Thermocouple cold junction compensation.

You could just put another thermocouple at the junction and
correct with that.

Michael

Herman Family wrote:

How does that work? I use a diode and resistive voltage divider.

Jerry
--
Engineering is the art of making what you want from things you can get.
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It's been too long, but I recall something about wiring the
hot thermocouple to a second thermocouple (backwards) and
then measuring the resultant voltage.

I'd prefer the voltage divider and diode..

Michael

Herman Family wrote:

Yes, but there's more.


I do too for private use. The time to design and calibrate isn't
warranted at a professional hourly rate.

The most accurate reading is had by immersing the auxiliary (reverse
connected) thermocouple's junction in as ice bath. Short of that, one
uses a temperature-dependent voltage that imitates the cold junction
over the ambient temperature range. The cited synthetic cold junction
from Omega is one such.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF

¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF¯AF

Thank you for your reply.  So far I conclude the lowest cost solution
is to use an Analog Device temperature sensor to measure the
temperature of the cold junction.   The phrase reverse connected
thermocouple is one I have never heard before. What exactly does that
mean?

Howard

On Wed, 23 Apr 2008 01:11:40 +0000, Herman Family wrote:


f9df8ab5ba01@d45g2000hsc.googlegroups.com...

That only works if the second thermocouple is at a known temperature.  
Thermocouples only measure the temperature _difference_ between your
local (cold) junction and the remote (hot) junction.  To find the actual
temperature of the hot junction you need to know the temperature of the
cold junction.

Putting another thermocouple at the cold junction will only work if it's
at a known temperature.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Thermocouples can really be a PITA.  Keep in mind that every connection you
make is a potential thermocouple.  In precision circuits, every relevent
juction is accounted for, down to the materials used for the male and
female connectors used for the thermocouple, and even the solder.


--
Scott
Reverse name to reply

Many years ago when electronic circuits were almost totally analogue, I
worked for a chart recorder manufacturer, there we used BC107
transistors mounted on the signal terminal block for CJC but I have no
idea of the circuit arrangment

Steve

hrh1818 wrote: