Hazardous area classification, explained
Zones, divisions, gas groups and temperature classes decide which equipment may sit in a classified area. IP and NEMA ratings answer a different question.
PNP / NPN (sourcing / sinking)
DC sensor output wiring styles.
PNP (sourcing) switches the +24 V side; NPN (sinking) switches the 0 V side. Sensor type must match the input module's common wiring or signals read inverted — or never arrive.
See also: PLC · Remote I/O
Use the concept: 4–20 mA loop scaling · PLC FAT & SAT checklist template · Process instrumentation: signal, measurement and control
In depth
PLC FAT and SAT checklist: test behavior and handover evidence
Plan factory and site acceptance around requirements, observable results, failure states, approved changes and recoverable project files.
PLC analog input scaling: raw counts, 4–20 mA and diagnostics
Map raw counts into engineering units, check the configured channel range, and keep signal-quality diagnostics separate from the displayed value.