Instrument Hysteresis Calculator
Hysteresis is the difference between readings taken with rising and falling input at the same point. Enter the upscale and downscale outputs of a 4 to 20 mA instrument to find it.
- Hysteresis = |down − up| ÷ 16 mA × 100 at each point
- Largest value = 0.150 % at 50 %
Upscale and downscale readings
| Point | Upscale | Downscale | Hysteresis |
|---|---|---|---|
| 0 % | 4.002 | 4.006 | 0.025 % |
| 25 % | 7.995 | 8.012 | 0.106 % |
| 50 % | 11.990 | 12.014 | 0.150 % |
| 75 % | 15.992 | 16.010 | 0.113 % |
| 100 % | 20.004 | 20.004 | 0.000 % |
Hysteresis Formula
Apply each point by approaching from below on the upscale run and from above on the downscale run, without overshooting. The 100 % point is shared by both runs.
Worked example
At 50 % the upscale reading is 11.990 mA and downscale 12.014 mA, a difference of 0.024 mA, which is 0.15 % of span.
Frequently Asked Questions
What is hysteresis in instruments?
The difference in output for the same input depending on whether the input was rising or falling.
How is hysteresis tested?
Run the calibration upscale to 100 % and then back downscale, recording the output at the same points in each direction.
Is hysteresis included in accuracy?
Usually yes: reference accuracy specifications combine linearity, hysteresis and repeatability.
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