Magnet mounting for non-contact proximity probe 1

[politeknik]

Hi,
Any recommended magnet mounting for non-contact proximity probe?it's intended to be used as temporary installation at hydro turbine-generator

 

[GregLocock]

Guessing that you are talking about real money, glue one to the measuring point and compare it witha magnet.

Of course if you supplied the mass and geometry of your probe, and the required precision and frequency range, somebody might be prepared to give less accurate but easier advice.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Strong]

A rare earth magnet would do fine as far as giving good frequency response. If you are trying to mount probes on a machine that's running, then support would have to be a well designed to avoid touching probe to shaft. The other issues are SAFETY and loss of DC volts reference setting for absolute position of shaft. If machine is shut down (a wise method), then I would consider using Super Glue or epoxy to mount probe support instead of magnet. You can easily set gap and and follow DC volts after startup for shaft position. I have used adhesive, but not magnet for temporary probe mounting. Don't make the job more complicated that it has to be!

Walt

 

[politeknik]

Mr Wald,
Thanks for your input.
In addition to that, i currently used manually fabricated brackets ( 'L' shape bracket ) for proximity probe installation, however it give less accurate result. And then i'm thinking about magnet mounting instead of using those brackets.Installation also will be done at standstill condition.The measurement will only take place for commissioning of that machine after overhaul works.

 

[GregLocock]

A good trick is to measure the vibration of the base and sensing head of your probe with acelerometers. That'll tell you whether your mounting system is good.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Strong]

Perhaps your 'L' bracket was too thin and vibrated? I have used aluminum blocks that are stiff and can be easily attached with adhesive. Perhaps your shaft target surface is causing errors? Subtraction of slow roll measurement can help results. Other vibration measurement methods include bearing housing and shaft rider using accelerometer or seismic velocity sensor.

Walt

 

[ronfrend]

Another consideration if mounting a prox probe temporarily is that the target area of the shaft will not be perfectly smooth as it has been exposed to the atmosphere as well as anyone nearby with a hammer or wrench (not forgetting the size 12s that most technicians seem to wear). You will get unusual spikes and frequencies. Make sure your probe has a "scratch filter" to get rid of spurious spikes from surface scratches.

On the positive side, I have used magnet mounts with prox probes successfully. The one thing you MUST know is the natural frequency of the probe/mounting arrangement. I find the easiest way is with the machine stopped and then carry out a bump test (I actually "pluck" test). If you find the natural frequency is close to a run speed you will have bad measurements and you will have to modify the support system.

Ron Frend

http://www.predicon.net