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Join Date: Feb 2009
Posts: 3

detecting rotation of motor

02/15/2009 1:15 PM

Want to detect whether motor is rotating.

Is there any device for this purpose?

Aim is to switch off supply if motor is not moving.

THANKS.

Prashant.

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#1

Re: detecting rotation of motor

02/15/2009 4:50 PM

Google "zero speed switch" or sensor.

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#2

Re: detecting rotation of motor

02/15/2009 4:51 PM

Yes---A zero speed switch?

Do you have PLC control or a hard wired motor starter with aux. contacts?

Is the motor coupled to something else.

There are a lot of options.

K T

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#3

Re: detecting rotation of motor

02/15/2009 5:56 PM

Zero-speed sensors present an interesting challenge: From a ZS sensor's point of view, what actually constitutes zero speed? That is to say, is there a shaft RPM greater than zero but below which a ZS-sensor (however implemented) would indicate that the shaft is not rotating when, in fact, it is rotating, albeit slowly? In some applications this could have disastrous consequences, as you can imagine.

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#4

Re: detecting rotation of motor

02/15/2009 6:26 PM

We use an ordinary proximity sensor in some of our motors. A timer receives the pulses and is continually reset each time it receives a pulse. If the pulses stop, the timer runs through and triggers an alarm.

For most of our motors, we have current sensors. We sense over-current as well as under-current. Whichever alarm is triggered, we investigate.

regards,

Vulcan

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#5
In reply to #4

Re: detecting rotation of motor

02/15/2009 6:50 PM

zero speed may be a catch phrase of sorts.

We use every kind of imaginable means to interlock equipment using motion sensors, physical limit switches, inductive prox switches, photo eyes, opitcal roto pulsers and even some analog positioning with encoders, servo, serco control inputs to PLCs---you name it.

I wasn't comfortable with "zero speed switch", the first time I heard it--But I knew what it was and just adapted to the term.

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#6

Re: detecting rotation of motor

02/15/2009 7:34 PM

Here's a possibility:

http://www.ab.com/safety/prod_directory/interlock_switches/guard_locking_switches/cu2_stop_motion_det/

The time for determining that rotation has stopped can be extended to up to 40 minutes - trouble is, if it was keeping a guard locked, you'd have to wait for the preset discrimination time (up to 40 minutes) before you could open the guard!

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#7

Re: detecting rotation of motor

02/15/2009 10:48 PM

Which is this application, where supply is ON, but motor is not running?

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#10
In reply to #7

Re: detecting rotation of motor

02/16/2009 11:39 AM

Which is this application, where supply is ON, but motor is not running?


In fact I want to switch off the supply of motor if it stops running (due to any fault condition).

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#8

Re: detecting rotation of motor

02/16/2009 3:06 AM

Reasons for a non rotating electric motor:

  • No terminals voltage at all → No problem, no need to switch off
  • Locked rotor condition → Motor current must be much more higher than normal running. The current value can be used to trip the motor
  • In a three phase motor, one of them is out → Motor in two phases cannot run and current is higher as in the previous case. Similar solution

Kind regards

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#9

Re: detecting rotation of motor

02/16/2009 4:41 AM

We use current sensing switches made by Hawkeye. They can be purchased though Kele Controls.

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