AN AUTOMATIC TEMPERATURE CONTROL PYROMETER
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 completed 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.
FIG. 132.—Portable thermocouple testing molten brass.