How to suppress interference in the limit switch signal of the motion controller MC?

Improving the immunity of the limit switch signal in the motion controller requires design tailored to its dry contact characteristics. At the input, a defined logic level is provided via pull-up or pull-down resistors, typically ranging from 4.7kΩ to 10kΩ. A parallel RC low-pass filter is used, with the capacitor value set according to the mechanical contact bounce time, typically from 0.1μF to 1μF. A parallel bidirectional TVS diode, such as ESD5V0D3B, is used to suppress high-voltage transients induced in the line. Shielded cables should be used for the signal lines, with the shield grounded at the controller end. For long lines, a damping resistor of several tens of ohms can be connected in series at the entry point.

On the PCB layout, filtering and protection devices should be placed close to the input terminals. In the software, a digital debouncing algorithm, such as multiple sampling voting, should be implemented. For critical safety limits, a dual-channel redundant design can be adopted, along with diagnostics. Simulated field interference testing is conducted to ensure that the limit signal does not trigger falsely under noise and responds reliably during actual operation.