Bias mode function

By default (power-ON) the opamps stages biasing point is at a 0 offset from the GROUND of the circuit. This will be the most useful mode of operation as it yields full unidirectional output range for DC measurements.

Bidirectional measurements

You can enable bidirectional mode by tapping¬†the uA & mA touch-pads simultaneously. This effectively switches to half-supply biasing of the op-amps, and enables the output positive [+] terminal to swing both positively and negatively WRT to the [-] negative terminal. This allows measuring AC currents and shifts the output range to [+/-1.65]A. This mode is similar to the behavior of EEVBlog’s uCurrent¬†which has a fixed bidirectional mode.

Probably 99% of use cases in the lab require DC measurements. Unless you have a specific reason to use Bias Mode, perhaps for its bidirectional AC current measurements ability, or explore how biasing affects the opamp’s noise isolation, you should use the CurrentRanger in unidirectional mode (Bias Mode OFF).