4 to 20 mA Analog Scaling Table
Build a scaling table for any 4 to 20 mA loop: % of signal, mA, PLC raw counts and engineering value, with a square root option for DP flow loops.
Download
- Calculator sheet with a worked example
- How to Use sheet with steps
- 70 built in formulas, no macros
- Yellow input cells, grey results
- Calculation sign off block
- Excel, Google Sheets and LibreOffice
Worked Example
These are the results of the example already filled in the workbook. Replace the yellow cells with your own data.
Scaling table
| Signal (% of span) | Current (mA) | Raw counts | Value (units) | Value (% of range) | Displayed | Notes |
|---|---|---|---|---|---|---|
| 0 | 4.000 | 0 | 0.00 | 0.0 | 0 (cutoff) | |
| 5 | 4.800 | 1,382 | 11.18 | 22.4 | 11.18 | |
| 10 | 5.600 | 2,765 | 15.81 | 31.6 | 15.81 | |
| 20 | 7.200 | 5,530 | 22.36 | 44.7 | 22.36 | |
| 25 | 8.000 | 6,912 | 25.00 | 50.0 | 25.00 | |
| 30 | 8.800 | 8,294 | 27.39 | 54.8 | 27.39 | |
| 40 | 10.400 | 11,059 | 31.62 | 63.2 | 31.62 | |
| 50 | 12.000 | 13,824 | 35.36 | 70.7 | 35.36 | |
| 60 | 13.600 | 16,589 | 38.73 | 77.5 | 38.73 | |
| 70 | 15.200 | 19,354 | 41.83 | 83.7 | 41.83 | |
| 75 | 16.000 | 20,736 | 43.30 | 86.6 | 43.30 | |
| 80 | 16.800 | 22,118 | 44.72 | 89.4 | 44.72 |
… and 2 more rows in the download.
About this Calculator
Loop checks need quick conversions between mA, raw counts and engineering units. This table removes mental arithmetic errors, especially for square root flow loops.
Basis: mA = 4 + 16 × %; raw = raw min + (raw max − raw min) × %; value = LRV + span × % (or × √% for square root).
How to use
- Enter range, unit and raw count limits of your input card.
- Choose square root for DP flow loops.
- Set the low flow cutoff.
- Use the table for loop checks and HMI verification.
Formulas used
- mA = 4 + 16 × p.
- Raw = raw min + (raw max − raw min) × p.
- Value = LRV + span × p, or × √p for square root.
Related tools
Frequently Asked Questions
Why does 25 % signal show 50 % flow?
With square root, flow = √0.25 = 0.5 of maximum.
What raw range does my PLC use?
Check the input card manual; Siemens S7 uses 27648 for 100 %.
Why a low flow cutoff?
The square root is steep near zero, so noise looks like flow.
Learn more on the blog
4 to 20 mA current loop explained
A practical guide on instrumentationblog.in that explains the engineering behind this workbook.
Read Full Article