Non Contact On-Off Status Monitoring of Motor

What kind of motor & motor drive?

April 30,2010

Any motor operating on AC 50 Hz.Present range is up to 60 HP.

What difference does it make ? Clarify the doubt.

Muni Razdan

If the motors were driven with speed controllers/VFDs etc., it would be necessary to distinguish between "Motor Stopped" and "Motor Power Off".

As these motors appear to be directly connected to the AC supply, I assume you are looking for sensors which will indicate whether the motor is moving or stationary.

Then again, you could still be looking for a signal indicating that the motor power is or should be on or off (by monitoring either the current to the motor, or the state of the motor contactor(s)).

"Motor On-Off status" is not as straightforward at it seems at first sight. You must clarify the doubts.

April 30,2010

1. Motors are not driven through, in present case, through Speed controllers/ VFD.

2. Presently, we take a signal from relay contact and actuate our relay, 240 V, 50 Hz or 24 V DC and then take auxiliary contact of our relay to micro controller. This is for digital inputs.

3. Alternately, conductor of secondary of a 0-5 A CT signal passes through an isolating CT with hole ensuring isolation.

This latter approach guarantees status irrespective of Controller / VFD situation you mention.

4.The need for a non-contact measurement arises where customer is unwilling to touch existing relay contact or is averse to installation of a CT in a running plant.

5.All kinds of ideas can be considered from motion sensors, IR sensor(used for contact less tachometer), audio sensors (with simple amplifier circuits with tunable thresholds / signature detections which can be microprocessor detected) or video (low cost CCDs with basic image processing algorithms).

I hope above clarify some doubts but do ask for any more information.

How does one attach a file in this communication?

Regards

Muni Razdan

"This latter approach guarantees status irrespective of Controller / VFD situation you mention." - but FYI the definition of 'ON' could still include 'moving'.

"How does one attach a file in this communication?" - unfortunately, one doesn't. CR4 has no mechamism for attachments. You can include images within a post (use the green camera symbol - - at the top of the comment edit box), and you can copy and paste text from other documents, but that's about it.

The easiest way is monitoring the motor current either with a optically insulated sensor (for example from AVAGO) or with a current transformer.

May 02,2010

Thanks.

Please advise the model number as their seem to be any number at site.

Roughly,what is the price range like of this sensor ?

Muni Razdan

My anti-skid braking system on my Dodge Caravan uses a toothed wheel and a magnetic sensor. This is non-contact, and would require only a moment to install on any part of a shaft. Such sensors would be as close as your nearest GM dealership! However, you can simply order the appropriate components from sources on line.

This should be pretty much "off the shelf" . For instance, toothed wheel sensors sets here, or Honeywell's mag sensorsare

very effective, and easily obtained and installed.

There are ammeters that have a U-shaped end rather than a CT that closes completely around the wire to be sensed. It seems that this concept would be ideal for your needs. A "clamp-on" style of CT would also work.