Power line filters are a type of passive component that creates an electronic filter to deliver appropriate frequency characteristics to electrical circuits. Power line filters connect the electronic device with an external line to reduce conducted frequencies like radio frequencies (RFI) or electromagnetic interference (EMI) between the equipment and the connecting power line. This prevents any degradation in the circuit's performance.
Signal filters are frequently placed between the sensor transmitter and the controller (or more likely, the multiplexer feeding the controller). In process control applications, these filters should be analog (hardware) devices designed specifically to minimize high frequency electrical interference.