I need a "resistance to voltage or current" device

[mckeand13]

I need to make a test to verify correct parts are installed in an assembly. I'm looking for a correct motor voltage. I have verified that the different voltage motors we use have very different resistances across the leads.

I'd like a device then, that will turn a resistance value into a voltage or current that I can use as an analog input to a plc. I can then determine if it's the correct motor based on parameters that I set.

Has anybody ever used/seen/heard of a device to do this before?

Thanks!

 

[Skogsgurra]

Sending a constant current through the winding should do the trick. If you use 1 mA, you will get 1 mV/ohm. For motor windings, you will probably want to use 1 A or something in that range to get 1 V/ohm. Many ordinary linear power supplies (lab supplies) can usually be set to deliver an adjustable constant current. Use Kelvin connection (separate current and voltage connections) for best accuracy.

Gunnar Englund

http://www.gke.org

 

[NWBeaver]

This sounds like an application for a circuit known as a "Wheatstone Bridge".

You can do a Google for Wheatstone Bridge and find all the info you need, but in a nutshell, it is a bridge circuit using several known resistances and one unknown resistance (your motor winding), and a voltmeter. When the circuit is balanced (the resistance values are equal) the voltmeter reads 0 volts. Different unknown resistances will cause different voltage readings across the bridge.