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Extreme Temperature – Fluid Level Sensors


Figure 1. On the left, the full sensor is shown and on the right, the black casing is removed.


There are several laboratory fluid systems that required fluid level monitoring to help control very elaborate equipment processes. This new float sensor has four sensing positions, three of which are dedicated to monitoring hot fluid levels, and the fourth to sense a low fluid level cut-off point. The fourth sensing point is for safety reasons. It ensures that heating coils are never exposed above the fluid level, which could set up a very dangerous situation.

  • Ability to operate at very hot temperatures up to 200°C as the normal operating environment
  • Meets EU WEEE directive 2002/96/EC
  • Meets RoHS directive 2002/95/EC
  • Designed to work in hot and cold liquid temperatures
  • Hermetically sealed
  • Dynamically tested contacts
  • Reliable switching
  • Millions of reliable switching operations
  • Single and multipoint liquid level sensing for an assortment of liquid systems running either hot and/or cold fluids
Figure 2. Showing a full tank with LED indicator.

Figure 2. Showing a full tank with LED indicator.

Figure 3. Showing a low tank with LED indicator.

Figure 3. Showing a low tank with LED indicator.

Standex Electronics Once Again Leads the Way Developing Specific Float Sensors Solving Full Solutions Requirements

Often, designing a sensing system requires  more than ‘off the shelf’ solutions. More and  more applications require unique component  development specific to a given set of circumstances.

In this application, the sensor must operate at  extreme temperatures where the float and magnet must withstand operating temperatures as high as 200°C.  Standex Electronics’s approach has  been to use only the most reliable materials that have demonstrated their quality and reliability in  the field for the life of the system.

The magnet and stainless steel float are attached by a stainless steel rod, (see Figure 2).  The magnet/rod are captured in a plastic sleeve.  The PCB is immediately outside this plastic  sleeve and senses the movement of the float  and magnet. In this manner, the four detection  points are monitored.

The fluid levels will naturally increase as the liquids are heated and expand; and conversely, the fluid level will decrease as the fluid bath temperature cools. Evaporation of the fluids can also occur, particularly at the higher temperatures, potentially reducing the liquid levels.

Most reed sensor offerings supply only the reed  sensor. Standex Electronics’s new design encompasses it all – the reed sensor, the float, and  the magnet along with a PCB and its associated  circuitry. This saves the designer a valuable amount of time by only having to specify and  qualify one component. They no longer have to work with several different suppliers and coordinate between them.

Since this sensor requires some electrical  circuitry, using a printed circuit board with plated thru solder holes guarantees reliable connections using automated wave soldering systems. The hermetically sealed reed switches are properly placed and positioned in their predetermined sensing locations.

Another critical element is the acknowledgment that during assembly, problems can occur.  Standex Electronics tests all sensors 100% for all operating conditions, but in addition, tests for dynamic contact resistance (DCR). Essentially, this test is a guard against the many faults that can occur during assembly. If the reed contacts have any internal contaminations; or the reed  capsule has been stressed or a slight crack has occurred, the DCR test will detect these conditions and reject the sensor. This testing is carried out in an automated testing system. Standex Electronics’s design for manufacturing approach provides a long reliable life in the field.

Consult our engineering group with your specific applications.


**Consult the factory for more options not listed above.

Find out more about our ability to propel your business with our products by visiting or by giving us a contact today! One of our brilliant engineers or sales leaders will address your project!

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