EPCOS has developed two PTC components with stainless steel packages for sensing the level of liquids. The B59050D1100B040 is suitable for measuring water levels and can be operated within a temperature range of between 10°C and 65°C. The B59050D1120B040 is designed for liquids with a thermal conductivity of λth >0.12W/mK such as oil or fuel. The permissible temperature range in this case is between -25°C and 50°C.
To prevent overheating, the PTC elements should be operated at a voltage <18V. The tip of the PTC element can emit different thermal losses. The transition from liquid to air and vice-versa causes these losses to change very quickly, and as a result, the resistance of the PTC element. This allows the device to record very simply and exactly whenever a liquid goes above or below a certain level.
In contrast to level measurement with mechanical contacts, PTC-based systems operate with no moving parts. Moreover, complex electronics such as those required by ultrasonic or optical systems are unnecessary.
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