Calorimetric monitors contain no moving parts. They work well with contaminated media because the inline units don't disrupt the flow and probe-style devices must be inserted only a few millimeters into the flow to get a signal. They are very repeatable and ideal for flow/no-flow and set-point applications, but rarely are considered accurate enough to be classified as a meter. If fluid temperature rises quickly, the calorimetric monitor could read this as a change in flow rather than temperature.
Ideal applications include flow/no-flow monitoring for pumps, ventilation systems and dosing operations.
Magnetic inductive sensors contain a solenoid coil, measuring tube and electrodes. They take advantage of Faraday's law of induction. The solenoid coil produces a magnetic field and the charged particles entering the magnetic field are driven to the outside of the tube wall. This creates a voltage, proportional to flow rate, that is measured by the electrodes.
Many such meters can totalize flow. And, unlike paddle wheel and vortex meters, which don't work reliably with highly viscous fluids, viscosity generally has no effect on magnetic inductive units. In addition, suspended solids and debris in the fluid don't affect them. However, the fluid must be electrically conductive, which rules out use with hydrocarbons.
Magnetic inductive meters are ideal for fluids containing particles and debris and for flow conditions requiring totalizing.
ONLY PAY FOR WHAT YOU NEED
I've highspotted devices most commonly used for non-critical flow detection, but numerous other technologies can handle process applications. The accuracy required, media, and environmental conditions will dictate which sensor best suits a particular application.
Remember, when dealing with non-critical flows, consider less accurate devices with fewer features. They can provide suitable performance at lower cost.
RICHARD TALLANT is a product manager for Turck, Minneapolis, Minn. E-mail him at Richard.Tallant@turck.com.