Flow components support efficiency

12 December 2012

Smooth-running, long-lasting service from engineering equipment requires the correct specification of even simple components such as flow sensors, says Kevin Castonguay, product marketing manager for Gems Sensors and Controls.

For a process to achieve optimum levels of efficiency it is vital that even relatively simple components need to be specified and operated correctly. This need is as urgent as it ever was – energy efficiency is an increasingly important item on the industrial agenda, not only to protect profits but also to reduce emissions and meet increasing leglislative demands by increasing sustainability.

Where sensors are concerned, it is important to be aware that there are many components available today that can support efficiency, resulting in reduced energy consumption and costs. Mechanical and electronic flow sensors and switches, for example, can provide increasingly consistent output, enabling the maximised performance of higher level systems. These devices are also subject to continuous refinement and improvement in terms of performance, resistance to corrosion and in their flexibility and adaptability within engineering systems. As a result of these efforts, some impressive innovations have been achieved.

Robust, solid-state flow switches suitable for fluids with large particles and slurries, are available that are immune to changes in viscosity. While components with moving parts show a natural tendency to jam, wear or break, these new flow sensors offer greater resistance to failure.

Solid state options
One powerful solid-state option is the electromagnetic flow sensor, which is suitable for use with the majority of electrically conductive liquids, pastes and slurries. Because these ultrasonic flow measurement devices are capable of accurate flow measurement across a wide velocity range they are especially useful in systems that experience low load periods and low flow. These sensors are also of benefit in retrofit installation projects when pipeline cannot be isolated as they are so easy and cost-effective to install.

In the HVAC industry the enhanced performance of flowmeters can play a vital role in system management. The best of today’s differential pressure flowmeters can withstand a wide range of temperatures and pressures making them a reliable solution for measuring the flow of liquids, gases and steam across the HVAC industry in applications such as natural gas boilers, boiler stacks and chilled water.

The Gems Sensors & Controls FS-600 flow switch, for example, can function for years even in applications without filtration. Its sensor tip houses a heater element plus two transistors – one located in the sensor tip, closest to the flowing fluid, and one bonded to the cylindrical wall. The transistor at the tip is used to detect changes in the flow velocity of the liquid, while the second provides a reference for ambient fluid conditions. By heating the transistor at the tip of the probe, a measurement of how fast heat is conducted away from it by the flowing liquid is compared against the difference in temperature between the second transistor. This provides a calculation of fluid velocity. When fluid velocity is high, the temperature differential is lower; when fluid velocity is low, the temperature differential is greater.

Advances have also been seen in the development of paddlewheel fluid flow sensors. These components are now available with solid-state electronics that provide accurate flow rate output, plus highly visible paddlewheel rotors for easy visual confirmation when monitoring dynamic fluid flow within fluid lines. As liquid passes through the sensor, a magnetic rotor spins at a rate proportional to flow. The magnetic fields turning with the rotor excite a static Hall Effect sensor and generate a series of voltage pulses. The best of today’s paddlewheel fluid flow sensors can monitor fluids with flow rates ranging from 0.4 to 227l/min with accuracy typically between 5% and 7%.

Even this brief examination of modern flow sensing technology illustrates how advances in the design and construction of flow sensors has increasingly enabled manufacturers to optimise industrial equipment and minimise maintenance. Small yet sophisticated components such as flow sensors offer a compact, durable and low-cost option for engineers and designers, and the current wave of flow sensors contains a range of components suitable for a variety of sensing operations in many applications.

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