ML1100 DC Voltage and Amps

[Scada Tom 0]

For an ML1100 I want an input from a 0-30 VDC source, I can do that with a voltage divider and a DC input module

For DC current, I need a shunt, max of 5 amps, MY input, does anyone have a source for DC shunts?

[Ken Roach 194]

Murata, Crompton, Simpson, Galco... any company that makes a DC ammeter will also make shunts.

Let's say you get a 0.01 ohm shunt, so 5 amperes flowing through it will drop just 50 mV.    You'll want a signal conditioner to convert that millivolt signal to a 0-10V DC signal for the MicroLogix analog input channels (or 4-20, if you choose to add expansion I/O and use current loops).

The signal conditioner amplification is necessary, I think, to give you a reasonable resolution on the analog input channel.   

The MicroLogix 1100 built in analog inputs are only 10 bit resolution, so they give 0-1023 counts for 0-10V.    That gives you roughly 1 count per millivolt, so your resolution would be only about 0.1 amperes on a 5 A current flow.

That's assuming you are measuring that 30V DC... if you're measuring a higher voltage you *definitely* want a isolating signal conditioner to protect the PLC.

 

This isn't based on much experience on my part measuring DC power with a logic controller, just on my understanding of how shunts and PLC analog inputs work.