4-20 mA and 0-10 V Scaling Calculator
Convert an analog signal (4-20 mA, 0-10 V and other standard ranges) to a pressure, temperature, level or flow value, or work out what signal a given value should produce.
Signal and range
LRV and URV are the lower and upper range values the transmitter is configured for. The upper value can be smaller than the lower one for a reverse-acting range.
Signal to process value
Process value to signal
How it works
An analog transmitter reports its measurement as a current or a voltage. The bottom of the range gives the lowest signal level and the top of the range gives the highest. The relationship is linear, so the signal span is spread evenly across the process range.
signal = low + (value − LRV) / (URV − LRV) × (high − low)
4-20 mA: low = 4, high = 20 0-10 V: low = 0, high = 10
Common signal ranges
| Signal | 0% of range | 100% of range | Notes |
|---|---|---|---|
| 4-20 mA | 4 mA | 20 mA | Industry standard for field instruments. Immune to wire resistance and noise, and has a live zero. |
| 0-20 mA | 0 mA | 20 mA | No live zero, so a broken wire looks like zero. |
| 0-10 V | 0 V | 10 V | Common for drives, actuators and short cable runs. Affected by voltage drop and noise. |
| 2-10 V | 2 V | 10 V | 0-10 V with a live zero, often used in HVAC. |
| 1-5 V | 1 V | 5 V | A 4-20 mA signal across a 250 Ω resistor. |
| 0-5 V | 0 V | 5 V | Common on sensors and embedded controllers. |
Worked example
A pressure transmitter is ranged 0 to 150 PSI and the PLC reads 12 mA.
- (12 − 4) / 16 = 0.5, so the signal is 50% of span.
- 0 + 0.5 × (150 − 0) = 75 PSI.
In the other direction, 100 PSI gives 4 + (100 / 150) × 16 = 14.667 mA.
With a 0-10 V signal on the same 0-150 PSI range, 3.3 V is 3.3 / 10 × 150 = 49.5 PSI, and 100 PSI is 100 / 150 × 10 = 6.667 V.
Reading out-of-range signals
Many instruments follow NAMUR NE43, which reserves currents outside the normal range for diagnostics. Below about 3.6 mA or above about 21 mA usually means a fault, such as a broken wire, a shorted loop or a failed transmitter. The calculator flags these. Check your instrument's manual, because the exact failure currents are configurable on many devices. A voltage signal with a live zero (2-10 V, 1-5 V) can be checked in the same way.
Common questions
Should I use 4-20 mA or 0-10 V?
For long cable runs, noisy environments and anything critical, use 4-20 mA. Current is not affected by wire resistance, and the 4 mA floor lets you detect a broken wire. 0-10 V is simpler and cheaper for short runs inside a panel or between a PLC and a nearby drive.
What if my PLC input shows counts instead of mA or volts?
Analog input cards report raw counts (for example 0-32767). Find which count matches the bottom and top of the signal in the card's documentation, then scale between them. The PLC analog scaling calculator does that step.
Does the calculator include loop resistance or 250 Ω resistors?
No. If your input reads volts across a resistor, convert the voltage to current first: volts divided by resistance gives amps (1-5 V across 250 Ω is 4-20 mA).
Calculations are provided for convenience and education. Verify results against your instrument documentation before relying on them for design, commissioning or safety decisions.