Vibration Sensor (Accelerometer) Calibration for Bearing Monitoring

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Practical Procedure · Calibration

Vibration Sensor (Accelerometer) Calibration for Bearing Monitoring

Applies to: Piezoelectric accelerometers and vibration transmitters on rotating equipment (fans, motors, mill bearings) | Equipment needed: Vibration calibrator (reference shaker), multimeter, manufacturer's sensitivity spec sheet
Accelerometer Reading Bearing Vibration
The sensor converts mechanical vibration into an electrical signal
Accelerometer
Vibration signal (time domain)
The bearing housing vibrates at a frequency and amplitude tied to its mechanical condition. The accelerometer's internal piezoelectric crystal generates a tiny voltage proportional to that vibration, which the transmitter converts into a standard signal for trending — rising amplitude over time is what flags a developing bearing fault long before it fails.

Before You Start

  • Get the sensor's rated sensitivity (mV/g or pC/g) from its datasheet or nameplate — every accuracy check depends on comparing against this reference value.
  • Confirm whether the installed unit is a standalone accelerometer feeding a monitoring system, or an integrated 4-20mA vibration transmitter — the verification approach differs slightly.
  • Note the mounting method (stud-mounted, adhesive, magnetic) since mounting quality significantly affects high-frequency response and can itself be a source of false readings.

Step 1 — Visual and Mechanical Check

  • Inspect the sensor mounting for looseness, corrosion, or cable damage — a loose sensor will show erratic, unrealistic vibration spikes that have nothing to do with the actual bearing condition.
  • Verify cable routing avoids sources of electrical noise (VFD cables, contactors) since accelerometer signals are low-level and vulnerable to interference.

Step 2 — Reference Shaker Calibration Check

  • Mount the sensor on a calibrated reference shaker set to a known, fixed vibration level (commonly 1g at a reference frequency like 100 or 160 Hz, per calibrator spec).
  • Compare the sensor's output against the expected value calculated from its rated sensitivity.
  • If the reading is significantly off from the calculated expected value, the sensor's sensitivity has drifted — piezoelectric sensors can lose sensitivity with age, heat exposure, or physical shock.

Step 3 — Loop/Output Verification (If Vibration Transmitter)

  • For an integrated 4-20mA vibration transmitter, verify the output at a known input vibration level matches its configured range (e.g., 0-1 in/sec = 4-20mA).
  • Check alarm/trip setpoints against the plant's vibration standard (commonly referencing ISO 10816 or the OEM's specific limits for that machine class).
Field note: A sudden change in vibration reading is far more useful diagnostically than the absolute number alone. Always keep a trend log — a bearing going from 2mm/s to 4mm/s over two weeks tells you far more than a single reading of "4mm/s, seems okay."

Common Mistakes to Avoid

  • Mounting a replacement sensor loosely "for now" — even a temporarily loose mount produces misleading data that can trigger false trips or mask a real developing fault.
  • Ignoring cable routing near VFD or high-voltage cabling, then troubleshooting the sensor for a noise problem that's actually electrical interference.
  • Comparing raw acceleration values across different measurement points without accounting for differing sensor orientations (radial vs axial) — direction matters for diagnosing the fault type.

This is a general field procedure — specifics vary by sensor brand and plant vibration monitoring standards. Adjust to your own SOP where needed.

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