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

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Pyrometers
Armor plate makers sometimes use the copper ball or Siemens' ...

Sulphur
SULPHUR is another element (symbol S) which is always found i...

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

The Electric Process
The fourth method of manufacturing steel is by the electric f...

Quenching
It is considered good practice to quench alloy steels from th...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

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

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

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

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

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

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

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

High Speed Steel
For centuries the secret art of making tool steel was handed ...



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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