Looking at slide #3 of the 5th lecture, I'm reminded of the concerns you might have measuring a high-side shunt in a high voltage/high power circuit.
If you're measuring with a scope or data logger, you need to use 2 single-ended channels, one on each side of the shunt, because a scope or data logger normally have a grounded (earthed) chassis. If you try connecting the ground clip of a single-ended scope channel to the low side of a shunt, you could destroy the instrument due to high currents flowing from the UUT through the instrument's chassis to earth.
If the instrument's channels are differential or if you have a differential probe, then you can measure the voltage across a shunt with one channel of the instrument.
Floating a scope or data logger's power source is a bad idea if you're attmempting to make a high side shunt measurement with a single channel because the instrument's chassis could be at a high and dangerous voltage with respect to earth. One brush against the instrument and you get a potentially lethal shock.
rswanson: using an op amp to square an analog signal is fairly easy--check app notes from any major analog vendor, it's a classic circuit configuration. I know some early but still valid app notes from ADI show how to do it.
To all: remember, when you talk with an experienced vendor, they will raise issues you may not have even thought you needed to be worried about--but hey, it's worth listening to what they say, even if it may not be a concern of yours in the end, in your situation.
rswanson: by analog, I meant a basic op amp scaled to transform the input signal x the resistor size--you don;t really need to do a true multiplication of two unknown analog signals. And I think vendor like Microchip do make power-measurement ICs which combine analog and digital blocks in one easy-to-apply device.
Suggestion to the moderator: Have the comments add to the bottom of the list or something so that when comments are made, the page doesn't skip and it's not so hard to read the older posts
Looks like for some of you, learning about the SMU was a good thing! Agilent, Keithly make them, I am sure there are others as well. And maybe NI has some simialr setup, too, don't know.
In a previous lecture, Bill you mentioned using an analog IC as opposed to using "all digital" to determine power. Would you mention one or two of the IC's you use? Thanks
SMU was Stimulus - Measurement Unit in some of the larger ATE installations I was involved with. Same kind of idea, but certainly not bench top eqipment, more like a 19" rack cabinet.
Need to know what you are measuring and the rating of the test equipment. In my area we measure milliamps at low voaltage to 100's of amps at medium voltages ( 1- 6 Kv)
In case you want to get a head start, here's the first question of the day: For those doing AC-line related measurements, how "sine-like" is your AC signal? And how do you know this?
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