Motor RPM Measurements

[AdamAReid]

I need to measure the RPM of the output shaft of my motor. I was thinking of using an incremental encoder, or some kind of tachometer. I'm looking for the most cost effective solution. What are my options in terms of RPM Measurement? Can anyone out there help me?

Thanks,
AAR

 

[electricpete]

How about a hand-held strobotach. You adjust the frequency of flashes until the shaft appears to stop. I believe that will be one of the cheapest solutions.

 

[AdamAReid]

Thanks Pete...

That would be an option.. but the application will be remote (at the bottom of the ocean, actually), so I won't be able to take the readings myself.

What I'd like is a device that sends me some form of signal (analogue or ditial). Then I could enter this signal, among others coming in, into a data logger and use this to monitor the preformance of the motor... but I'm getting ahead of myself. What I need for the time being is simply a remote rpm measuring device. Any other good ideas?
Thanks
AAR

 

[Lewish]

I have answered this question before, but I don't know the thread number.
There are companies that manufacture a clear plastic disk that mounts on the motor shaft. It has opaque lines on it. You put a "U" shaped opto-detector, such that the opaque lines interrupt the light beam in the opto. This will give you some number of pulses per revolution of the motor. The clear disk is about $2.50 in the quantities we use and the opto is about $1.00. That is as cheap as I have heard of.

 

[snpyon]

I personally use the red lion IMI series coupled with a pnp type hall effect proximity sensor to detect the key way on the output shaft, i have found that Red lion instrumentation has provision for data to be sent via twisted pair to a remote display or to a chart recorder...

 

[GusD]

You don't mention if you need a spot RPM check or would the speed feedback signal would be used for control or other.We use several types of deices to measure speed from strobelights(there are some low priced)hand tachos etc.
For our machinery control we use Speed Encoders (pulsetype).This is fairly pricey and unless you expect fairly precise speed regulation probably you wouldn,t use it.We also use simple Tacho Gen DC that puts out 100v DC per 1000 rpm.These are fairly common and cheaper than Pulse Enc.My favorite is a little AC tacho (alt) that put out the same 100v/1000rpm.These are pretty well trouble free if they were installed proerly.Not too much to go wrong with these things.
GusD