Measuring amperage with a PLC

[Bolt]

What would it take to build some PLC logic to measure amperage of a load (3 phase, 20-30 amps under normal load), and do something with the PLC when it goes out of range?

Is there some sort of coil that I can run each leg through (seperately) and run back the PLC? Does this have an analog input source?

 

[rsdoran]

You could use these relays or transducers for inputs to the plc.
http://www.crmagnetics.com/

The relays are really easy to work with, read on them first.

 

[RichardB]

Ohio Semitronics would be another source for Current/Power/Voltage measuring products.


https://www.ohiosemitronics.com/

 

[TConnolly]

A second for OhioSemitronics...

UNLESS, the load is a motor. If its a motor then I recommend
http://www.loadcontrols.com which makes transducers specifically designed for motors.

 

[WireGuy1950]

I second RSDoran's recomendation of CRMagnetics, but I have used the CRD4170/80 model with 3-phase input coils and 0-5vdc individual outputs which you can then scale in the PLC and do whatever else you need to do then.

 

[BobB]

Why not use a digital power monitor with Modbus RTU comms? That is my normal practice these days as I get a whol;e lot more info.

 

[SLC_Integrator]

Why not use a digital power monitor with Modbus RTU comms? That is my normal practice these days as I get a whol;e lot more info.

What if its an AB PLC or some other device that doesnt talk Modbus?

All PLCs support 1-5v or 4-20ma whereas Modbus requires a Prosoft card or similar and a bunch of code to make it work.

I say stick with some kind of transducer that gives an analog output.

 

[BobB]

I am quite surprised if AB and others have not supported Modbus RTU at least. The most common form of comms in industrial applications? WOW!!!

 

[SLC_Integrator]

Micrologix will do Modbus RTU slave but thats about it.

I think Prosoft make 90% of their revenue from people wanting their SLC or CLX to talk Modbus.

 

[rsdoran]

It all depends on need, if just wanting know when an over current condition has occured the relay may work. If needing to monitoring the actual range of current involved then something else may be ne.

Any the suggestions it just depends on the depth of the necessary.

 

[allscott]

I am quite surprised if AB and others have not supported Modbus RTU at least. The most common form of comms in industrial applications? WOW!!!

Most AB platforms only support Modbus throug a third party card (prosoft). And they are a PITA to set up. AB is pushing it's own industrial networks and I would assume that is why they don't seem to be interested in Modbus.

 

[Tom Jenkins]

The in rack cards from ProSoft are a PITA. However, I've found the Din rail units to be much simpler and they offer a lot more options.