Sometimes I need to calibrate devices which have current outputs. Typically the devices output 4...20mA currents and I have been using a calibrated 250Ohm precision resistor(goes to a single-ended data acquisition channel) to measure current output( measure of course as a voltage and then divide by the resistor value).
This is very common way of measuring such current loops. But my concern is that none of the current sourcing devices I encounter have specified output impedances in their manuals/datasheets. Here is an example device.
As you see there is no output impedance mentioned in the manual. So I was thinking to be on the safe side maybe it is better to use an active circuit to minimize the possible error due to the current source's output resistance and the 250Ohm shunt combination:
I also see some noise time to time. So my aim is to measure the current as precise as possible and the error should not be more than 1%. In this case I'm not even sure if it would be waste of time to make an active circuit. The problem is I don't know these device's output impedances so that I could estimate the error when shunted with 250Ohm.
What is output impedance of such current output devices roughly? Is it worth to worry about precision here and to use an active circuit? I would appreciate any ideas.