FAQ: Custom Heater Assemblies

Custom heater assembly that includes a sealed cartridge
heater, thermowell, and thermocouples (multiple).

What is a custom heater assembly?

In general terms, a custom heater assembly is a device that transforms electrical current to heat energy, is designed in a way that accommodates the needs of a unique heating requirement, and is used for the heating of gases, liquids, plastics, or metals.

What is a thermowell?

A thermowell is machined metallic tube used to house and protect sensors or heating elements. Thermowells not only protect heaters and sensors from erosive or corrosive media, they also allow for easy removal and replacement without exposing the process media.

What is a cartridge heater?

A cartridge heater is a cylindrically shaped electric heating element intended to be inserted in holes in metal platens or immersed in flowing media. The design incorporates a ceramic bobbin wound with nichrome resistance wire, carefully centered inside a metallic tube, and then backfilled with magnesium oxide (MgO), which provides electrical insulation. Cartridge heaters can be either swaged (compacted MgO) or un-swaged (loosely filled MgO). Swaging allows for maximum heat transfer to outside surfaces while keeping internal heater temperatures as low as possible, and preserving dielectric qualities.

What is a sealed cartridge heater?

A sealed cartridge heater incorporates all of the characteristics of a standard cartridge heater but is additionally sealed with BCE’s proprietary epoxy seal making it vacuum compatible. The seal additionally elongates heater life, especially in high humidity and moisture environments.

What electrical tests are performed on heaters?

Heaters undergo 3 main electrical tests: Resistance, MegOhm and Hipot.

A resistance test is performed using a fluke meter to ensure that the heater is manufactured within the correct tolerances of the electrical specifications. Heater leads are connected directly to the fluke meter leads to perform the test.

A MegOhm or Insulation Resistance test is performed using a megohmmeter. As its name implies it tests for any breakdown in a heater’s insulating material. The test is performed by supplying low to medium voltage to the insulating material for a small period of time.

A Hipot test is also used to assess the dielectric strength of the heater’s insulating material. In addition to performing a Dielectric Withstand Test like the Megohm, it can also perform a Dielectric Breakdown Test. This means that the heater insulating material is shocked at very high voltages until failure is achieved. This is more commonly performed on samples as it destroys the heater.

What is a thermocouple?

A thermocouple is a thermoelectric device that measures temperature. When the wire junction of its two dissimilar metals changes in temperature, a small voltage is created. The voltage is then used to calculate the temperature using the thermocouple’s reference table.

What is an RTD?

RTD stands for "resistance temperature detector". It is generally constructed of a fine and pure metallic wire wound around a ceramic or glass core. The relationship between wire resistance and temperature is used to sense the temperature of other devices.

Electric Heating Element in Thermowell for Vacuum Applications, with Feedthrough and Multiple Thermocouple Sensors

Click on image for larger view.

BCE has designed a high temperature electric heating elements with thermowell, type K thermocouples, and the vacuum feedthrough all in one package. Referred to as the "High-Temp Vacuum Thermowell Assembly", it provides researchers and vacuum equipment OEMs a robust, laser-welded design integrating heating element, vacuum feedthrough, and multiple type K thermocouples.

The thermocouples can be easily mounted to any part in a vacuum chamber by the means of shims with mounting holes. Furthermore, they can be positioned with ease due to integrated compression fittings, which also allow for easy replacement of the thermocouples should the need arise.

A 304 Stainless Steel flange achieves a vacuum tight seal into any vacuum or degassing chamber port and there is virtually no outgassing, enhancing performance in high-vacuum environments.

Finally, a cartridge heater embedded inside an Aluminum 6061 thermowell allows for uniform and efficient heating of the chamber.

Scientists, researchers and engineers can all benefit from this high vacuum, barrier-breaking design.

For more information visit this link, or call BCE at (510) 274-1990.

Vacuum Thermowell and Heater Assembly Simultaneously Heats and Monitors Semiconductor Wafer's Temperature

BTU requirement and temperature control are critical in the fabrication of silicon wafers in the semiconductor industry. Seldom can a product provide both a thermally effective means to heat wafers and simultaneously monitor their respective temperature. BCE’s Vacuum Thermowell and Heater Assembly achieves both of these criteria. Its aluminum thermowell houses a cartridge heater capable of supplying uniform heat, which can be monitored through an embedded thermocouple.

Furthermore, a flange at the end of the thermowell allows for easy installation into any vacuum port and provides an effective seal via its dovetail O-ring groove. An aluminum construction further ensures that the entire assembly remains lightweight and inexpensive to machine, reducing overall product cost. Moreover, multiple RTDs are hermetically sealed into the thermowell to allow for precise temperature monitoring of wafers and other components while maintaining vacuum integrity. They can be positioned and designed for any application, as can the thermowell. In order to prevent any outgassing and minimize release of contaminants into the chamber, the RTDs are sealed using BCE’s proprietary epoxy meeting NASA’s low outgassing spec and are available with Kapton leads.

Check out the BCE Vacuum Thermowell & Heater Assembly web page for more detail.