How to select the best level measurement technology

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Charlie Sorbo, Level Product Manager for Gems Sensors and Controls, looks at the how new technology and the need to boost efficiency has driven the development of level measurement components.

How to select the best level measurement technologyIn many industrial and process applications, level measurement is a fundamental requirement. As a result, the demands of OEMs and end users alike have driven the designers and engineers behind level sensors to provide components that offer increased reliability, lower maintenance costs and far greater levels of precision. All these innovations in level measurement offer huge potential but to get the best from any component you need to ensure the right specification for your operations.

When specifying a level measurement requirement, there are several factors to consider. Cost is rarely the primary one, since the original saving made by selecting the low-cost option is often outweighed by the demands on maintenance. More important factors are the nature of the process material that is to be measured and its material characteristics. Temperature and pressure levels will need to be considered, as will the substance of the tank that holds the material. Specification also depends heavily upon whether the process material is a liquid, a slurry or a solid.

Level measurement options are available for a range of applications. Among the most familiar level measurement methods employed are RF capacitance, conductance (conductivity), hydrostatic gauging and ultrasonics. These have continued to evolve to address the changing nature of the applications concerned. For example, diesel engines are under constant threat of contamination from the ingress of water, as the subsequent corrosion can cause serious damage to the injection pump and injectors. This is a particular issue for high-efficiency engines, especially modern ones, where moisture in the form of condensation is a common problem. In response, the conductivity sensor has evolved to provide increasingly reliable service in detecting the level of water in fuel and lubricating oil. 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 and controlling level.

No moving parts

Gems Sensors & Controls recently launched the WIF-1250, a no-moving-parts option for use in high-efficiency diesel engines, as well as diesel fuel storage tanks and compressor crank cases. 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 options 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. Approaches such as this add reliability to fluid measurement; historically, the presence of water in fuel would have more likely been discovered after some damage had been done, whereas today’s solutions prevent problems from occurring in the first place.

Electro-optic sensors offer a further method of measuring level. An electro-optic 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; however, when liquid rises in the vessel to immerse the prism, 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 with the potential to operate within extreme temperatures ranging between -40degC and +125degC, offering ingress protection ratings of IP66 and upwards, which can be utilised even within extreme environmental conditions.

As illustrated by the example of high-efficiency diesel engines, the increasing sophistication of modern engineering systems demands ever-tighter degrees of process control, and this has led engineers to develop ever more advanced level measurement systems. For example, wireless capabilities have recently been added to enable the transmission of level data to be sent over longer distances without signal degradation. It therefore pays engineers to stay up to date with level measurement developments from a defensive point of view; increasing legislation across industry sets stiff requirements for reliability and sustainability, and the newest level measurement technologies are powerful tools in helping plant engineers to meet these goals.

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