User manual

You can keep using the µCurrent in this mode with the LED ON if desired, it simply uses more battery
power.
The in-built timer will take about 0.2 of a second to light the LED, so it’s possible to move the power
switch through the BATT CHECK mode and not have the LED light if you are quick enough.
Output Voltage Range
The MAX4239 is a rail-to-rail output device, so is capable of fairly close to the supply rails on the
output. Given that the power supply will be at least +/-1.35V for a working battery, that allows for an
output voltage that approaches this figure within a few millivots.
Normally though the µCurrent will be used with your multimeters mV range which will be typically up
to a maximum of 999.99mV for a 10000 count meter. So there is some head-room left if you want to
push it higher for any reason.
Output Units
The output units are scaled by the shunt resistors and gain of U1 to be precisely 1mV per range unit.
So the output will be 1mV per mA, 1mV per uA, or 1mV per nA.
This makes it easy and logical to directly read on your multimeters mV range. So if you read 100mV
on your meter, that equates to 100mA, 100µA, or 100nA depending upon the range you have
selected.
AC Performance
The AC performance is shown in the accompanying screen shots as measured with an Audio
Precision analyser with a 1V output level on the uA range. There is little performance difference
between the ranges.
The nominal bandwidth is 2KHz, as the THD starts to increase exponentially after this. This figure is
quite sufficient as most meters have a 1KHz response on AC current ranges.
Overloads
Fuses have been omitted from the design to ensure as low a total burden voltage as possible.
Therefore you must be careful to ensure that the input is not connected directly across a supply
voltage capable of providing a current that exceeds the selected range. Failure to take care here can
result in a blown shunt resistor.
Connectors
The connectors are standard 4mm banana plugs, with standard 19mm spacing. This allows the use
of various types of adapters if required. The screw terminal type connectors are used for the current
input, which is convenient for connecting to existing wiring without test leads. The top screw part can
be completely removed to enable some short “shrouded” banana plug test leads to fit.