User manual

Testing
Testing is fairly straightforward. You will need a power supply and some suitable resistors (or decade
resistance box), and your multimeter.
Insert the battery and switch to BATT CHECK mode. The LED should light within 0.2 seconds. Switch
to ON mode and the LED should turn off.
Measure the DC voltage from the negative output connector (VGND) to one then the other side of the
battery in order to check the split supply system. You should get approximately +/-1.5V and both
values should match closely.
Connect the Voltage Output terminal to your multimeter set to the mV DC range. With nothing
connected you should measure zero on all three current ranges.
Select a resistor suitable for each range to give you a decent current level around say half of your
meters full scale. E.g. for a 5V supply, use a 47R 1W (106mA), 47K (106µA), and five 10M resistor in
series (100nA).
Connect your test resistor in series with your supply and the Current Input terminals. Ensure that you
have the correct range selected before switching on your supply voltage, you don’t want to blow any
shunt resistors!
Your meter should read approximately 106mV (mA), 106mV (µA), and 100mV (nA) for the values
mentioned. You can double check your values by measuring the actual resistor values and supply
voltage and calculating the current if desired.
If these currents match then your µCurrent is ready for operation, as the “calibration” is inherent within
the precision 0.1% components used.
The output value should not differ between BATT CHECK and ON modes.
It might be handy to check the battery current also. It should be around 0.7mA with the LED off, and
around 3mA with the LED ON.
Don’t forget to switch OFF when you are finished measuring.
The last step is simply screwing the PCB onto the box. With typical infrequent use the battery should
last many years.
That’s all there is to it, you now have a precision current measurement tool ready for those more
demanding modern applications.
I hope this article has got you thinking about the impact burden voltage can potentially have on your
current measurements.
Blank PCB’s, kits, and fully built units are available from the authors web site.