Quiz Corner: Differential pressure flowmeter accuracy statements

Which of the following forms describe how the accuracy of a differential pressure flowmeter would typically be expressed?

A. Percent of rate
B. Percent of full scale
C. Percent of measured value
D. Percent of calibrated span
E. Percent of span

This question is one that would be asked in a plant but it is not precise enough to elicit a definitive answer. The primary element (such as an orifice plate) has an accuracy expressed as a percentage of rate (Answer A) or measured value (Answer C). However, the accuracy of its differential pressure transmitter can be expressed as a percentage of full scale (Answer B), calibrated span (Answer D), span (Answer E), upper range limit or a combination thereof.

Additional complicating factors

The accuracy of a differential pressure measurement system includes the performance of the primary element and its transmitter. The transmitter accuracy expressed as a percentage of rate increases as flow decreases, so the combined accuracy expressed as a percentage of rate will be different at different flow rates.