GB646078A - Improvements in indication and control of constituent-potentials - Google Patents

Abstract

646,078. Degree of carburization. LEEDS & NORTHRUP CO. Feb. 3, 1948, No. 3186. Convention date, May 30, 1945. [Class 38 (iv)] [Also in Groups II, XXXVI and XXXVIII] Apparatus for measuring and controlling the degree of carburization of ferrous material comprises a metal filament subjected to the same temperature and atmosphere as the work, and means for determining the change in resistance of the filament, which is indicative of the degree of carburization. An element 30 containing the metal filament 31, Fig. 2, is suspended in the furnace C, Fig. 1, and consti. tutes one arm of a Wheatstone bridge W being balanced by an element 40 with the same temperature coefficient, also in the furnace but shielded from the carburizing atmosphere, a predetermined difference in resistance between elements 30 and 40 being determined by the position of the contact 56 of a slide-wire 48 on the bridge W, the attainment of this condition being indicated by the lack of unbalance current through a galvanometer 54, any unbalance current operating relay to control the flow of carburizing medium through valve 21. In a modified circuit, Fig. 3, the automatic compensation for temperature-resistance changes is afforded by thermocouple 66, operating through a detecting instrument 65 and relay to introduce a connection into the bridge circuit by mechanically effecting the position of contact 70 on slide-wire 69, thus compensating for temperature-resistances changes in element 31. The thermocouple 66 and associated circuit may also be used to control the temperature of the furnace. The apparatus may also be applied to control and measure similar processes such as nitriding. Transmitter.-The resistance element 30 comprises a metal wire 31, Fig. 2, threaded through two holes in a ceramic former 33 which has a series of openings 35 to expose the wire to the atmosphere. In another form, Fig. 4, the wire 31 is wound on an oval cross-sectioned former 84 supported between a fixed contact plug 104 at the lower end, and a spring-loaded plug 100 at the upper end, inside a tubular housing 80 of chrome-nickel alloy, with openings 81, 82 to expose the wire 31 to the carburizing atmosphere. The wire-wound former 84 is thus separately replaceable.