Calibration of Vibration Instruments
6.1 Accelerometers and velocity sensors
The standard calibration service includes the following parameters:
- Sensitivity at 160 Hz (other frequencies can be used, per request), using a quasi-simultaneous comparison with the response of the working standard accelerometer.
- Frequency response (10 Hz to 10 kHz), obtained by simultaneous comparison of the responses of the tested device and the working standard. Pink noise is used as excitation for accelerometers and white noise for velocity sensors.
A basic calibration service is offered only for accelerometers. It includes the test of the sensitivity at 160 Hz (other frequencies can also be used) and the frequency response in the domain from 70 Hz to 10 kHz.
6.2 Vibration exciters and calibrators
The three main parameters (acceleration, frequency, and distortion) characterizing the exciter vibratory motion are measured for every combination level/frequency implemented in the tested device.
- The acceleration is measured using a reference accelerometer, as an average over about 5 seconds after the motion stabilized; the exciter is re-started and the measurement is repeated 4-5 times, and the global average is reported.
- In a similar way, the vibration frequency is measured as an average over several seconds.
- The total harmonic distortion is tested either with a distortion meter or using the analyzer method over a frequency domain from 20 Hz to 20 kHz. In both cases, the fundamental is rejected and the level of the signal composed of the remaining harmonics is compared with the global signal.
For the instruments that include signal-conditioning circuitry allowing calibration of accelerometers, additional tests are provided:
- Accuracy of the indication within the dynamic range.
- A global test of the embedded calibration function performed using the reference accelerometer.
6.3 Vibration meters
With the standard calibration service, the vibration meter is thoroughly tested:
- By using electrical signals to check the accuracy, the manufacturer specifications, and the filters characteristics as indicated by the applicable standards.
- By a separate calibration of the accelerometer.
- In addition, a global accuracy check is performed using the laboratory reference calibrator.
With the Basic calibration service, the instrument with sensor is tested using mechanical excitation. The main characteristics are checked: accuracy of the available measurement modes (acceleration, velocity, or displacement), frequency response, linearity, and range attenuator check.