4–20 mA Scaling Calculator
Convert 4–20 mA, 0–20 mA, 0–10 V and 1–5 V signals to engineering units, percent and PLC analog counts (0–27648, 0–32000…), with a 4/8/12/16/20 mA table.
Formulas
- Ratio r = (signal − signal low) ÷ (signal high − signal low) · for 4–20 mA, r = (mA − 4) ÷ 16
- Engineering value = eng. low + r × (eng. high − eng. low)
- % = r × 100
- Count = count low + r × (count high − count low)
Example: a 0–10 bar pressure transmitter at 12 mA gives r = 0.5 → 5 bar, 50 %, and 13824 on a 0–27648 count range.
Count presets and sources
Even for 4–20 mA the count range depends on the PLC analog input module and its data format setting. The values below come from the manufacturers' documents; check the manual of your module for the actual values. If yours is not listed, choose «Custom».
| Preset | Range | Source |
|---|---|---|
| SIMATIC S7-1500 · ET 200 (0–27648) | Unipolar input: 0 = low, 27648 = high. 27649–32511 overrange, -1 to -4864 underrange, beyond that overflow/underflow | Siemens, SIMATIC S7-1500/ET 200 Analog value processing Function Manual (A5E03461439-AC, 06/2014), Table 3-4 Unipolar input ranges |
| MELSEC iQ-R (0–32000) | 4–20 mA (R60AD6-DG 2-wire transmitter input) and 0–20 mA (R60AD4 and other current inputs) → digital output 0–32000 | Mitsubishi Electric, MELSEC iQ-R Series Product features – Analog – Specifications |
| Compact I/O 1769-IF4 · Engineering Units | 4–20 mA → 4000–20000 (3200–21000 full range), 0–20 mA → 0–20000, 0–10 V → 0–10000, 1–5 V → 1000–5000 | Rockwell Automation, Compact I/O Analog Modules User Manual (1769-UM002B-EN-P, 07/2005), Table 3.7 Valid Input Data |
| Compact I/O 1769-IF4 · Scaled-for-PID (0–16383) | 4–20 mA, 0–20 mA, 0–10 V → 0–16383 (4–20 mA spans -819 to 17407) | Rockwell Automation, Compact I/O Analog Modules User Manual (1769-UM002B-EN-P, 07/2005), Table 3.7 Valid Input Data |
NE 43 range warnings
NAMUR recommendation NE 43 has 4–20 mA transmitters use 3.8–20.5 mA for measurement values and signal a failure at 3.6 mA or below or 21 mA or above. When the signal type is «4–20 mA» the status uses these limits. A transmitter's failure output (for example 3.6 mA or 21.6 mA) is often configurable, so check its manual too.
References: Vaisala PR-33 — Default mA output value · Endress+Hauser RMA42 Operating Instructions (BA00287R)
FAQ
Why is 4 mA zero percent?
4–20 mA is a «live zero» signal: current flows even at 0 %. With 0 mA you could not tell a zero reading from a broken wire, so 4 mA is 0 % and a current well below it means an open loop. 1–5 V uses 1 V as 0 % for the same reason.
The count in my PLC differs slightly from the calculator
A few counts of difference from resolution, filtering and calibration are normal. If it is far off, check the module's input range setting (4–20 mA or 0–20 mA) and data format (raw, engineering units, scaled for PID, etc.) first.
How do I get the engineering value from a count?
Type the PLC value in the Count field to get the engineering value, current and percent. As a formula: value = low + (count − count low) ÷ (count high − count low) × (high − low).
To read sensor values over serial or Modbus and plot them live, use PortDock Plot.