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Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

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

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

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

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

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

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

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Annealing Method
Forgings which are too hard to machine are put in pots with ...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

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

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

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

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Hardness Testing
The word hardness is used to express various properties of me...

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

The crankshaft was the most highly stressed part of the entir...

Compensating Leads


By the use of compensating leads, formed of
the same material as the thermo-couple, the cold junction can be
removed from the head of the thermo-couple to a point 10, 20 or 50
ft. distant from the furnace, where the temperature is reasonably
constant. Where greater accuracy is desired, a common method is
to drive a 2-in. pipe, with a pointed closed end, some 10 to 20
ft. into the ground, as shown in Fig. 128. The compensating leads
are joined to the copper leads, and the junction forced down to
the bottom of the pipe. The cold junction is now in the ground,
beneath the building, at a depth at which the temperature is very
constant, about 70 deg.F., throughout the year. This method will usually
control the cold-junction temperature within 5 deg.F.

Where the greatest accuracy is desired a compensating box will
overcome cold-junction errors entirely. It consists of a case enclosing
a lamp and thermostat, which can be adjusted to maintain any desired
temperature, from 50 to 150 deg.F. The compensating leads enter the box
and copper leads run from the compensating box to the instrument,
so that the cold junction is within the box. Figure 129 shows a
Brown compensating box.

If it is desired to maintain the cold junction at 100 deg.: the thermostat
is set at this point, and the lamp, being wired to the 110- or
220-volt lighting circuit, will light and heat the box until 100 deg.
is reached, when the thermostat will open the circuit and the light
is extinguished. The box will now cool down to 98 deg., when the circuit
is again closed, the lamp lights, the box heats up, and the operation
is repeated.

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Previous: Correction By Zero Adjustment

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