Electronics > Beginners
I keep ruining circuits with oscilloscope
DDunfield:
--- Quote from: mikerj on May 28, 2019, 09:33:40 am ---This should be a high impedance, try putting your multimeter in mA mode and measuring current between PSU outputs and ground, this should give a very small current in the uA range.
--- End quote ---
Only problem with using a meter in current mode to verify that no significant current is flowing is -- what if you are wrong (isn't that why you're testing)?
If this happens, at best you'll pop a fuse in the Multimeter (proper replacements can be expensive) or if a cheap unfused meter you could smoke the meter and/or the DUT.
Leave your meter in voltage mode and measure voltage across a couple-K resistor between the PSU and ground. If it is a high impedance leakage, you should read a very low value, (you can work out the actual current with Ohms law if you want). If you are wrong, the worst you'll do is smoke a cheap resistor (be aware that it could get very hot in this case).
Dave
Shock:
Someone brought up a good point a few weeks back about charging the cap in an oscilloscopes input and then on the next measurement unknowingly discharging into a sensitive circuit/component.
dnwheeler:
Are you sure it's your o-scope probing causing the problem? Perhaps the timing is just coincidence - you're doing the same steps in approximately the same order, so the same failure could just be happening at the same time after power-up.
djacobow:
Why do you believe that PSU has isolated outputs? Looking at the datasheet I see no mention of isolation at all.
http://www.farnell.com/datasheets/2718447.pdf
Assuming it is not isolated, depending on the orientation of the power plug coming in, I'd expect the negative terminal to be shorted to neural or hot. If the latter, then hooking up the scope "ground" to that should create excitement, no?
Audioguru:
It is illegal (and deadly) to have a power supply to have one of its output wires connected directly to an AC wire. Maybe this one is shorted like that.
Since the servos did not work properly BEFORE the 'scope was connected then the 'scope is not the problem.
I agree that the cheap Chinese products might have their power polarity marked backwards.
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