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?
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asked Jan 29, 2014 at 16:51
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\$\begingroup\$ 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. \$\endgroup\$– Adam LawrenceCommented Jan 29, 2014 at 18:37
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\$\begingroup\$ That's a good idea, but I dont have a one at hand now... \$\endgroup\$– mFeinsteinCommented Jan 29, 2014 at 19:06
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\$\begingroup\$ 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. \$\endgroup\$– Spehro 'speff' PefhanyCommented May 29, 2014 at 22:25
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\$\begingroup\$ 89V? I just know the 87V, and there isnt any 89V at Fluke's website either.... \$\endgroup\$– mFeinsteinCommented May 30, 2014 at 2:05
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2 Answers
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Is it there a recommended way to measure this kind of "mixed signal"?
Use a DMM with a AC+DC TRMS measurement capability?
answered Jan 29, 2014 at 17:14
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\$\begingroup\$ I fogot a "using a regular DMM" :P \$\endgroup\$ Commented Jan 29, 2014 at 19:06
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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.
answered Jul 28, 2014 at 23:21
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\$\begingroup\$ 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... \$\endgroup\$ Commented Jul 29, 2014 at 12:32
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\$\begingroup\$ 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. \$\endgroup\$ Commented Jul 29, 2014 at 12:45
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\$\begingroup\$ 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. \$\endgroup\$ Commented Jul 30, 2014 at 13:09