The scenario
A packaging machine uses three 24 VDC photoelectric sensors with PNP outputs to drive relay coils; each relay contact gates an NPN transistor that energizes a solenoid valve coil with inductive flyback protection.
What is in this drawing
Read the decisions behind it.
01
Used relay contacts to isolate the PNP sensor circuit from the NPN output stage
02
Added flyback diodes and base resistors for clean switching of inductive solenoid loads
For relay interface boards that convert PNP sensor inputs into NPN sinking outputs for solenoid banks, such as packaging, palletizing, or assembly line controls.
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