How are the precision and accuracy of a differential pressure transmitter calculated?

You see "0.075%" on the nameplate of a differential pressure transmitter and actually believe it? Once the turndown ratio is increased, the temperature shifts, or static pressure rises, the accuracy is no longer that figure.

So, how should the accuracy of a differential pressure transmitter be calculated?

Differential pressure transmitters come in two types: standard (base) units and remote-seal units. For standard units, the accuracy is directly stated in the performance specifications—such as 0.075%, 0.05%, or 0.04%.

For units equipped with remote-seal capillaries, factors such as the specific process application must be considered; these require factory testing and calibration, and the overall accuracy typically falls within the 0.1% to 1% range.

Regarding accuracy calculation (for standard units): the reference accuracy is found on the nameplate (e.g., 0.075%, 0.05%, 0.04%), but this figure applies only to a 1:1 turndown ratio.

If the actual operating turndown ratio is 5:1 or 10:1, you must consult the manufacturer's catalog or manual for the calculation formula, as the actual accuracy may not meet the nominal rating.

Therefore, whether dealing with differential pressure or standard pressure transmitters, while the turndown ratio might technically reach up to 100:1 (or higher), it is generally not recommended to exceed 10:1—unless the resulting loss in accuracy is acceptable.