Calibration Table Generator (3 / 5 / 9 Point)

How a calibration test table works

A transmitter calibration check compares what the instrument should output at known inputs against what it actually outputs. The test points divide the range evenly — for a 5-point check at 0, 25, 50, 75 and 100% of span — and at each point the ideal output current follows the standard scaling:

The acceptance band converts the instrument's tolerance, usually stated as a percentage of span, into current:

Readings inside I_ideal ± ΔI pass. The "as found" column records the instrument's condition on arrival — before any adjustment — and "as left" records it after adjustment. Keeping both is what turns a calibration into usable history: as-found data reveals drift rate, which is what calibration-interval decisions should be based on.

Worked example

Range 0–100 kPa, tolerance ±0.25% of span, 50% point:

1. Ideal current at 50%: 4 + 0.5 × 16 = 12.000 mA
2. Tolerance in current: 0.0025 × 16 = 0.040 mA
3. Acceptance band: 11.960 to 12.040 mA
4. Applied input for the point: 0 + 0.5 × (100 − 0) = 50 kPa

Bench practice notes

• Approach points from one direction at a time. When checking the upscale sequence, don't overshoot and come back — that defeats the hysteresis measurement.
• Your reference must be better than the tolerance. Rule of thumb is a 4:1 test uncertainty ratio: to verify ±0.04 mA you want a calibrator good to ±0.01 mA.
• Give the instrument time. Allow the reading to settle at each point, especially on temperature instruments with long time constants.
• Record as-found before touching anything. The most valuable number in the whole procedure is the one most often skipped.

Frequently asked questions

How many points should a transmitter calibration check use?

A 5-point check (0-25-50-75-100%) is the industry norm for routine verification. Use 3 points for a quick check and 9 or more when characterising linearity or after repair.

Why check points going up AND down?

Approaching each test point from both directions reveals hysteresis — a difference between rising and falling readings caused by mechanical friction or sensor behaviour that a one-direction check hides.

What does a tolerance of ±0.25% of span mean in mA?

Span in current terms is 16 mA, so 0.25% of span is 0.04 mA. A 12.000 mA ideal point would accept readings from 11.960 to 12.040 mA.

Provided for reference and education. Verify independently before use in safety-critical work. See our disclaimer.