A differential pressure flow transmitter measures with an accuracy of 0.05% of calibrated span. What is the flow accuracy of the differential pressure transmitter at 10% of flow rate?

A.  0.05% of flow rate   

B.  0.50% of flow rate   

C.  1% of flow rate   

D.  5% of flow rate

Answer A is not correct because 0.05% of flow rate is far superior to 0.05% of calibrated span. One might think that the accuracy at 10% of flow rate would be 0.50% of flow rate. However, 10% of flow generates only 1% of differential pressure, so Answer B is not correct. The accuracy of the differential pressure flow transmitter operating at 1% of differential pressure would be 5% of flow rate (0.05 x 100 / 1). Answer D is correct.

Additional complicating factors

Operating pressure, operating temperature and ambient pressure adversely affect transmitter performance. These effects can be many times larger than the differential pressure flow transmitter accuracy in some applications and environments.

David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.