Instruments for Measuring Temperature in Industry

Temperature is a statistical quantity that characterizes the thermal state of a body proportional to the kinetic energy of its molecules. Note that the system unit of measurement is the kelvin, not the commonly used degree Celsius. This is because the absolute zero is taken as zero on the Kelvin scale, so any temperature by default will be positive.

Another important point is that temperature cannot be determined directly, like the linear dimensions of a body. The parameter is measured by indirect signs – changes in physical properties. These properties of the body are called thermometric. Measuring temperature means converting the measurement signal into one of the thermometric properties.

Several methods are used in industry to determine temperature, based on changes in the physical properties of bodies and media:

• Thermal expansion of a liquid or gaseous medium, solid body when the temperature rises.
• Change in pressure inside a closed volume – manometric principle.
• Change in electrical resistance under the influence of temperature: the method is used in thermistors.
• Thermoelectric effect.
• Electromagnetic radiation of a heated body.

General classification of instruments

The principle for dividing measuring devices is the physical properties of bodies used to measure temperature. Depending on this, several groups of instruments are distinguished:

• Expansion thermometers. These devices allow recording temperature over a wide range: from -190 to +500 degrees. The principle of operation is based on the property of bodies, liquid or gaseous medium to expand when the temperature rises. Expansion thermometers are further divided into liquid glass and mechanical types.
• Manometric thermometers. They have approximately the same measurement range, and the principle of temperature determination is based on the change in pressure of the medium. When heating a liquid, gaseous, or vaporous medium in a closed circuit, its volume changes, and therefore the pressure on the walls of the circuit changes.
• Electrical resistance thermometers. They allow measuring temperature in the range from -200 to +650 degrees. The instruments measure the electrical resistance of the medium, which changes when heated or cooled.
• Thermocouples. They measure only positive temperatures up to +1800 degrees. The principle of operation is based on the property of metals or their alloys to generate an electromotive force, the magnitude of which is proportional to temperature changes.
• Pyrometer – a device for non-contact measurement of the working medium temperature. The instrument determines the characteristics of the energy emitted by bodies, which change when heated or cooled.

Application area of temperature measurement sensors

For most technological and production processes, temperature is a key factor, control over which allows achieving maximum product quality. Measuring the thermometric characteristics of the working medium helps avoid emergency situations, equipment failure, and production stoppage. Here are just a few examples of the widespread use of temperature measuring instruments in industry:

• Modern automotive manufacturing involves performing many operations for additional processing of materials with various properties. Many manufacturers offer a separate line of measuring equipment for the automotive industry, allowing control and optimization of the work process through the introduction of infrared thermometers and thermal imagers.
• Temperature sensors are widely demanded in the polymer industry, production, and processing of plastics. Injection molding or thermoforming of polymer films requires continuous temperature measurement of the production process in a non-contact way. Properly selected equipment allows achieving maximum quality and minimizing the percentage of defects.
• Temperature control is necessary in the production and processing of metals. Measurements are performed non-contact, especially when it comes to controlling the working parameters of metal on a rolling mill, during bulk stamping, or hardening by induction heating of blanks. The introduction of high-precision temperature measuring instruments helps manufacture quality products, reduce production costs, and optimize the technological process.
• Laser welding and cutting require continuous temperature control, and permissible parameters vary greatly for each material. Infrared sensors are in demand in this field, which non-contact measure the temperature at joints or cutting points, adjusting it to achieve maximum productivity.
• Preventive equipment maintenance is the key to quality and uninterrupted production. During maintenance of mechanical or electrical equipment, operation of air conditioning systems, it is important to use high-quality infrared thermometers and thermal imagers. High-precision devices allow early detection of defects or weak points in the production chain – areas of overheating and underheating. This reduces the risk of serious malfunction and lowers maintenance and repair costs.