company news about Temperature Sensor: Something You Need to Know

A temperature sensor is a device that converts temperature signals into measurable electrical signals (such as voltage, current, resistance, or digital signals), and is widely used in industrial automation, consumer electronics, medical equipment, automotive electronics, environmental monitoring, and other fields.

1. Classification

Temperature sensors can be classified based on measurement methods and working principles:

1.1 Classification by Measurement Method

Contact-type temperature sensors

The sensor directly contacts the measured object and measures temperature through heat conduction. The advantage is high measurement accuracy, suitable for liquid and solid temperature measurement, but the response speed is relatively slow and may be affected by the environment. Typical applications include thermocouples, RTD (thermoresistors), and thermistors.

Non-contact temperature sensor

Measures temperature by detecting the infrared radiation emitted by an object, without physical contact. The advantage is that it has a fast response time and does not interfere with the object being measured. However, the measurement accuracy is affected by the emissivity of the object's surface. Typical applications include infrared thermometers and thermal imagers.

1.2 Classification by Working Principle

(1) Thermocouple

A thermocouple is based on the Seebeck effect, where an electric potential is generated at the junction of two different metals due to the temperature difference.

- Wide measurement range (-200°C ~ 2300°C), suitable for extreme temperature environments.

- Fast response time (millisecond level), resistant to high temperatures, and vibration-proof.

- However, the accuracy is relatively low (±1°C ~ ±5°C), and cold junction compensation is required.

Common types

- K-type thermocouple (nickel-chromium - nickel-silicon): The most commonly used, suitable for -200°C to 1260°C.

- J-type thermocouple (iron - copper-nickel): Suitable for reducing environments, 0°C to 760°C.

- T-type thermocouple (copper - copper-nickel): Suitable for low-temperature measurements, -200°C to 350°C.

- S/R-type thermocouple (platinum-rhodium - platinum): Used for high-temperature measurements (0°C to 1600°C), high accuracy but high cost.

(2) Thermoresistor (RTD, Resistance Temperature Detector)

The RTD measures by utilizing the characteristic that the resistance of metals (such as platinum, copper, and nickel) changes with temperature.

Features

- High accuracy (±0.1°C ~ ±0.5°C), good stability, suitable for long-term monitoring.

- Wide measurement range (-200°C ~ 850°C).

- However, the response is relatively slow (second-level), expensive, and requires a constant current source for driving.

Common types

- PT100 (platinum resistor, 100Ω at 0°C): Industrial standard, good linearity.

- PT1000 (platinum resistor, 1000Ω at 0°C): Higher sensitivity, suitable for long-distance transmission.

- Cu50 (copper resistor, 50Ω at 0°C): Lower cost, but narrower temperature range.

(3) Thermistors

Thermistors are semiconductor devices whose resistance changes significantly with temperature, and they are classified as NTC (negative temperature coefficient) and PTC (positive temperature coefficient).

NTC Thermistors

The resistance decreases as the temperature rises, with high sensitivity (±0.05°C).

- However, they have strong non-linearity and require lookup tables or the Steinhart-Hart equation for conversion.

Typical applications: Electronic thermometers, lithium battery temperature monitoring.

PTC Thermistors

The resistance increases sharply at a specific temperature and are often used for over-temperature protection.

Typical applications: Motor overheat protection, self-recovery fuse.

(4) Digital Temperature Sensor

The digital temperature sensor integrates an ADC and digital interfaces (such as I2C, SPI, 1-Wire), directly outputting digital signals without the need for additional signal conditioning circuits.

Features

- Strong anti-interference ability, suitable for embedded systems.

- No calibration required, easy to use.

(5) Infrared Temperature Sensor (IR Thermometer)

The infrared sensor measures temperature by detecting the infrared radiation emitted by objects (with a wavelength of 3 to 14 µm).

Features

- Non-contact measurement, with extremely fast response (in the millisecond range).

- However, measurement accuracy is affected by the emissivity of the object's surface (such as metals require compensation).

Typical Applications

- Body temperature measuring guns (such as MLX90614).

- Industrial equipment thermal imaging (such as FLIR thermal imagers).

Key Performance Parameters of Temperature Sensors

- Measurement Range: The temperature range within which the sensor can operate normally, such as thermocouples can reach up to 2300°C, while NTC is usually limited to -50°C to 150°C.

- Accuracy: The range of measurement error, such as RTD can reach ±0.1°C, while thermocouples are generally ±1°C to ±5°C.

- Resolution: The minimum detectable temperature change, high-precision sensors can reach 0.01°C.

- Response Time: The time it takes for the temperature change to stabilize in the output, thermocouples can reach the millisecond level, while RTD is usually in the second level.

- Linearity: Whether the output is linear with temperature, RTD has better linearity, while NTC has stronger non-linearity.

- Long-term Stability: The degree of sensor drift over time, platinum resistance <0.1°C/year.

Temperature Sensor Selection Guide

1. Temperature Range: Select thermocouple for high temperatures, RTD or NTC for low temperatures.

2. Accuracy Requirements: Select RTD for high accuracy, NTC for low cost.

3. Response Speed: Select thermocouple or infrared sensor for rapid measurement.

4. Environmental Factors: Select armored thermocouple for corrosive environments, waterproof packaging for humid environments.

5. Output Signal: Embedded systems prefer digital sensors (I2C/SPI).