FEATURE u Sensors & Sensing Systems
Making the most of thermal sensors
In industrial heating applications, temperature sensors are key components that provide temperature feedback, used to monitor and control the process. However, there is a lot more to them than this, as Johann Lainer, Senior Marketing Communications Specialist at industrial technology company Watlow, explains.
T
he global temperature sensors market is expected to be valued at over seven million pounds by 2026. And it’s easy
to understand why the market is burgeoning. Temperature sensors are employed virtually everywhere. For example, sensors are used throughout heat pump systems, which are becoming an increasingly popular alternative energy option. Currently, there are over 40,000 heat pumps in operation in Ireland, a country that is also working towards a 2030 heat pump target. Sensors have two main functions: to determine and maintain the temperature of an object or environment, and to alert the system of dangerous temperature levels. Without temperature sensors, a system is essentially blind. While some simple thermal systems can rely on a thermostat device to maintain a relative temperature within five degrees Celsius, many processes require a far greater degree of accuracy. This is where temperature sensors come in. However, with various types and purposes of thermal sensors, how do engineers determine which is best for a given application and how to correctly apply them?
TYPES OF SENSORS There are two categories for temperature sensors. Firstly, contact sensors include resistance temperature detectors (RTDs), thermocouples and thermistors that must be in contact with the solid, liquid, or gas it’s measuring. Secondly, non-contact sensors involve thermal imaging and infrared sensors, which determine temperatures from a distance by measuring the thermal radiation emitted by an object or heat source. These sensors are often found in hazardous environments where there are high temperatures, such as high voltages or within moving machinery. Two of the most commonly-used sensors in thermal applications are RTDs and thermocouples. RTDs use resistance to determine temperature of a source. They are often used in industrial applications because they are comprised of metal, instead of ceramic or polymer, and are highly stable and accurate,
16 October 2021 Irish Manufacturing
making them ideal for repeatable precision and a more accurate assessment of a processing system.
Thermocouples measure the temperature delta between two points, using a metal junction of two dissimilar types of wire to measure the micro-voltage. Changes in voltage are read by a process controller, which calculates the relationship between voltage and heat. This allows engineers to adjust the temperature of the heater bundle to increase, decrease or maintain the ideal temperature for an industrial process. Thermocouples are available in a variety of models and technical specifications, making it crucial to identify the right type and material of thermocouple for an application. It’s recommended that Type J is the most common for heat trace applications because of its broad temperature range. Types T and E are used for more moderate temperatures, while Types K and N are primarily used for high temperatures often used in heat treating and aerospace applications. However, it’s best to turn to a reliable heating equipment manufacturer
who can adapt a solution for your unique application. Watlow, which manufactures temperature sensors including thermocouples and RTDs, used its expertise to develop an industrial thermocouple that supported an aircraft manufacturer in heat treating engine components. The manufacturer needed a thermocouple that could easily route through the furnace wall and be safely used in temperatures exceeding 1,000 degrees Celsius. Meeting these design requirements, Watlow delivered a thermocouple that overcame these challenges for easy and safe use.
SUITABLE SENSOR PRACTICE In addition to the type of sensor chosen for an application, understanding where temperature sensors fit into a production line is also key to making the most out of them. To achieve an accurate, reliable and durable performance from industrial temperature sensors, several considerations must be made. First, sensors should be placed in the areas
that represent critical process steps, such as inlets and outlets of heater bundles. Additional
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