Proximitor probes DC voltages not equal to gap

Dears when I measure the voltage gap and measure the gap between shaft and probe tip I do not get the same. I.e 10V DC gives me 0.62mm. As per calculation should give me a gap of 1.27mm (10VDC). When I gap the probe using the casing ,at 10 volts I get 1.27mm. I suspect shaft material issue. What should I do? I was thinking to put resistor between common and line wires to reduce the voltage....

Hadrian H. Beaton

Original Post

You might have an issue caused by, in case 1, the measurement on the shaft, you are reading a curved surface.  In case 2, measuring against the casing, I presume the target is a flat surface.  In this regard, what is the exact probe and proximitor being used and what is the shaft diameter at the target area?  I’d verify proper extension cable length as well.

You mention material...do you know what the shaft material is?

I would not add any form of resistor to the circuit until you understand the issue better.

 

Hi. We measuring vibration on shaft of pignone 8 stage barrel pump shaft. I am having instrument team check cable resistance as per bn chart to ensure correct cable length...yes mpi.  i am worried shaft surface were inadvertently hardchromed.....cable length are 0.5m and 4.5m assumed...

 

 

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