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Microamps and Millivolts Measurements on UT61E
JenniferG:
So this is normal? I shouldn't return it? I have 12 days to return it. The millivolts vs volts is off about the same as well.
I'll have to study burden voltage and shunts and all that in multimeters.. I'm a newb. I just don't know if I got a lemon and only have aroudn 10 days to return it. Seems like Uni-T would of picked a better value for shunt resistor which is mroe accurate.
joeqsmith:
Yes, it's normal for the UT61E and others and basic circuits 101.
--- Quote ---Seems like Uni-T would of picked a better value for shunt resistor which is mroe accurate.
--- End quote ---
Like anything, it's a tradeoff. If you want a constant burden, use an external shunt and measure the voltage across it.
rsjsouza:
As others have said and the references that were sent to you also make it clear, it is not a lemon but a normal behaviour that does not indicate any problems with it. Any meter that measures currents with a shunt resistor will have this behaviour.
bdunham7:
--- Quote from: JenniferG on December 08, 2022, 12:30:36 am ---So this is normal? I shouldn't return it? I have 12 days to return it. The millivolts vs volts is off about the same as well.
--- End quote ---
Yes, the issue of shunts, resistance and the so called burden voltage (the voltage drop across the meter in the current ranges) is an issue with any meter and does not represent a defect. You should do what I suggest with your other meter in series just to make sure that the entire difference is actually due to this and there isn't some other problem. The readings will vary, but the two meters should agree (within tolerances) at all times if they are in series.
The millivolts vs volts would concern me a lot more as there isn't a similar, readily apparent reason for it if the difference is significant. Can you elaborate on that?
JenniferG:
--- Quote from: bdunham7 on December 08, 2022, 01:16:41 am ---The millivolts vs volts would concern me a lot more as there isn't a similar, readily apparent reason for it if the difference is significant. Can you elaborate on that?
--- End quote ---
Doing a PWM write of 7 (out of 255 values -- 8 bit) from pin 46 on Mini Mega 2560 to a resister/LED (same DIY vactrol as above for amperage test). The red terminal is connected to the resistor leg and the other terminal to ground. It reads 0.1418V -- as approximately predicted beforehand -- on volts setting and 67.2 mv on millivolts setting.
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