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NTC Thermistor in Electric Water Heater
2022/12/20 03:12:34

With the improvement of national living standards, people's requirements for comfortable water use are getting higher and higher, and electric water heaters have become the first choice for consumers' household water because of their constant temperature water output. In order to ensure that the electric water heater can continue to maintain constant temperature and its safety, NTC thermistors are generally added as components for temperature monitoring. Specifically, thermistors are used in the following situations:

First, precise temperature control

If an electric water heater wants to achieve accurate temperature control, one of the necessary conditions is the outlet NTC temperature sensor, which is generally set at the outlet to control the outlet temperature. Some smart electric water heaters will also set an NTC temperature sensor at the water inlet, and the other end is connected to the circuit board, according to the principle of circuit voltage division, when the water temperature changes, the voltage at both ends of the internal NTC thermistor also changes, the CPU can get an accurate water temperature value through A/D conversion according to this voltage signal. In the use of electric water heaters, the constant temperature accuracy is generally required to be ≦± 2 °C, which also requires NTC thermistor to have high accuracy and sensitivity.

Second, test whether the inner tank is water leaked

One of the key components of the storage electric water heater is the inner tank, water leak of the inner tank will lead to rust and corrosion of the surface and shell of the inner tank, even lead to circuit failure and explosion, endangering the life and property safety of consumers. Therefore, manufacturers of electric water heater will use the water leak detection system to test the inner tank to improve the quality of the product. Specifically, a V-shaped water chute is installed at the bottom of the inner tank body of the electric water heater, its function is to gather the water leak out of the inner tank. An NTC thermistor is set at the bottom of the water chute, and combined with the detection circuit located on the controller, it is possible to detect whether the inner tank leaks water at any time.

At room temperature and pressure, the thermal conductivity of air is 0.023 W/(m.k) that of water is 0.59 W/(m.k), the heat transfer capacity is much higher than that of air. By adjusting the detection circuit parameters of the NTC thermistor, more current flows through the NTC thermistor, and the NTC thermistor heats up itself. According to the negative temperature characteristics of thermistor, combined with the different rates of heat dissipation in different environments, it can be determined whether the NTC thermistor is in air or water to determine whether the inner tank is leaking. (Thermistor dissipate heat slowly in air and has little change in resistance value; Fast heat dissipation in water and has large change in resistance value)

To this end, NTC thermistors used on electric water heater mainly have the following characteristic requirements: 
1. Fast reaction speed and high sensitivity; 
2. Great consistency; 
3. High accuracy; 
4. Resistant to moisture and high temperature.

HT series high temperature resistant NTC thermistor independently developed and produced by EXSENSE Electronics Technology Co., Ltd. can well meet the requirements of electric water heater. It has the characteristics of moisture resistance, high accuracy, great stability, fast response speed, etc. It is suitable for the control circuit of electric water heaters requiring fixed point temperature measurement.

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