Two Channel Current Sensor for High Voltage Range

This board is built using a 2 x INA149 precision unity-gain difference amplifier with a very high input common-mode voltage range. The project can be used as a current sensor for high-voltage applications, INA149 provides a common-mode voltage range of +/-275V. The project operates with a wide supply range from +/-5V to +/-15V.  The circuit measures current by sensing the voltage drop across a series of resistors R_S, R4, and R12. The application circuit shows the INA149 used to measure the supply currents of a device under test. The sense resistor imbalances the input resistor matching of the INA149, thus degrading its CMR. Also, the input impedance of the INA149 loads R_S, causes a gain error in the voltage-to-current conversion. Both of these errors can be easily corrected.