Meterman 37XR User Manual

The µCurrent A professional precision current adapter for Multimeters By David L. Jones ([email protected]) www.alternatezone.com/electronics/u

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

Construction Apart from the connectors and switches the entire design uses surface mount components. This was done in order to give a professional loo

Testing Testing is fairly straightforward. You will need a power supply and some suitable resistors (or decade resistance box), and your multimeter.

Using the µCurrent to measure current drain of the author’s µWatch. (Guess where the name came from?...)

Specifications • 3 Current ranges: o +/- 0-300mA (70µV / mA burden voltage typical) o +/- 0-1000µA (10µV / uA burden voltage) o +/- 0-1000nA (10

Complete Schematic Diagram

FFT Spectrum with a 1KHz signal on the uA range.

Noise Floor mA range

THD vs Freq on the uA range

At small displayed currents the burden voltage is usually not an issue, but at larger displayed currents (relative to Full-Scale) the burden voltage c

Let’s now say you need to do the same thing on a modern circuit or chip with say a 1.2V power supply. That same 200mV burden voltage is now a whopping

Take the above example again, the Meterman 37XR would drop a whopping 2V (10mV*200) on its mA range for 200mA. Not much good when your supply voltage

The burden voltage of the µCurrent is a fixed 10µV/µA and 10µV/nA on the lower ranges, and varies on the mA range due to the switch resistance, but 7

An auto-zero amplifier is basically the combination of a normal op-amp (Ab), with a “nulling” op-amp (Aa) that continually corrects for the DC offse

The pseudo-random clock used in the MAX4239 also helps to reduce the effects of intermodulation distortion as AC signals approach half the chopping fr

You will notice that the virtual ground is connected to the sense side of R1, this means that the sense voltage for R2 and R8 also flow through this

You can see how it works in the accompanying functional diagram. There is a precision resistor diver, voltage reference, and an output circuit with