From: Jim Yanik
Date: 1/17/2004 10:17 AM Central Standard Time
Message-id:

(B2431) wrote in
:

From: Jim Yanik
Date: 1/16/2004 6:53 PM Central Standard Time
Message-id:

"John R Weiss" wrote in
news:Sp%Nb.73504$nt4.98595@attbi_s51:

"Phil Miller" wrote...

Yes really, on every jet engine TIT is Total Inlet Temperature.

Yep.

I ask because I came across an interesting paragraph in the
T56-A-15 service manual yesterday. Went like this...

...measures the turbine inlet temperature by means of
thermocouples...Eighteen thermocouple assemblies are mounted in the
turbine inlet casing of each engine...One thermocouple of each
assembly is connected to the turbine inlet temperature indicating
system, and...one...is connected to the electronic datum control
system. The 18 indicating system thermocouples are connected in
parallel [!!] by the indicator turbine thermocouple harness
assembly,

I'm surprised you ever doubted the truth on this one!


So, let's revise.

That's going a bit too far... Nobody can revise the Tarver
Chronicles! :-)


bimetallic thermocouples generate millivolt signals,and paralleling
them would not work.Standard practice is to series-connect them,and
compare to a reference junction.Do these assemblies include signal
processing to convert the mV signal to a digital form,which could then
be sent on a parallel bus?

--
Jim Yanik
jyanik-at-kua.net

On every aircraft I ever worked on thermocouples were in parallel if
there were two or more.

Dan, U.S. Air Force, retired


Well,I guess they aren't bimetallic thermocouples,then.
Anyone have any speculation on what sort of signal will work with a
parallel connection?

--
Jim Yanik
jyanik-at-kua.net


All thermocouples are bi-metallic.

OK, try this on for size. Jet engines use chromal-alumal (type K) and recips
use iron-constantan (type J) thermocouples. The wires are also made of the same
type of material. If you mount several thermocouples in parallel then all plus
wires match and all minus wires match. As far as the cold junction end is
conserned the hot end has one thermocouple.

If you mount them in series you get plus -- minus -- plus-- minus etc. This
will introduce one heck of an error if it works at all.

If you ever get a chance to look at a jet engine look at the EGT ring of
thermocouples. You will see they are in parallel.

Dan, U. S. Air Force, retired