Hi guys and girls.
I have a power supply of 480V DC that powers some equipment (quite steadily and boring, no signals or exciting stuff) that pulls 0.8 amps. I wanted to do some measurements on this and I thought it was going to be very simple, but oh no, not so much. I would like to measure the voltage and the current the gear is consuming using picoscope, because its nice to see what is going on.
Since 500 volts is quite high I started with reading up on people that have tried the same, and I quickly found that first of all there was a good chance of frying the gear and a differential probe was the way to go, so I bought two of the chinese ones that everyone loves because of the low price.
My idea was to just use the differential probe directly across the 500VDC source, and that worked like a charm. My next idea was to put two resistors in series with the equipment, one for each line, thinking both of them would consume some volts. I would then be able to measure the voltage, and that voltage across one of the 4 ohm resistors should also give me a pretty good idea what the current in the system is doing.
When measuring a handheld scope using one 1x probe, it works pretty good I have to say. But, seeing that I want to save this and use as reference later on, the picoscope is what I really wanted to use.
Using a differential probe actually worked pretty good, but I thought it was a bit to noisy at 50x. One solution then would be to up the resistance a bit, but I cant steal to much of the voltage either. So, I thought about using the a-b differential method using two probes connected together and then measure across the resistor. A calculation in Picoscpoe would then give me the DC voltage across the resistor, and I was hoping to see the same as the handheld oscilloscope. Unfortunately that did not happen. When I connected the probes across the 4 ohm resistor, they both gave me a channel overrange alarm and the numbers made no sense whatsoever. The laptop and the picoscope is not grounded or connected to power anywhere.
Any idea what is causing this, and better, is this what is expected or can I adjust my experiment to give me better values.
I have a picoscope with 4 inputs. Two differential probes 50x/500x. 2x 4 ohm resistors, or even 2x 10 ohm resistors. The goal is just to be able to read the amps in my circuit, and I dont have much fancy equipment to be able to do that.
Thanks for any inputs on this.