Flow Switch Features Easy Setup

Accurate setup is perhaps the most time consuming and tedious aspect of an instrument technician's job. Calibration requires that settings be checked against known conditions so that readings are meaningful to the process.In the case of an component like a flow switch, determining setpoints requires a technician to know limiting flow rates and pick devices accordingly.

By Dick Johnson, CONTROL ENGINEERING September 1, 1998

KEY WORDS

Process control & instrumentation

Flow sensing/measurement

Calibration

Accurate setup is perhaps the most time consuming and tedious aspect of an instrument technician’s job. Calibration requires that settings be checked against known conditions so that readings are meaningful to the process.

In the case of an component like a flow switch, determining setpoints requires a technician to know limiting flow rates and pick devices accordingly. In a real-life process, however, actual flowrate limits may not be precisely defined. When the application requires an alarm condition to be recognized if a flowrate falls below or rises above preset limits, efector inc.’s (Exton, Pa.) SI flow switch can do the job.

The parent company of efector, ifm electronic (Essen, Germany), began using film technology and pioneered the production of “flexible circuits” used in their sensor lines. The flexible printed circuit boards (PCBs) allowed computing power to be “rolled up,” or “folded” so that it would fit into much smaller form factors than run-of-the-mill rigid PCBs. This “compressed” computing power became the basis for many of efector’s compact sensors, eventually leading to SI’s design.

How it works

The SI flow switch operates on the calorimetric princple—it uses the cooling effect of a flowing fluid to provide reliable flow rate detection of both liquids and gases. The unit offers a major advantage over mechanical devices because it has no moving parts that can break off or stick—only a robust probe is in the fluid stream.

The computing part of the SI package allows an operator to teach the switch high and low flow rates in a given application. The setpoint alarm can then be positioned using flush pushbuttons on the housing at any value from 1 to 99% of the high flow rate. According to Karl Klinger, product manager for Fluid Sensors, “The SI is the only microprocessor-based, pushbutton flow switch currently available.”

In addition, the SI offers various modular mounting options, which allow users to position the LEDs marking percent total flow to the best viewable location in the piping setup. The flow switch features a “lock out” function that prevents unintentional changes to the setup. The device can also to be set up remotely from a pushbutton or PLC through a programming wire routed with the power/output cable.

Application specifics

The efector SI is said to provide exceptional compensation for fluid stream temperature changes. It has a temperature response rate of 572 8F/min, which allows the switch to accurately monitor applications that experience rapid temperature changes. The device also features a maximum pressure rating of 4,350 psi. This high-pressure rating provides reliable operation in most applications, especially those exhibiting pressure spikes due to valve closings. Wetted parts are made of corrosion-resistant 316 stainless steel. The switch is compatible with a wide variety of chemicals.

The flow switch is intended for use in both process and discrete manufacturing operations. Specific industries include automotive, welding, machine tool, chemical, pulp and paper, wastewater treatment, and power generation. The SI is priced at $250.

For more information on the efector inc., visit www.controleng.com/info .


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