January/February 2013
Certification Review

ISA Certified Automation Professional (CAP) program

Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

CAP question

Which one of the following flow sensors naturally generates a pulsed output as a representation of the flow rate:

A.     orifice plate with differential pressure transmitter

B.     thermal mass flowmeter

C.     turbine meter

D.    magnetic flowmeter

CAP answer

The correct answer is C, "turbine meter." Turbine meters almost universally use a magnetic pickup to determine the number of rotations of the spinning turbine element.  Each time a magnetized blade passes the pickup sensor, a pulse is generated. The volumetric flow rate can be determined by counting the number of pulses in a unit of time.

Answers A, B, and D are not correct; each of these flowmeter types generally produces an electrical signal, with a magnitude that is proportional to flow rate. Each of these flowmeter types could be outfitted with a transmitter capable of transmitting pulses, but only the turbine meter from the choices above naturally generates pulses (with frequency proportional to flow rate).

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition, ISA, 2006.