Check instrument circuits: 4–20 mA loop voltage budgets, intrinsic safety entity parameters to IEC 60079, thermocouple and RTD conversion with cold-junction and lead compensation, and fire and gas detection loop voltage.
Loop voltage budget for a 2-wire loop-powered transmitter — wire voltage drop, transmitter headroom, and maximum cable length by AWG.
IEC 60079-14 entity concept — voltage/current/power and capacitance/inductance checks (with the 1% rule) for combining a barrier with IS field apparatus and cable.
NIST ITS-90 thermocouple mV-to-temperature with cold-junction compensation (K/J/T/E), plus IEC 60751 Callendar-Van Dusen RTD conversion with lead-wire compensation.
Standby and alarm-condition voltage budget for a multi-detector fire/gas initiating device circuit with an end-of-line resistor.
Why 4-20mA loops deliberately never use zero for zero, how the intrinsic safety entity concept lets you combine certified components without a full system drawing, and why thermocouples and RTDs fail in completely different ways.