This automation industry quiz question comes from the ISA Certified Automation Professional (CAP) certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.
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
e) none of the above
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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).
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.
Reference: Nicholas Sands, P.E., CAP and Ian Verhappen, P.Eng., CAP., A Guide to the Automation Body of Knowledge. To read a brief Q&A with the authors, plus download a free 116-page excerpt from the book, click this link.