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Instrumentation & automation

4-20 mA loops, RTDs and thermocouples, orifice plates, RS-485 and Profibus networks and PID tuning.

4-20 mA loop

Check whether the supply can drive a 4-20 mA loop with cable, 250 Ω receivers, barriers and indicators up to the NAMUR NE 43 alarm current, and scale mA to engineering units, with square root for flow.

Load, lift-off, cable, NE 43

RTD and thermocouples

Convert temperature to Pt100 and Pt1000 ohms (Callendar-Van Dusen) or to K, J, T, E, N, R, S and B thermocouple mV (ITS-90), and back, with cold junction, class tolerances and 2-, 3- and 4-wire lead error.

Ohms, mV, cold junction, classes

Orifice plate

Size an orifice plate per ISO 5167-2 for liquid or gas: β and bore by iteration with the Reader-Harris/Gallagher equation, expansibility, validity limits, permanent pressure loss and Table 3 straight lengths.

β, C, ε, straight runs, ISO 5167

RS-485, Modbus and Profibus

Check an RS-485 network: maximum segment length by baud rate (TIA-485-A and the Profibus DP table), devices per segment, repeaters and terminators, and Modbus RTU scan time from the bytes of each function.

Length, nodes, scan time

PID tuning

Paste the reaction curve from an open-loop test, fit a first-order-plus-dead-time model and compute P, PI and PID by Ziegler-Nichols, Cohen-Coon and lambda, in ideal and parallel forms, with the simulated response.

Reaction curve, ZN, lambda