Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Temperature Sensing Type

Reed switches in deep freezers
Temperature Sensing Type Application in Deep Freezer

Normally, Reed Switches are used in collaboration with magnets in all the other types of applications. A Thermal Reed Switch is not actuated with a magnet but is constructed in such a way that it is used for temperature sensing. When a Thermal Reed Switch is used in an application to check if a set temperate as been met, such applications can be classified as Temperature Sensing Applications.

Normally, temperature is sensed using a Thermocouple, which uses two dissimilar metals to detect a change in temperature by means of a potential difference produced at the output. This needs to be electronically compensated to allow for more accurate readings. For this, additional calibrated controllers are required, which monitor the temperature and then trigger outputs at set the sensed temperature. This is not only expensive, but is not required for simple temperature sensing applications.

Simpler temperature cut-outs such as bimetallic switches are also constructed using two dissimilar metals that undergo differential expansion and break contact at the sensed temperature. The disadvantage is that depending on the control circuit current, the set point also varies. These types of switches, being mechanical in nature, wear out and cause changes in the sensing temperature. They are also prone to corrosion. Thermistors, on the other hand, do have a fast response time, but the power lines require shielding, and their resistance-temperature characteristics are not linear. Also, if the control circuit current is not low, it tends to heat up the device, and alters the temperature sensing point.

The Thermal Reed Switch overcomes all these problems. It consists of a reed switch, two permanent magnet, and a special alloy that conducts the magnetic flux lines between the two permanent magnets, at temperatures lower than the Thermal Ferrite’s Curie Point. This keeps the reed switch closed. When the ambient temperature crosses the Thermal Ferrite’s Curie Point, the flux no longer passes between the exterior magnets, and the reed switch contact opens. This is a highly repeatable temperature cut-out that works for the rated wattage of the reed switch which also means that thermal reed switches can be constructed for various loads.

Thermal reed switches find applications in over-heat protection and in precise temperature switching. Thermal reed switches are also available in cut-in cut-out differentials ranging from 3°C to 8°C. This wider temperature differential helps cooling fan circuits in over-heating applications to get turned off after sometime, and the narrow temperature differential helps in triggering alarms which can go off as soon as the temperature drops by 2-3 degrees.

Thermal reed switches can also sense sub-zero temperatures as low as -30°C and can also used to maintain the temperature of a bath for example, at a set temperature. Functionality of Level sensors can also be improved by adding a temperature cut-out. Needless to say, that Thermal Reed Switch can replace expensive thermistor, bimetallic switches at a fraction of the cost. Some examples of Temperature sensing applications are listed below.

Example Applications

Thermal Reed Switches in Aquariums for controlling Water Temperature

Aquarium Temperature Due to their accurate temperature cut-in and cut-out, Thermal Reed Switches can maintain an...Continue reading ->

Thermal Reed Sensors for Sensing Temperature on Boats

Reed switches in finding boat engine temperature Thermal reed sensors can also be used in a variety of applications on boats...Continue reading ->

Thermal Reed Sensors in Automobile Temperature Sensing

Reed switches in temperature sensing Thermal reed sensors can be mounted on the engine block to sense high temperatures...Continue reading ->

Thermal sensors in Temperature control in deep freezers, coolers

Reed switches in deep freezers In deep freezers, coolers and heaters, the temperature needs to be maintained within a...Continue reading ->

Reed switches in Instant Water heaters and Power showers

Reed switches in instant water heater Instant Water heaters and power showers use reed switch based Flow switches to detect...Continue reading ->

Thermal Reed Switches in Rice Cookers

Reed switches in rice cooker heater control After rice has cooked, rice cookers need to keep the rice warm at say,...Continue reading ->