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Technique for Controlling the Temperature of Diffusion Furnaces

IP.com Disclosure Number: IPCOM000078944D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Dunkel, WE: AUTHOR

Abstract

The present system consists of a master furnace using a platinum resistance thermometer at the highest possible temperature.

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Technique for Controlling the Temperature of Diffusion Furnaces

The present system consists of a master furnace using a platinum resistance thermometer at the highest possible temperature.

The recent development of platinum resistance thermometers into practical devices, permits a reference point which does not change in accuracy or precision with time and temperature. Previous thermocouples could not be maintained at a temperature without a continuous loss in accuracy. The master system is then used to calibrate control thermocouples. With the addition of look- up tables or digital-to-digital conversion, the resistance signal is transformed into an equivalent voltage signal. This signal is fed to a digital process control computer, for controlling all furnaces which contain individual thermocouples within their control loops.

A master signal is used to compensate for the aging of the loop thermocouples. The frequency with which correction is required is a function of temperature and time, as well as the permissible drift in accuracy permissible for the heat treatment. The present computer-controlled thermocouple calibration system compensates for the drift that is inherent in thermocouples. This avoids breakage of control thermocouples, errors introduced by transfer of accuracy to control thermocouples, and from control thermocouples onto internal furnace control systems. In addition to these disadvantages, previous techniques required skilled man power for the...