troubles with uCurrent GOLD

[Tif]

Hi,

I recently acquired a new uCurrent GOLD via welectron. I wanted to use it to do some measurement today, but as it is my first time with this device, I ran some tests before.

The issue I encountered is that when powering on the uCurrent with nothing connected to its inputs, I get 1,7 mV at the output for the mA and uA ranges, and 3,4 mV for the nA range. When I connect a current source at the input, the output almost doesn't change.

I am using a 121GW to measure the output voltage, and tried with an oscilloscope with no improvements.
I checked the battery voltage which is 3,09V.
I visualy inpected the board and I don't see any bad soldering.

May the uCurrent have been damaged during transport? I you have any idea to fix the issue, you are welcome!

[SilverSolder]

Fresh battery?

[Tif]

The battery is new (I bought it a few months ago and never used it until now). The voltage of the battery is 3,09 V so I don't think it comes from this...

[coromonadalix]

Normally  the current gold is an current to voltage conversion adapter, i dont see any offset adjustment or an zero adjustment

IF you short the inputs, does the output goes to zero ??   and try it with another meter too,  the 121gw is not a perfect meter

Specifications – µCurrent™ GOLD

    3 Current ranges:
        +/- 0-1250mA (20µV / mA burden voltage typical) * switch contact resistance plays a role here. 10uV due to the shunt resistor.
        +/- 0-1250µA (10µV / uA burden voltage)
        +/- 0-1250nA (10µV / nA burden voltage)
        NOTE: Higher currents are available by increasing the battery voltage, to a maximum of 5.5V, which would give +/-2250mA/2250µA/2250nA maximum)
    Output Voltage Units:
        1mV/mA
        1mV/µA
        1mV/nA
        NOTE: You simply read your mV multimeter range as if it were mA/µA/nA

[Tif]

In the original uCurrent article, page 13, it is stated that

With nothing connected you should measure zero on all three current ranges

I agree that there is no circuitry to compensate for the offset, but I didn't think the offset would be that high!
Anyway, it doesn't explain why the output voltage doesn't change when the input current does.

[Tif]

Unfortunately I don't have any other meter around, but I have an oscilloscope that shows similar results.

[coromonadalix]

If the ucurrent is under warranty i would not play in it and void anything,  issue an rma ...

You could check U4 pin3 if you have 1/10 th of the same output voltage you have, but were dealing with very low values here, anything can or could interfere

You have 2 successives x 10 amplifications here ...  same check could be done on U1

You could check the virtual ground between the -batt  and R10 (vgnd)  if you have half battery voltage at anytime

J4   ground output is a vitual ground ... for U1 U2 U4 supply lines

Does the switches are physically okay ?

[alex-sh]

@Tif

121GW has got a uCurrent built-in, i.e. no need to have a stand alone uCurrent.