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.
HART protocol
Digital overlay on 4–20 mA.
Highway Addressable Remote Transducer: FSK digital signal superimposed on 4–20 mA wiring for device configuration, diagnostics, and multi-variable reads without new cable.
See also: 4–20 mA current loop · Fieldbus
Use the concept: Subnet calculator · 4–20 mA loop scaling · Compressed air leak cost calculator
In depth
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.
Modbus polling and timeout budget: calculate the slow path
Estimate serial transaction time, include silent intervals and device response, and prevent offline devices from consuming the entire polling cycle.