I need to monitor current drawn (around 500mA) in a 24VDC solenoid circuit, without adding to or changing the actual levels, and then pass this information to my data acquisition equipment via a 4-20mA loop.

Any help understanding how to do this would be appreciated.

 

Sounds like what you need is a Hall Effect current sensor with a 4-20 mA output. Because we are talking about DC there is no burden voltage. You must be careful to select one that is suitable for DC current in the range that you need. But it should be an OTS item. Try DigiKey for the Honeywell sensors for a start.

Regards
cww

 

As well as the method Curt suggests you could use just a simple shunt e.g., 0.1 Ohm and monitor the voltage drop across it with a mV input card (50 mV @ 500 mA).

If you want to provide current test points, use a forward biased diode in series with the coil, you can then connect your meter without interrupting the circuit.

Roy