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  • Vibration Calibrator

    Fig. 1: Vibration Calibrator

    Accelerometer convert mechanical vibrations into electrical voltages. The sensitivity determines which voltage is produced by a certain vibration. This is a characteristic feature of each sensor. In order to determine the sensitivity of accelerometers a vibration calibrator is used.

    A vibration calibrator generates a sinusoidal mechanical vibration signal with defined amplitude and frequency. The adjustable values are traceable to national or international standards.

    During calibration, the accelerometer is assembled on a moveably mounted steel bolt of the vibration calibrator (typically by screw). This steel bolt is set to vibrate by electrodynamic or piezo-actuatoric systems.

    Fig. 2: Accelerometer on a vibration calibrator

    A reference vibration sensor and control electronics are responsible for ensuring that the set amplitude of the vibration calibrator is independent of the sensor mass (see Fig. 1). Nowadays, accelerometers with over 500g mass can be calibrated on mobile battery operated vibration calibrators. The determination of sensitivity is done by comparing the actual vibration amplitude to the measured output voltage of the accelerometer. This process can either be carried out using a software ("Calibrator" in VibroMatrix). Or, the output of the accelerometer is connected to a vibration calibrator and the determined sensitivity is displayed, as shown in Fig. 2 (dashed line). Triaxial accelerometers are calibrated by mounting the three axes of the sensor to the vibration calibrator one after another.

    A vibration calibrator can generate a wide range of amplitudes and frequencies. Thus, the frequency can be typically varied between 16 and 10 kHz and the amplitude from 1 to 10 m/s2. A widely used calibration frequency is 159,2 Hz (equals an angular frequency of 1000 Hz). This frequency has the advantage that vibration acceleration, vibration velocity and vibration displacement possess the same numerical values (e.g. 1 m/s², 1 mm/s, 1µm).