INDUSTRIAL-CONTROL
Relay Interface for PLC Input: PNP Sensor Coil Input, NPN Contact Output
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CASE ANALYSIS
Scenario
A 24 V PNP proximity sensor output must interface to an NPN-sinking PLC input; an interposing relay isolates the sourcing sensor from the sinking input.
Key decisions
- Use a relay with coil driven by the PNP output and a flyback diode across the coil
- Wire the relay common to the PLC input and NO to 0 V so the closed contact sinks current from the PLC pull-up
When to reuse this
Reusable for any PNP sensor to NPN PLC input conversion using a single interposing relay and DC coil supply.
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circuit-single-relay-interface-for-plc-input-pnp-proximity-sensor-co