EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: alexbn71 on September 15, 2019, 02:10:10 pm
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Hi all,
I assmbled myself a uCurrent GOLD but I have a strange issue during test (at 5V). With 47R(1W) and 47K I get exactly 106mV with the correct range selected (correct polarity on my multimeter).
I have a strange issue with nA range and 50M resistor. The rading is unstable, oscillating between 70-100mV and the polarity is negative!
what could cause this behavior?
Thanks
Alex
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If all parts are ok and properly assembled, it might be flux you used for soldering.
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After cleaning it with alcohol it seems more stable but this does not explain why the voltage is reversed on the output.
The Input voltage has the correct polarity (+2.4mV) and the same polarity as 47R and 47K resistors... I don't undesrstand how can be inverted (-100mV) on the output, in nA range.
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If I look at the right schematic on nA range it doesn't have a shunt , so is relativily high impedance ( 10K ) and could be easily susceptible to mains or other fields influence .
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After cleaning it with alcohol it seems more stable but this does not explain why the voltage is reversed on the output.
The Input voltage has the correct polarity (+2.4mV) and the same polarity as 47R and 47K resistors... I don't undesrstand how can be inverted (-100mV) on the output, in nA range.
What flux/solder you have used? With SMD it's impossible to completely clean without ultrasonic bath or other equipment which can reliably wash under the parts. I don't think -100mV is something extraordinary what cannot be caused by flux.
Also if you made variant without capacitor in parallel to R7, in combination with LMV321 from certain vendors it may cause such issue. So if that's the case, try soldering 1uF ceramic cap in parallel to R7.
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If I look at the right schematic on nA range it doesn't have a shunt , so is relativily high impedance ( 10K ) and could be easily susceptible to mains or other fields influence .
10k resistor is a shunt.