>
>Bob,
>
>I posted this basic question to the RV-list and got no response...
Sorry, I must have missed it. I scan through about 300 pieces
of list-server traffic a day looking for items on which I can
be helpful . . . they slip by from time to time. . .
>I have a single cylinder CHT system. I'd like to buy 3 more thermocouples
>and run four thermocouples to a 4 way switch, then through a ~6" wire to the
>gauge.
>
>I usually see dire warnings about changing the length of the thermocouple
>leads. What's the scoop?
Thermocouple lead length is critical only for the old, self-powered
termocouple instruments of WWII vintage. Many of these instruments
had accessory resistors mounted external to the instrument so that
the installer could change the lead length and then recompensate
using the external resistor. ANY electronic instrument that reads
thermocouples is not so crippled. You can get a short tutorial
on thermocouples at:
http://www.aeroelectric.com/articles/excerpt.pdf
>Also, IF I can't do it that way, could I determine a baseline with a CHT
>probe installed per plans, write down those readings, then hook up the
>(innacurate?) 4 cht system with the switch to see relative differences for
>the purpose of balancing CHT's through baffle mod's? After balancing the
>temps, I could go back to the one CHT system.
It's both practical and not too difficult to put a two pole,
4 position switch in your thermocouple pathways following the
guidlines in the above article. To make the termocouple wires
solderable with ordinary tin-lead solder for switch connections
you need to first "tin" the ends with silver solder. The silver
solder will make the thermocouple alloy solderable with ordinary
materials at more benign temperatures friendly to the rotary
switch.
There are commercial, off the shelf thermocouple switches that
allow you to simply strip the wire and capture it under a screw
driven clamp. Most of these are bulky ol' hogs . . . not terribly
friendly to a modern, tightly spaced lightplane panel.
>Thanks in advance,
>
>Kyle Boatright
>
>
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 )
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http://www.aeroelectric.com
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