Seismic transducers calibration system

It is necessary to conduct seismic transducers calibration in the low-frequency range, where the relative measurements method used for vibration transducers calibration, does not provide sufficient accuracy of the results. It is attributed to the fact that the reference accelerometers have uneven FR in the low-frequency domain. Hence, seismic transducers calibration requires implementation of the different approach.

The use of displacement sensor allows to solve the issue of precise reproduction of vibration at low-frequency level as well as control the test parameters throughout calibration process.

Application spheres

Seismic transducers calibration
Seismic transducers verification
Velocimeters calibration
Displacement sensors calibration

Operating principles

seismic transducers calibration scheme - general layout

The seismic transducer is mounted on the shaker (vibration exciter).

The displacement sensor is mounted in such a way, so that to align the laser beam with the measuring axis of the calibrated transducer.

The transducers are connected to the input channels of the FFT Spectrum analyzer. The signal from the generator (i.e. from the output channel of the FFT spectrum analyzer) is sent to the charge amplifier and to the coil of the vibration exciter. The generator scans the set frequency range and maintains the set vibration level based on the readings of the displacement sensor.

The measuring principle is as follows: the displacement sensor is used to control parameters of the vibration, produced by the vibration exciter – i.e. displacement and frequency level.

Based on this data, it is possible to calculate vibration velocity and vibration acceleration in the real-time mode as well as to adjust the voltage level that is applied to the vibration exciter. Hence, it is possible to control the parameters in accordance with the set test profile.

Upon stabilization completion, there is performed analysis of the calibrated seismic transducer. It allows to calculate the necessary conversion factor for the set frequency level. The measurements are performed at each point of 1/3 fractional-octave-band for all the frequency range of the calibrated seismic transducer. Then it is possible to evaluate FR non-uniformity.

The program allows the user to set frequency range and amplitude of the vibration displacement to be used for the calibration procedure. Based on the readings of the displacement sensor, there is determined a value of vibration level. Then the measured value of the voltage at the seismic transducer output is divided by the vibration level value.

It is also possible to edit the test protocol template.

System components

Note

In order to implement other test types using the shaker (vibration oscillator) system, we recommend you to purchase FFT Spectrum analyzer in the “VCS” configuration (i.e. shaker controller), which includes such programs as “Broadband random vibration”, “Classical shock”, “Vibrational shock”, etc.

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