AutoQuiz: How to Calibrate a Magnetic Flowmeter

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program. This question comes from the Level I study guide, Domain 3, Troubleshooting. Level I represents a professional who has a five-year total of education, training, and/or experience.

Which of the following is not necessary when zeroing or calibrating a magnetic flowmeter?

a) calibration factor for the flow tube assembly
b) flow tube full of process material
c) proper grounding
d) warm-up period for the fluid in the system
e) none of the above


Click Here to Reveal the Answer

Magnetic flowmeters use Faraday’s law of magnetic induction as the basis of their operation.

Magnets apply a magnetic field to a tube through which the fluid is flowing and an electric potential generates across the tube that is proportional to the velocity of the fluid flowing through the pipe.

Then, knowing the density of the fluid, the velocity of the fluid, and the cross sectional area of the pipe, the meter has enough information to calculate the mass flow rate of the fluid.

To work, this flowmeter must be on a pipe that is insulating type, so the potential that generates does not short circuit. Another requirement is the fluid that is flowing needs to be able to conduct electricity, at least to some degree so Faraday’s laws of induction can apply.

Water, for example, works as it has a sufficiently high level of conduction for the flow meter to operate.

The magnetic flowmeter is the third most common flowmeter behind differential pressure and positive displacement flowmeters.

The correct answer is D, a warm-up period for the fluid in the system is not necessary.

Image Credit: Flow Control magazIne

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