Shunt Calibration

The shunt resistor on SB201 has ±1% accuracy and can therefore cause inaccurate measurements if the SB201 is not calibrated for the real resistance. The shunt resistance is calibrated in factory, but if a recalibration is needed due to e.g. reprogramming the following procedure can be used.

The calibration is done by measuring the actual current that is drawn from the battery and compares this to what SB201 reports. The electronic load is not accurate enough, so an accurate amperemeter has to be connected on the SB200 where the red jumper is normally placed.

Set the load to e.g. 500mA and check what the amperemeter measures and read the shunt resistor value and current from the SB200 PC software. If the amperemeter shows 490mA, SB200 reports 495mA and the shunt resistor value is set to 10000µΩ the following equation can be used to calculate the real resistance of the shunt resistor.

Rshunt, real=10000µΩ×495mA490mA=10102µΩ

Type the calculated shunt resistor value in the Shunt Resistance edit box (click on the shunt resistance image to open) and then push the write button. The current reported by SB201 should now be the same as the ampere meter. The SB201 firmware has thereby been calibrated to use the actual resistance of the shunt and tracks rather than the nominal value of the shunt itself.

Figure 1. Commands used for Calibrating the Shunt Resistor Value