Patent GB-628556-A (GB)
Title: High temperature elastic-fluid temperature-responsive system
IPC: G01K1/00
Filed: 1946-06-27
Abstract: 628,556. Thermometers. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. June 27, 1946, No. 19306. Convention date, July 13, 1945. [Class 97 (iii)] [Also in Groups XXXV and XXXVIII] The temperature of a very hot fluid is measured by passing it through a conduit in which its temperature is reduced, and measuring the volumetric and the mass flow through the conduit as well as the pressure in the conduit, from which the temperature can be calculated by the gas formula. One or other of these factors may be kept constant so that the other factors vary with temperature. As applied to the measurement of temperature of a high temperature (1700-3000‹ F.) fluid in a conduit 10, Fig. 1, a small proportion of the fluid is bled off into a conduit 11 containing an orifice 12, where it is cooled by fins 11a to a workable temperature and finally exhausts to the atmosphere. The differential pressure hw across the orifice 12 controls the bellows 13 connected to oppose the torque of a spiral spring 14 and adjusting the inductor 15 which, with resistor 16, forms an impedance bridge across the alternating current supply 17. The unbalance voltage derived from mid-points 15a 16a is fed to an amplifier and phase shifter 18 whose output controls a two-phase motor 19 which mechanically rewinds spring 14 and restores the bellows 13 at the same time as it adjusts contact 20a of a voltage divider 20. A second two-phase motor 32 is controlled from the output of an amplifier and phase shifter 33 which amplifies the unbalance voltage obtained from an impedance bridge consisting of an inductor 27, varied by the differential pressure over a second orifice in tube 11 by means of bellows 25 and spring 26, an adjustable resistor 28, a resistor 30 varied by static pressure in the tube 11 as measured by pressure-responsive device 31 and a resistance thermometer 29. The displacement characteristics of 27, 29 and 30 are such that the operation of motor 32 is proportional to the mass flow w through conduit 11. By means of a two-position clutch 33 motor 32 can operate either to maintain this flow constant by means of throttle 42 or to rebalance the impedance bridge and position the moving contact of a voltage divider 21 having an inverse square law characteristic so that its positions corresponds to the valve 1/w<SP>2</SP>. As voltage divider 20 is fed with A.C. through voltage divider 21 the signal from its movable contact at terminals 20b is indicative of the factor hw/w<SP>2</SP>, i.e. the inverse of the density of the fluid. If the fluid in conduit 10 is maintained at a constant pressure, this signal will also vary linearly with the temperature of the fluid in conduit 10. When pressure P in the conduit 10 is not constant, a pressure-responsive device 35 sets the position of a movable contact 36a of a voltage divider 36 fed by A.C. from the movable contact 20a so that the electrical signal at contact 36a is proportional to Phw/w<SP>2</SP>, i.e. the absolute temperature of the fluid in the conduit 10. This signal is balanced against that of the adjustable contact 37a of a voltage divider 37 by rebalancing amplifier 39 and twophase motor 40. This signal appearing at terminals 41 may be used for indicating, controlling, or recording purposes, and a scale is also provided with voltage divider 37 on which the temperature may be read. In a modification the apparatus derives measurement representative of the average temperature of the fluid flow at a plurality of points.