How Do Temperature Sensors Work?

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Temperature sensors work by providing readings via electrical signals. Sensors are composed of two metals that generate an electrical voltage or resistance when a temperature change occurs by measuring the voltage across the diode terminals. When the voltage increases, the temperature also increases.

Temperature sensors are devices that provide readable temperature measurements via an electrical signal. The most basic way to measure temperature is using a thermometer; this measures how hot or cold something is. With advances in technology, we now have access to a variety of temperature sensors that are much more accurate.

Temperature sensors are extremely beneficial and necessary for a wide range of applications. In fact, you may even use them more often than you think! They are used for microwaves, refrigerators, and water heaters in your home. Temperature sensors are also used in the field; for example, thermometers play a vital role in geotechnical monitoring and renewable energy. 

This article will explain how temperature sensors work, the different types of sensors, and the most common applications they are used. 

How Do Temperature Sensors Work?

Temperature sensors measure temperature readings via electrical signals. They contain two metals that generate an electrical voltage or resistance when a temperature change occurs. 

The sensor plays a vital role in maintaining a specific temperature for a variety of industries, including medical applications, HVAC systems, and electrical appliances in our homes. Temperature sensors are critical for accuracy and temperature control in industries like these. 

Temperature sensors work by measuring the voltage across the diode terminals. When the voltage increases, the temperature also increases, which is then followed by a voltage drop between the transistor terminals and the emitter (in a diode). 

The sensors come in different types, which are categorized based on their connection. There are two main categories when it comes to temperature sensors, depending on the type of application being used or the industry you are working in:

  • Contact Temperature Sensors
  • Non-contact Temperature Sensors

Contact Temperature Sensors

Contact temperature sensors measure the degree of hotness or coldness of an object or substance via direct contact. They are generally used to detect a wide range of temperatures in different solids, liquids, or gases. 

Non-Contact Temperature Sensors

These temperature meters are never in direct contact with an object or substance, therefore, they are widely used in hazardous environments such as power plant industries. They measure how hot or cold something is via radiation emitted by a heat source. 

To understand how temperature sensors work, we will go into more depth on each type of temperature sensor below. 

Different Types of Temperature Sensors

To understand how temperature sensors work, contact and non-contact temperature sensors are further split up into the following types:

  • Thermometer 
  • Thermostat
  • Thermistors
  • Thermocouples
  • Negative Temperature Coefficient (NTC) Thermistor
  • Semiconductor-based Temperature Sensor 
  • Resistive Temperature Detectors (RTDs)

Thermometer

When we think of temperature, we all know how to measure temperature with a thermometer, especially the mercury-filled glass thermometer you probably used back in high school. However, there are many types of thermometers now available. 

Bi-metal thermometers are a type of contact temperature sensor that consists of a connected gauge and stem. The sensor tip contains a spring that sits inside the stem sensing end, which attaches to a rod, leading up to the gauge needle. It is the movement in the sensing coil when heat is applied that causes the needle in the gauge to move, displaying the temperature reading. 

How Do Temperature Sensors Work?
Bi-metal thermometer

Gas-filled and liquid thermometers are also a type of contact temperature sensor that works similar to bi-metal thermometers; however, they have a bulb that is either filled with a gas or liquid. The bulb is located inside the sensing end of the probe, which when heated expands the gas, or heats the liquid, signaling the attached rod to move the needle, displaying the temperature reading.

How Do Temperature Sensors Work?
Gas-filled thermometer

Thermostat

Thermostats are a type of contact temperature sensor that includes a bi-metallic strip containing two dissimilar metals (aluminum, nickel, copper, or tungsten). 

It is the difference in the coefficient of linear expansion of the two metals that creates a mechanical bending movement when exposed to heat. 

Thermistors

Thermistors or thermally sensitive resistors change their physical appearance when a temperature change occurs. They consist of ceramic materials (oxides of nickel or manganese/cobalt coated in glass) that allow them to be easily disfigured. 

Most thermistors have a negative temperature coefficient (NTC). This means when an increase in temperature happens, their resistance decreases. However, some thermistors have a positive temperature coefficient (PTC); when the temperature rises, the resistance increases. 

How Do Temperature Sensors Work?
Thermistor

Thermocouples

Thermocouples are one of the most common temperature sensors due to their reliability, accuracy, sensitivity, simplicity, and wide temperature operating range. 

They have two wires that contain two dissimilar metals (e.g. copper and constantan) that connect at two different points to form a junction. One point is known as the “cold junction”, kept at a specific temperature, and the other is known as the “hot junction”. It is the voltage between the two wires that records the temperature change. 

Thermocouples may not be as accurate as resistive temperature detectors (RTDs); however, they are much more cost-effective and have an extensive temperature range (-200 °C – 1750 °C). 

How Do Temperature Sensors Work?
Thermocouple

Negative Temperature Coefficient (NTC) Thermistor

An NTC thermistor is a sensitive temperature sensor that reacts to very small temperature changes, providing high accuracy and huge resistance, even at low temperatures. NTC thermistors have a range of -50 °C to 250 °C. As soon as the temperature starts to increase, resistance rapidly drops. It is important to note, that because of the large resistance and fast reflection, NTC thermistors require linearization. 

Semiconductor-based Temperature Sensor

Semiconductor-based temperature sensors (also known as IC sensors) have a dual integrated circuit (IC) containing two similar diodes. The diodes and temperature-sensitive voltage measure the temperature. These sensors give a reasonably linear output; however, they are less accurate between 1 and 5 °C. 

Semiconductor-based sensors are ideal for embedded applications, but unlike other temperature sensors, their electrical and mechanical performance are not as robust as thermocouples and RTDs. 

How Do Temperature Sensors Work?
Semiconductor-based Temperature Sensor

Resistive Temperature Detectors (RTDs)

Resistive temperature detectors (RTDs), also known as resistance thermometers, are a type of temperature sensor that gives very precise measurements. They are made from high-purity conducting metals (platinum, copper, or nickel) that are wound into a coil. Their electrical resistance is similar to a thermistor temperature sensor. 

Platinum RTDs are the most accurate, therefore, they are more expensive. At Atlas Scientific, we believe in providing customers with the highest quality and most accurate measuring tools, which is why all of our temperature sensors are made from Class-A platinum. 

How Do Temperature Sensors Work?
Resistive Temperature Detectors

Model PT-1000 Temperature Sensor 

The Atlas Scientific PT-1000 probe is a Class-A high purity platinum RTD temperature probe with a thick silicone rubber cable. The 304 stainless-steel tip quickly conducts heat from the environment to the platinum sensor inside, giving you low latency and highly accuracy readings.

We also have the Micro PT-100 temperature kit designed for microfluidic and other small space applications.  

Specifications of PT-1000 Temperature Sensor

Sensor TypePT-1000 Class A platinumRTD
Range-200 °C – 850 °C
Accuracy+/- (0.15 + (0.002*t))
Body MaterialSilicone rubber
Cable81 cm (32”)

As RTDs are passive devices, they do not produce an output on their own. An external device, such as an EZO-RTD Circuit is used to measure the resistance of the sensor, generating a voltage, and providing you with accurate temperature readings. 

What Applications Use Temperature Sensors?

Temperature sensors are extremely useful for a variety of industries to cater to both commercial and consumer needs. Below are the most common applications that use temperature sensors.

Medical Applications

Temperature sensors are used for quick and accurate measurements of patient temperatures. They are also used in MRI imaging machines and portable ultrasound scanners. 

Electrical Appliances In Our Homes 

Temperature sensors are used in many electrical appliances that you probably didn’t know about. They are found in refrigerators to keep food and drinks cold, in ovens for cooking food to specific heats, and in air conditioners/wall heaters. They are also found in battery chargers to prevent under charging and overcharging electrical appliances. 

Oil Mining

Temperature sensors are fundamental for safe and effective practices in the oil mining industry. Oil drills are equipped with inbuilt temperature sensors that notify workers when they need to stop drilling. 

Vehicles

Temperature sensors are found in radiators inside different vehicles. These warn you if the temperature of the engine becomes too hot, which prevents the engine from exceeding its temperature limit. They are also used in climate control settings, allowing you to cool or warm the inside of the vehicle. 

HVAC Systems

HVAC systems require temperature sensors to provide optimal temperatures for a particular room or building. They are also useful for detecting leaks, such as air conditioning units. 

Renewable Energy

Renewable energy sources require an effective production of energy to function; therefore, they depend on temperature sensors to regulate and measure temperature. Temperature sensors are required for wind turbines, biomass combustion applications, solar heating pumps, and geothermal monitoring. 

Chemical Industries

Chemical industries use high-quality and effective temperature sensors to measure extremely high temperatures in chemical reactions. 

Integrated Circuits 

Integrated circuits are found in desktop computers, laptops, mobile phones, and other electronic devices we use daily. They are dependent on integrated silicon temperature sensors to avoid overheating. 

Summing Up Temperature Sensors

Temperature sensors are found in our daily lives, whether it be in your home or the industry you work in. Temperature sensors are composed of two metals that generate an electrical voltage or resistance when a temperature change occurs by measuring the voltage across diode terminals. 

Temperature sensors come in many types depending on the industry or application being used, however, resistive temperature detectors (RTDs) are the most popular because of their very precise measurements.

If you are unsure exactly which temperature sensor will best suit your needs, do not hesitate to reach out to the world-class team at Atlas Scientific.

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