Umair Gaines
Temperature sensors are devices that provide readable temperature measurements via an electrical signal. They are used in a variety of applications, from household appliances like refrigerators and ovens to industrial applications like controlling the heat of electrical radiators. One of the most common types of temperature sensors is the thermocouple, which consists of two wires of dissimilar metals that generate an electrical voltage proportional to the change in temperature. Other types of temperature sensors include resistance temperature detectors (RTDs), thermistors, and semiconductor-based sensors. These sensors play a vital role in maintaining specific temperatures and preventing overheating in various industries.
| Characteristics | Values |
|---|---|
| Definition | Devices that provide readable temperature measurements via an electrical signal |
| Basic form | Thermometer |
| Use cases | Microwaves, refrigerators, water heaters, MRI machines, ultrasound scanners, ovens, computers, industrial applications, medical applications, laboratory applications, etc. |
| Types | Contact Type Temperature Sensors, Vibrating Wire Sensors, Thermocouples, Resistive Temperature Detectors (RTDs), Thermistors, Semiconductor-based Temperature Sensors, Non-contact or remote temperature sensors, etc. |
| Function | Measure the degree of hotness or coolness of an object or substance |
| Accuracy | Varies depending on the type of sensor |
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What You'll Learn
Thermocouples
Temperature sensors are devices that provide readable temperature measurements via an electrical signal. They are extremely beneficial and necessary for a wide range of applications. Temperature sensors are critical for accuracy and temperature control in industries such as medical applications, HVAC systems, and electrical appliances in our homes.
The two junctions of a thermocouple are known as the cold junction and the hot junction. The cold junction is kept at a specific temperature, while the hot junction is the measuring junction that is subjected to temperature change. When the hot junction is heated or cooled, an electric current is created, and the difference in voltage produced by the two metals is used to determine the temperature measurement.
The behaviour of a thermocouple is described by the Seebeck effect, where a temperature-dependent voltage is produced due to the presence of two dissimilar electrical conductors forming an electrical junction. The accuracy of thermocouples is relatively low, ranging from 0.5 °C to 5 °C, but they operate across the widest temperature range, from -200 °C to 1750 °C.
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RTDs
Temperature sensors are devices that provide readable temperature measurements in the form of an electrical signal. They are used in a variety of applications, from household appliances like microwaves, refrigerators, and water heaters to scientific and industrial applications. One of the most popular temperature sensors is the RTD (Resistance Temperature Detector), also known as a resistance thermometer.
When choosing an RTD, it is important to consider the instrument that will be used to read the sensor and select a compatible element type. The most common RTDs have a base resistance of 100 ohms at 0°C and a temperature coefficient of 0.00385 Ohm/Ohm/°C. Accuracy is also a key consideration and is determined by the base resistance tolerance and the temperature coefficient of resistance tolerance. RTDs are widely used in applications where accuracy and drift-free performance are more important than cost, such as scientific, industrial, and pharmaceutical manufacturing processes.
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Thermistors
A thermistor is a thermally sensitive resistor that exhibits a continuous, small, incremental change in resistance correlated to variations in temperature. The term "thermistor" is a portmanteau, derived from the term "thermally sensitive resistor". It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape, and then encapsulated with an impermeable material such as epoxy or glass.
There are two types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). With an NTC thermistor, when the temperature increases, resistance decreases. NTC thermistors are widely used as inrush current limiters and temperature sensors. They are the sensor of choice for applications that measure temperature at a desired base point. They are ideal when very precise temperatures are required. NTC thermistors have a range of -50 °C to 250 °C.
PTC thermistors, on the other hand, exhibit an increase in resistance as temperature rises. PTC thermistors are used as self-resetting overcurrent protectors and self-regulating heating elements. They are commonly installed in series with a circuit to protect against overcurrent conditions, acting as resettable fuses.
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Contact and non-contact sensors
Temperature sensors are devices that provide readable temperature measurements via an electrical signal. They are used in a wide range of applications, from everyday items like microwaves, refrigerators, and water heaters to more complex systems in the medical, HVAC, automotive, and aerospace industries.
Temperature sensors can be broadly categorized into two types: contact and non-contact sensors. Contact temperature sensors, as the name suggests, require direct physical contact with the object or substance being measured. Common examples of contact sensors include liquid-in-glass thermometers, thermocouples, RTDs (Resistance Temperature Detectors), and thermistors. Thermocouples, for instance, consist of two wires of different metals bonded at two points, creating a varying voltage that reflects changes in temperature. RTDs, on the other hand, are made of high-purity conducting metals like platinum, copper, or nickel wound into a coil, and they change their electrical resistance in response to temperature variations.
Non-contact temperature sensors, on the other hand, do not require physical interaction with the object being measured. They are often used when contact is undesirable or impossible. For instance, non-contact sensors are useful when contact would damage the object or sensor, when contact would significantly change the object's temperature, or when the object is in a remote or inaccessible location. Non-contact sensors operate based on Planck's law of thermal radiation and are also known as radiation pyrometers, IR pyrometers, or optical pyrometers. They use reflective or refractive optics to isolate and define radiation from the measured target, and they can provide measurements over a large area or at a distance.
Both types of sensors have their advantages and are chosen based on the specific application and requirements. Contact sensors generally provide good accuracy and responsiveness, while non-contact sensors offer the advantage of remote or challenging measurements without interfering with the object or system being measured.
In summary, contact and non-contact temperature sensors offer distinct approaches to measuring temperature, catering to a diverse range of applications and ensuring accuracy and convenience in various fields.
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Applications of temperature sensors
Temperature sensors are used in a wide range of applications, from everyday items to industrial processes.
In everyday life, temperature sensors are present in thermometers, microwaves, refrigerators, and water heaters. They are also used in cars to monitor the temperature of the engine and the surrounding environment.
In the geotechnical monitoring field, temperature sensors are employed to monitor the internal temperature of structures such as bridges, dams, buildings, power plants, concrete structures, railway tracks, soil, and water bodies. This helps in structural analysis and ensuring the safety of these structures.
Temperature sensors are critical in various industries, including medical applications, HVAC systems, and electrical appliances. They play a vital role in maintaining specific temperatures and accuracy in temperature control. For example, in the petrochemical industry, temperature sensors are used to prevent overheating and ensure the safe operation of equipment.
Temperature sensors are also used in laboratory research, process control, and industrial automation. They can be categorized into contact and non-contact sensors, depending on their mode of operation. Contact sensors physically touch or are immersed in the medium they are monitoring, while non-contact sensors do not require direct contact.
Additionally, temperature sensors are essential in equipment used for creating life-saving medications, where accuracy and responsiveness are critical for quality control.
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Frequently asked questions
Temperature sensors are devices that provide readable temperature measurements via an electrical signal. The most basic way to measure temperature is using a thermometer, but there are now many types of temperature sensors with varying levels of accuracy.
Temperature sensors work by measuring the voltage across diode terminals. When the voltage increases, the temperature increases, followed by a voltage drop. Sensors use different types of metals with distinct expansion coefficients, and temperature changes affect the wire's tension and its vibration frequency.
Temperature sensors are used in a wide range of applications, from everyday items like microwaves, refrigerators, and water heaters, to medical applications, HVAC systems, and electrical appliances. They are also used in industrial applications to control the heat of electrical radiators, and in the automotive and aerospace industries.
The two main types of temperature sensors are contact and non-contact sensors. The four most common types of temperature sensors, ranging from high to low accuracy, are Negative Temperature Coefficient (NTC) Thermistors, thermocouples, semiconductor-based integrated sensors (ICs), and Resistance Temperature Detectors (RTDs).
