ISA Certified Control Systems Technician (CCST) program

InTech, Jun 2006

Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

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.

CCST question

Which type of flowmeter measures flow by measuring volume directly?

A. Coriolis

B. Magnetic

C. Positive displacement

D. Differential pressure

CCST answer

A Coriolis-type mass flowmeter measures the flow rate by determining the torque caused by the radial acceleration of the fluid. It does not measure the volume of the liquid passing through the tube; it measures the amount of mass flowing through the device.

A magnetic flowmeter is a device for measuring volumetric flow rate across a fluid stream by setting up a magnetic field perpendicular to the direction of flow. A flowing conductive fluid then generates a voltage proportional to fluid speed.

A positive-displacement flowmeter measures the flow by breaking it up into discrete elements or packages of fluid. Each package has a known volume. One determines the flow rate by counting how many discrete elements pass through the meter per unit time.

A differential pressure flowmeter (dP) uses a primary element to place a constriction in the flow stream, causing a drop in pressure. Then one uses the resulting pressure drop to calculate the flow rate. Flow rate is proportional to the square root of the difference in pressure one can calculate it using Bernoulli's equation.

Of these four methods only C-positive displacement-measures the volume directly.

For information about the CCST program, go to www.isa.org/ccst.