motor running sensor

[realolman]

Does anyone know of a sensor that could be just "stuck" to the side of a fractional H.P ac motor to sense if the motor was running or not.

I know I could use a current transformer on the motor leads. Right now I'm using a 120vac to 5vdc solid state relay. I'd really like to be able to do it without disturbing the existing wiring. All I want to know is if it is running or not . I can read from 0 to 5vdc

Seems to me there ought to be a magnetic field around a running motor that could be sensed by something.

.
thanks

 

[james wuebker]

Not sure if you can put a prox. sensor on the motor. You would need something for the prox. to sense while the motor is turning.
Jim

 

[Bob NH]

You could use a rotation sensor or a tachometer. If you just want to stick something on the motor, you could mount an accelerometer/vibration sensor to the motor and tune it to pick up a small range of vibrations. It would require calibration.

 

[petersonra]

I guess it depends on whether you want to know whether the motor is actually turning, pulling current, or energized. Each can be sensed without too much trouble.

An auxiliary contact off the motor starter might be adequate for your purposes, depending on what your purposes are.

 

[jim dungar]

What you are looking for is a "zero speed" indicator. Red Lion Controls makes a self contained one that is based on a magnetic pickup. Most of the proximity switch style, like those from Square D, require a seperate power source. All of the ones I have seen cost more than $100. If I was doing it I would not ignore a small/tiny current sensor like those from Relay In a Box (RIB).

 

[hockeyoligist2]

What you are looking for is a "zero speed" indicator. Red Lion Controls makes a self contained one that is based on a magnetic pickup. Most of the proximity switch style, like those from Square D, require a seperate power source. All of the ones I have seen cost more than $100. If I was doing it I would not ignore a small/tiny current sensor like those from Relay In a Box (RIB).

Something I have done, on the cheap side, is use a ice cube timer and a proxy. But that was on a belt and pulley system with low rpm. I cut a notch in the hub of the pulley to break the signal to the timer. On another that had an aluminum pulley I just used the set screw as a "pickup" for the proxy.

 

[petersonra]

Something I have done, on the cheap side, is use a ice cube timer and a proxy. But that was on a belt and pulley system with low rpm. I cut a notch in the hub of the pulley to break the signal to the timer. On another that had an aluminum pulley I just used the set screw as a "pickup" for the proxy.

the only thing you have to worry about is if the miserable pulley stops with the set screw under the prox switch. you need to make sure the timer resets on an edge only.

 

[jim dungar]

the only thing you have to worry about is if the miserable pulley stops with the set screw under the prox switch. you need to make sure the timer resets on an edge only.

Two timers, one that must be "turned off" and one that must be "turned on", will overcome this problem.

 

[hockeyoligist2]

The one that I used would time out if it wasn't reset by a make, break cycle.