Selecting the proper liquid level sensor
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Selecting the proper liquid level sensor requires the consideration of a number of different factors. 1. Continuous or Point Sensing Fluid level sensors can operate either continuously or by point sensing. Point sensing involves taking measurements at certain instances. Point fluid level sensors often trigger an alarm or turn off the system based upon a specific limit. Continuous sensors provide a constant measuring and indication of the level of the liquid. 2. Direct or Indirect Fluid level sensors measure position and level either by direct or indirect methods. Direct measurement includes methods that directly sense position and level. Indirect measurement involves the sensing of other factors such as pressure head, which can then be translated to height or level. Indirect methods are not suitable when other parameters involved, such as liquid density, are variable. 3. Contact or Non-contact Fluid level sensors measure using either contact or non-contact methods. Contact methods involve physical contact between the device and the liquid, while non-contact methods measure without touching the media. Non-contact methods are the best choice for servicing corrosive media. 4. Internal or External Fluid level sensors can be mounted either internally or externally. Internal sensors are inserted inside the tank or vessel that incorporates the measured media. External sensors are mounted externally outside the tank or vessel. External sensors are the best choice when internal access for sensor maintenance would interrupt the industrial process or operation. 5. Materials Fluid level sensors can be made from a variety of different materials depending on the type of device and the media being addressed. Nylon - oils and fuels Polypropylene - hot water applications Polyphenylene sulfide (PPS) - aggressive acids Stainless steel - high temperature fluid applications |