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.
4–20 mA current loop
Analog signaling standard.
Two-wire analog standard: 4 mA = 0%, 20 mA = 100%, with 0 mA indicating a broken wire (live zero). Immune to voltage drop over long runs; the default field signal for transmitters and valves.
See also: HART protocol · PLC
Use the concept: 4–20 mA loop scaling · Process instrumentation: signal, measurement and control · Engineering unit converter
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.