[DeTomaso] (no subject)

[Edward A. Nauman]

Asa Jay,

 

The problem with T/C's is the non-linearity and the ice-point reference
compensation required.  Any dissimilar metal junction will form a
thermocouple (Seebeck effect) which will

produce a current when there is a temperature difference across the
junction.  When the thermocouple wire transitions to copper (or brass on the
gage) it forms another thermocouple

in series with the measurement thermocouple and hence generates an offset
voltage proportional to the temperature at that location (cockpit in this
case).  There are I.C.'s like 

Analog Device' AD595 that perform the reference temperature compensation as
well as a scaled linearized output (mV/deg F) that work well, but you would
still have to match the output

to the current drive required by a particular gage.  It's not difficult if
you have a background in electronics.  There are cockpit turbine outlet
temperature (TOT) indicators in aviation that are driven directly from a
thermopile (several T/C's in parallel).  Thermopiles can generate enough
current to drive a meter but the difference is that the cockpit temperature
variation is trivial compared to

turbine exhaust temps.  A 25 degree offset to a 1000 degree measurement
temperature isn't a lot of error when reading an analog gage, but 25
compared to 212 is.  If you are really interested in accurate temperature
measurement (or any kind of measurement for that matter) email me off line
and I would be glad to help you.

 

 

 

>I was querying if anyone had thought about using s TC or RTD for a  

>temp sending unit, and if so, what kind of analog gauge they could  

>hook it to, that would look good as a replacement for the stock gauge.

 

 

 

Edward A. Nauman\

C.E.O.

Smart Litez Inc

 

Palmdale, CA. 93551

(661) 305-7636