Voices: Real Answers

How to decide between PNP and NPN

What signal level sensors and I/O modules should you standardize on?

By Mike Bacidore, editor in chief
Nov 5, 2016

A Control Design reader writes: My question arises due to machines we received at our manufacturing plant in Arizona from an OEM in Asia. All of the PLC 24 Vdc digital input modules were NPN (sourcing 24 V dc) and our plant’s standard is PNP inputs (sinking 24 Vdc inputs). These signal levels (sourcing input module with sinking sensor vs. sinking input with sourcing sensor) seem like they will double the number of input modules and sensor spare parts we stock. We need to make some decisions on NPN vs. PNP transistors.

Read More