair Days
Trip 12-15× baseline Automatic shutdown Immediate (seconds)

Implementation Requirements

Hardware

  • Permanently installed sensors (not route-based)
  • Dedicated monitoring hardware with shutdown capability
  • Redundant sensors for critical trips (2-out-of-2 or 2-out-of-3 voting)
  • Reliable power supply (UPS backup)
  • Hardwired shutdown capability independent of software

Safety Systems Integration

  • Connection to DCS/PLC safety system
  • Redundant trip circuits
  • Fail-safe design (sensor failure causes trip or alarm)
  • Regular testing of trip function
  • SIL (Safety Integrity Level) rating for safety-critical applications

Response Time

  • Detection to shutdown initiation: < 1 second typical
  • Total shutdown time: depends on equipment (seconds to minutes)
  • Must be fast enough to prevent damage
  • Balance speed with preventing unnecessary trips

Trip Event Management

When Trip Occurs

  1. Immediate: Equipment automatically shuts down
  2. Alarm: Operators notified of trip condition and cause
  3. Data Capture: Vibration data before/during trip saved
  4. Investigation: Determine root cause
  5. Lockout: Prevent restart until cleared

Post-Trip Actions

  • Inspect equipment for damage
  • Analyze saved vibration data
  • Identify fault that caused trip
  • Repair identified problem
  • Verify trip setpoint was appropriate
  • Document event and learnings

Trip Reset

  • Require manual reset (not automatic)
  • Verification that cause addressed
  • Authorization for restart
  • Post-trip inspection completed

False Trip Prevention

Proper Setpoint Selection

  • High enough to avoid nuisance trips
  • Low enough to protect equipment
  • Typical: 20-30% margin above danger alarm
  • Account for transient vibration during startups

Time Delays

  • Short delay (1-5 seconds) confirms sustained condition
  • Prevents trips from momentary spikes
  • Must be short enough for protection
  • Balance nuisance trip prevention vs. response speed

Voting Logic

  • Require two sensors to agree (2-out-of-2)
  • Or two of three sensors (2-out-of-3 voting)
  • Prevents single sensor failure from false trip
  • Increases reliability

Testing and Verification

Functional Testing

  • Periodic testing of trip function (annually minimum)
  • Simulate high vibration or inject test signal
  • Verify shutdown executes properly
  • Test all redundant channels
  • Document test results

Calibration

  • Sensors calibrated regularly
  • Trip setpoints verified
  • System response time measured
  • All components in trip chain tested

Regulatory and Standards Context

API 670

  • Mandatory vibration trip for turbomachinery > 10,000 HP
  • Specifies setpoints, voting logic, testing
  • Industry standard for critical equipment

Safety Systems Standards

  • IEC 61508 (functional safety)
  • IEC 61511 (process industry safety)
  • SIL ratings for trip systems

Trip levels represent the ultimate protective threshold in machinery monitoring systems, automatically shutting down equipment when vibration indicates imminent catastrophic failure. Proper trip level setting, implementation with redundant reliable hardware, regular testing, and integration with safety systems ensure this critical last line of defense functions correctly to prevent equipment destruction and safety incidents in high-value, critical rotating machinery.

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