Heating elements, thermal sensors and resistance thermometers
for industrial applications. Tips for selecting according to your needs.
Heating elements, thermosensors and resistance thermometers are components of electrical thermal engineering. They are among the key functional components of countless products, systems, processes and technologies. In almost all areas of modern life, they enable the precise and safe regulation, control and monitoring of thermodynamic processes. Mostly invisibly installed, they can be found in household appliances and automobiles, in plastics and packaging systems, in medical and laboratory equipment, in electrotechnical and microelectronic systems, and in numerous applications in industrial automation, mechanical engineering, fluid technology and toolmaking.
Heating elements are used for the targeted, homogeneous supply of defined heat and thermal values in components, tools, processes and products. They are available in various designs for many installation positions and tasks.
Thermal sensors and resistance thermometers, on the other hand, are used for fast detection, measurement and monitoring of temperature (limit) values. They cover a wide performance spectrum and, depending on the design are suitable for various connection and installation situations.
In the field of heating elements of thermocouples/resistance thermometers, technical development is progressing continuously. In addition to the increasing demands on quality, energy efficiency and flexibility of products and applications the trend towards miniaturization of assemblies is also providing innovative impetus. Heating elements, thermosensors and resistance thermometers are among those components that can be very easily integrated into compact and space-saving designs, enabling the realization of highly efficient thermodynamic processes. They serve as fundamental system components for industrial automation and quality assurance.
Heating elements
As primary designs for heating elements, cartridge heaters, flexible tubular heaters and coiled tubular cartridges in particular cover a wide range of technical applications.Cartridge heaters are rod-shaped heating elements of different lengths, diameters, geometries and connection types. They have various VDE certifications, comply with UL and CSA standards, and are also offered in protection class IP67 (dust/waterproof). Depending on the design, they are suitable for maximum temperatures of up to 750° C. They differ in terms of their sheath materials (e.g. nickel, stainless steel) and electrical properties.
Cartridge heaters of the hotrod® product family are among the central components of the hot runner systems of many molds for plastic injection molding. Typical applications also include the heating of cutting knives in textile processing plants, of sealing bars in film packaging machines and hot stamping dies in identification technology. Other applications include the internal heating of injection molding nozzles, the heating of embossing rollers in paper processing machines and the temperature control of laboratory equipment.
Foundry Cartridge Heaters
Foundry cartridge heaters are primarily used in foundries. Here, one of their main tasks is the optimum temperature control of the melt flowing through the pouring neck into the mold. For easy installation, they have angle blocks, pipe sections or metal link hoses.
High-performance cartridge heaters
High-performance cartridge heaters are characterized not only by their compact, slim design but also by their suitability for working temperatures of over 750° C. They are the domain of high-temperature cartridges. Their domain is high-temperature applications such as those found in power plants, blast furnaces or in turbine and rocket construction. They are also the preferred choice for research and development projects.
Spiral cartridge heaters
Spiral cartridge heaters are available as rigid and bendable versions. Versions with carbide cutting blades are specially designed for use in textile and film processing. Simple, rigid spiral cartridge heaters are regarded as a cost-effective solution with a long service life, while the bendable variants can be adapted to the specified environment up to a length of 3,000 mm and a bending radius of 15 mm.
The tubular heating elements of the hotflex® series can also be installed very flexibly. Thanks to their flexibility, they are suitable for applications in which high temperatures of up to 700° C have to be supplied through narrow-angled passages. They ensure optimum, precise heat transfer, for example in heating plates or in temperature control surfaces. They are available in round and square cross sections of different sizes. They can be inserted into milled recesses without the need for special tools. Various connection types ensure their uncomplicated integration into heating and temperature control systems.Coiled tubing cartridges
Another large group of heating elements are the helical cartridges of the hotspring® series. They are also available in numerous designs and sizes with different power densities and power distributions. Depending on the design, they have round or flat cross-sections as well as different connection variants and clamping mechanisms for fastening in their structural environment. The type of clamping mechanism affects the efficiency of heat transfer between the heating element and the mold or component.
Coiled tubing cartridges achieve shell temperatures of up to 750° C. Their most important applications include heating the hot runner nozzles and manifolds of molds in plastic injection molding. In machines for the production of film and pouch packaging, they are used to heat the sealing bars and sealing heads. In foundry and process technology, they are used to temper machine nozzles.
The distinguishing features of helical cartridges are the number and geometry of their windings. They can be cylindrical, plate-shaped, meander-shaped or conical, as well as very tight or open. Another selection criterion is the surface load of the jacket of a helical cartridge when installed.
Thermal sensors and resistance thermometers
Measuring, monitoring and documenting temperature curves and values is one of the most important disciplines in almost all technical fields. For this purpose, the thermosensors and resistance thermometers of the hotcontrol® product line are used, which are available in numerous variants for many connection and installation situations. They are used in the manufacture of electronic and electrotechnical components as well as in process, chemical, laboratory and process engineering, in plastics technology and in toolmaking. Thermosensors and resistance thermometers differ in design and function. What all versions have in common is that they follow DIN 2768-m in their dimensions.
Thermal sensors consist of two wires of different metallic materials. Their function is based on temperature and electrical voltage. If the temperature at the measuring point changes, the electrical charges of the wires shift in different ways, resulting in an electrical voltage that can be measured and interpreted. Thermocouples cover wide temperature ranges, but are limited in accuracy.For higher demands on measurement accuracy, resistance thermometers are the better choice. Here, the resistance is measured via an electrical conductor, whereby a defined relationship exists between the resistance and the temperature. This can be represented as a characteristic curve. Resistance thermometers for calibration technology, for example have wire-wound measuring resistors made of platinum. They offer a detectable temperature range of up to 400° C and score with high accuracies.
Thermocouples
Thermocouples are calibrated according to various criteria. Widely used are types J, K, T and E. Rarer and designed for high-temperature applications are types R, S, and B. Thermocouples can sense wide temperature ranges and are suitable for applications with simple and medium accuracies. They can also be designed to the US ANSI standard.
Sheathed thermocouples occupy a large space within thermal sensors. They are offered in many diameters (0.6 to 6.0 mm) and with various connecting leads, their dimensions complying with the tolerance specifications of EN 61515. Depending on calibration, wire material and standardization (IEC, DIN, ANSI), they can be used for measuring ranges from -40° C to 760°C or -40°C to 1,100 °C. Mineral-insulated thermocouples are among the thermal sensors with the largest and highest measuring ranges.
There are also thermocouples whose special designs are adapted to various installation and mounting situations. These include designs for plugging in as well as thermocouples with bayonet locks. There are also angle thermocouples, surface thermocouples as well as variants with clamping band geometry, with fastening rings or also for flange mounting. Depending on the variant, they comply with DIN or IEC standards and are suitable for measurements from 0°C to 260°C, 0°C to 360°C or 0°C to 400°C.
Resistance thermometers – platinum solution for very high accuracies
In the field of resistance thermometers, sheath resistance thermometers are of particular importance. They have electrical conductors made of platinum and differ in the type of connecting cable (PFA, GLS, silicone) and connection options. Widely used are platinum sheath resistance thermometers of the Pt100 type, which have an electrical resistance of 100 Ω at 0°C. The second important type has an electrical resistance of 1,000 Ω at 0° C and is designated Pt1000. Both types are suitable for measuring ranges from -60° to 600°C.
Furthermore, there are also different designs within the resistance thermometers, which are adapted to the mounting possibilities of different constructive environments. Important here are variants with angled measuring head as well as for plugging in or pushing in and with various bayonet locks. Depending on the design, these resistance thermometers cover measuring ranges from 0° C to 360° C or 0° C to 400° C.
Thermocouples and resistance thermometers for automotive engineering
For automotive engineering, there are thermocouples and resistance thermometers that are adapted for use in engine compartments, catalytic converters, turbochargers, oil pans and exhaust tracts. In particular, these include ready-to-install mineral-insulated thermocouples and platinum mineral-insulated resistance thermometers with union nuts and for screwing in for measuring ranges from -40° C to 1,100° C or -60° C to 600° C.
Also tailor-made for automotive use are wire thermocouples and self-adhesive versions for easy surface mounting for measuring ranges from 0° C to 260° C. For higher measuring ranges from 0° C to 860° C, variants with spring-loaded measuring heads, friction sensors and plug-in thermocouples are suitable for monitoring temperatures on brake discs.
High-strength thermal sensors and resistance thermometers
Thermocouples and resistance thermometers with transition sleeves made of an innovative hybrid material are available for applications that require high thermal and mechanical stability, particularly at the transition zone between the measuring tip and the connecting cable. With a transition sleeve that is heat-resistant up to 400° C, they offer high operational reliability and service life even under extreme conditions.
Images: HOTSET, Adobe Stock
