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How to check linearity of vibration probe(Axial&radial)

How to check linearity of vibration probe(Axial&radial)? , is the most highlighted question. Let’s discuss it.

Most of engineers and technicians think its very difficult to play with vibration instruments because in normal operation you face very minimum chances to touch these instruments. Follow the following steps one by one for linearity check and calibration of vibration probe and proximeter.

Test Instrument for vibration probe

Digital Multi-meter
TK-3 vibration calibration device

Procedure for Linearity checking of vibration prove

Obtain work permit from Operations.
Explain to the operation that the work will be carried out is Vibration probe linearity test. Ask the operations to ensure that the stated compressor/fan is ready & safe to perform the linearity test. By-pass the vibration ESD interlocks, if it is required during plant operation using deviation form.
Before removing vibration probes, ensure that lube oil and seal oil should be stop.
Remove vibration probe and open the respective junction box where proximitor of vibration probe is mounted.
Ensure that vibration probe is properly connected to its own extension cable.
Mount vibration probe on micrometer of TK-3 by using appropriate adaptor. Set probe in close vicinity of micrometer spindle at zero reading on micrometer.

Measure DC voltage between common and supply terminal of its proximeter using digital multimeter and ensure that it’s voltage should be between -22.5 to -24 VDC
Connect digital meter across common and output terminal of proximeter and note down its reading at zero micrometer position.

Rotate and move the knob of micrometer from zero position to 10 mills so micrometer spindle goes away from the face of probe and note down multimeter voltage reading.
Likewise you rotate micrometer position knob in step of 10 mills gradually up to 100 mill and note down corresponding digital multimeter reading.
Calculate the reading of micrometer 0 to 100 mill Vs corresponding voltage reading of multimeter.
Calculate the linearity scale factor of vibration probe using above calculation. It should be 2000 +-10% milli volt/mill. Proximeter using digital multimeter and ensure that it voltage should be between -22.5 to – 24 VDC.