outgassing

[zappedagain]

This Electrical Engineer is working on some electronics that will be in a small enclosure with free space optics in an industrial application. Are there any standards for outgassing limits for optical components (I don't want to fog the optics). Space electronics use TML (total material loss) and CVCM (collected volatile condensable material) specifications (1% TML and 0.1 CVCM). Are there similar specs for optical components?

Z

 

[IRstuff]

There probably is, but I've NEVER seen one imposed, even in military systems

TTFN
faq731-376

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[zappedagain]

Interesting. This may be apples and oranges, as I see some RTV compounds qualify for space applications, but the optical engineers that I know avoid RTV like the plague.

Z

 

[racookpe1978]

Hmmmn.

(1) ar eyou in a pure vacuum environment, where the outgassing will be the only gas being generated?

Are you in a "controlled ventilated" (atmospheric) but very "pure" atmosphere like a IC chip maker cabinet, where atoms/cubic meter matter?

 

[zappedagain]

I'm in a hermetic enclosure, so my gases are controlled. My light source is a 9 micron fiber optic, so while I don't think I'll be counting atoms, any obfuscation above 0.9 micron in diameter could have a significant effect.

Z

 

[racookpe1978]

Tough call.

It is always easier for a company (an engineer) to call out some "official" specification so the contract appears more "official" than it really is. And, by appearing fficial" the contract often gets by review back in back offices easier than if the specifications are made up to fit the real world as it really is. 8<)

Ain't gonna be the case here.

If the outgassing is going to cause a major impact, and if in your judgement as an engineer responsible for the assembly the owner and bid-receiver of the contracted part and assembly are going to be affected by the outgassing of material from the part being bought - then, well, you HAVE to specify in the contract that "Materials supplied will NOT out gas no more than 0.0001 of (material) at (1.234 of wyyz concentration of vacuum at 3.455 of pressure after 1.234 of hours of exposure at 5.678 degrees (C?/F?) for 6.789 hours measured by jklmnop calibrated instrument at s.tuvwy temperature conditions."

YOU are the person writing the contract. For $$$,$$$.$$ YOU get to write the specifications that are needed.

 

[zappedagain]

Contract, what contract? I just get to design it to the poorly written spec and then take responsibility if it fails. My optical engineers want it 'clean'. Space electronics want 1% TML and 0.1 CVCM. I expect I'll end up somewhere in between.

Z

 

[racookpe1978]

Well, the "contract" is your specific written requirement to another person to the work.

Now, if you are "buying" goods or services from another company, then - well, yes, it is a formal contract we are used to seeing complete with bid specifications and warranties, and "lawyer-talk" about money, etc. But a 'contract": is also a simple drawing or requirement for a welder and supplier in the back office to buy and install a resistor or a motor, weld up a fabricated support for the motor, and hookup a battery strong enough so the rocket motor vibrations won't break both the motor and battery.

What does help while writing the contract/drawing/specification/purchase order is a formal ANSI or NASA or MIL-SPEC because those have been tested and people are used to seeing them. They might be more rigorous than what you need, thus more expensive. But they are also "expected" and so can be delivered at the higher price. A local specification from a local single company might be more expensive, and you are making assumptions - as you wrote above - about the trade-offs.