Small Diameter Pencil/Cartridge Heaters-Description

Split-Sheath Design
Uniform Heating
Lengths From 1/2" Inch to 6 Inches
1/8" and 4mm Diameters
Unique Hot Tip

Patented high-temperature design provides these advantages:

• When energized, thepatented split-sheath expandsinto contact with surrounding bore for maximum heat transfer, fast response.
• When de-energized, thesplit-sheath contractsfor easy, slide-out removal. Sunrods are guaranteed never to sieze in the bore.
• Uninterruped hot zone andfully heated tipprovides unmatched heat distribution without cold spots. (See upper photo).
• Slender continuous leadssimplify wire management. High flexibility allows free motion when heating "floating" components.
• The result is a miniature cartridge heater offering longer life, uniform temperatures, and easy installation in the smallest devices.

NPH's 1/8" Cartridge Heater with Swaged-In Leads-Simplifies Wiring

Extending Miniature Heater Life:

Designing cartridge heaters with reduced watt-density multiplies service life.

The industry-standard warrantee for electric cartridge heaters is 2000 hours, or one year on single shift. This is a reasonable life expectancy for many applications. But some applications demand much more. Life expectancies of five, seven or even ten years are not unreasonable for some mission-critical applications:

• Blood warmers used in medical theaters must never fail
• Battery conditioners for EVA spacesuits on the International Space Station must last ten years before replacement, due to payload costs
• Here on earth, high throughput semiconductor chip testers must operate without significant downtime for the 5 year life of the equipment. For these applications, a service life of 50,000 to 90,000 hours is a requirement that is both reasonable and attainable.

How can it be done?

For every heater power loading (See "Calculating Watt-Density", at bottom) there is a maximum operating temperature that will guarantee 2000 hours life. This is the "Critical Temperature" for that power loading. (See chart below).

Power Chart - System Temperature versus Maximum Watt-Density

Go above the Critical Temperature by 100 degrees and life will be cut to a third, to 666 hours. But go below it by 100 degrees and heater life will be tripled, to 6000 hours! We can use this relationship to determine the watt-density at a given system temperature that will yield thousands of hours of extra life.

For Example...

How Do You Reduce Watt-Density?

Your heater watt density may not have to be reduced. Many miniature heating applications inherently require relatively little wattage, due to their small mass. This often results in a minimal power loading on a 1/8" miniature heater. In these cases, miniature cartridge heaters are often under-loaded by 200 to 400 degrees, relative to the Critical Temperature. Their 2000 hour life expectancy* may be multiplied up to 81 times!