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How temperature sensors work and their different types

Measuring temperature is one thing and reading temperature is another. If you want to use temperature to track things like time spent in a store, you have your work cut out for you. This blog post will cover the three main types of sensors. Then it will go into more detail about each one.

We all use temperature sensors to control our homes. Many of us even have them in our cars and trucks. Everywhere we go, we are more likely to find a sensor. You can buy temperature sensors from places like Amazon. We even use one of these DIY projects

What are the temperature sensors?

This device responds to changes in temperature by generating a signal. This can be an analog or a digital output, depending on the sensor. There are three main types of temperature sensors. They include Analog, Digital, and Thermocouple.

That is great for temperature. But it is not your typical temperature sensor like you would find in your smartphone.

We measure temperature with thermistors made of metal oxide semiconductors in most cases. We also refer to them as MOSFETS. This is because they are inexpensive and simple to use.

Analog

An analog temperature sensor will measure the voltage between two points. This is because they connect to the ground. They also have a reference voltage that keeps them at the same potential as the ground (0V). They convert the temperature into a voltage level.

Thermocouple

A thermocouple converts temperature into one of two voltages. It does this by measuring the difference between two terminals. The difference between these two terminals is the “thermocouple voltage.” This gives you a range of 0V to 200V or more, measured by an analog-to-digital converter. This is the most common type of temperature sensor in use today.

Digital

These devices convert the temperature into a digital binary output. Also, they measure the voltage difference between two terminals in the device. It may also measure the current difference.

One common digital sensor is the “thermistor.” It measures the resistance between two terminals. It consists of a particular type of semiconductor material.

The most common form of a digital temperature sensor is the “thermistors.” We make it by adding a resistor to a thermocouple.

What do temperature sensors do?

temperature sensor arduino

Temperature sensors are thermometers. But they are cheaper and more reliable than the glass thermometers we’ve all used. This has improved because a glass thermometer can break. Unfortunately, it can also become less accurate in a few seasons. A common example is the glass thermometer outside your farmhouse. Glass thermometers are not very precise. It takes only a slight temperature difference to cause them to stop working.

Rayming PCB & Assembly design these devices to convert “temperature” into digital bitstreams for communication purposes. A temperature meter depends on the voltage across the diode relay as the primary signal. Other sensors send a current through an element, which produces a voltage. We then measure this voltage by a differential amplifier. Then we convert it into a digital signal by an ADC (analog-to-digital converter).

Many devices can send a digital signal even if they do not have a voltage output. The sensor either sends a modulated output or sends a continuous analog signal.

The most common modes of communication for temperature sensors are

Continuous

The continuous mode requires no extra power supply. This is because the sensor does not use more current from the power source. This is how most temperature sensors work.

Modulated

This type of communication enables temperature sensors to communicate with other temperature sensors. These are sensors that can receive this type of signal. When a temperature sensor sends a modulated signal, it functions to turn it on or off.

Temperature sensor applications

We use heat and temperature sensors for monitoring the environment in many industries. For example, we use temperature sensors in consumer goods and the following areas

1. Industrial Applications

We use temperature sensors in industrial applications for temperature control and process monitoring. But, we can use it to check the temperature of equipment and liquids.

Temperature sensors give accurate temperature readings, even at high or low temperatures. We can use them in various ovens, cars, boats, pools, and planes.

2. Automotive applications

We use temperature sensors for monitoring temperature in automotive industries. They can withstand extreme temperatures (both hot and cold). Temperature sensors can track outside air temperature. It can also track the temperature of liquid stored in the vehicle’s tank. Temperature sensors used in this application include thermistor-based analog or digital sensors. These are sensors that can detect both low and high temperatures.

3. Scientific and laboratory applications

Temperature sensors can track the temperature of lab equipment and processes. These applications include spectrophotometers and thermoscopes. Also, thermocouples are helpful in scientific applications. They include infrared spectroscopy, mass spectrometry, and metallurgy). They measure both atmosphere and vacuum temperatures alike.

4. Medical Applications

Temperature sensors can track the temperature in the food and pharmaceutical industries. Besides, we use sensors in storage areas and transfer points.

5. Databases

We use temperature sensors for applications that need long-term temperature monitoring. Some include horticulture and agriculture. But, we use this type of sensor in the greenhouse industry. It can withstand low or high temperatures.

6. Motorsport

We use temperature sensors in automobile racing and motorsports. They track the temperature of the fuel, oil, and lubricants. It ensures that they remain within a designated range during competition.

7. Domestic appliances

We use thermostats for temperature control in home and office appliances. One can use them to track air conditioning, refrigerators, heaters, washers, and blowers.

Thermostats can maintain the desired temperature. They turn off or on the appliance to maintain the desired temperature.

8. HVAC applications

We use temperature sensors in heating and cooling systems. They regulate the temperature in our homes and offices. Temperature sensors used in this application can withstand high temperatures. We make them with special materials. As a result, they do not melt even after prolonged exposure to extreme temperatures. So they can resist high temperatures.

Temperature sensors designed for this application are many. They include

Mercury-in-glass thermometers,

Solenoid thermometers,

Thermistor-based temperature sensors,

Bimetallic temperature strips,

Electronic thermometers.

9. Transit

Temperature sensors track the temperature of fuel, oil, and lubricant in vehicles. They are also used as part of the engine control system. They tack temperature (such as diesel engines).

10. Oil and gas industry

We use temperature sensors in the oil and gas industries. They track the temperature of the fuel, fuel oil, natural gas liquids, and hydrocarbons. We can also use them in well logging applications. They detect the pressure at a well by measuring the temperature of fluids that flow through the well.

How does the temperature sensor work?

Most people use temperature sensors to measure heat. First, they manufacture them with materials that can convert heat into electricity. Then, it ends the sensor’s signal to the system. The basic principle of working of a thermal sensor is

1. Heat is proportional to the amount of heat generated by an object.

2. The material whose temperature changes. This is in proportion to the object change of temperature acts as a sensor.

3. A thermistor helps make a temperature sensor convert heat into electrical signals. It works like a resistor that has resistance to electricity. So, it shows the change in resistance whenever the temperature changes.

4. The temperature sensor usually uses the principle of thermal resistance. Thermal resistance is the heat transfer property that changes against the temperature change.

A temperature sensor connects to the system using a cable in common use. Sometimes we call it temperature sensing cable. Temperature sensing cable consists of thermistors to convert temperature changes into electrical signals.

It consists of a magnetic material (usually iron). You may also find an electric material in a temperature sensing cable. When there is a drop in the temperature, the magnetic material attracts more of the flux. This flux flows through it. The electric signal sent to the system refers to how much voltage passes through the sensing. It also refers to the converting elements of the temperature sensing cable.

Thermal design and measurement

We refer to thermal design or heat flow systems as thermal engineering. We can use them for energy transfer as thermal engineering. One can classify thermal analysis into statistical and scientific analyses. Statistical analysis can track the temperature of a heat transfer system. It uses ordinary observations. So, the scientific analysis uses various computer modeling methods. It estimates the properties of sub-systems or heat flow systems.

Temperature measurements

The most basic type of temperature measurement is the thermometer. It is an instrument that measures temperature. You can do it by measuring other properties of the object it is in contact with. A common type of thermometer is a mercury-in-glass thermometer. It uses the principle of mercury’s expansion and contraction to measure temperature.

We also use solenoid thermometers (also called platinum-iridium thermometers). They have a unique design. A current passes through two solenoid coils separated by a certain amount of space. When the temperature of the fluid rises, the flux of current increases. So, the distance between the coils decreases and vice versa.

Thermocouples are another type of thermometer used for accurate measurement. They have a unique design. It uses two different types of metal with a high potential difference between them. When there is any temperature change, the voltage changes in equal proportion. The amount of voltage obtained depends on the amount of current. It passes through the two types of metal and depends on their temperature difference.

Types of temperature sensors

There are various types of temperature sensors in the market. We use such sensors in many environmental, medical, aerospace, automotive, and electronics applications.

The most common types of temperature sensors are

1. Contact Type Temperature Sensors

Contact type temperature sensors are the most used in industrial applications. They have a unique design that uses a thermal contact between two metals. As a result, the metals have their specific temperatures. When you bring them in contact, get an electrical signal due to a thermistor. As a result, they can detect temperature, pressure, level, and other physical changes.

2. Non Contact Type Temperature Sensors

Non-contact type temperature sensors are also popular. They have a unique design to measure electromagnetic radiation. These are radiation emitted by the object on temperature. We do the measurement using a wire-protected coil using a shield made of iron or nickel. It is the material that absorbs radiation from the object. Then. It generates an electric current. There are several types of non-contact type temperature sensors

a. Thermistor Temperature Sensors

We use thermistor temperature sensors in applications. The heat source is not in physical contact with the object—for example, ovens, furnaces, and gas burners. The thermistors can measure the temperature at a remote location. Temperature sensors are available for various ranges of temperatures and resistance values.

b. Thermostats Temperature Sensors

A thermostat is a temperature switch. It cuts off the electric power to the equipment when it reaches the greatest temperature. The thermal switch works on the principle of bimetallic materials used in it. These materials have the property of expansion and contraction with a temperature change. A bimetallic strip consists of two metals (usually iron and other material). They have different expansion properties, i.e., different expansion rates exposed to heat.

c. Resistive Temperature Detectors (RTD)

We use these sensors in industrial applications. It is applicable where the heat source is not in physical contact with the object. There are two types of these temperature detectors

i. Solid State RTDs (SSRTD)

The resistance of solid-state RTD decreases as temperature rises. So, these temperature sensors are available in different operating temperature ranges. Also, these temperature sensors can work in a submerged state through water or oil.

ii. Ceramic RTDs (CRTD)

The resistance of ceramic RTD decreases as the temperature rises. So, these temperature sensors are available in different operating temperature ranges. You can also find them in various resistance values.

d. Thermocouples

We use thermocouples in applications where the heat source is in contact with the object. Examples include furnaces, gas, and burners. The thermocouple action of resistance depends on the temperature difference between exposed parts. Thermocouples are available in many materials and different operating temperature ranges.

e. Negative Temperature Coefficient (NTC) Thermistor

As the name suggests, these thermistors have a negative temperature coefficient. As temperature decreases, the resistance value of the NTC thermistor increases. These are available in various types and can measure extreme temperatures.

Thermoelectric (TE) temperature sensors work based on the Peltier effect. It also depends on the quantitative theory of heat flow between two junction points. We find them in a single-phase material. This is when there is a potential difference between them. One junction point gets heated, and the other gets cooled down.

f. Semiconductor-Based Sensors

These temperature sensors can measure temperature with the help of semiconductors. We can use them in power electronics, process control, and automation. Such embedded sensors are applicable in various industries. An example of this sensor include

Model ETT-10V Vibrating Wire Temperature Sensor

This vibrating wire sensor uses the Peltier effect to measure temperature. The sensor consists of very thin coiled wires. It has different metals with low voltage values. This is because they have a unique design. This design change in resistance value is proportional to the change in temperature. This happens when the temperature increases. As a result, it obtains the coil’s vibration, due to which it generates an electrical signal.

Model ETT-10TH Resistance Thermistor Probe

This thermistor probe consists of a thermistor. You will find it inside a thick-walled glass tube with a metal shield around it. The metal shield helps to prevent the external vibrations from reaching the sensor. This reduces the error during measurement due to external temperature changes.

We use GPS in monitoring systems for various applications. They include automation, safety, and security. They are applicable in many industries. We can use them in any environment, from outdoors to indoors. GPS sensors give accurate measurements of speed, location, direction, etc.

Model ETT-10PT RTD Temperature Probe

The Model ETT-10PT RTD Temperature probe can measure temperature. It uses the help of a particular type of resistor known as RTD. It works on the principle of the Peltier effect. The probe consists of two thin coiled wires with two different metals. When we apply a potential difference between them, one wire gets heated. The other gets cooled down. Hence, it gives an electrical signal due to the Peltier effect.

Encardio-Rite Thermocouple

The Encardio-Rite thermocouple is a non-contact temperature sensor used in safety and security. The sensor consists of two metals with different coefficient values when heated up. These metals are copper and silver. So, the resistance of the metal decreases as temperature increases. It depends on the knowledge of the generated voltage value. We use it to get the distance between two points and measure the temperature of objects.

3. Solid State Type Temperature Sensors

Solid-state-type temperature sensors are helpful in industrial applications. They help in non-physical heat sources such as ovens and furnaces. They need a high power supply and measuring the temperature. This type of sensor consists of two types

i. Heated element sensors (HES)

We use these sensors in industrial applications. The heat source is not in physical contact with the object. They include furnaces and ovens. They consist of a wire with a thermocouple attached to it. The wire gives an electrical signal whenever it gets heated up due to the Peltier effect. We measure them by an amplifier in the sensor. It has only one input terminal and a single output terminal.

ii. Thermocouple

The thermocouple consists of two wires with different metals. Their resistance value varies due to the temperature you expose them to. This provides a change in voltage value as resistance changes. We use these sensors in various industries. Applications include power electronics, process control, automation, etc.

What to consider when choosing a temperature sensor

1. temperature sensitivity

Sensitivity tells us the range of temperature a sensor can read. We sometimes refer to them as range accuracy. This measures a sensor’s ability to react to changes in temperature. High sensitivity means reading smaller temperature changes. Low sensitivity means reading larger temperature changes.

For example, placing the sensor in a colder environment requires more power. This is because the thermistor has less resistance at higher temperatures.

2. Temperature range

Sensors come in many different types depending on the application. E.g., in industrial or medical applications, the sensors have different temperature ranges. For example, a thermistor has zero to two thousand degrees Fahrenheit range. So, a resistance thermometer covers the temperature range of 10 to 100 °C (51-212 °F).

3. Power operating temperature range

The power operating temperature range is the temperature that the sensor can withstand. It helps it not to have significant performance degradation. We usually express it as specified greatest operating temperature (in °C).

4. Accuracy and stability

Accuracy is the precision with which a sensor can read a specific temperature. It should be high enough to fulfill the needs of the application. Stability refers to how well a sensor will read the same temperature after some time. We usually express it as drift.

5. Output type

Sensors produce output related to temperature in various ways. But it does so most via an analog voltage, compared against a trigger point. So we use it as an indicator for digital use.

6. Size and Package

Electronic components used in sensors are usually small. Many of them are transistors or integrated circuits. So, we to know what size the sensor will be to determine the size of the circuit needed to interface with it.

7. Packaging

Most sensors come in standard packaging. They consist of a plastic case and reel for convenient transportation and storage. If in doubt about the package type available, please see the sensor instruction. You will find the manufacturer’s information on sensors. You can also contact them to know their specific performance specifications.

Conclusion

Temperature sensors are electronic devices that provide information related to temperature. They include thermistors, thermocouples, and resistance temperature detectors. Thermistor and thermocouple are the two main temperature sensors used in different applications. We use a thermistor to show the temperature of the surface. Additionally, we use a thermocouple to measure temperature within a junction. Both types of sensors are very efficient in detecting temperature. They are their applications. But, imagination is the only thing that limits them. The thermistor is a solid-state type sensor. The thermocouple is an electrical junction type sensor. It uses a small piece of metal as a resistance element.

You should make sensor selection with the utmost care. Consider accuracy and stability the most. Finding, identifying, and buying them can be quite complicated.