Heater resistors apply a controlled level of heat to a specific area. In theory, a given
power input to a fixed resistor will deliver a specified temperature at a specific point.
In some applications, the variance in the heat level applied and its stability is not
important. In others, it is critical. This impacts the type of heater resistor chosen for the application, its design, manufacture and cost.
In this post, we consider the types of heater resistors available on the market. We
also discuss typical applications and performance expectations.
Heater Resistor Performance Expectations
A heater resistor should deliver the required thermal pattern across a heated
surface. This sometimes includes delivering different levels of heat to different zones.
The resistor performance depends on the application. Many applications need a fast
response and ramp-up times. Operating temperatures range from below zero to high hundreds degrees centigrade.
Most applications require robust heater resistors that can survive a specified level of vibration or shock. In some cases, high humidity or chemical elements in the
environment are an issue.
With the increased use of portable devices, size constraints (particularly height) are
a concern. This can be a particular problem in medical applications. Size and
footprint constraints are often the dominant factor when it comes to choosing a
resistor technology.
Types Of Heater Resistor
Fundamentally, heater resistors are power resistors. The dominant types are,
therefore, Wirewound resistors and thick film resistors. The structure of a thick film
resistor makes it ideal for heating applications.
Wirewound resistors are most common where size is not an issue and cost is a key
driving factor. Where film resistors are chosen, the film print can be on a wide range of substrate materials. From steel to Aluminium Nitride, depending on the application requirements.
Thick film resistors are generally smaller than their Wirewound equivalents. They are
lower profile and where space is limited the substrate can be shaped to fit in difficult
to access areas.
Heater Resistors In Medical Applications
Thick film heater resistors are found in a wide variety of medical applications,
including incubation of cultures, to heat fluids before injection, DNA analysis and
diagnostic equipment.
Medical applications require controllable heat delivered to a specific area, often over an extended period, with a uniform steady state.
Repeatability of a procedure is often a requirement in medical applications and this can place demands on the design and construction of the resistor. The space
available to fit the resistor device and access for maintenance or replacement are
common challenges.
Industrial Applications
Industrial applications for heater resistors usually require a rugged and reliable
device. There is a large range of applications, including outdoor enclosure warmers, de-icers, liquid processing, CCTV lens anti-fog and many more.
The choice of the resistor depends on the application and cost limitations. For some
applications, a low cost, low specification device may suffice, in others performance
cannot be compromised, or space may be an issue.
Automotive Applications For Heater Resistors
Applications range from high volume, relatively simple applications, such as heater blowers or window demisters to specialist automotive applications, including fuel heaters on racing cars.
A quick internet search for heater resistors will show many listings for car heater
resistor listings. These are generally low-cost Wirewound devices supplied in high
volume by the major resistor manufacturers.
Heater Resistors In Electronic Systems
Heater resistors are used in a wide range of electronic systems to lower the humidity
or to keep equipment at an acceptable temperature.
As the demand for portable devices continues to grow, so does the demand for
smaller and lower profile devices. This drives demand for thick film rather than
Wirewound devices.
Cost Considerations
Cost is influenced by the specification and, therefore, material selection and
manufacturing processes. It is also directly related to the quantity required.
For lower performance applications costs are low. However, in some applications
(such as automotive) relatively low-performance devices also have stringent long term reliability requirements. This can impact materials and manufacturing processes and increase the cost.
In other applications (such as medical) device failure is not an option. Hence
although cost remains a concern, it is often not the primary consideration.
Where a standard device from one of the major heater resistor manufacturers will not meet the specification a custom heater resistor manufacturer can often deliver a solution in low to medium volume.