A few weeks ago, I discussed how to calibrate middle to low end DMMs using a precision voltage reference such as REF01. Of course, you can perform similar calibrations using a precision current reference as well. And in many cases using a precision current reference is a better choice as it can be used to generate voltage references as well using precision resistors.
TI‘s REF200‘s (dual current source/current sink) is one such suitable precision current reference for this task. It has high accuracy (100µA ±0.5%), very low temperature coefficent (25ppm/°C) and is relatively inexpensive (under $5). Its specifications rival some of the older current standards.
The simplest way to use REF200 is to utilize either of its two independent current sources. In this case we obtain a 100 µA reference current. Because REF200 has a built-in current mirror, you can obtain currents of 50µA, 100µA, 200µA, 300µA or 400µA easily.
Because the current reference is placed in series in the circuit in relation to the external component under test, there is no need for a switch to turn on or turn off the circuit. Thus when no external circuitry is connected, there is no standby current so we do not have to worry about batteries when the current reference is not in use.
The following picture shows the 100µA reference current measurement on a BK Precision 2709B. As mentioned above only one of the two 100µA on-chip current sources is used. The REF200 is powered by two 9V batteries (in the black project box next to the meter).
Here is another picture showing the reference current reading on a 6½ multimeter (Keithley 196). As you can see, the current sourced from REF200 is very accurate and in this case the accuracy is significantly better than the stated 0.5%.