How Do Temperature Sensors Work?

Last updated: July 1, 2021

Temperature sensors are specialised instruments that use electrical signals or energy to measure the temperature of an object or environment. They are used in myriad industries and applications to determine the temperature of the domain. These instruments are a critical part of any equipment or environment that needs a specific temperature to function, and they are used to monitor and record temperatures and signal any changes. Temperature sensing is a vast and multifaceted science, utilising various factors such as resistance, voltage, infrared, and diverse material to determine temperature. These sensors measure an array of objects and environments and come in two main types, namely contact sensors and non-contact ones.

What Are Temperature Sensors?

Temperature sensors are electronic devices used to measure the temperature of a particular environment or object. They sense the temperature and then convert this input data into electronic data to record and highlight temperature changes.

There are various temperature sensors on the market, and each works in different ways and works better for different applications. Some models rely on direct contact with the object they are monitoring, and these are known as contact temperature sensors. Others, however, can indirectly gauge the temperature of an object or environment using infrared technology, which is known as non-contact temperature sensors. They do not have to touch the object in order to read the temperature. Non-contact models often utilise infrared (IR) technology and can remotely read how much energy is being emitted by the particular object from a safe distance.

Let’s explore these two types of temperature sensors in greater detail, namely contact instruments and non-contact ones. Sensors include:

Different Types of Temperature Sensors and How They Work

Contact Sensors

As the name suggests, contact sensors have to be in direct contact with the object to read the temperature and convert the necessary data.

There are few prominent contact sensors, and these include thermocouples, thermistors, and resistance temperature detectors. Let’s explore them in greater detail and see how they work:

Thermocouples: These thermocouple devices are made up of two conductors; each of these wires is made of a dissimilar metal such as iron and constantan, chrome and alumel or platinum alloy. These two conductors (in wire form) are joined and form a particular junction. When exposed to heat, voltage is generated, and this corresponds directly to the input of temperature. This process is known as the thermoelectric effect.

These instruments are popular for a few reasons as they are often inexpensive and utilise simple materials.

Thermistor: The next contact sensor is the thermistor, and these are often hailed as being more precise in their readings than thermocouples. Essentially, this thermometer device works via resistance, and this resistance depends upon the temperature output. When the temperature is high, resistance decreases, and when the temperature drops, resistance increases. These devices come in two types: the Negative Temperature Coefficient (NTC) and the Positive Temperature Coefficient (PTC).

Usually, these thermistors are made of polymers or ceramics and can measure minor drops or increases in temperature, as small as 0.05 of a degree. For this reason, they can very accurately determine the temperature range.

Resistance Temperature Detectors (RTD): These are much like thermistors. However, they use metal rather than ceramics. They are one of the most expensive thermal sensors around and offer very accurate temperature readings. They sense the temperature by reading the changes in resistance on a metal resistor which is located within the device.

Non-Contact Sensors

Non- contact sensors, as their name suggests, are able to conduct a temperature measurement without having to have physical contact with the object. There are various types and styles around. However, they all work by reading thermal radiation. Some instruments are hand-held, fix-mounted, battery-operated, or portable.

A non-contact infrared sensor can measure temperature from a distance, much like the temperature guns that have become commonplace during the current pandemic. However, by gauging how much infrared energy is being emitted, they can read the temperature within a range of the object without physically touching it. These devices exist under the broader category of ‘thermal radiation thermometers.’

In pandemics, such as Covid, or Ebola, these machines are often used to check the temperature of travellers without transmitting viruses or bacteria amongst those being tested. They offer a digital reading of the person’s temperature, and the data is processed accordingly. This limits the possibility of cross-contamination, rendering passengers and those reading the temperatures safe.

Nonetheless, since they are not in direct contact with the object being measured, they can be prone to specific shortfalls. For example, errors might arise if radiation is reflected from a hotter surface or body or if the person holding the device is particularly hot.

Non-Contact Sensors: How they work 

Infrared sensors gauge temperatures from a distance by reading the thermal radiation that is emitted from the object, person, or heat source. These are often used in applications where it is best to remain at a distance from the object. Infrared sensors and thermal imaging are the most popular non-contact temperature sensors and work by sensing the temperature that the object emits. These instruments use Planck’s Law of Thermal Radiation to read infrared waves via microns.

What Are Temperature Sensors Used For?

These instruments are used in diverse applications and an array of industries from the automotive sector to medical institutions.

Non-Contact Models

Non-contact sensors are a great choice in environments where objects are constantly moving around or where cross-contamination is possible, such as at airports when travellers are being tested for fever or illness. They also work well in situations where contact might dramatically impact the temperature and give a false reading or where objects are very far away and cannot be easily accessed because of a particular atmosphere. In essence, these determine the ambient temperature of the area.

Contact Temperature Sensors 

These machines are used in diverse settings, including food processing plants, the automotive industry, environment control purposes, and medical devices.

When conducting any temperature reading, it is imperative to be aware of external factors that might impact the reading. Therefore, when utilising these instruments, be mindful of influencing factors so that the data can be analysed appropriately and understood. This awareness will ensure that the digital display is the same as the actual temperature and result in accurate results.

Ultimately, the type of temperature detector will depend largely on your application. In hazardous or dangerous situations, a non-contact instrument is always advised.