current measurementvfdvoltage measurement
Is it possible to measure the output of a Variable Frequency Drive without relying on it's display data? I tried to measure the line voltage with a DMM and current with a clamp meter but it shows inaccurate results. I'm running the motor at 50Hz and the carrier frequency is 6kHz if that matters.
Thank you in advance!
While a wall adapter is usually isolated, it likely isn't rated to 1kV. A simple solution would be to find a DMM with logging capability and CAT III/IV 1kV isolated external power source or long battery life. Here are some candidates:
Another option is to use a simple micro with an ADC, float the whole circuit at chassis voltage, then use proper isolation techniques (more than just optoisolation -- if you're not sure I suggest another question) to communicate with a PC over your preferred serial connection (UART -> opto -> RS232 -> USB -> opto -> PC, with cable shield voltage measurement and warning, would be my choice). Note that this means you can't touch anything on the floating (hot chassis) side of the widget. This way you can eliminate the power supply isolation worries by just using a battery, and still run it easily for 6 months to a year without replacing it, following thought on power consumption and sleep modes (ie: MSP430). Also note that a sputtering machine generates electrical noise, so you may need to use RS485 with error detection/correction algorithms.
I like using the closed-loop Hall effect LEM current transducers for this sort of application. They're a lot cheaper than a genuine current probe for a scope (only about $20 or $25), have excellent accuracy and bandwidth from DC up to a couple hundred kHz.
The particular one I've linked has a +/-6A range, but you can put a couple loops through to get +/-3A full scale. Just feed it a reasonably clean +5V and Robert's your uncle.
If you want to make more of a project of it, you can offset the output with differential output between the LEM and a 2.5V reference, or actually subtract it with an op-amp and bipolar supplies, but for most purposes, just adjusting the scope zero will do the trick.
Best Answer
Not so easily. It's a really "dirty" signal if you look at it on an oscilloscope. You would need something like a power meter with fairly wide bandwidth, and to measure both current and voltage together (ie. simultaneous samples at a high sample rate, likely with anti-aliasing) and the meter would have to multiply and integrate the result .
Such meters certainly exist, but maybe they are not so affordable.