The temperature sensor works by providing a reading through an electrical signal. The sensor consists of two metals, which generate voltage or resistance by measuring the voltage across the diode terminals when the temperature changes. When the voltage increases, the temperature also increases.
A temperature sensor is a device that provides a readable temperature measurement through an electrical signal. The most basic way to measure temperature is with a thermometer; this measures how hot or cold something is. With advances in technology, we can now use a variety of more accurate temperature sensors.
Temperature sensors are very useful and necessary for a wide range of applications. The following will explain how temperature sensors work, the different types of sensors, and their most common applications.
How do temperature sensors work?
Temperature sensors measure temperature readings through electrical signals. They contain two metals that produce a voltage or resistance when the temperature changes.
The sensors play a vital role in maintaining specific temperatures in a variety of industries, including medical applications, HVAC systems, and the appliances in our homes. Temperature sensors are critical to the accuracy and temperature control of such industries.
Temperature sensors work by measuring the voltage across the diode terminals. As the voltage rises, so does the temperature, and then a voltage drop occurs between the transistor terminals and the emitter (in the diode).
There are different types of sensors, which are classified according to their connections. Temperature sensors fall into two main categories, depending on the type of application used or the industry you work in.
- Contact temperature sensors
- Non-contact temperature sensors
Contact temperature sensors
Contact temperature sensors measure the hot or cold level of an object or substance by direct contact. They are commonly used to detect various temperatures in different solids, liquids or gases.
Non-contact temperature sensors
These thermometers never come into direct contact with an object or substance, and therefore, they are widely used in hazardous environments such as the power plant industry. They measure the heat or coldness of something through the radiation emitted by the heat source.
To understand how temperature sensors work, we will describe each type of temperature sensor in more depth below.
Different types of temperature sensors
In order to understand how temperature sensors work, contact and non-contact temperature sensors are further divided into the following types.
- Negative temperature coefficient (NTC) thermistors
- Resistance Temperature Detectors (RTD)
- Semiconductor-based temperature sensors
A bimetal thermometer is a contact temperature sensor that consists of an attached gauge and stem. The sensor tip contains a spring located inside the inductive end of the stem that is attached to a rod that leads to the gauge needle. The movement of the induction coil when heated causes the needle in the gauge to move, thereby indicating the temperature reading.
Gas-filled and liquid thermometers are also contact temperature sensors that operate similarly to bimetal thermometers; however, they have a gas or liquid filled bulb. The bulb is located inside the sensing end of the probe and when heated, it expands the gas or heats the liquid, signaling the connecting rod to move the needle and display the temperature reading.
A thermostat is a contact temperature sensor consisting of a bimetallic strip containing two different metals (aluminum, nickel, copper or tungsten).
When exposed to heat, the difference in the linear coefficient of expansion of the two metals produces a mechanical bending motion.
Thermistors or thermistors change their physical appearance when there is a change in temperature. They consist of ceramic materials (nickel or manganese/cobalt oxides plated on glass) that can easily damage them.
Most thermistors have a negative temperature coefficient (NTC). This means that their resistance decreases as the temperature rises. However, some thermistors have a positive temperature coefficient (PTC); as the temperature increases, the resistance increases.
Negative Temperature Coefficient (NTC) Thermistors
NTC thermistors are sensitive temperature sensors that respond to very small temperature changes and provide high accuracy and great resistance even at low temperatures.NTC thermistors have a temperature range of -50 °C to 250 °C. Once the temperature starts to rise, the resistance drops rapidly. It is important to note that NTC thermistors require linearization due to their high resistance and fast reflection.
Thermocouples are one of the most common temperature sensors because of their reliability, accuracy, sensitivity, simplicity and wide temperature operating range.
They have two wires that contain two different metals (e.g. copper and bronze), which are connected at two different points to form a junction. One point is called the “cold end” and is held at a specific temperature, and the other is called the “hot end”. The temperature change is recorded by the voltage between the two wires.
Thermocouples may not be as accurate as resistance temperature detectors (RTDs); however, they are more cost effective and have a wide temperature range (-200 °C – 1750 °C).
Semiconductor-based Temperature Sensors
Semiconductor-based temperature sensors (also called IC sensors) have a dual integrated circuit (IC) that contains two similar diodes. The diodes and temperature-sensitive voltage measure temperature. These sensors provide a reasonably linear output; however, they are less accurate between 1 and 5 °C.
Semiconductor-based sensors are well suited for embedded applications, but unlike other temperature sensors, they are not as robust electrically and mechanically as thermocouples and RTDs.
Resistance Temperature Detectors (RTD)
Resistance temperature detectors (RTDs), also known as resistance thermometers, are temperature sensors that provide very accurate measurements. They are made of high purity conductive metals (platinum, copper or nickel) wound into coils. Their resistance is similar to that of a thermistor temperature sensor.
What applications use temperature sensors?
Temperature sensors are useful for a variety of industries that meet both commercial and consumer needs. The following are the most common applications that use temperature sensors.
Temperature sensors are used to quickly and accurately measure a patient’s body temperature. They are also used in MRI imaging machines and portable ultrasound scanners.
Appliances in our homes
Temperature sensors are used in many appliances that you may not know about. They are found in refrigerators to keep food and drinks cold, in ovens used to cook food to a specific temperature, and in air conditioners/wall heaters. They are also found in battery chargers to prevent undercharging and overcharging of appliances.
Temperature sensors are located in the radiators of different vehicles. These warn you if the engine is getting too hot, thus preventing the engine from exceeding its temperature limits. They are also used in climate control settings, allowing you to cool or heat the interior of your vehicle.
Temperature sensors are the foundation of safe and effective practices in the oil extraction industry. Oil drilling rigs are equipped with built-in temperature sensors that notify workers when they need to stop drilling.
HVAC systems require temperature sensors to provide the optimal temperature for a specific room or building. They can also be used to detect leaks, such as in air conditioning units.
The chemical industry uses high quality and effective temperature sensors to measure the extremely high temperatures in chemical reactions.
Renewable energy sources need to produce energy efficiently to function; therefore, they rely on temperature sensors to regulate and measure temperatures. Wind turbines, biomass combustion applications, solar heat pumps and geothermal monitoring all require temperature sensors.
Integrated circuits are found in the desktop computers, laptops, cell phones and other electronic devices we use every day. They rely on integrated silicon temperature sensors to avoid overheating.
Temperature sensors are found everywhere in our daily lives, whether in your home or in the industry where you work. Temperature sensors consist of two metals that produce voltage or resistance by measuring the voltage across the diode terminals when the temperature changes.
There are several types of temperature sensors depending on the industry or application being used, but resistance temperature detectors (RTDs) are the most popular because they are very accurate in their measurements.
If you are interested in temperature transmitter or have a need for other instruments such as water analysis instruments, flow meters, level meters, or pressure measurement instruments, please feel free to contact Apure’s professional level team.