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Strange readings when measuring current.

DMM7510 7½-Digit Graphical Sampling Multimeter
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Ilya Grudovik
Posts: 18
Joined: October 30th, 2018, 1:54 pm
Country: Belarus

Strange readings when measuring current.

Post by Ilya Grudovik » November 26th, 2018, 1:20 am

Measure the current with open inputs:

10µA range - 1.4 pA
100uA range - 24 pA
1 mA range - 127 pA
range 10 mA - 647 pA

These are excellent numbers around 0.1 ... 0.2ppm

Measure the current with shorted inputs:

10µA range - 33nA (3300ppm !!!)
100 uA range - 330nA (3300ppm !!!)
1mA range - 3.3mkA (3300ppm !!!)
10mA range - 28mkA (2800ppm !!!)

These figures are possible in the presence of thermal EMF = 33 µV at the input (28 µV for the last range)

And this is not a thermo emf jumper. After measuring the DCV, I see nanovolts.

This is something internally.

Moreover, this displacement does not create any problem if we measure the "current source".

But it creates problems when measuring the current that generates a voltage source and series resistance. And a two-year error of 20 ppm we get at a voltage of just 1.65V and less. Unfortunately, I have nothing to test this hypothesis.

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