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RE: COZY: Re: CHT Lead Length

Subject: RE: COZY: Re: CHT Lead Length
From: Robert L. Nuckolls III <nuckolls@aeroelectric.com>
Date: Fri, 25 Feb 2000 08:55:32
 t.au>

>I have a Rocky Mountains engine monitor and plan to set it up to monitor all
>four cht's and egt's.  An electronics savvy friend of mine modified a video
>switching/sequencing kit which has 8 small relays so that I could take 8
>thermocouples and drive them through to the monitor and it would cycle
>through each one in turn (with adjustable delay set by a potentiometer).
>I'm just about to install it now.  Would you anticipate any problems with
>this set-up?

  Can't tell. I think there's a risk that it will not. Video is
  generally carried on coaxial cable with all signals sharing
  a common ground via chassis connections and shielding. Switching
  in this product may well be carried out in manner I've depicted 
  in Figure 14-7A of the thermocouple article found at:

  http://www.aeroelectric.com/articles/excerpt.pdf

  For error free switching of thermocouples, you need two pole
  switching with resonable care to to exactly the same thing to
  both sides of the thermocouple path to avoid introduction 
  of un-compensated new thermocouples that cause error.

>Can I mount it above the radio stack or should I put it
>further away from the panel to avoid any noise getting into the audio
>system?

  Thermocouple wiring carries no noise . . . it may be routed
  with other wires and close to potential noise victims.


       Bob . . .

     --------------------------------------------
     ( The only time you don't fail is the last ) 
     ( time you try something, and it works.    )
     ( One fails forward toward success.        )
     (                     C.F. Kettering       )
     --------------------------------------------
       http://www.aeroelectric.com



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