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Steel Making

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

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

Nickel-chromium
A combination of the characteristics of nickel and the charac...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

Machineability
Reheating for machine ability was done at 100 deg. less than ...

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

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

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

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

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

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

Carbon-steel Forgings
Low-stressed, carbon-steel forgings include such parts as car...

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...

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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...



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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