Originally Published MPMN
Resistors Keep Their Cool
Medical equipment designers can replace bulky conventional heaters with resistive heating elements made of thick film on stainless-steel substrates.
Keeping a low profile has become as necessary to the design of some medical devices as it is to cops on a stakeout. And with lives at stake, the heat is on engineers to employ components that not only aid in maximizing device real estate, but also offer design flexibility and multiple functions. Answering this call is IRC, a supplier of resistive and electronic components, which has created a line of ultra-low-profile resistive heating elements that enable precise temperature control.
Building on the company’s WDBR series of thick-film-on-steel power resistors, this new line of film resistors features a ceramic dielectric glaze that is applied directly onto stainless steel. Because they have fewer layers of heat gradients affecting the element’s thermal-transfer function, the resistors allow for faster, more-precise temperature control than conventional thermal elements. And, unlike traditional heating components that can take up to several minutes to power up and down, these resistive heaters can rise to a desired temperature within seconds. Moreover, they can maintain that temperature for as long as required and then quickly cool down to be touch-safe.
“The thermistor response is less than one second,” says product manager Wilson Hayworth. “The beauty of the product is that there is little thermal mass. When you depower, there is no latent heat.” This capability is not only beneficial for temperature control of such medical devices as blood transfusion warmers, sleep apnea humidifiers, and sterilization equipment, but also translates into significant overall power efficiency.
Available in planar and tubular forms, the resistors are offered in a range of standard configurations. The nonintrusive assembly of the tube-shaped elements eliminates sealing issues and provides direct in-line heating to fluids, according to Hayworth.
But the flexible components lend themselves to customization. “You can design your system around a traditional heater, or you can design the exact heater you need using these resistors,” he explains. IRC can customize the configuration of the resistor on a stainless-steel substrate to perform application-specific functions. To do so, the company uses a screen-printing layout process rather than metal forming to produce a specific heating circuit.
With custom design requests have come several alternative uses for the resistors. Moonlighting as ultra-high-power surge resistors, the elements can be employed to function as low-pass filters in MRI and CT scanners. They can also be used in surgical laser instruments for preheating or to reduce power during idle periods.
IRC Inc., Corpus Christi, TX
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