Sensor signal scaling calculator — 4-20mA / 0-10V
Convert a 4-20mA or 0-10V sensor signal into its engineering value — and back — from the transmitter’s minimum and maximum range.
Scale a live sensor signal
Formula: value = min + (max − min) × (signal − 4) / (20 − 4). A 4-20mA transmitter uses live zero — 4 mA is 0% — so a broken wire reads below 4 mA. 0-10V has a true zero and is common on PLC analog inputs.
Reverse — signal for a target value
Works backwards from the target engineering value to the mA the transmitter must send, using the same minimum and maximum range above.
About: 4-20mA is live-zero (4 mA = 0%, so a broken wire shows as below 4 mA); 0-10V has a true zero and is common on PLC analog inputs. AO Ctrl stocks the sensors, transmitters and analog I/O used with these signals:
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Frequently asked questions
How do I convert 12 mA to an engineering value?
The calculator maps the 4-20mA span linearly: value = min + (max − min) × (signal − 4) / (20 − 4). With the default range of 0 to 100 units, 12 mA — the exact midpoint of the 4-20mA span — converts to 50 units, which is also 50% of span.
Why is 4 mA used as the zero instead of 0 mA?
4-20mA is a live-zero signal: 4 mA represents 0% and 20 mA represents 100%, so a broken wire or failed transmitter reads below 4 mA instead of looking like a valid zero reading. This is the reason the scaling equation subtracts 4 from the live signal. 0-10V, by contrast, has a true zero and is common on PLC analog inputs.
What mA should a transmitter output for 50% of a 0-100 range?
For the reverse conversion the calculator uses signal = 4 + ((target − min) / (max − min)) × 16. For a 0-100 engineering range, 50 units needs 4 + (50/100) × 16 = 12 mA. The same arithmetic with the 0-10V span gives 5 V at mid-range.
AO Ctrl provides this tool for reference only.