Industrial Engineer · phase 2 of 16 · noun

4-20 mA Current Loop

Analog signaling method in which 4 mA represents the live zero and 20 mA represents full scale.

The Explain card

Plain English: A current loop sends a measurement as a current that varies between 4 and 20 mA. Four means the bottom of the range and twenty means the top.
Example: A flow meter spanned for zero to 100 gallons per minute puts out 12 mA at 50 gallons per minute. The input card reads 12 mA and the program scales it to 50.
Why it matters: Current holds up over a long cable in a way voltage cannot, so loops survive hundreds of feet of conduit. The live zero at 4 mA means a broken wire reads 0 mA and can be flagged as a fault rather than as an empty tank.
Hook: Four is zero, and zero is a broken wire.

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

The technician connects the pressure transmitter's 4-20 mA Current Loop to the PLC analog input and verifies the reading during commissioning.

Why these words

4-20 Hindu-Arabic numerals joined by modern range notation states the conventional span in compact numerical form
mA SI-style symbol using Latin milli, thousand, and A for ampere identifies milliamperes as the measurement unit
current Latin currere, to run, through Anglo-French curant names the electrical quantity used by the signal
loop late Middle English loop, a doubled or closed path, of uncertain origin describes the closed circuit through the connected devices

Where it came from

Origin: English instrumentation coinage combining numerical range notation, the electrical unit symbol mA, and the established phrase current loop
Entered the language: 1950s
What changed: General words for flowing electricity and a closed path became a fixed industrial-instrumentation label, with the numerical prefix distinguishing one standard from other loop formats.

How it is spelled

Pattern: A hyphen joins the numerical endpoints.
Pattern: The SI prefix m remains lowercase while A remains uppercase because ampere is named after André-Marie Ampère.
Pattern: A space separates the numerical range from the unit symbol.
Breaks the pattern: The unit symbol mA is case-sensitive and has no period or plural ending.

Spelled like

Broken into chunks

What it sits beside

Same subject

Same shape

industrial analog signal formats

current-loop equipment

Phase 2: PLC I/O and Field Signals

Where the controller meets the machine: discrete and analog signals, the wiring conventions behind them, and the field devices that send them.