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Engineering Toolbox/Transmitter Zero / Span Error Check

Instrumentation & Calibration

Transmitter Zero / Span Error Check

Quantify the 4 mA endpoint error, 20 mA endpoint error and observed output-span error from a two-point transmitter check.

Two-point check

Apply the configured LRV and URV with a suitable reference standard and record the actual analog output.

mA
mA
±% span

Use the OEM, calibration procedure or project acceptance criterion. No generic transmitter tolerance is assumed.

Diagnostic purpose

Separate endpoint offset from output-span error.

The two-point pattern is useful before deciding what kind of adjustment—if any—is appropriate for the transmitter technology and calibration procedure.

Do not confuse trim functions

On an analog transmitter, zero and span adjustments may directly alter the transfer function. On a smart/HART transmitter, reranging, zero trim, sensor trim and analog-output trim are different operations. Use this page to quantify the observed analog-output error, then follow the device manual and calibration procedure.

Output-span error = (Measured URV mA − Measured LRV mA) − 16 mA

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