Current monitoring/Motor load monitoring

[Wizlock]

Hello, I was wondering if anyone got any suggestions for equipment that might be used to determine if a motor is running or not. Nothing too advanced, not undershoot or overshoot. Today the feedback from the motor that determines if it's running or not is only a NO on the contactor. If it's unplugged it will still say that it's running.

 

[JesperMP]

See this previous post:
http://www.plctalk.com/qanda/showpost.php?p=56411&postcount=9

We use it to sense if 1 out of 3 phases is missing. You can possibly just monitor 1 phase. It is quite inexpensive.

 

[JohnCalderwood]

You are right, the NO contact on the contactor basically tells you that the control circuit is healthy and the contactor has been energised.

For many drives (albeit conveyors, rotary valves, fans) we have a rotation sensor on the driven part.
We also fit local isolators with an aux contact, so that if this is switched off, then you lose the healthy signal and cannot energise the contactor.

If you have an ammeter on the motor and know the normal loaded current, then if that is much less, then assume it is not running.

 

[Wizlock]

Thank you for your input, I was able to find these which are similar and perfect for my intentions. Rotation sensor is out of the question for this type of installation.

http://www.nktechnologies.com/current-sensing-switches/as1-compact-case-current-sensing-switch/

 

[JesperMP]

Our first version of sensing phase current was something like that.
But we found that the fixed leads were a hassle. Unless you PLC is right next to the power curcuit(s) you want to monitor, you have to provide some intermediary terminals to extend the wires.

 

[osmanmom]

if the coupling shaft broken

 

[tragically1969]

Our first version of sensing phase current was something like that.
But we found that the fixed leads were a hassle. Unless you PLC is right next to the power curcuit(s) you want to monitor, you have to provide some intermediary terminals to extend the wires.

Difficult to know the set-up but just put it at the cabinet end on the output of the contactor

 

[Tom Jenkins]

I've used the NK devices in various configurations for years. They have lots of models, including many with terminals instead of pigtail leads. They are also available at AutomationDirect.com

 

[tragically1969]

if the coupling shaft broken

How do you know its got a coupling shaft ?

There would be more to worry about if a coupling shaft had broken than if the motor was running or not........

 

[osmanmom]

i don't know whether the motor got coupling or not,i only guess

may i know what type of motor do not have coupling?

 

[tragically1969]

may i know what type of motor do not have coupling?

A motor doesn't have a coupling......it's purely dependent on what the motor is driving.

 

[Phil Buchanan]

Hello, I was wondering if anyone got any suggestions for equipment that might be used to determine if a motor is running or not. Nothing too advanced, not undershoot or overshoot. Today the feedback from the motor that determines if it's running or not is only a NO on the contactor. If it's unplugged it will still say that it's running.

We could serve you better if we had more detailed info on the load you are trying to monitor. Is it a fan, pump, conveyor, etc.?

Also I know a lot of people do it but measuring current alone is really a poor indicator of accurate load for protection purposes. Measuring power is much more accurate and linear. Motors still use current even under no load as you have magnetizing current and no load losses to deal with. Each motor no load current is very different and depends on windage, air gap, etc.

For accurate power measurement I like to use this line of products http://loadcontrols.com/

I have a couple hundred of these installed and we really like them. We use them on conveyors, slurry pumps and plastics reclaim and edge trim grinders.

 

[osmanmom]

A motor doesn't have a coupling......it's purely dependent on what the motor is driving.

thank's for the info.


Others are the load consistence ?

 

[Wizlock]

We could serve you better if we had more detailed info on the load you are trying to monitor. Is it a fan, pump, conveyor, etc.?

Also I know a lot of people do it but measuring current alone is really a poor indicator of accurate load for protection purposes. Measuring power is much more accurate and linear.

For accurate power measurement I like to use this line of products http://loadcontrols.com/

I have a couple hundred of these installed and we really like them. We use them on conveyors, slurry pumps and plastics reclaim and edge trim grinders.

The motor is used in a vibration feeder. AC 230V, pulling 11A at delta.

 

[Wizlock]

It is to give feedback to intouch screen if the motor is on or not. Now it can give a false impression if the plug is out, but the contactor is activated (will show that it is running). Also it will be used in the program as a interlock function for other equipment.