Temperature > 10 – Types of Temperature Sensors

A temperature sensor is a device that responds to a physical/chemical stimulus in a specific and analogically measurable manner.

Of the many types of temperature sensors available, such as glass thermometers, bimetallic thermometers, gas expansion thermometers, thermistors, thermocouples, resistance thermometers, and others, the most widely used industrially are thermocouples and resistance thermometers.

Since thermocouples measure a wide range of temperatures and are relatively coarse, they are most often used in industrial and process applications where accuracy may be a less important factor.

Resistance thermometers, on the other hand, are fragile in nature and require installation in protective sheaths. They are generally considered to be the most accurate temperature sensor available, in addition to providing excellent stability and repeatability.

Resistance thermometers: high precision and stability temperature sensors

Thermoresistance sensors are temperature sensors that stand out for their high precision and excellent repeatability of readings. Although they are mainly made of platinum, it is also possible to find models made of other materials, such as nickel or copper.

The operation of these temperature sensors is based on the principle of variation of ohmic resistance as a function of temperature. It is also worth mentioning that their sensor element consists of a resistance in the form of a high-purity platinum, copper or nickel wire, encapsulated in a glass or ceramic bulb.

In this context, when we talk about thermoresistance, it is important to highlight that it is identified by the material that makes it up and, immediately afterwards, by the resistance it presents at 0°C.

As an example, we can mention the PT-100 model. Using the nomenclature of the material, we can define its raw material – platinum – and its resistance, in this case 100 ?. On the other hand, an NI-500 will be a nickel thermoresistance that presents a resistance of 500 ? at 0°C.

Within their range of use, these temperature sensors offer much greater precision and stability than thermocouples. Furthermore, when properly protected with protective tubes and wells, they adapt to any environment.

The resistance-temperature curve of these products is usually more linear than other types of sensors, eliminating the need for special wires.

On the other hand, thermoresistance sensors are more expensive than thermocouples used in the same range. They also deteriorate more easily if their maximum operating temperature is exceeded.

For these temperature sensors to function properly, some important precautions must be taken. Among them, it is worth mentioning that the thermoresistance sensors must be completely immersed in the process. From this, it will be possible to avoid heat loss through conduction through the wires and sheath.

Therefore, the minimum immersion length (15 x the sheath diameter) and the use of protective materials with low thermal conductivity are also recommended.

All Alutal products and services adopt a certified quality management system, such as the international standard ISO-9001:2008. And for this and many other reasons, the company acts as a market leader in thermometry, standing out as one of the most remembered brands in the main segments in which its products operate.

With export processes to several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - the company also has its own laboratory for analyzing and calibrating thermocouples.

To see the complete list of the company's products, as well as request a detailed quote for each of them, access the Alutal portal right now. There, you will have access to the most varied equipment and services, such as: temperature transmitters, thermowells, extension and compensation wires and cables, protection tubes, pyrometers and, of course, temperature sensors of various types.

It is worth noting that these products and services can be used in different application segments, such as the automotive, steel, aluminum extrusion sectors, etc. 

Thermocouples: learn about the temperature sensors used in different segments

Thermocouples are widely used equipment in the industrial thermometry market. They can be defined as temperature sensors with the potential to be used in a wide range of measurement processes.

The electrical reaction used to create temperature sensors was discovered by chance in 1821 by Estonian physicist Thomas Seebeck. At the time, the scientist discovered the thermoelectric effect from a combination of different metals that produced an electrical voltage, the potential of which depended on the materials used to make it up and the temperature at which they were found.

Since their creation, these devices have undergone several updates, and today there are different models available on the market. In general, they have predictable output voltages and are capable of withstanding high temperatures.

Thermocouples can be found in a wide range of formats. They can be incorporated into a probe or in a structure that provides a fast response time.

In relation to the functions they perform, they are not expensive and, when of good quality, provide precision and a long useful life. Among the main models of these temperature sensors, we can highlight the thermocouple types E, K, T, J, among others.

Type E thermocouples can be used in oxidizing, inert or vacuum atmospheres. However, they are not recommended for alternating oxidizing and reducing atmospheres. Compared to other commonly used temperature sensors, they have greater thermoelectric power – something quite advantageous for those who want to detect small temperature variations.

In this context, type K thermocouples stand out for being general-purpose. They are low-cost and, due to their popularity, are available in a wide range of probes. The temperatures covered by this product vary between -200 °C and 1200 °C.

On the other hand, the type T thermocouple is recommended for inert, oxidizing or reducing atmospheres. It has good precision due to the great homogeneity with which the copper can be processed.

At temperatures above 300° C, copper oxidation becomes very intense, reducing its useful life and causing deviations in its original response curve.

The J-type thermocouple can be used in reducing, neutral or oxidizing atmospheres. However, it is not recommended in atmospheres with high humidity levels or at low temperatures, as the JP thermoelement can become brittle.

Alutal, a company that has been operating in the Industrial Thermometry market since 1994, manufactures a series of thermocouples that can meet your business needs. All temperature sensors manufactured by the company adopt a quality management system certified by the international standard ISO-9001:2008.

Alutal has export processes to several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - and the company also has its own laboratory for thermocouple analysis and calibration.

To see the complete list of products, as well as request a detailed quote for each one, visit the Alutal portal right now.

There, you will have access to a wide range of equipment, such as: temperature sensors, thermowells, extension and compensation wires and cables, protection tubes, pyrometers, among others.

Gas Expansion Thermometers: Temperature Sensors Are Ideal for Remote Mounting

In many industrial activities, temperature plays an extremely important role. Therefore, if its measurement presents inaccurate results or is performed with poor quality equipment, numerous complications can occur in the processes.

For this reason, it is necessary to use products such as gas expansion temperature sensors – thermometers suitable for applications in the process industry, manufacturing of machines and equipment.

The gas expansion thermometer comprises a pressure measuring element by means of a capillary tube connected to a flask that is exposed to the temperature to be measured.

Therefore, since the gas measuring element and the connecting tube do not have the same temperature as the bulb, their volume must be larger, since the errors introduced by the temperature measuring element and capillary pressure are generally insignificant.

These temperature sensors are usually used in the chemical, petrochemical and process industries in general. They can also be used for local measurement of exhaust gas temperature or oil temperature in diesel engines, turbines, compressors, high-vibration machines, among others.

Generally, the measurement occurs without any contact with the environment, and is universal in plants, machines, packaging, tanks, equipment construction and the food industry.

Gas expansion thermometers with capillaries are used in assemblies that have measurement points that are difficult to access or in remote assemblies, that is, with measurement points far from the indication location.

As previously presented, this temperature sensor consists of a metal bulb connected to a metal capillary and a sensor element. Thus, the gas fills the entire instrument and, based on the temperature variation, expands, elastically deforming the sensor element.

In this way, the sensor element is coupled to a pointer that can rotate freely on a graduated scale. According to experts, since the relationship between the deformation of the sensor element and the temperature is proportional, this instrument provides a linear reading.

Although it does not manufacture gas expansion thermometers, Alutal, a company that has been operating in the Industrial Thermometry market since 1994, manufactures a series of temperature sensors that can meet the needs of your business.

First of all, it is important to highlight that all sensors manufactured by the company adopt a quality management system certified by the international standard ISO-9001:2008.

Alutal has export processes for several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - and the company also has its own laboratory for analysis and calibration of thermocouples.

To see the complete list of products, as well as request a detailed quote for each of them, access the Alutal portal right now. There, you will have access to the most varied equipment, such as: temperature sensors, thermowells, extension and compensation wires and cables, protection tubes, pyrometers, among others.

 

Glass thermometers: temperature sensors made with mercury

When we talk about temperature sensors, the glass thermometer stands out as one of the most popular on the market. It basically consists of a glass capillary tube, sealed under vacuum, and a bulb containing mercury.

Before understanding more details about this product, specifically, it is important to highlight that thermometers were created by the mathematician, astronomer and physicist Galileo Galilei in 1592.

Using an inverted tube with water and air, he created a type of thermometer in which the increase in external pressure causes expansion in the air and, consequently, raises the water level inside the tube.

In this way, these instruments were manufactured based on expansion, giving preference to materials with a high expansion coefficient - this is because they were easily altered. In this context, it is possible to highlight mercury as a product with a high expansion value, increasing in volume with the slightest variation in temperature.

Because it is an opaque and dark liquid, mercury in glass temperature sensors is relatively easy to identify, and even the glass acts as a magnifying glass, making the temperature displayed even more visible.

However, it is worth noting that mercury is toxic to humans and the environment, where it can bind to other chemical elements and form methylmercury, which makes it even more harmful.

Temperature sensors made with mercury were discontinued in the European Union in 2007, when their sale was banned. In the United States, 13 states have laws that prohibit the manufacture, sale and distribution of these instruments.

According to information released by the Ministry of Health, methylmercury can cause complications for the liver, kidneys and central nervous system, even leading to symptoms such as speech and hearing difficulties, loss of motor coordination, sensory disturbances and muscle weakness. In more extreme cases, it can lead to death.

However, in quantities as small as those present in a thermometer, it is unlikely to cause health problems, according to an assessment by the United Kingdom's National Health Service (NHS).

Finally, it is worth remembering that glass temperature sensors are just one of the many models and functions. Most devices of this type are used to perform measurements in industrial processes.

If you want to learn more about industrial thermometry, how about getting to know Alutal? The company, which has been operating in the market since 1994, manufactures a series of thermocouples that can meet your business needs.

All temperature sensors manufactured by the company adopt a quality management system certified by the international standard ISO-9001:2008.

Alutal has export processes to several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - the company also has its own laboratory for analyzing and calibrating thermocouples. To see the complete list of products, as well as request a detailed quote for each one, access the Alutal portal now. 

Thermistors: learn about the temperature sensors used in various industrial processes

Widely used as temperature sensors in industrial applications, thermistors can be defined as thermally sensitive resistors. The characteristics of this equipment can show large changes in resistance with a small change in body temperature, due to the change in the concentration of charge carriers.

Basically, there are two types of thermistors: the NTC (Negative Temperature Coefficient) type, which stand out for significantly decreasing their electrical resistance with increasing temperature, and the PTC (Positive Temperature Coefficient) type, which significantly increase their electrical resistance with increasing temperature.

NTC thermistors can be used as internal temperature sensors of an environment or to indicate the temperature reached by a liquid sample during its cooling or heating.

In addition, according to experts, NTC thermistors as temperature sensors offer a fast response time. They are sensitive to changes in voltage and current, and also have high stability.

It is also worth mentioning that, in general, they are also used in instrumentation for scientific research, medical equipment, telecommunications, home appliances, the automotive sector, military applications, among others.

Depending on the type of application, these temperature sensors are intended for measuring reasonable absolute temperature values, as is the case in medical applications. However, at other times, they are used for industrial applications, being used to measure temperatures of thousands of Kelvin.

NTC temperature sensors are usually used more because they are easier to manufacture. It is worth mentioning that they also have an incredible sensitivity to temperature increases.

However, this characteristic has a disadvantage: due to its high sensitivity, the temperature curve of the NTC sensor is not linear, presenting an exponential behavior. Therefore, a circuit is required that approximates the exponential curve to a linear curve with correction factors.

On the other hand, PTC thermistors present variation in their resistance only from a certain temperature, which is called the transition point.

Although it does not manufacture thermistors, Alutal, a company that has been operating in the Industrial Thermometry market since 1994, manufactures a series of temperature sensors that can meet your business needs.

First of all, it is important to highlight that all sensors manufactured by the company adopt a quality management system certified by the international standard ISO-9001:2008.

Alutal has export processes to several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - and the company also has its own laboratory for analyzing and calibrating thermocouples.
To see the complete list of products, as well as request a detailed quote for each of them, visit the Alutal portal right now.

There, you will have access to the most varied equipment, such as: temperature sensors, thermowells, extension and compensation wires and cables, protection tubes, pyrometers, among others. 

Bimetallic thermometers: extremely accurate temperature sensors

Among the various models of temperature sensors, bimetallic thermometers can be used in different industrial processes. However, before understanding more details about this product, it is important to highlight that thermometers were created by the mathematician, astronomer and physicist Galileo Galilei, in 1592.

Using an inverted tube with water and air, he created a type of thermometer in which the increase in external pressure causes an expansion in the air and, consequently, raises the water level inside the tube.

Specifically regarding bimetallic thermometers, it is worth mentioning that they are based on the expansion effect of a material composed of two metallic components with different expansion coefficients.

The expansion occurs when a metal bar connected to another bar of a different metal is cooled or heated. This contact will result in different changes in lengths that will produce a bending of the bar.

This bending is used to open or close valves, as well as to turn electrical circuits on or off - in some cases, even to record the amount of current flowing through the bar.

The first type can be constructed in a similar way to liquid thermometers: a bar, straight or not, moves a recording pointer when it expands.

The most widely used and accurate temperature sensors of this type exploit the difference in expansion between materials such as copper, iron and brass, etc. To do this, bimetallic blades are constructed in a spiral shape that bend as the temperature increases or decreases.

Finally, in this movement, the blade drags - at its end - a pointer that moves along a graduated scale or graphically records the temperature variation on moving paper.

In general, thermometers have excellent precision, repeatability and are manufactured with a carbon steel and non-ferrous metal housing. In addition, it is also worth noting that they are very resistant to handling, as well as highly durable and low cost.

However, it is worth remembering that it is necessary to do research to find out which model is ideal for the location or product where it will be applied.

If you want to know more details about devices like this, get to know Alutal - a company that has been operating in the Industrial Thermometry market since 1994 and manufactures a series of temperature sensors that can meet the needs of your business.

First of all, it is important to highlight that all sensors manufactured by the company adopt a quality management system certified by the international standard ISO-9001:2008.

Alutal has export processes to several countries - such as Bolivia, Venezuela, Argentina, Ecuador, Chile, South Africa, Colombia, Italy and the USA - the company also has its own laboratory for analysis and calibration of thermocouples.

To see the complete list of products, as well as request a detailed quote for each of them, visit the Alutal portal right now. There, you will have access to a wide range of equipment, such as: temperature sensors, thermowells, extension and compensation wires and cables, protection tubes, pyrometers, among others.