Author Topic: nA/uA readings issue [SOLVED]  (Read 245 times)

alexsh1

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nA/uA readings issue [SOLVED]
« on: November 13, 2018, 09:20:06 AM »
Hello all,

After tinkering with the CurrentRanger, I discovered the following issue:


I had to increase "average" as I am using it exclusively with the OLED screen.
Otherwise, no other changes to the firmware.

Any idea whtat's causing it please?
« Last Edit: November 13, 2018, 08:02:52 PM by Felix »

Felix

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Re: nA/uA readings issue
« Reply #1 on: November 13, 2018, 10:32:42 AM »
Alex,
Thanks for the video,
The OLED reading is given by sampling the output via the SAMD21's 12bit ADC, but I would not expect that behavior.

What is the reading in uA on a DMM vs the OLED? Please test this with OLED connected and disconnected. When you disconnect OLED please power cycle the unit (OFF, then ON without OLED)

I am primarily interested in the output directly from the opamps to be always accurate. The software averaging for the ADC readings can always be tweaked or optimized based on findings like this or use cases which I haven't encountered. In my limited testing, I have seen instances where noise picked up by cables can cause that type of thing.
Essentially a 4uA (wrong) reading means the ADC is reading 1-2mV on from the output. That could perhaps explain this.
« Last Edit: November 13, 2018, 10:37:57 AM by Felix »

alexsh1

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Re: nA/uA readings issue
« Reply #2 on: November 13, 2018, 11:29:30 AM »
Felix,


I have tested it with DMM only going through a power cycle as I outline above.
The DMM readings are pretty much the same I see on the OLED display - it shows some low uA reading and 144nA so something is wrong.
I am using quality cables and very-very low resistance. Changing cables did not produce a different result.

Felix

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Re: nA/uA readings issue
« Reply #3 on: November 13, 2018, 04:26:56 PM »
I posted a longer response in your other thread,
But could you please try to power the DUT from a battery instead, see if the same is true?

alexsh1

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Re: nA/uA readings issue
« Reply #4 on: November 13, 2018, 04:57:49 PM »
Thank you Felix - I am going mark this thread as solved.
 Funny enough, I just recently tested the noise and ripple on this chinese PSU. It is very precise in terms of V/A, but very noisy.
« Last Edit: November 13, 2018, 09:52:23 PM by alexsh1 »