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Athermalization Bellows Assemblies Athermalization Bellows Assemblies FREQUENTLY ASKED QUESTIONS Q: What are athermalization bellows enough that engineers can use it in a well in precision electromechanical assemblies? variety of ways from adjusting optical applications that are sensitive to A: Athermalization (atherm) bellows focus to triggering electro-mechanical temperature. They can be used assemblies are filled and sealed flexible systems at specified temperatures. like thermostats to trigger heat bellows assemblies that translate changes or cooling system valves or other in temperature into precise linear Q: Where is athermalization helpful? components when temperature mechanical motion. A: Atherms are useful in a variety of rises or falls. In precise metering Atherm bellows assemblies take applications. They are commonly used applications, they can adjust advantage of the flexible, expandable in optical applications because of the orifice openings so that the mass flow of nature of precision electroformed metal precision required to maintain the gas or liquid is normalized independent bellows, and the steady volumetric properties of sensitive optics over the of temperature. expansion of incompressible fluids with range of operating temperatures. These assemblies provide changes in temperature. These bellows Other applications put temperature- temperature-dependent mechanical assemblies have known temperature- dependent length change to mechanical actuation without the need for dependent rates of length change use, similar to the operation of a programming or electricity. Their simple, depending upon the fluid used in the thermostat’s bimetallic strip. And robust design lets them operate through assembly. atherm assemblies can shield delicate hundreds of millions of repeatable cycles Each end of the bellows connects to systems from the effects of without drawing power or requiring system components using stock fittings temperature change. recalibration. or custom fittings designed Thus, engineers use atherm bellows to meet customer requirements. These assemblies as back-ups to electrical fittings allow the dimensional change of controls that can continue to operate in the bellows to translate into mechanical the event of power loss. These axial motion that effects the desired assemblies can also entirely displace change in the system. electrical systems with improved reliability and energy efficiency. Q: What is athermalization? A: The term athermalization is Q: How does the bellows assembly most commonly heard in optics Athermalization bellows assemblies provide translate temperature change into applications. Optical engineers use precise temperature-dependent mechanical mechanical motion? atherm assemblies to give their systems actuation without the need for programming or A: The bellows assembly is filled with an optothermal stability, meaning that the electricity. incompressible fluid. The volume of the systems’ optical properties are immune fluid sealed within the bellows assembly to changes in temperature. Q: Where can atherm bellows will expand or contract in response to Athermalization applies to non-optical assemblies be used? changes in temperature. applications, too. More generally, then, A: Common athermalization applications The bellows in the assembly has a an atherm is a device that uses like adjustments to the focal lengths of constant effective area. This constant components which undergo linear, optical lenses or mirrors to prevent effective area combined with the temperature-dependent changes in temperature-related drift are ideal for volumetric thermal characteristic of the length in order to affect or counteract atherm bellows assemblies. In infrared fluid causes linear, axial movement of temperature-dependent changes in the applications they control the flow of liquid the bellows assembly in response to the system. nitrogen or other fluids used to cool the temperature change. In athermalization systems, the rate of black body that is used for IR reference. For example, a bellows might couple to length change is determined by the a rod that controls an orifice, a valve assembly’s makeup. It is precise Atherm bellows assemblies also work stem, or a lens. In each case, Sponsored by Servometer ADVERTISEMENT a different connector is needed. In fact, the majority of bellows assembly connectors are custom designed based on the needs of the application. Q: How do the atherm bellows assemblies operate with respect temperature? A: Atherm bellows assemblies can be designed to operate at temperatures ranging from -130° to 300°F. Each assembly is designed for a specific temperature range which corresponds to range of movement, expressed in length per degree of temperature (i.e. in/°F). The ATHERM BELLOWS specific temperature range and deflection rate depends on the fluid selected. For example, a stock atherm bellows NEW! ASSEMBLIES assembly from Servometer is designed for a temperature range of 10° to 300° F. Within that range, it provides movements of 0.0002 in/°F. This makes it ideal for use in applications requiring reliable precision motion or adjustment in response to the temperature. Q: How big is an atherm bellows assembly? Advantages: A: Precision electroformed bellows come • Precise temperature-dependent mechanical actuation in a wide variety of sizes. Their diameters range from 0.250 to 9 in, and they can be without the need for programming or electricity. as long as 9 in. Atherm assemblies can be designed using any diameter within this • Mechanically modulate heating and cooling systems. range. Suppliers such as Servometer stock components in the most common • Operate through billions of repeatable cycles without sizes, diameters ranging from 0.313 to drawing power or requiring recalibration. 1.625 in. These sizes are readily available for prototype designs and proof-of- • Act as analog back-up solution to electrical controls that concept testing. Custom components can can continue to operate in the event of power loss. be designed for applications with needs outside the above range. “Specializing in Custom Configurations” Q: How can I get the right atherm bellows assembly for my application? Technical Features: A: The design of an atherm bellows assembly is typically application specific. • Temperature Range: -130° to 300° F Consequently, the most effective design • Diameter Range: .020” up to 9” will result from a collaboration between • Length: up to 9” the application specialist and an engineer experienced in bellows design and athermalization. Engineers at suppliers Call 973-785-4630 to speak such as Servometer can work with you to recommend the right assembly given your with an application specialist application’s temperature range and the movement required. www.servometer.com Sponsored by Servometer SVM-MDFAQ-Jan-2018.indd 1 12/08/2017 9:49:15 AM.
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