My company uses many different techniques to measure the current draw of DC motors. When controlling the motor with a mosfet driven by a PWM signal, the current trace is a square wave. Some DAQ devices measure this current differently and some require specific filters. Is there a standard (ASTM prefferably) for measuring this current?

 

IMO, if the waveform is not sinusoidal or pure dc, it is always measured as rms.

 

The best way is to use a resistor which is heated by the curent and a small thermistor to get this temp.
This way you really see the current and not anything like rms or blocks and sampling time problems.