| Electronics > Projects, Designs, and Technical Stuff |
| Measuring PWM current? |
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| iXod:
For a PWM voltage, is using a shunt and observing voltage with oscilloscope the only way to get even a ballpark current measurement? Thanks. |
| jmelson:
--- Quote from: iXod on April 28, 2019, 09:16:11 pm ---For a PWM voltage, is using a shunt and observing voltage with oscilloscope the only way to get even a ballpark current measurement? Thanks. --- End quote --- Well, in cases where you actually NEED to measure current, you can use an instrumentation amp. I used the AD620 in a PWM servo drive to measure the voltage across a small resistor (fraction of an Ohm). The actual voltage was above the ratings of the AD620, so I used a set of matched resistors to make a pair of voltage dividers. So, both inputs of the voltage dividers was seeing a 60 V square wave, but the difference between them was less than 1 V. It worked amazingly well, you needed to look VERY closely at the scope to see any trace of the common mode leaking through. Jon |
| iXod:
But the output of the inst. amp will also be PWM, yes? Which will require... an oscilloscope to measure the current. |
| OM222O:
you must use a true rms to dc chip like this one: https://www.analog.com/media/en/technical-documentation/data-sheets/AD636.pdf |
| iXod:
--- Quote from: OM222O on April 29, 2019, 01:28:37 am ---you must use a true rms to dc chip like this one: https://www.analog.com/media/en/technical-documentation/data-sheets/AD636.pdf --- End quote --- But PWM can't be accurately measured (or converted?) when using RMS means--the whole reason for my initial post. |
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