Calibration Error Calculator
Check a 4 to 20 mA transmitter calibration. Enter the range and the measured outputs at five test points to get the error at each point in percent of span and a pass or fail against your tolerance.
- Expected mA = 4 + 16 × percent ÷ 100
- Error % of span = (measured − expected) ÷ 16 × 100
- Each point is compared with ± 0.25 %
Calibration results
| Point | Input | Expected | Measured | Error (% span) | Result |
|---|---|---|---|---|---|
| 0 % | 0 | 4.000 mA | 4.012 mA | +0.075 % | Pass |
| 25 % | 2.5 | 8.000 mA | 8.006 mA | +0.038 % | Pass |
| 50 % | 5 | 12.000 mA | 12.018 mA | +0.113 % | Pass |
| 75 % | 7.5 | 16.000 mA | 15.985 mA | −0.094 % | Pass |
| 100 % | 10 | 20.000 mA | 20.051 mA | +0.319 % | Fail |
How Calibration Error Is Calculated
Error (% of span) = (Measured − Expected) ÷ 16 mA × 100
Expressing error as a percentage of span makes results comparable between instruments of different ranges, and matches how most transmitter accuracy specifications are written.
Worked example
At 100 % input a transmitter outputs 20.051 mA instead of 20.000 mA. Error = 0.051 ÷ 16 × 100 = +0.319 % of span, which fails a ±0.25 % tolerance. A span adjustment is needed.
Frequently Asked Questions
How do I calculate percent of span error?
Subtract the expected output from the measured output, divide by the output span (16 mA for 4 to 20 mA) and multiply by 100.
What tolerance should I use for a transmitter calibration?
Use your site procedure. A common choice is the manufacturer accuracy or a process requirement such as ±0.25 % or ±0.5 % of span, and it must be larger than the uncertainty of your calibrator.
What is the difference between as found and as left?
As found readings are taken before any adjustment and show how far the instrument drifted. As left readings are taken after adjustment and prove it now meets tolerance.
Learn more on the blog
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