4–20Industrial Measurementinstrumentation explained clearly
From physical quantity to trustworthy process data

Understand industrial measurement from sensor to control system

A process value becomes useful only after the sensing element, transmitter, signal path, input system, scaling and data quality all work together. This site follows that complete measurement chain.

Start with the measurement chain →Try the calculators
A simplified measurement chain
Processpressure · temperature · flow · level
→
Sensorphysical effect becomes a measurable response
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Transmitterconditions and scales the measurement
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I/O / DAQdigitizes and delivers the value
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Control / historianuses, displays and records the value
4–20 mAanalog
HARTdigital overlay
Fieldbusnetworked
DAQsampled data
The core idea

A measurement is a chain of transformations

The display may show one number, but that number depends on process connection, sensing principle, signal conditioning, calibration, environmental effects, conversion, scaling and data handling. Understanding the chain makes troubleshooting and specification much easier.

MeasurandThe quantity intended to be measured, with a defined condition and context.
SensorResponds to a physical phenomenon such as resistance, strain, pressure differential or electromagnetic induction.
TransmitterConverts the sensor response into a standardized, conditioned or digital output.
Signal pathWiring, isolation, network, input modules and configuration carry the value onward.
Measurement resultScaling, calibration status, uncertainty and process context determine how much confidence to place in the value.
mA

4–20 mA, HART & signals

Why current loops remain common, how scaling works, and where digital device information fits.
CAL

Calibration & traceability

As-found/as-left results, reference standards, traceability and why adjustment is not the same as calibration.
±

Accuracy & uncertainty

Separate error, tolerance, repeatability, resolution and measurement uncertainty instead of treating them as synonyms.
P

Pressure measurement

Gauge, absolute and differential pressure, transmitters, impulse effects and application context.
Q

Flow measurement

Differential pressure, magnetic, Coriolis, vortex, ultrasonic and other flow principles.
P&ID

Tags & P&IDs

How standardized identifiers and symbols help teams connect drawings, instruments, loops and maintenance records.
Interactive

Scale a 4–20 mA signal

Convert a loop current into engineering units for any linear configured range.

Open the 4–20 mA calculator →
Calibration aid

Calculate indication error

Compare an indicated value with a reference value and express the difference as raw error, percent of reading and percent of full-scale span.

Open the error calculator →