Design Manual › Instrumentation & control › Loop & cable sizing
FREE ENGINEERING TOOL · I&C UNIT 1

4–20 mA Loop & Signal-Cable Sizing

Will that instrument actually work at the end of the cable? Voltage-drop budget for two-wire (loop-powered) transmitters, load-capability check for self-powered 4–20 mA outputs, the HART 230–600 Ω window, IS-barrier budget, and copper cable sizing with tropical temperature correction. Built for Southeast-Asian plants.

1Instrument & run

2Loop loads & supply

Vendor-convention converter — "16.6 V incl. 250 Ω" vs terminal voltage
Enter the number printed on your datasheet; the tool converts it so the two conventions never get double-counted.
—

Results — is the loop viable?

Cable R (2L)
—Ω
Total loop R
—Ω
V at instrument
—V
ItemValueUnit
Given this cable, the loop is viable to:
Cross-section0.50.751.01.52.5 mm²
Max one-way run (m)—————

Instrumentation this loop settles on

DutyInstrumentBasis

Quote this loop's instruments at factory price

Analysers, the 24 V supply and cable at the manufacturer's ex-works price — our margin comes solely from the export tax rebate. Signal cable is normally bought locally; we size it here so your local purchase has a number behind it. RS-485 surges on this loop are covered by the LW-10 (Unit 2 of the I&C manual).

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Sources & parameter basis

[1]Emerson/Rosemount load limitation — R_max = 43.5·(Vsupply−10.5); HART ≥250 Ω; a 250 Ω loop needs ≥16.6 V. Terminal minimum 10.5–12 V.
[2]Chinhui Automation cable guide — EJA "16.6 V incl. 250 Ω" convention; I_check 24.4 mA; ρ 0.0188 @35 °C, 0.0217 @75 °C; 300 Ω load ceiling.
[3]Multicalci instrumentation calculators — ρ_20 0.0168 Ω·mm²/m, α_Cu 0.00393 /K, R_max formula, 1.3× safety on V_tx_min.
[4]IEC 60228 conductor resistance maxima at 20 °C (Ω/km).
[5]HART Foundation / Endress+Hauser — total loop load window 230–600 Ω for HART signalling.
[6]Jiuyuhub published product data (jiuyuhub.com) — 4–20 mA outputs rated into loads <750 Ω (DO6000Y / MS6000SG / PH6000C); SE10A 24 V DC, HART/Modbus.
Full derivation, worked examples and the two-vendor convention note: Instrument-Loop-Power-Cable-Calculation-Sheet.md (calculation book, Unit 1 of the I&C manual).
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Company emails get priority review. Your data stays in your browser — nothing is uploaded.
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