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Characteristics of Temperature Measuring NTC Thermistors and Their Application Scenarios
2023/02/07 03:02:37

As professional NTC manufacturer, EXSENSE Electronics Technology Co., Ltd. also provides customers with the best temperature sensing and temperature measurement solutions. At present, the main temperature measuring components in the industry are: NTC thermistor, platinum resistance as typical representative of the thermal resistance, thermocouple. This article is simply introduced and analyzed from several aspects such as principle, accuracy, sensitivity, reliability, price, application scenarios, etc. to help the majority of users select models.

First, NTC thermistor

NTC thermistor has been around for more than 80 years since it came out in the 1930s, 1940s. It mainly uses spinel-type thermal sensitive ceramics formed by manganese, cobalt, nickel and other metal oxides as the main function, with high cost performance, sensitive temperature sensing, fast response, etc..

Its functional principle is generally considered to be that Due to the 3D layer electrons of the transition metal elements in NTC ceramics can jump on different ions to achieve conductance, and the jump is related to the corresponding activation energy ΔE, thus reflecting the phenomenon of thermal activation. Then for a specific NTC thermistor, its conductance at a specific temperature is determined, and the corresponding resistance is also determined, so this phenomenon is used to detect temperature.

The resistance accuracy of NTC thermistor is now generally between 1% to 5%, some high-end manufacturers can achieve high accuracy of 0.5%, and EXSENSE Electronics can achieve a maximum resistance accuracy of 0.3% currently. So what is the temperature accuracy? 

Due to the deviation of components in circuit design and other temperature measurement circuits and the resolution of the client-side MCU, it should be pointed out that the temperature sensing accuracy really measured by the client is not equivalent to the NTC thermistor itself, but it is generally very similar, the resistance accuracy of NTC at room temperature is equal to about 0.2℃-0.25℃ per percentage point. Therefore, EXSENSE Electronics can achieve ultra-high-precision temperature measurement of 0.1℃, TWS Bluetooth headsets and medical-grade body temperature sensor currently on the market are two of the applications. For the entire NTC market, the accuracy of NTC is reflected in the high degree of customization, ranging from cost-effective solutions for the general consumer electronics market to high-accuracy solutions for the high-end market. Recommended index: ★★★★★.

The sensitivity of NTC is greatly affected by the type of encapsulation, but in general, due to its small structure and core part composed of metal electrodes and ceramics with high thermal conductivity, NTC has a very short response time, and the fastest thermal time constant can be achieved 0.3 seconds (typical). Applications on instantaneous smart toilets are typical examples of this direction. Recommended index: ★★★★★.

The reliability of NTC is slightly inferior to other categories, but it can also reach a roughly comparable level. At present, the functional parameter drift rate of most NTC in the market is between 1%-3% during its life cycle, EXSENSE Electronics and a few other first-class manufacturers can control it to a level of about 0.3%-0.5%, corresponding to a temperature drift of only about 0.1℃, that is, a state similar or even better than other high-end levels in the life cycle. Recommended index: ★★★★.

In terms of price, because the materials used in NTC are generally lower except for cobalt oxide, the overall cost is more cost-effective than other types (except for NTC thermistor chip products with gold electrodes used in high-end fields). Index: ★★★★★.

In terms of application, NTC thermistor occupies the main part of the temperature sensing and temperature measurement market, which are widely used in:

1) Smart home: kitchen appliances (rice cooker, electric kettle, induction cooker, electric cooker, water heater, etc.), air conditioner, refrigerator, etc.;
2) Automobile: automotive air conditioning, air intake, water temperature, oil temperature, motherboard, especially new energy vehicle BMS system, IGBT module, etc.;
3) Smart wearable devices: bracelet, TWS Bluetooth headsets, smart underwear, etc.;
4) Medical: forehead thermometer, electronic thermometer, body temperature sensor;
5) Digital products: computers, mobile phones, especially smart phones, each using up to 10-15 NTC thermistors;
6) Optical communication, infrared thermoelectric reactor, etc.

The reasons are: excellent accuracy, great sensitivity, high reliability can meet most industry requirements. However, it should be noted that conventional NTC performs poorly above 500℃, on the one hand, its temperature coefficient (Alpha) is small at high temperature; On the other hand, the reliability of scenarios above 500℃ is average, so the application scenario recommendation index:

Applications below 300℃: ★★★★★
Applications at 300-500℃: ★★★
Applications above 500℃: Not recommended

2. Platinum resistance (RTD)

Thermal resistance typically represented by platinum resistance is another major branch of temperature measuring element, which functionally uses the characteristics of positive temperature effect of the resistance value of most metal materials for temperature monitoring. Platinum resistance uses precious metal platinum as the functional body, coupled with its sputtering and etching process, so its main features:

1) Accuracy: The resistance accuracy is extremely high, up to 0.04%, but because its temperature coefficient is only 0.38%, its highest temperature accuracy is also roughly 0.1℃, similar to high-end NTC thermistor. Recommended index: ★★★★★.

2) Sensitivity: The sensitivity of platinum resistance is greatly affected by the type of encapsulation, but in general, due to its small structure and core part composed of high thermal conductivity metal and ceramic, its response time is extremely short. However, its temperature coefficient is only 0.38%, which is too small compared to 4%-5% of NTC thermistors. Recommended index: ★★★★.

3) Reliability: The core part of platinum resistance is composed of metals and ceramics with high thermal conductivity, and some of them are protected by glass glaze. Therefore, its reliability is excellent, but it should be noted that its platinum line is easy to lead to the connection problem. Recommended index: ★★★★★.

4) Price: The core part of platinum resistance is composed of precious metals and ceramics, so the price is higher. Recommended index: ★★★.

In general, platinum resistor is generally used in automotive, industrial and some high-end consumer electronics due to their own characteristics. Due to the high price, great high temperature reliability, small thermal coefficient,etc., the application scenario recommendation index:

Applications below 300℃: ★★★
Applications at300-600℃: ★★★★★
Applications above 600℃-850℃: ★★★★

Third, thermocouple

Thermocouple is the principle of bimetals being heated to form a thermoelectric potential to sense temperature, which is different from NTC thermistor and platinum resistors using RT curve characteristics, which use their own VT curve. Due to the material, structure, process and other factors of the thermocouple itself, its main features:

1) Accuracy: Relying on calibration, high accuracy can be achieved. Recommended index: ★★★★★.
2) Sensitivity: Due to the large encapsulated body, the sensitivity is poor. Recommended index: ★★★★.
3) Reliability: The core part of the thermocouple is made of metal and protected by the encapsulated body. Excellent in terms of reliability. Recommended index: ★★★★★.
4) Price: The core part of most thermocouples is composed of precious metals, and the process is also more complicated, so the price is high. However, some of them use base metals, so the price range is large. Recommended index: ★.

In general, thermocouple due to its own characteristics, the application is generally concentrated in automotive, industry, etc. Due to the high price, high temperature resistance and other characteristics, the application scenario recommendation index:

Applications below 300℃: ★
Applications at 300-600℃: ★★★
Applications above 600℃: ★★★★★

In general, NTC thermistor, platinum resistor and thermocouple have their own advantages and disadvantages, they also have their own application fields. NTC thermistor is suitable for batch or customized parts below 300℃; Platinum resistance is suitable for 300℃-600℃ industrial and some automobiles; Thermocouple is biased towards hotter industrial or engine scenarios. EXSENSE Electronics specializes in the R&D, production and manufacturing of NTC, focusing on high-accuracy, high-reliability and fast-response NTC solutions.

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