In industry, accurately measuring temperature is crucial to ensuring operational efficiency, quality, and process safety. Among the most used temperature sensors is the thermocouple, valued for its durability and ability to operate at high temperatures. Alongside it, other contact and non-contact models make up the market and offer specific solutions for different production demands. See which are the most popular.
What is a temperature sensor?
A temperature sensor is a device that detects the temperature of a medium, whether solid, liquid, or gas, and converts it into a signal, usually electrical, that can be interpreted by an electronic system. This signal allows temperature monitoring and regulation.
Also known as a temperature probe, this sensor consists of a sensing element. This element is often housed within a protective sheath, usually metal, to protect it from mechanical or chemical damage. A cable connects to this assembly to carry the signal to the electronic system.
On the market, temperature sensors are divided into three main categories: Thermocouples, Resistance Thermometers (RTDs) and Thermistors.
These sensors measure a physical property that changes predictably with temperature. They are classified as contact and non-contact sensors.
Contact sensors, like the three main types mentioned, need to touch the object to measure its temperature.
Non-contact sensors measure temperature from a distance by capturing infrared radiation emitted by the heat source.
It's important to note that the term "thermometer" refers to the complete measuring instrument (sensor + reading electronics). The sensors are the components that perform the initial detection.
Thermocouples
The thermocouple is one of the most versatile and widely used sensors in industry. It is economical, robust, and covers a wide temperature range. Its response time depends on the construction: exposed junction models are very fast, while those with robust protective wells are slower.
Its operation is based on the Seebeck Effect: two wires of different metals are joined at one end (measurement junction). The temperature difference between this end and the other end (reference junction) generates a small voltage, which is proportional to the temperature.
Os types of thermocouples most common are:
Type J: Made of Iron and Constantan (Copper-Nickel alloy). Typically operates from 0°C to 750°C, but its use is limited in oxidizing environments above 500°C.
Type T: Composed of Copper and Constantan. Excellent for humid environments and cryogenic temperatures, with a range of -250°C to 350°C.
Type K: Composed of Chromel (Nickel-Chromium) and Alumel (Nickel-Aluminum). It is the most popular general-purpose thermocouple, with a wide range from -200°C to 1250°C.
Type N: Made of Nicrosil and Nisil. Offers greater stability and oxidation resistance than Type K at high temperatures (up to 1260°C), making it a superior alternative in many applications. Accuracy varies depending on the thermocouple class (e.g., Class 1 or 2).
RTD Sensors (PT100 and PT1000)
RTD (Resistance Temperature Detectors) sensors are based on the variation in a metal's electrical resistance with temperature. They are known for their high accuracy, stability, and repeatability.
PT100: This is the most common design. It uses a thin platinum wire or film with a resistance of 100 Ω at 0°C. Its measurement range is approximately -200°C to 850°C, although for long-term stability, continuous use is often limited to around 650°C.
PT1000: Works identically, but has a resistance of 1000 Ω at 0°C. The higher resistance minimizes error caused by the resistance of the connecting cables, making it ideal for installations with two-wire connections or very long cables.
NTC and PTC thermistors
Thermistors are highly sensitive sensors made of semiconductor materials. Their main characteristic is a large variation in electrical resistance for a small change in temperature.
NTC (Negative Temperature Coefficient): Resistance decreases as temperature increases. They are ideal for precision measurements in more limited and specific temperature ranges.
PTC (Positive Temperature Coefficient): Resistance increases abruptly at a specific temperature. They are primarily used as overload sensors or resettable fuses, not for accurate temperature measurement.
The operation of both is based on measuring their resistance by an electronic circuit, and not on detecting “electrical impulses”.
10 Alutal temperature sensors and applications
Alutal offers a variety of solutions, from conventional thermocouples to sensors for high-vibration environments, ideal for the chemical, petrochemical, steel, and oil and gas industries. See our most popular equipment:
Thermocouple / Thermoresistance TIM/TRS: combines thermocouple and resistance thermometer for monitoring chemical and petrochemical process pipelines, offering high reliability even in aggressive environments.
Conventional Ceramic Thermocouple TCC: designed for high temperature, ideal for ovens and harsh industrial processes, with durable ceramic insulation.
Mineral Insulated Thermocouple TIM: offers thermal stability and resistance to external interference, perfect for chemical and petrochemical pipelines.
Mineral Insulated Thermocouple with TMP Protection Well: protects the sensor against wear and facilitates maintenance without interrupting the process, ideal for chemical and oil and gas industries.
Helical Protection Wells: increase the lifespan of thermocouples, protecting against pressure and corrosion, allowing replacement without stopping the process.
Thermocouple / Thermoresistance TRP – Sensors for industrial pipelines, combining precision and reliability in chemical and petrochemical processes.
Thermocouple / Thermoresistance AF-TC R/S/B: developed for blast furnaces in steel mills, they withstand high temperatures and vibrations, ensuring reliable measurements.
Thermocouples with Metallic Protection TMM and TCM: offer metallic protection that extends service life, allowing replacement without interrupting industrial processes.
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Thermocouple / Thermoresistance for high vibration: they are recommended for environments with intense vibration, as they guarantee precision and durability even under constant movement, such as in steel mills and heavy processes.
