4-20mAmp supply for testing

[jwhitmore]

I'm currently working on a 4-20mAmp sensor system, so to test this I wondered if I could get a piece of kit that would emit a 4-20mAmp signal, maybe in a standard wave form like a sine wave or something, but with very long period. I'm taking a sample every one or two minutes so given that sampling rate some formula, can't remember which, would dictate the frequency of the signal that I'd recognise as what I was expecting.

Maybe given that really low frequency the easiest thing to do would be to rig up a circuit to a micro controller that could output a current. Seem to remember an early eev blog video on creating a current sensor. Not exactly calibrated but maybe?

I'm embedded SW so have limited experience of test gear, (can just about use a scope ;-) so maybe a basic signal generator can do this. My only issue might be that I'm going to leave the unit on for a soak test of weeks duration.

[langwadt]

I'm currently working on a 4-20mAmp sensor system, so to test this I wondered if I could get a piece of kit that would emit a 4-20mAmp signal, maybe in a standard wave form like a sine wave or something, but with very long period. I'm taking a sample every one or two minutes so given that sampling rate some formula, can't remember which, would dictate the frequency of the signal that I'd recognise as what I was expecting.

Maybe given that really low frequency the easiest thing to do would be to rig up a circuit to a micro controller that could output a current. Seem to remember an early eev blog video on creating a current sensor. Not exactly calibrated but maybe?

I'm embedded SW so have limited experience of test gear, (can just about use a scope ;-) so maybe a basic signal generator can do this. My only issue might be that I'm going to leave the unit on for a soak test of weeks duration.

a 4-20mA input is usually just a resistor to ground so the the input current generates a voltage suited for ADC, for example 150R for 0-3.3V with 0-22mA

so a signal generator between the input and ground would most likely work, just remember to take the output impedance of the generator
into account 

[orion242]

Something like this this is what alot of hvac techs use.

http://www.kele.com/tools-and-test-equipment/signal-generators.aspx

A current limited power supply or a lm317 setup in current control would get the job done for alot less.

[jwhitmore]

Thanks a million for the info, I'm tempted to build something based on the lm317 but I'll have to think about it.