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Wiring thermocouple wire to read delta temperature

M

Mike in Arkansas

Jan 1, 1970
0
I need to measure the inlet and outlet air temperature of an apparatus
to find the Delta T or rise. Is there a method of wiring the (T type)
thermocouples to read only the temperature rise? I've messed about
with it for a while and done a google search and looked through my tc
manual to no avail. Any help appreciated.
Thanks, Mike
 
D

Don Cleveland

Jan 1, 1970
0
Mike in Arkansas said:
I need to measure the inlet and outlet air temperature of an apparatus
to find the Delta T or rise. Is there a method of wiring the (T type)
thermocouples to read only the temperature rise? I've messed about
with it for a while and done a google search and looked through my tc
manual to no avail. Any help appreciated.
Thanks, Mike

Take a look a the following paper:
http://cfa-www.harvard.edu/cfa/oir/MMT/www.mmto.org/MMTpapers/pdfs/ctm/ctm99
-2.pdf

The first page deals with delta temp measurement.

Using Type T Thermocouples, wiring the Constantans together, and reading the
signal between the two copper wires,
has the advantage of eliminating the junction at the Terminal Block.

Don Cleveland
 
J

John Jardine

Jan 1, 1970
0
Mike in Arkansas said:
I need to measure the inlet and outlet air temperature of an apparatus
to find the Delta T or rise. Is there a method of wiring the (T type)
thermocouples to read only the temperature rise? I've messed about
with it for a while and done a google search and looked through my tc
manual to no avail. Any help appreciated.
Thanks, Mike

Thermocouples are inherently differential.
Could not just a *single* thermocouple be strung across the inlet and outlet
measuring points?.
regards
john
 
S

Spehro Pefhany

Jan 1, 1970
0
Thermocouples are inherently differential.
Could not just a *single* thermocouple be strung across the inlet and outlet
measuring points?.

You need a junction at each measuring point. This is do-able with
three pieces of wire. Doing it the way I suggested removes any errors
from temperature differential between further junctions at the
measuring device. Whether it's one Constantan wire or two closely
similar ones spliced together makes no difference to the output, nor
is the temperature at that "junction" of any great importance (though
I'd not want it too different in case the alloys were not exactly
matched). Making the junctions from three pieces of wire (with the
copper taken from the same roll of wire) would yield the best
accuracy. BTW, thermocouple only approximately measure difference in
temperature, they are nonlinear and also the output is also dependent
on the absolute temperatures.

Best regards,
Spehro Pefhany
 
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