Different types of temperature Sensors have different applications in consumer electronics, industrial, home appliances, or commercial products. For example, temperature sensors are used in air-conditioning and heating systems, microwaves, industrial machines, aircraft to measure the temperature and control the device accordingly.
In this article, we will discuss What are different types of temperature sensors? how they work and their applications. Click this link to know the various types of sensors and their applications.
What is a Temperature Sensor?
A temperature sensor is a type of sensor used to measure the temperature of a body, surface, liquid, or air using an active or passive sensing element. In other words, a temperature sensor measures the degree of hotness or coldness of a surface, liquid, gas, or air.
Types of Temperature Sensor
Following types of temperature sensors are available to measure the temperature of surrounding air or a surface. Each technology has its advantages and limitations.
- Thermocouples
- RTD (Resistance Temperature Detector)
- Thermistor
- Semiconductor-based Temperature Sensor.
- Infrared Temperature Sensor.
- Thermometers
Let’s discuss each of the above temperature sensing technologies in detail.
1. Thermocouple
Thermocouples are the most commonly used types of temperature sensors consisting of two junctions (Hot and Cold Junctions) of dissimilar metals welded together.
Voltage is produced at the junction because of the temperature difference. And this voltage is used to determine the temperature.
Thermocouple Materials
| Type | Positive Material | Negative Material | Temperature Range (ºC) |
|---|---|---|---|
| B | Platinum Rhodium – 30% | Platinum Rhodium – 6% | 0 to 1800 |
| C | Tungsten 5% rhenium | Tungsten 26% rhenium | 0 to 2300 |
| E | Chromel (nickel 10% chromium) | Constantan (nickel 45% copper) | -270 to 2000 |
| J | Iron | Constantan (nickel 45% copper) | -210 to 760 |
| K | Chromel (nickel 10% chromium) | Alumel (nickel 5% aluminum and silicon) | -270 to 1370 |
| S | Platinum 10% Rhodium | Platinum | -50 to 1770 |
| T | Copper | Constantan | -270 to 400 |
Note: Above Values are for indicative Purpose Only.
Advantages of Thermocouple
Thermocouples temperature sensors have the following advantages.
- Simple in Design
- Ease of use
- Good response time to the change in temperature.
- Working limit from -200ºC to up to +1750ºC
Disadvantages of Thermocouples
Thermocouples temperature sensors have the following disadvantages.
- Non-Linear Nature
- Low Accuracy
- Less Stable
2. RTD (Resistance Temperature Detector)
RTD works on the principle that any change in temperature results in a change in the electrical resistance of the conductive material.
Any Increase in the temperature results in an increase in electrical resistance. Whereas a decrease in temperature decreases the electrical resistance of the conductive material. This change in electrical resistance is measured to determine the relative change in the temperature. Following two types of RTD are available in the market:
- Thin Film Type
- Wire wound Type
RTD Materials
Platinum, nickel, and copper materials are widely used to manufacture conductors in RTD. But out of these materials, platinum is more preferred because it is highly stable, chemically inert, and can function over large temperature ranges.
Advantages of RTD
RTD has the following advantages.
- Highly Precise
- Stable Reading
- Linear change in resistance with temperature.
- Change in electrical resistance is relatively easy to measure compared to change in voltage.
Disadvantages of RTD
RTD has the following disadvantages.
- High Cost
- Self Heating
3. Thermistor
Thermistors are thermally sensitive resistors. Similar to RTD, thermistor electrical resistance changes with temperature change.
But thermistors are different from RTD because thermistors use resistive material instead of conductive material used in RTD. Therefore change in resistance in the thermistor is higher compared to RTD.
Types of Thermistor
Negative Temperature Coefficient (NTC) Thermistors
NTC resistance decreases with an increase in temperature. They are used for temperature sensing applications.
Positive Temperature Coefficient (PTC) Thermistors
PTC thermistor’s electrical resistance increases with an increase in temperature. They are used in electrical circuit protection applications.
Advantages of Thermistor
- Small Size
- Low Cost
- Fast Response
- More Sensitive
- Higher Accuracy
Limitations of Thermistor
- Non-Linear Temperature Response Curve
- Self Heating Problem
- Limited temperature Range
Thermistor Materials
Thermistors are made of oxides of manganese, nickel, or cobalt coated in glass and encapsulated in epoxy resin.
4. Semiconductor Based Temperature Sensor
Semiconductor types of temperature sensors consist of temperature-sensitive voltage and current diodes. A voltage or current passing through diodes changes with a temperature change.
To calculate temperature, this change in temperature and voltage value is mapped in the controller or processor.
IC-based temperature sensors come along with other sensors such as pressure and humidity sensors in one package. As a result, sensor cost and size reduction are feasible.
Most consumer electronics and IoT products are using semiconductor-based sensors. Semiconductor-type temperature sensors are available as SMT components and have linear output.
5. Infrared Temperature Sensor
Infrared temperature sensors work by focusing the infrared energy coming from a body onto a thermopile sensor. The thermopile sensor absorbs IR radiations and converts them into heat.
Afterward, the generated heat is converted into an electrical signal. The IR thermometer processor utilizes an electrical signal to determine the body temperature.
To determine the body temperature, IR-Thermometers compare the IR radiations emitted by the object and a reference point. This ensures environmental temperature has a minimal impact on thermometer reading. Click this link for more details on infrared thermometers.
6. Liquid Thermometers
Liquid (mercury or alcohol) based thermometers are the oldest type of temperature sensor. They consist of a glass tube filled with mercury or alcohol.
The rate of change in the volume of mercury is directly proportional to the change in temperature. Any change in the volume of the liquid material indicates a temperature change.
We will keep updating more details on various types of temperature Sensors. Please add your comments, suggestions, or questions on different types of temperature Sensors in the comment box. We suggest you also read this article on the benefits and disadvantages of automation.
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