Speed Sensing

[mbailey]

Is anyone using laser tachometers for sensing shaft speed for use with a vibration analyzer? I would like to take vibration data without having to stop the machine to put reflective tape on the shaft and I want an accurate speed measurement. Just interested in your thoughts and troubles that these devices might have.

Thanks, Mbailey

 

[IRstuff]

without the tape, the laser tach cannot count rotations.

TTFN

 

[eemotor]

I have used a laser tachometer with a vibration analyzer. However, it was necessary to mount a strip of reflective tape on the shaft.

 

[nbucska]

Is there any place which gives high contrast? if there are
e.g. 12 spokes, you could sense them and divide by 12.



<nbucska@pcperipherals DOT com> subj: eng-tips

 

[ScottyUK]

Hi mbailey,

To do vibration analysis you should really use a signal which gives you a phase reference signal as well as just speed. Bently Nevada's term for this is 'keyphasor'. It is a pulse which occurs once per revolution and allows the displacement of the shaft to be determined relative to the bearing housing.

Have a look at how the vibration specialists like Bently-Nevada and Emerson CSI take their measurements. Both are best known for their products which use inductive sensing, but they might have an optical version available.

Nbucska's idea is a good one if you can manage with speed only and no phase information. Do you have, for example, a coupling or similar where you could use an inductive sensor to detect the bolt heads as they rotate past the sensor? This could be installed without stopping the machine, although whether you would want to work so close to a rotating coupling is a question to consider. If it is a temporary installation, a mag-mount base which would normally carry a clock gauge could provide an easy method of mounting the sensor.



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If we learn from our mistakes,
I'm getting a great education!

 

[aolalde]

If only the scalar speed of the shaft (rpm or rps) is required, use a stroboscopic light. When the light frequency matches the shaft speed, the shaft appears to be standstill . This will help when you are not allowed to stop the machine and attach a reflective tape or put angle marks.

 

[dgallagher]

There are two laser tach sensors I am aware of that will sense rpm without a reflective target. One is made by CSI and the other is Monarch. Here is a link to the Monarch tach - it will trigger off contrasting color targets, keyways, bolt heads or blades - has TTL pulse output for interface to the vibration analyzer:

http://www.reliabilitydirect.com/tachometerproducts/MON-Smart_Laser.htm

 

[ScottyUK]

Try the following link:

http://www.bis.fm/bis/pages/browse_...770&pcn=Frequency+/+RPM&pgn=Tachometer+Probes

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If we learn from our mistakes,
I'm getting a great education!

 

[dgallagher]

Scotty: As an FYI, the Compact tach you link to requires reflective tape - issue is that mbailey can not stop the shaft to mount the tape. The referenced smart laser does not need to use reflective tape.

 

[ScottyUK]

Thanks dgallagher - I obviously can't read the summary data! How did I miss that??



------------------------------

If we learn from our mistakes,
I'm getting a great education!