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Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Case-hardening Treatments For Various Steels
Plain water, salt water and linseed oil are the three most co...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

Compensating Leads
By the use of compensating leads, formed of the same materia...

Lathe And Planer Tools
TO FORGE.--Gently warm the steel to remove any chill is parti...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

Double Annealing
Water annealing consists in heating the piece, allowing it to...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Drop Forging Dies
The kind of steel used in the die of course influences the he...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....



Correction For Cold-junction Errors






Category: PYROMETRY AND PYROMETERS

The voltage generated by a thermo-couple of an electric pyrometer is
dependent on the difference in temperature between its hot junction,
inside the furnace, and the cold junction, or opposite end of the
thermo-couple to which the copper wires are connected. If the
temperature or this cold junction rises and falls, the indications
of the instrument will vary, although the hot junction in the furnace
may be at a constant temperature.

A cold-junction temperature of 75 deg.F., or 25 deg.C., is usually adopted
in commercial pyrometers, and the pointer on the pyrometer should
stand at this point on the scale when the hot junction is not heated.
If the cold-junction temperature rises about 75 deg.F., where base metal
thermo-couples are used, the pyrometer will read approximately 1 deg.
low for every 1 deg. rise in temperature above 75 deg.F. For example, if the
instrument is adjusted for a cold-junction temperature of 75 deg., and
the actual cold-junction temperature is 90 deg.F., the pyrometer will
read 15 deg. low. If, however, the cold-junction temperature falls below
75 deg.F., the pyrometer will read high instead of low, approximately
1 deg. for every 1 deg. drop in temperature below 75 deg.F.

With platinum thermo-couples, the error is approximately 1/2 deg. for
1 deg. change in temperature.





Next: Correction By Zero Adjustment

Previous: Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer



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