How to resist EMI in industrial servo analog commands?

Servo analog commands (such as speed/torque setpoints, typically ±10V) are highly susceptible to EMI, leading to control fluctuations. Etymotic's EMI-resistant design includes:

1) Input filtering: An RC low-pass filter is installed at the analog input, with the cutoff frequency set according to the signal bandwidth (e.g., 100Hz). Resistors (e.g., 1kΩ) are placed close to the port, and capacitors (e.g., 100nF) are placed close to the ADC.

2) Common-mode rejection: A differential input ADC or operational amplifier is used, and the shielding of the command lines is grounded at a single point on the driver.

3) Isolation: An isolation operational amplifier or isolation ADC module is used between the analog command source and the servo driver to break ground loops.

4) PCB layout: Analog command traces are kept as short as possible, away from digital and power lines, and surrounded by ground lines.

5) Software filtering: Digital filtering (e.g., moving average) is added after ADC sampling.

These measures can attenuate high-frequency noise superimposed on the analog command by more than 40dB, resulting in speed control fluctuations of <0.1%, meeting the requirements of high-precision servo applications.