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Figure 1: The LLF Series of liquid-level sensors is used where sensitive detection is required.
Polypropylene is most often used for hot-water applications and with acidic liquids such as those used in metal cleaning. It is also used for lower-temperature food operations (up to 105°C). The material is a good fit for commercial appliances and equipment, as well as several general-purpose applications. An example is the Standex-Meder LS03 Series electronic level sensors with magnetic floats. The sensor comes in PP (Polypropylene) for water applications and dilute acids and PA (Polyamide) for use in oil, gasoline (petrol), and brake fluid.
Polyphenylene sulfide (PPS) is used with aggressive acids and many industrial-grade liquids as it features excellent chemical resistance.
Very often, we find liquid-level sensors offered in several material options as with the RSF40 Series from Cynergy3 (Figure 2). Offered in nylon, polypropylene, or PPS, and offering a choice of gasket materials to suit most commonly used liquids, the series is a compact internal fitting device that is ideal for size-sensitive applications such as vending machines, commercial washing machines, and evaporator units. This series is mounted on the inside of a tank.
Figure 2: Mechanical dimensions of the RSF40 Series by Cynergy3, available in nylon, polypropylene, or PPS.
Stainless steel is used with aggressive or corrosive liquids including acids, chemical-based liquids, salt water and coolant, and offers an explosion-proof alternative to plastics. It is suited to industrial, military, heating, motorsports, and automotive applications. Stainless steel is generally used in sensors for high-temperature and high-pressure environments and corrosive conditions.
The Standex-Meder LS02 Series (Figure 3) features a stainless-steel housing, two versions based on applications such as water and dilute acid apps, and an option for use in oil, gasoline, and brake fluid. The applications for this device include liquid container monitoring in household appliances, automotive applications, test and measurement, and control technology.
Figure 3: The Standex-Meder LS02 Series combines a stainless-steel housing with either polypropylene or polyamide versions based on application.
While these sensor materials represent the majority of applications, others are also used. Kynar polyvinylidene fluoride (PVDF), for example, is used when there is a need for chemical and solvent-resistant properties. The material has high purity, so it is often used for medical, food handling, and sensitive test equipment. Buna-N (Nitrile rubber) is used for aromatic hydrocarbons, and dilute acids and bases as with fuel tanks, hydraulic fluid storage, and transmissions. Brass is often used in petroleum-based liquids such as gasoline, lubricant oils, in-vehicle, generator, or hydraulic applications.
At times, level measurements must be external and performed at a distance from the material. This is true with molten materials or glasses, and within environments where the liquids may be not only corrosive, but emit toxic fumes. In these cases, optical sensing is used. Rather than being in direct contact with the liquid, these sensors rely on the light transmitting, reflecting, and refracting properties of materials being processed.
Any commercial or industrial process involving the filling or storing of a liquid in a tank or vessel will benefit from the use of a liquid-level sensor. Liquid-level sensors in particular are used in applications where the liquid level to be measured is important (if for no other reason than the costly nature of the liquids involved). As an example, consider alcoholic beverages, where each inch of liquid level resident in the huge vat may represent tens of thousands of dollars, so the sensor material used is critical.
By using a Chemical Compatibility Chart, users have a good indication of the suitability of sensor materials relative to a wide range of liquids. It may still be necessary in some cases, however, to obtain a sample sensor to test compatibility.
In this article we have discussed the options an engineer has in choosing materials for a fluid level sensor and presented a sampling of available product. For more information on the products mentioned in this article, use the links provided to access product information pages on the Hotenda website.