In applications where the readout boards are remotely located, a voltage output current sense amplifier such as the ON Semiconductor NCS21xR series can be converted to a precision current output. The precision output current measurements are read more accurately as it overcomes the errors due to ground drops between the boards or systems.
Remote current sensing
As shown in Figure 1, the RIOUT resistor is added between the OUT pin and the REF pin to convert the voltage output to a current output which is taken from the REF pin to the readout board (this creates an Improved Howland Current Pump). This circuit is intended to function with low potentials between the boards due to ground drops or noise. The current output is simply the relationship of the normal output voltage of the Current Sense Amplifier:
A resistor value of 1 kΩ for RIOUT is a convenient value as it provides 1 mA/V scaling.
On the readout board, for simplicity, RITOV can be equal to RIOUT to provide identical voltage drops across both. It is important to take into consideration that RITOV and RIOUT add additional voltage drops in the current measurement path. The current source can provide enough compliance to overcome most ground voltage drops, stray voltages, and noise. However, accuracy will degrade if noise or ground drops exceed 1 V.