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

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

Connecting Rods
The material used for all connecting rods on the Liberty engi...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

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

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

Care In Annealing
Not only will benefits in machining be found by careful anne...

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

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

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

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

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

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

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

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

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...



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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