How to use this on a job
Write down two known points: what the input reports at the bottom of the measuring range, and what it reports at the top. Those two pairs define the line. A vendor name by itself does not define an analog scale.
- 01
Enter the low and high input values from the configured channel. They can be mA, volts or raw counts. Enter the matching engineering endpoints and their unit.
- 02
Read the live value and its position along the span. The unclamped result shows what the measurement says; the clamped result shows what a display limited to the nominal range would show.
- 03
Reverse the direction when planning an injection test. Enter a desired engineering value and calculate the signal or raw count that should produce it. Record the 0%, 25%, 50%, 75% and 100% points.
Work through one example
y = y₀ + (x − x₀) × (y₁ − y₀) ÷ (x₁ − x₀)
For a 4–20 mA transmitter covering 0–10 bar, 12 mA is halfway through the electrical span and therefore 5 bar. At 2 mA the line extrapolates to −1.25 bar, while a clamped display reads 0. The disagreement tells you to investigate rather than trust the display.
Before you trust the answer
Clamping an under-range measurement can hide a wiring fault as a valid zero. Keep the diagnostic status separate from the displayed value. A raw range such as 0–27648 needs confirmation for the actual module and range configuration; check its diagnostics in the manual too.