Patent GB-613116-A (GB)
Title: Improvements in or relating to electric temperature-responsive devices
IPC: G01K7/34
Filed: 1945-09-28
Abstract: 613,116. Temperature-indicating systems. MURRAY, E. A., COURSEY, P. R., STEATITE & PORCELAIN PRODUCTS, Ltd., and DUBILIER CONDENSER CO. (1925), Ltd. Sept. 28, 1945, Nos. 25273/45 and 30965/46. [Class 40 (i)] [Also in Groups XXXV and XXXVI] In a temperature indicating, recording or controlling system the temperature-sensitive device comprises a condenser having a temperature-sensitive ceramic dielectric based on alkaline earth titanates, e.g. as disclosed in Specification 574,577, [Group XXXVI], having a permittivity exceeding 100 at normal room temperatures and a pronounced peak in its permittivity temperature curve, e.g. as in Fig. 10 (not shown). By using various proportions of barium titanate, strontium titanate and calcium titanate for the ceramic the peak can be moved along the temperature axis as desired so that sensitive measurements, using only those portions of the curve on one or other side of the peak where the slope is substantial, can be made throughout the range - 80‹ C. to well above 100‹ C. Preferably, the ceramic dielectric forms a small openended cylinder 100, Fig. 12, with outer and inner silver electrodes 101, 102, formed thereon by spraying, firing or cathodic dispersion. The outer electrode is soldered to a metal cap 103 sealed to an outer tube 104 of thin metal or glass or ceramic metallized to facilitate attachment of the metal cap 103 and to provide an electric connection between the electrode 101 and the terminal '109. The upper end of the tube 104 is sealed by an insulating plug 105 through which is sealed a wire 106 connecting the inner electrode 102 to terminal 108. Figs. 13 to 15 (not shown) illustrate further constructions where the outer electrode is contacted by the atmosphere and the cylindrical condenser is sealed at its upper end to the tube 104. The capacity of the condenser or its variations may be measured in any suitable way, e.g. by an A.C. bridge method wherein the temperature is indicated or recorded either by the amount of manual adjustment of the balancing arm to achieve balance, or by the intensity of the out-of-balance current, Figs. 1, 2 (not shown). Fig. 3 shows the temperature-sensitive condenser 20 connected in a bridge circuit balanced at a temperature determined by the adjustable condenser 21. Unbalance of the bridge resulting from a variation of the condenser temperature causes energization of a relay 28 to break the circuit of the heating or cooling (as appropriate) circuit 29 for the chamber 30 housing the condenser, thereby stabilizing the temperature thereof. The balancing arm 21 of the bridge may comprise a further temperature sensitive condenser similar to 20, but kept at a constant temperature so that the difference between two temperatures may be indicated, recorded or controlled. In an alternative arrangement, Fig. 5 (not shown), the temperature-sensitive condenser is connected in the tuned grid circuit of a valve oscillator, variations in temperature resulting in corresponding frequency changes of the oscillator, being indicated on a frequency meter (indicator or recorder) in the anode circuit. The variable frequency may be heterodyned with a fixed frequency and the beat frequency measured to indicate the temperature, Fig. 6 (not shown). The fixed frequency may be derived from a stabilized oscillator, or, as in Fig. 7 (not shown), from an oscillator also controlled by a temperature-sensitive condenser so that the beat frequency serves as a measure of the difference of two temperatures. A null method may be used to measure the beat frequency variations. To stabilize the temperature of a chamber 69, Fig. 8, a temperaturesensitive condenser 60 therein controls the frequency of an oscillator 62, the output of which is fed to the tuned grid circuit of a detector 65. The valve output is sufficient to operate a relay 66, only under resonance conditions, to break the heater circuit 67 for the chamber 69, thereby stabilizing the temperature at a value for which the frequency of oscillator 62 is slightly off tune. The arrangement may be used, alternatively, for controlling the tuning of the grid circuit 63, 64. In Fig. 9, temperature-sensitive condensers 60, 70 control respectively the frequency of the oscillator 62 and the tuned grid resonant frequency. Resonance, corresponding to identical temperatures of the condensers 60, 70, is indicated by an audible or visual device 71 in the detector anode circuit. Subsequent variation in temperature in either of the condensers is indicated by the amount of adjustment of impedance 72 necessary to restore resonance. In all cases, the frequency measuring device 28, 66 may be replaced by a warning indicator or operate a thermostat. Specification 601,109, [Group XXXVI], also is referred to.