An Automatic Temperature Control Pyrometer

: The Working Of Steel

Automatic temperature control instruments are similar to the Brown

indicating high resistance pyrometer with the exception that the

pointer is depressed at intervals of every 10 sec. upon contact-making

devices. No current passes through the pointer which simply depresses

the upper contact device tipped with platinum, which in turn comes

in contact with the lower contact device, platinum-tipped, and the

circuit is comp
eted through these two contacts. The current is very

small, about 1/10 amp., as it is only necessary to operate the relay

which in turn operates the switch or valve. A small motor is used to

depress the pointer at regular intervals. The contact-making device

is adjustable throughout the scale range of the instrument, and an

index pointer indicates the point on the instrument at which the

temperature is being controlled. The space between the two contacts

on the high and low side, separated by insulating material, is

equivalent to 1 per cent of the scale range. A control of temperature

is therefore possible within 1 per cent of the total scale range.

Figure 131 shows this attached to a small furnace.