How to prevent interference to the dry contact signal of the frequency converter

To protect the dry contact input signals of a frequency converter from interference and prevent false triggering, both hardware and software measures are needed. Dry contact signals are passive switching signals, such as start, stop, and fault reset signals. Hardware protection measures include: connecting an RC snubber circuit in parallel at the dry contact signal input terminal; a resistor and capacitor connected in series across the signal line and ground to absorb contact bounce and suppress high-frequency interference from spatial coupling. The RC time constant should be much smaller than the minimum interval of signal change. A resistor should be connected in series on the signal line to limit current and work with a capacitor for filtering. For long-distance leads, shielded twisted-pair cable must be used, and the shielding layer must be grounded at a single point at the frequency converter.

Optocouplers can be used at the input circuit front end of the frequency converter for isolation, completely cutting off the conduction path of external interference; this is the most effective method. If an optocoupler is used, the current-limiting resistor and RC snubber circuit on its input side are still required. In terms of PCB layout, the dry contact input circuit should be centrally located and away from noise sources. In terms of software, digital filtering and debouncing processing should be performed on the input signal. By using simple RC filtering, shielding, and optocoupler isolation, combined with the basic components of Audiotronics, reliable acquisition of dry contact signals in industrial noise environments can be ensured.