How can optocoupler isolation improve interference immunity in industrial servo systems?

In servo systems, optocouplers are used for isolated transmission of digital signals (such as fault, enable, and PWM signals). Improving their noise immunity requires optimization in both selection and application. Audiotech's improvement methods include:

1) Selection: Choose optocouplers with high common-mode transient rejection (CMTI) (e.g., >50kV/μs) to resist common-mode transients caused by switching noise.

2) Circuit Design: Provide independent and clean power supplies for the primary and secondary sides of the optocoupler, and use PWR power inductors and decoupling capacitors for filtering. Add a Schmitt trigger or RC filter at the optocoupler output (secondary side) to eliminate noise glitches.

3) Layout: Place the optocoupler in the center of the PCB's isolation strip, strictly separating the primary and secondary wiring, maintaining a creepage distance of >8mm.

4) Speed Matching: Select optocouplers with sufficient speed but not excessively fast speeds, as excessively fast optocouplers are more sensitive to noise.

After optimization, the optocoupler isolation circuit can withstand common-mode noise up to 5kV/μs, ensuring that critical control signals do not malfunction under strong interference, thus improving the overall system reliability.