-20 degree C

Discussion in 'General Electronics Chat' started by bug13, Jul 24, 2013.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi guys

    I may need to design a timer to control something under -20 degree C in high amplitude, what are the problem I will need to solve and what advice do you have for me.

    Is it going to be very hard, or easy?

    Any info is appreciated, thanks guys!!
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    -20C isn't *that* cold -- but some things don't work well at such temps, like LCD displays and Alkaline batteries.

    If you need a display, use LEDs. If you need a battery(ies), use Lithium.

    Also, keep in mind that voltage regulators, references, crystals, crystal oscillators are designed to have their nominal values around 25C. You will need to compensate/adjust these things if accuracy is desired.
     
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  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    High amplitude? Did you mean high altitude?
     
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  4. WBahn

    Moderator

    Mar 31, 2012
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    You will want to pay the extra money for Industrial Grade components since most Commercial Grade components are only rated to 0°C or perhaps -10°C.
     
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  5. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks for your info, I am glad that -20 isn't that cold. :)
     
  6. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks for correcting me :)
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Being from Florida, have you ever experienced -20°C? Of course, being originally from Wisconsin, I know the natives often say it's getting a little "nippy" out when it gets that cold. :rolleyes:
     
  8. joeyd999

    AAC Fanatic!

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    -20C would be unbearable to me. But electrons -- they don't mind so much, *usually*.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Oh c'mon, that's only -4°F. Cold yes, but hardly unbearable. Great running weather. And yeah, I'm just 2 miles south of the Wisconsin border. ;)
     
  10. crutschow

    Expert

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    It's interesting the BJTs tend to slow down as it gets cold while MOSFETs speed up. I've actually worked on CMOS multiplexers that work down to around 10°K for cryogenically cooled IR detectors.
     
  11. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    That's very interesting to know, thanks.

    Have you come across an app note that talk about all the think I will need to know when designing a circuit at low temperature?
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    MOSFETs also speed up as the temperature goes up. This makes them a good choice for bore-hole instrumentation in deep wells. The speed up for each are due to different mechanisms. IIRC, the slowest temp is not too far away from room temp.
     
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  13. bwack

    Active Member

    Nov 15, 2011
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    As for wiring you will need wires with insulation material that doesn't crack in the freeze. I don't remember all the kinds.

    I've had trouble with power cables from a batterybox to a light on the bicycle handlebars in winter time. The cable shorted the battery durring a cold ride. Then I switched the cable, and the same happened again after the next ride in the cold. It was a spiral cable with multiple wires inside and it had the standard pvc insulation material. The insulation had cracked and shorted the + and - wires. Probably due to stress and stiff/frozen material.

    Then I read somewhere that a nordic distributor of some chinese led bicycle lights (magicshine?) switch the original cables with silicone coated wires for "nordic conditions" (cold). :) There are other matierals too. Anyway, mind the insulation material at -20C !
     
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  14. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    That's useful for me, thanks!

    That lead me to think, Do you think the PCB will crack too?? As the timer I mention in my OP, it will be mounted somehow on a little rocket. So I think it will have quite a bit of vibration too when it launch.
     
  15. bwack

    Active Member

    Nov 15, 2011
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    I haven't heard of problems with pcb's in the cold.
    Rockets, that sounds like a stressing environment, but for a small pcb maybe not that critical as for a larger pcb mounted in a housing that can bend, vibrate or expand to heat/cold.

    I must pass on this one I don't know.
     
  16. crutschow

    Expert

    Mar 14, 2008
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    For high stress environments you can encapsulate the PCB in a solid potting compound. We did that for electronics in a smart canon shell that was subject to about 20,000 G's when the shell was fired. For that, the IC bond wires between the IC chip and the pins needed to be aluminum since gold wires (often used in high rel ICs) were so dense they would sag under that much force.
     
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  17. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks crutschow, encapsulate the PCB in a solid potting compound sounds like a good idea, I have never thought of that.

    Do you need to use a crystal oscillator in your design? Does the acceleration at launch have a big impact on the reliablity of the clock? I'm hoping to have at least +/- 10ms accuracy of my timer.
     
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