If I measure voltage drop between terminals of my bench power supply (spec) I get -15 mV when channel output is turned off.

Why it is not reading 0? I believe it's due to internal impedance of the power bench and surely accuracy of the bench is limited (technical spec says program accuracy is V: ±[0.5% of reading+2digits])- but, for channel being off shouldn't I read 0V?

When I apply voltage I still see difference between what power bench displays and what multimeter reads, though I am more happy with that as it gets smaller with voltage increasing (for 1V and 5V diff is 6mV). But diff is different for positive voltage (+6mV) and for 0 (-15mV).

I am experimenting with transistors, therefore I would like to get good accuracy for voltage/current. Ultimately I will trust my multimeter but would like to understand what I am working with.

  • \$\begingroup\$ Leakage current, I bet. I suspect that voltage will go away if you apply any sort of load to it. If you need really high accuracy, you're going to need a more expensive supply, but your experimentation should be possible cheaply with a potentiometer to limit current and a half-decent multimeter to measure it. \$\endgroup\$ – Hearth Jan 20 '19 at 18:32

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