Tuesday, September 12, 2017

Example of a Large Vacuum Chamber Used at NASA

Facility 238 is a large, vertical, cylindrical thermal vacuum chamber which is used for thermal vacuum and thermal balance testing, and baking out spacecraft hardware. Test articles are normally loaded through the top of the chamber using the building crane; however, small payloads can be transported through the personnel entrance. Ports for electrical feedthroughs, liquid/gas feedthroughs, and viewing are located around the perimeter of the chamber. A clean tent at the chamber entrance provides class 10,000 cleanliness conditions.

Mode of Operation


With the chamber dome rolled back, the overhead crane is used to lower the payload onto the support fixture. In most cases, special fixturing must be designed due to the uniqueness of the test article support system. Once installed, the payload is instrumented and connected to the ground support equipment via feedthroughs. Access to the chamber is throught a clean tent. The use of cleanroom procedures and the wearing of clean garments are required when working in the chamber.

Initial chamber evacuation is provided by two rotary piston mechanical pumps, with four closed cycle cryopumps for high vacuum pumping. Each cryopump is isolated from the chamber by a sliding gate main valve to allow off-line cool down and regeneration.

Parameters

  • Test Pressure: 5 x 10-7 mmHg
  • Shroud Temperature: GN2 mode -90°C to +90°C , LN2 mode -190°C
  • Chamber Pump: 4 cryopumps
Physical Characteristics
  • Test Volume: 12' x 15'
  • Payload Support: Floor level - 4' square platform
  • Side Wall: Hardpoints at 6' and 12' levels
  • Crane Capacity: 5 tons Viewports: 9" diameter
  • Standard Electrical Feedthroughs: 36 - 37 pin connectors (RF feedthroughs available on request)
Integral Instrumentation
  • Pressure: Capacitance manometer - Atm to 10-3 mmHg
  • Ion Gauge: 10-3 mmHg to ultimate
  • Payload Temperature: 324 channels of thermocouple or thermistor channels
  • Contamination Monitor: TQCM, coldfinger, residual gas analyzer

Friday, September 8, 2017

Custom Heating Element for Lab Mice Stabilization During MRI

Custom electric heating element for laboratory
Custom electric heating element developed for keeping
mice warm during MRIs.
Cancer researchers in the UK have developed a special electric heating system to keep lab mice warm during MRI's without electromagnetic radiation effecting the quality of the MRI.

Compatibility between MRI machines and resistive, electric heaters has been a challenge to manufacturers of heating devices. MRI's and electric heaters don't like each other because of the electromagnetic field given off by DC and standard AC voltages. That E/M field disturbs the image resolution and quality of the MRI.

In research and lab testing, mice and other rodents are examined via MRI technology. In order for the rodents to be compliant with the testing procedure, the mice are given anesthesia which lowers their body temperatures and can send them into hypothermia. In the past, this situation was corrected by warming the air around the animal sufficiently to warm their body. Air heating requires a significant amount of valuable space, so a different heating source that would both not conflict with the MRI output and also provide a more compact, economical solution was required.

While DC voltages and standard AC voltage caused problems with the MRI, the solution turns out to be a copper wire element, embedded in heating blanket, and powered by AC voltage in a frequency ranging between 10-100 kHz. 

Conclusion

High frequency electrical heating provides a simple means by which stable body temperatures can be maintained in the mouse. The space requirement for the heating apparatus around the mouse is minimized and the system can be extended to use arbitrarily shaped resistor systems. Image and spectral quality are not adversely affected by the presence of the AC used in the heater so MRI performance is not compromised. As such a new MRI-compatible mouse heating system has been developed and validated.

To read the entire article, An MRI-Compatible High Frequency AC Resistive Heating System for Homeothermic Maintenance in Small Animals, visit this link.

Wednesday, September 6, 2017

Polyimide Thermofoil Heaters Used for Space Applications

Thermofoil heaters of an all polyimide (adhesive-less) construction are used for high reliability space applications. They are ideal for extreme temperature fluctuations and have high tear and tensile strength. The specifications for the design and manufacture of these heaters are rigidly controlled, and rightly so. These heaters often perform critical heating application on satellites and other space craft.

Construction

A polyimide (Kapton) is used as the heater base material, also known as the substrate or mounting surface. A second polyimide layer over the heating element provides a protective enclosure.

Heater Element

The heating element is made of a Ni-600 Inconel (nickel-chromium-iron) alloy. Single or dual resistive elements may be used in the design, but the element must be must be of a single layer in cross-section. The element are normally an etched foil design with uniform in cross-section, and they have a minimum trace width of 0.010 in. (0.0254 cm) by design. Spacing between foil traces is tightly controlled and must not be less than 0.010 in. (0.0254 cm). The spacing between the outer foil trace and the heater edge (border trim) also cannot be less than 0.010 in. (0.0254 cm).

Lead Wires

Lead wires must be a minimum of 26 gauge when using high strength copper alloy conductors, and 24 gauge for all other copper conductors. Lead wire insulation must consist of polyimide (Kapton), polytetrafluoroethylene (PTFE/Teflon), or ethylene-tetrafluoroethylene (ETFE) materials.

Lead Termination


The termination of the lead wire has to be welded and contain a minimum of two weld points between the lead wire and landing bond pad. Lead wire terminations also need to be enclosed in a hardened Hysol epoxy potting, in order to secure lead wires to the heater so that lead pull stresses are not transmitted to the weld joint.
Power Rating

Polyimide thermofoil heaters used for space have a maximum power rating of 4.5 W/in2 (0.7 W/cm2) when suspended in still air at 25°C, although this specification is for test purposes only and is not indicative of the maximum power rating in application (with heater mounted to a heat sink). Actual rated power (or voltage) are specified in each application.
Visit this web page to view or download the entire NASA General Specification for Thermofoil Heater, All- Polyimide, Space Applications.

Thursday, August 31, 2017

Rapid Response Electric Heaters Designed for Clean Gases and Liquids

Mini Clean Flow Heater
Mini Clean Flow Heater
In advanced technologies such as analytical, biomedical, pharmaceutical, aerospace, electronics and laboratory applications, special purpose electric heating elements are required for heating high purity fluids and gases. These applications require rugged design, fast heat-up, tight control, high temperatures and the ability to withstand exposure to harsh solvents and corrosive gases. They also must be constructed in a way to prevent contamination of the process media.

The use of standard screw plug immersions heaters, screwed into a stainless steel welded vessels (known as circulation heaters) are almost always a misapplication for these unique requirements. Circulation heaters create more problems due to leaks, material compatibility, poor controllability, and bulky size.

BCE, a northern Californian manufacturer of custom heating elements offers it's Mini Clean Flow Heater specifically for these applications. These heaters are designed for heating "clean" liquids and gases normally found in fuel cell, bio-med, laboratory, food, semiconductor and pharmaceutical applications.

The Mini Clean Flow Heater operates in a liquid or gas stream providing very fast response times and accurate control capability.

The heating elements in the Mini Clean Flow Heater are isolated electrically from the process media, protecting them from contaminants and providing long life.

Summary:
  • Designed for heating of clean gases or liquids
  • Gas flow passes over an enclosed heated body; not exposed to resistive elements (Nichrome)
  • All parts exposed to gas flow are constructed of 304 stainless (other material available)
  • High temperatures
  • Custom wattages, voltages, inlet and outlet fittings (NPT, SAE, BSP &VCR) are available.
  • Made in U.S.A.

For more information, visit http://heater.belilove.com

Monday, August 28, 2017

Custom Electrical, Pneumatic, and Optical Feedthroughs

Equipment manufacturers and scientific researchers are continually challenged with supplying power, fiber-optic, control, and monitoring cables into (and out of) sealed vacuum vessels. Whether due to space restrictions, special geometries, or number and type of conductors, standard glass-to-metal or ceramic feedthroughs never quite fit the bill. Unfortunately, because of limited options, many designers are forced to compromise and go for an off-the-shelf solution.

You don't have to fit a square peg in a round hole anymore. Choose BCE custom feedthroughs for your next design.

http://www.belilove.com/feedthrough
(510) 274-1990

Monday, August 21, 2017

Kapton (Polyimide) Etched Foil Heating Elements

Kapton (Polyimide) Etched Foil Heating Element
Kapton (Polyimide) Etched Foil Heating Element.
According to Wikipedia, "Polyimides have been in mass production since 1955. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e.g. high temperature fuel cells, displays, and various military roles. A classic polyimide is Kapton ..."

Kapton etched foil heating assemblies are constructed from a very thin etched foil circuit embedded between two layers of Kapton, or one layer of Kapton and some other material (such as alumina.) The result is a heater with features perfect for a wide variety of industries - from aerospace, to medical and scientific equipment, to research & development applications. 

Kapton heaters provide excellent heat transfer to adjoining surfaces with the release of minimal contaminants through the use of this very low mass, low outgassing, high dielectric material.  They provide very even heat distribution extremely fast heat-up and cool-down rates. Additionally, they can be constructed in just about any shape, size, wattage or voltage. They are also ideal for applications where distributed wattage (heating profile) is required. 

Furthermore, when the heater and ceramic insulator is bound in such a way to meet NASA’s low outgassing specification, Kapton heater assemblies are ideal for use in vacuum applications.

For more information, visit http://heater.belilove.com. Also, take a fast look at the video below.

Thursday, August 17, 2017

9 Pin Vacuum Feedthrough: UHV Compatible Technology Serving the Semiconductor Industry

Some of the most stringent tolerances and vacuum requirements exist in the ever-expanding semiconductor industry. Tight restrictions in vacuum ports, high temperature applications and exposure to high stress environments further add to the challenge of designing an electrical feedthrough that can be manufactured quickly and installed with ease. An American multinational manufacturer of chips and microprocessors approached BCE with these exact requirements in order to replace their existing vacuum feedthroughs incapable of providing an adequate performance in ultra-high vacuum environments. Furthermore, their existing supplier had long lead times and the procured feedthroughs needed to be replaced often as their contacts would fail due to oxidation formation on the conductive layer.

SCOPE
  • The feedthrough needed to satisfy the following requirements: 
  • Ultra-High Vacuum (UHV) compatibility up to 1 X 10-10 atm.cc/sec 
  • Remain operable at temperatures exceeding 250°C 
  • Pins preventing oxidation of conductive layer for longevity 
  • 9 pin feedthrough configuration 
  • Voltage requirement: 750 AC RMS 
  • Current requirement: 7 AMPS 
  • Quick-turnaround on feedthrough manufacturing 
  • Robust seal withstanding high stress environments 
  • Ease in installation, simple design 
  • Low cost for application 
OUTCOME

All customer requirements were exceeded by BCE’s 9 pin vacuum feedthrough. Not only did it meet all electrical and configuration specifications, it provided a vacuum compatibility twice as much as that required by the customer allowing them to expand their capabilities to higher vacuum thresholds. It also remained operable at higher temperatures, nearing maximums of 300°C. Furthermore, the gold plated pins proved to be ideal in the prevention of oxidative layers inhibiting current flow. Moreover, BCE’s proprietary ceramic seal achieved the desired robustness and allowed the feedthrough to remain operable under high stress conditions. Finally, the client was equally impressed by BCE’s quick-turnaround time and competitive pricing.