In industrial temperature measurement, thermocouples and thermistors are two commonly used temperature sensors. Although both are used for temperature measurement, their operating principles, material properties, and application scenarios are different.
This introduces the comparison of thermocouples and thermistors. I hope it can help engineers and purchasers select the appropriate temperature sensor.
What is a Thermistor?
A thermistor is a component that senses temperature changes and changes its resistance accordingly. Commonly used NTC thermistors offer significant price advantages. Thermistor price and performance vary depending on their structure. Thermistors are highly sensitive and can be manufactured very small. So it enables measurements in confined spaces.
Advantages:
- Compact size;
- Easy to process into complex shapes and mass-produce;
- Resistance range: 0.1 to 100 kΩ;
- High stability;
- Strong overload capacity;
- High sensitivity: The temperature coefficient of resistance is 10 to 100 times higher than that of metal.
- Wide temperature range: Standard thermistor’s temperature range of -55°C to 315°C. High-temperature thermistors can measure temperatures exceeding 315°C. Low-temperature thermistors have a temperature range of -273°C to -55°C.
- Can measure the temperature of various confined areas within the body, such as spaces, cavities, and blood vessels.
Disadvantage:
- Highly nonlinear relationship between resistance and temperature;
- Poor component consistency and interchangeability;
- Poor stability;
- Thermistor components are prone to aging.
Thermistor Classifications:
Based on temperature characteristics, thermistors can be divided into three classifications. They are negative temperature coefficient thermistors (NTC), positive temperature coefficient thermistors (PTC), and critical temperature resistors (CTR).
NTC thermistor has a negative temperature coefficient. Their resistance decreases as the temperature increases. Products are available for temperatures ranging from ultra-low to ultra-high temperatures.
CTR thermistors also have a negative temperature coefficient. Their features are sharp drop in resistance within a certain temperature range. The temperature range of CTR thermistors is 0-150°C.
PTC thermistors have a positive temperature coefficient. Their resistance increases with increasing temperature. The temperature range of PTC thermistors is -50-150°C. They are widely used in electrical products for overcurrent protection, motor self-starting, and constant temperature heating.
What is a Thermocouple?
A thermocouple is a commonly used temperature-measuring element in temperature-measuring instruments. It directly measures temperature and converts the temperature signal into a thermoelectromotive force signal. This signal is then converted into the temperature of the measured medium by an electrical instrument. The appearance of various thermocouples often varies greatly depending on the application. However, their basic structure is generally the same. They typically consist of a thermocouple, an insulating protective tube, and a junction box.
Advantage:
- Customization and OEM;
- Many modules available;
- Simple structure;
- Low inertia;
- Wide measurement temperature range;
- Can transmit signals over long distances.
Disadvantage:
- Complex signal conditioning;
- Low accuracy;
- Susceptibility to corrosion;
- Poor noise immunity;
- Low sensitivity;
- Unsuitable for use in reducing atmospheres or in the presence of metal vapors.
Thermocouple Classification
Based on Sino-Inst’s years of experience supplying thermocouples, we have summarized the characteristics of different thermocouple types. You can refer to:
| Types | Material combination | Temperature range | Applicable Scenarios |
| B type | Platinum Rhodium 30% – Platinum Rhodium 6% | 0~1800℃ | High temperature oxidizing/inert environment (such as metallurgical furnace, glass melting furnace), strong stability but low sensitivity |
| S type | Platinum Rhodium 10% – Pure Platinum | 0~1600℃ | High-temperature precision measurement (such as laboratories and aerospace), high accuracy but high cost |
| K type | Nickel chromium and nickel silicon | -200~1300℃ | General purpose (industrial furnaces, boilers), cost-effective, but avoid sulfide and reducing atmosphere |
| E type | Nickel chromium andd copper nickel (Constantan) | -200~900℃ | Low temperature and high sensitivity scenarios (such as food processing and refrigeration equipment) have the highest thermoelectric potential rate |
| T type | Copper and Copper Nickel (Constantan) | -200~350℃ | Low temperature and negative temperature measurement (such as cold storage, laboratory), high precision and corrosion resistance |
| J type | Iron and Copper Nickel (Constantan) | -40~750℃ | Reducing atmosphere (such as chemical reactor), low cost but easy to oxidize |
| N type | Nickel-chromium-silicon and nickel silicon | -200~1300℃ | High temperature alternative to K type (such as heat treatment furnace), stronger oxidation resistance |
Thermistor vs. Thermocouple: in 6 aspects
This post focuses on the differences between thermistors and thermocouples. We will explain the differences between the two from various perspectives. It includes working principles, physical characteristics, accuracy, and measurement range etc.
Read More about: RTD vs Thermocouple: 8 Key Differences
Different Operation Principles:
The thermistor operation principle is based on the temperature sensitivity of the thermistor material. A thermistor is a resistor whose resistance changes with temperature. As the temperature increases, the resistance of a thermistor generally decreases. This characteristic enables the thermistor to convert temperature changes into resistance changes. The temperature value is converted according to the corresponding resistance value.
Thermocouples operate based on the thermoelectric effect (Seebeck effect). They consist of two electrodes made of dissimilar metals. When the temperature at contact between the two metals changes, an electromotive force (EMF) is generated. This EMF is proportional to the temperature, so thermocouples can infer the temperature by measuring the EMF.
Read More about: How does a Temperature Transmitter Work?
Different physical properties
A thermistor is a physical component that measures temperature by exploiting the property of an object’s electrical resistance changing with temperature. The resistance of a thermistor exhibits a linear relationship with temperature. Thermistors are typically made of metals such as copper, nickel, and iron, although some heavy metals such as platinum and gold are also used.
A thermistor is a physical component that measures temperature by exploiting an object’s sensitivity to temperature changes. The resistance of a thermistor changes with temperature. Thermistors are often made of semiconductors such as copper-zinc alloys and nickel-manganese alloys.
Different measurement ranges:
Thermistors have a relatively narrow measurement range. And they are typically used in lower temperature ranges. Generally, thermistors can measure temperatures from -50°C to +300°C or -100°C to +300°C. A thermistor is suitable for low temperature measurements.
Thermocouples have a wider measurement range. In general, the measurement range of thermocouples is from -200°C to +2300°C (or even higher).
A thermocouple is more suitable for measuring in high-temperature environments such as industrial furnaces and smelting furnaces.
Different Response Time:
Because thermocouple and thermistor perceive temperature changes differently, thermocouples have a faster response time than thermistors. Thermocouples are more sensitive to temperature changes. Therefore, they can react to temperature changes in real time. On the other hand, thermistors change their resistance slowly with temperature, which makes them less responsive to fast temperature changes.
Different Accuracy:
Thermistors have higher measurement accuracy. Their resistance changes relatively steadily with temperature. They can provide more accurate temperature measurements. Thermocouples usually have lower accuracy. Primarily due to the many factors that can affect the measurement process. such as ambient temperature and contact resistance. However, through specialized calibration and compensation, thermocouple precision can be improved. In the process of measuring temperature with a thermocouple, it requires cold junction compensation or cable compensation is required. Through these two compensation methods, the measurement results of the thermocouple are more accurate.
Different Application Areas
A thermocouple is used for temperature measurement in many industrial and commercial applications. such as controlling indoor temperatures, controlling temperature on production lines, and measuring temperature in laboratories.
A thermistor is more suitable for temperature measurement in home appliances, automotive air conditioners, smart homes, and other fields.
Sino-Inst Featured Temperature Sensor
Choosing Between Thermistors and Thermocouples
Sino-Inst has summarized the key differences between the two after years of experience. You can use this information to select your temperature sensor.
Thermocouples are the most commonly used temperature measurement sensors. Their main advantages are a wide temperature range and compatibility with various atmospheric environments. They are also rugged and inexpensive. They require no power supply and are the most affordable. Thermocouples are the simplest and most versatile temperature sensors. However, they are not suitable for high-precision applications.
Thermistors are made of semiconductor materials. Most of them have a negative temperature coefficient, meaning their resistance decreases as the temperature increases. Temperature changes cause large changes in resistance, making them the most sensitive temperature sensors. However, thermistors have very poor linearity. It is highly dependent on the manufacturing process. Manufacturers do not provide standardized thermistor curves.
A thermistor is very small and responds quickly to temperature changes. However, they require a current source, and their small size makes them extremely sensitive to self-heating errors. Thermistors offer good accuracy. However, they are more expensive than thermocouples and have a smaller temperature range. A commonly used thermistor has a resistance of 5kΩ at 25°C, resulting in a 200Ω change in resistance for every 1°C temperature change. Note that a 10Ω lead resistance only introduces a negligible 0.05°C error. They are well-suited for current control applications requiring fast and sensitive temperature measurements. Their small size facilitates installation in confined spaces. But we should care must be taken to prevent self-heating errors.
Read More about: Temperature Sensor vs Temperature Transmitter
What is the difference between a thermocouple, a thermistor, and an RTD?
| Classification | Thermocouple | Resistance temperature detector (RTD) | NTC thermistors |
| Material | Two different metals | Pure resistance | Ceramics (metal oxides) |
| Temperature measurement range | -270℃~2300℃ | -250℃~900℃ | -100℃~500℃ |
| Temperature measurement accuracy | ±0.5℃ | ±0.01℃ | ±0.1℃ |
| Thermal response | slow | slow | fast |
| Linearity | Nonlinear | Linear | Nonlinear |
| Incentive method | unnecessary | Current | Current |
| Output format | Voltage | resistance | resistance |
| Cost | low | high | middle |
Are thermistors more accurate than thermocouples?
Thermistors generally measure temperature with higher accuracy than thermocouples.
What is the lifespan of a thermistor sensor?
Generally speaking, the lifespan of a thermistor is over 10 years. However, this varies depending on the application scenario and conditions.
Under extreme ambient temperature conditions, the lifespan of a thermistor can be reduced.
In short, the differences between thermistors and thermocouples are significant. I believe you have a general understanding of them after reading the above. If you are still unsure about the choice, please contact us. Sino-Inst will customize a suitable solution for you free of charge.
Sino-Inst has been engaged in temperature measurement for many years and offers a wide variety of temperature sensors. There is always one that suits you. Furthermore, we will not raise prices due to tariffs.
