How to measure the PWM current with a DMM

I have a Fluke 87V, which is a True-RMS DMM, and I would like to measure the current in my circuit. I have 2 motors being driven by a PWM so I wonder if the DC current or the AC current measurement of the DMM will be do the job for the PWM current. Is it there a recommended way to measure this kind of "mixed signal" using a regular DMM as a Fluke 87V?

• You might want to consider a Hall effect sensor and an oscilloscope, which will show you both AC and DC current components up to reasonably high bandwidths. A good digital scope will compute RMS and average currents for complex periodic waveforms with ease. Jan 29, 2014 at 18:37
• That's a good idea, but I dont have a one at hand now... Jan 29, 2014 at 19:06
• Too bad you didn't buy the 89V, which has AC + DC TRMS measurement capability. A closed-loop Hall sensor as suggested by @Madmanguruman will only run you ~\$25 and might be all you need. May 29, 2014 at 22:25
• 89V? I just know the 87V, and there isnt any 89V at Fluke's website either.... May 30, 2014 at 2:05

Is it there a recommended way to measure this kind of "mixed signal"?

Use a DMM with a AC+DC TRMS measurement capability?

• I fogot a "using a regular DMM" :P Jan 29, 2014 at 19:06

What of sort frequencies, voltage levels?
(I'm not an AC power guy so if you blow something up...)
But I could imagine a shunt, and then a low pass and high pass filter. Just RC's if you can throw power away.. and move heat away. You'd have to work out the response functions.

• Well I guess that's not a bad idea for low power applications, but I was hoping to measure some 10A at least, and filtering this can be tricky... Jul 29, 2014 at 12:32
• OK 10 A's, what's the PWM frequency? With a 0.1 ohm resistor you'd have a volt of signal to play with. Or 20 milli-ohm use the 200mV range on the DMM. Jul 29, 2014 at 12:45
• It's more like a generic question, not specific to one particular case, so many people can benefit from this, even if they projects are different. Mine had a 3KHz PWM. Jul 30, 2014 at 13:09