Level Best—Keeping Up with Sensor TechnologySeptember 12, 2013 By: Charlie Sorbo, Gems Sensors and Controls
Level measurement plays a fundamental role in many industrial and process control applications. Driven by the demands of OEMs and end users alike, designers constantly improve level sensor reliability and precision and reduce maintenance requirements. These innovations offer huge potential. To achieve optimum sensor performance, however, you need to match the device's specifications with the application's requirements, and to do this, you must stay current with evolving sensor technology.
Selecting the Right Sensor
When specifying a level sensor, you should consider several factors. In most cases, it's a mistake to make cost a primary concern because the savings achieved by selecting a less expensive option is often offset by higher maintenance outlays. Instead, focus on the nature of the material to be measured, its material characteristics (e.g., liquid, slurry, or solid), temperature and pressure conditions, and the material composition of the tank holding the material.
The breadth of available level measurement options accommodates a wide range of applications. Among the most familiar level measurement methods are RF capacitance, conductance (conductivity), hydrostatic gauging, and ultrasonics.
Evolving Sensor Technology
All of these measurement methodologies have continued to evolve to address the changing nature of applications. For example, contamination from water ingress constantly threatens diesel engines by causing corrosion that seriously damages injection pumps and injectors. This is particularly true for high-efficiency engines, especially modern ones, where condensation is a common problem.
In response, the conductivity sensor has evolved to provide increasingly reliable service in detecting the presence of water in fuel. Conductive level measurement is achieved via the electrical conductance of the process material—typically a liquid with a low-voltage source—and offers a relatively low-cost, simple method of detecting water in fuel.
Gems Sensors & Controls recently launched the WIF-1250, a no-moving-parts device for use in high-efficiency diesel engines and diesel fuel storage tanks. The WIF-1250 contains integral, high-temperature-rated electronics that generate an alternating voltage to a probe tip. The presence of water completes the circuit, which in turn changes the condition of the transistor output. The output of the sensor can be used to actuate relays, indicator lights, or LEDs, as well as to interface with CMOS/TTL logic, PLCs, or microprocessors. Systems such as this add reliability to fluid measurement. Historically, the presence of water in fuel has been discovered only after damage has been done; whereas, today's solutions allow corrective action to be taken as soon as problems arise.
Another example of evolving level sensing technology can be seen in electro-optic sensors. This type of sensor contains both an infrared LED and a light receiver. Infrared light from the LED is directed into a prism at the tip of the sensor, and when no liquid is present, the light is reflected within the prism to the receiver. When liquid rises in the vessel to immerse the prism, however, the light from the infrared LED is refracted out into the liquid. At this point, there is no longer any light reaching the receiver, which actuates electronic switching to operate an external alarm or control circuit. There are now electro-optic components on the market that offer ingress protection ratings of IP66 and upwards and operate in temperatures ranging from –40°C to 110°C.
As illustrated by the example of high-efficiency diesel engines, the growing sophistication of modern engineering systems demands ever-tighter degrees of process control, and this has led sensor designers to develop more advanced level measurement systems. Recently, designers have added wireless capabilities to enable the transmission of level data over longer distances without signal degradation.
Increasingly, legislation and the need to stay competitive set stiff requirements for reliability and sustainability across the full range of industries, and the newest level sensors are powerful tools that help plant engineers to meet these goals. With this constantly evolving technology landscape, the engineer that stays up-to-date with level measurement developments achieves the level best.
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