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

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

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

Compensating Leads
By the use of compensating leads, formed of the same materia...

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

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

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

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

The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

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

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

Standard Analysis
The selection of a standard analysis by the manufacturer is t...

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

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

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

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



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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