A high power heater resistor is often used where the designer needs to apply a highly controlled level of heat to a small area such as in laboratory and medical fluid heating applications. They may also be used in more general applications such as condensation management, and anti-freezing in electronic equipment.
Rapid heating may be required in some applications. This, in turn, requires a high power resistor design, which generally increases the size of the resistor component. However, the size of the heater resistor component may often be limited by application constraints which presents a number of challenges including:
Speed of response.
Once installed the heater resistor component may be difficult to access so it must be mechanically robust, electrically stable and be able to offer a long service life despite exposure to regular temperature cycles.
Current flow through a resistor material produces a proportional heating effect. The challenge in many applications is the transfer of this heat to the surrounding area (or point contact) defined as the thermal efficiency. In medical or laboratory applications resistors may be shaped to make a direct contact with the area to be heated. In other applications, it may be necessary to employ an appropriate heat sink.
Wirewound resistors are suitable for some applications but the superior watt density and speed of response of thick film technology makes it the ideal choice for most applications. Depending on the substrate technology thick film technology can also be shaped to offer point contact heat delivery in some applications and/or fit areas where access or space are limited.
Thick film technology delivers excellent watt density (amount of heat energy emanating from a given surface area), the challenge then is to maximise the thermal efficiency. A common solution is to use a thick film resistor pattern on substrates with excellent thermal conductivity such as specialist steels, stainless steel and aluminium.
There are often trade-offs to be made between the resistor technology, the substrate and the component aspect ratio and dimensions to deliver a heater resistor that is fit for the application and delivers the best solution at an appropriate cost. A close relationship between a specialist thick film resistor manufacturer and the designer usually delivers the best result.