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Analog Signal Scaling Calculator — 0-10 V & 4-20 mA

Turn an analog control signal into the value it represents, or work out the signal a given temperature, pressure or humidity needs. Supports 4-20 mA, 0-20 mA, 0-10 V, 2-10 V, 0-5 V and 1-5 V, with live-zero and broken-wire checks.

Signal and range

Pick which way you want to convert, choose the signal type, then set the engineering range the transmitter or controller is configured for.

Convert

Signal → value Value → signal

Signal type

Engineering unit Free text — it is shown next to the result.

Measured signal

Unit Set automatically by the signal type.

Range minimum signal low end

Range maximum signal high end

Advanced — loop resistor and current-to-voltage

Sense resistor in the loop A 250 Ω resistor turns 4-20 mA into the classic 1-5 V input; many controllers have this built in.

How the calculation works

Every analog input is a straight line between two points. Convert the signal to a fraction of its span, then apply that fraction to the engineering range:

value = range min + [ (signal − signal min) ÷ (signal max − signal min) ] × (range max − range min)

Rearranged, the same expression gives you the signal from a known value. This is exactly what a controller does internally when it scales an input, and it is the calculation behind every “the input reads 12 mA, what temperature is that?” question on site.

Why 4-20 mA and not 0-20 mA

A 4-20 mA loop carries its zero at 4 mA, so the electronics always draw at least 4 mA. That gives the controller a way to tell a genuine zero apart from a dead loop: anything below about 3.6 mA is a broken wire, a lost supply or an under-range value, and anything above about 21 mA is a fault or an over-range excursion. The convention is standardised as NAMUR NE 43 and is what this tool flags for you.

Voltage or current?

4-20 mA is the right choice for anything leaving the panel. Current does not change with cable resistance, so a long run to a roof-top plant room does not turn into a temperature error.
0-10 V is normally for short, in-panel runs. It is cheap and universally understood, but a 10 m run of thin cable plus a few loose terminals can shift the reading by a degree or more.
2-10 V is the actuator convention. Starting at 2 V rather than 0 V lets the controller report a broken control wire instead of a legitimate “closed” command.
1-5 V is usually not a real instrument output. It is what a 4-20 mA signal looks like after it has been dropped across a 250 Ω sense resistor.
Keep the range tight. A transmitter configured 0-100 °C for a loop that only ever runs 8-14 °C spends less than 7 % of its resolution on the part you actually care about.

Worked examples

A 0-10 V duct temperature transmitter ranged 0-100 °C reading 6.4 V is at 64 % of span → 64 °C.
A 4-20 mA static pressure transmitter ranged 0-1000 Pa reading 12 mA is at 50 % of span → 500 Pa.
To command a damper actuator on a 2-10 V signal to 75 % open, the controller must output 2 + 0.75 × 8 = 8 V.