Motor Current Monitoring

[Old No. 7]

We have a customer that wants to monitor current on all the 480v motors on a piece of equipment - 5-6 motors, all 5 HP or less. Ideally, I'd like to find something with Ethernet/IP comms to eliminate adding another analog input card to the PLC, but that's not necessarily required. We could just put VFD's on everthing, but that seems like overkill and cabinet space may be a bit of an issue. I looked at the AB E300 overloads, but those look to be about the same price as just using a VFD. Current doughnuts and a transducer are an option, but I was hoping there was a more elegant solution.

 

[jaden]

I don't have exact part numbers, but Littlefuse has motor monitors that can be networked.

 

[JesperMP]

Current transformers with integral 4-20 mA transmitters are ubiquitous.
Forward the 4-20 mA signals to a local Ethernet/ip i/o node.
It is the way it is done, you use standard components, it does not cost an arm or a leg, it does not require much space. Elegant enough for me.

The "monitoring relays" that can be networked are usually bulky, require transformers on all legs, and are just way overkill if you just want to monitor 1 phase via your PLC.

 

[Tom Jenkins]

http://www.plctalk.net/qanda/showthread.php?p=753715#post753715

 

[EJ92]

Could This work?

 

[jraef]

What's the purpose? Monitoring current alone has its uses, but remember that current will fluctuate with voltage, not just with load. If you want to truly monitor load, you will get more useful information by monitoring kW, because that always represents the true shaft load on the motor. So for example if they want to monitor when a bit or blade is getting dull, do it with kW. If they just want to confirm that a motor is truly running, not just that the contactor is closed, then current is fine.

These guys have a nice line of retrofit current and/or kW sensors that use split core CTs so that you don't need to remove wires. You will see their distinctive blue color used in products sold by a number of other companies, they are the true manufacturer.
http://www.nktechnologies.com

 

[janner_10]

What's the purpose? Monitoring current alone has its uses, but remember that current will fluctuate with voltage, not just with load. If you want to truly monitor load, you will get more useful information by monitoring kW, because that always represents the true shaft load on the motor. So for example if they want to monitor when a bit or blade is getting dull, do it with kW. If they just want to confirm that a motor is truly running, not just that the contactor is closed, then current is fine.

These guys have a nice line of retrofit current and/or kW sensors that use split core CTs so that you don't need to remove wires. You will see their distinctive blue color used in products sold by a number of other companies, they are the true manufacturer.
http://www.nktechnologies.com

We have a customer that wants

This is normally the point common sense goes out the window!

 

[qwemx]

https://www.youtube.com/watch?v=hikcIW5h0y8

 

[Old No. 7]

Could This work?View attachment 45730

Possibly, although Modbus RTU isn't ideal.

https://www.youtube.com/watch?v=hikcIW5h0y8

Those are interesting. It's a shame they don't have an AB logo with Ethernet/IP comms

 

[Old No. 7]

Current transformers with integral 4-20 mA transmitters are ubiquitous.
Forward the 4-20 mA signals to a local Ethernet/ip i/o node.
It is the way it is done, you use standard components, it does not cost an arm or a leg, it does not require much space. Elegant enough for me.

Cheap and easy, where's the fun in that?