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Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Chromium when alloyed with steel, has the characteristic func...

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

Vanadium has a very marked effect upon alloy steels rich in c...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

The Thermo-couple
With the application of the thermo-couple, the measurement of...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

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

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

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

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Correction For Cold-junction Errors


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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