Signals and PLC · Glossary

What is a 4 to 20 mA Current Loop?

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A 4 to 20 mA current loop sends a measurement as a current between 4 and 20 mA, which is not affected by wire resistance.

4 to 20 mA Current Loop Explained

The transmitter regulates the loop current; the receiver measures it, usually as a voltage across a 250 Ω resistor. Because current is the same everywhere in a series loop, long cables do not change the signal.

The live zero of 4 mA powers two wire transmitters and lets the system tell a real zero from a broken wire.

4 to 20 mA Current Loop Formula

I = 4 + 16 × (PV − LRV) ÷ (URV − LRV)

I	loop current (mA)
PV	process value
LRV, URV	values at 4 and 20 mA

Example: Range 0 to 10 bar, 6.5 bar: I = 4 + 16 × 0.65 = 14.4 mA.

Calculators for 4 to 20 mA Current Loop

CalculatorAnalog Scaling CalculatorFree online calculator with formula and worked example.Calculator4 to 20 mA to Voltage Resistor CalculatorFree online calculator with formula and worked example.CalculatorSignal Converter CalculatorFree online calculator with formula and worked example.

Free Downloads

Free download4 to 20 mA Cheat SheetFree printable PDF cheat sheet.Free downloadLoop Check Sheet Format in ExcelFree download in Excel and PDF.Free downloadCold Loop Check ProcedureFree step by step procedure, Word and PDF.

Frequently Asked Questions

What is a 4 to 20 mA Current Loop?

A 4 to 20 mA current loop sends a measurement as a current between 4 and 20 mA, which is not affected by wire resistance.

Why current and not voltage?

Voltage drops along the cable; current does not, and it is less affected by noise.

What does 12 mA mean?

Exactly 50 % of the calibrated range.

Learn more on the blog

4 to 20 mA current loop explained

A practical guide on instrumentationblog.in with more detail on 4 to 20 mA current loop and how it is applied on real plants.

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