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

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

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

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

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

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

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

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

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

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

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

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

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

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

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

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

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



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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