What you'll learn
Drive a 24 VDC pneumatic solenoid through an interposing relay. The PLC output only energises the relay coil; the relay contact switches the field load. Add a flyback diode at the solenoid to clamp the inductive voltage spike when the valve is switched off.
Lab time: ~15 minutes.
Lesson briefing
PLC Relay Output to Solenoid Valve
Drive a 24 VDC pneumatic solenoid through an interposing relay. The PLC output only energises the relay coil; the relay contact switches the field load. Add a flyback diode at the solenoid to clamp the inductive voltage spike when the valve is switched off.
Why it is wired this way
The interposing relay protects the PLC and allows separate load protection. A flyback diode is reverse biased in normal operation: cathode to +24 V and anode to 0 V. Reversing it creates a short; omitting it exposes the contact and electronics to a high transient.
Commissioning standard
Before energising, prove protective earth and continuity, verify the drawing terminal-by-terminal, then energise through the protective device and measure the expected supply, signal and return values. Never use this training panel as a substitute for the machine manufacturer’s instructions, risk assessment, isolation procedure or applicable electrical standard.
Hints
Wire PLC Y0 to relay A1 and return A2 to 0 V.
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This lesson uses 8 placed components on the lab canvas. Components are vendor-neutral (no proprietary trademarks); the wiring rules apply to any equivalent industrial part.
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