Temperature Sensors and Controllers for Cartridge Heaters
Published March 4, 2019
The sensor for the control of part temperature is an important factor in application design. Sensors should be placed between the working surface of the part and the heaters. Measuring the temperature of the part approximately 1/2” away from the heaters is generally recommended. Note that this value was used to develop the Fit Graph that is commonly used in the election of the maximum allowable Watt density (see Frequently Asked Questions on the next page). Depending on the application, there are a variety of other temperature sensors and controllers that can be used. One of the more popular sensor types used for cartridge heater applications are surface mount sensors. Thermocouples,RTDs and Thermistors are available with either an adhesive backing or the ability to be cemented to the surface being heated. There are also bolt on and magnetic surface mount type sensors available.
Control of power is also an important consideration, particularly in high Watt density applications. Inexpensive on-off controls are frequently utilized, but they often result in wide excursions in the temperature of the working parts and the heaters which can significantly shorten their life. Thyristor power controls and other digital temperature controllers are valuable in that they effectively eliminate on-off cycling which substantially extends the life of high Watt density heaters, they come in many different sizes with many output and input choices. Thermocouple and RTD inputs are the most popular with a DC pulse output. DC pulse outputs allow the user to use larger relays to switch the heater load.
