High-Side Current Sensing
Placing the current sensing element on the positive supply line rather than on the chassis side. This way the chassis reference is not disturbed and leakage or short circuit currents at the motor terminal are also included in the measurement. In return, the measuring circuit has to work at supply level.
Low-side sensing is cheaper because the shunt resistor sits close to chassis and the differential voltage can be read directly. However, an offset equal to the drop across the shunt appears; all circuits in the system now see a shifted reference rather than the real chassis. At high currents this offset can cause false triggering on digital inputs.
The advantages of high-side sensing:
- A leakage or short circuit from the motor terminal to chassis is visible in the measurement; with a low-side arrangement this current is missed completely.
- The system chassis stays as a single, clean reference.
- Because it sits on the same line as reverse polarity and overcurrent protection, the protection logic is simplified.
A low-value shunt resistor or a Hall type sensor is used as the sensing element. There is loss in the shunt too: a 1 milliohm shunt produces 0.9 W at 30 A. Hall type sensors provide galvanically isolated measurement and eliminate this loss, but in return they have a zero offset that varies with temperature.
The context in which this term is used: DC motor and driver fault diagnosis matrix