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Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

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

Tungsten
Tungsten, as an alloy in steel, has been known and used for a...

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

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

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

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

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

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

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

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

The Influence Of Size
The size of the piece influences the physical properties obta...

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...



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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