Patent GB-417203-A (GB)
Title: Improvements in or relating to temperature indicating apparatus
IPC: G05D23/20
Filed: 1933-04-13
Abstract: 417,203. Regulating combustion. BAILEY METER CO., 1050, Ivanhoe Road, Cleveland, Ohio, U.S.A.-(Assignees of Ryder, J. D. ; 11448, Euclid Avenue, Cleveland, Ohio, U.S.A.) April 13, 1933, No. 11092. Convention date, April 14, 1932. [Class 51 (i).] In a temperature measuring and controlling apparatus, the temperature-sensitive elements are arranged in a Wheatstone bridge, the galvanometer of which controls the operation of indicating devices and a control device through the medium of two electron-discharge devices. The Figure shows a system for indicating and recording temperatures of a furnace 1 and for regulating the supply of fuel through a valve 3. The thermocouples 4, 5 arranged within the furnace and the exit thereof respectively are adapted to be switched alternately into a bridge circuit by a motor-driven cam switch 33, the bridge circuit comprising a battery 43, against which the thermocouple E.M.Fs are balanced, and a galvanometer 46. Associated with the thermocouples 4, 5 are balancing resistances 44, 45 and motor operated indicating and recording apparatus 10, 18 which are switched into the bridge simultaneously with the associated couple. The needle 48 of the galvanometer is adapted to be clamped in a fixed position periodically by a motor-driven cam 61 and contacts 49, 50 on pivoted levers 51, 52 operated periodically by cams 54, 55, co-operate with a contact on the pointer to control valves 66, 70 which control the motors 9, 17. Assuming the thermocouple 4 is switched into circuit and a variation of temperature occurs, the galvanometer pointer is deflected in one or other direction and is clamped in the deflected position. Simultaneously, the levers 51, 58 are allowed to approach each other in order that one or other contact 49, 50 may engage the pointer contact. This contact is closed for a time dependent on the deflection of the pointer so that the grid potential of the associated valve is correspondingly controlled. Normally the valves are supplied from the A.C. mains 28 through transformers 73, 75 and are biassed to pass unidirectional current in the plate circuits, but when contact is established at the galvanometer pointer the grid potential of the corresponding valve is altered to stop the plate current. The motor 9 associated with the thermocouple 4 has its field windings 7, 8 connected in circuit with the primary windings of transformers 73, 75 so that normally the fields are equal and opposite and no rotation occurs. When, however, the plate current of one of the valves is stopped the equality is upset and the motor rotates in the appropriate direction. The motor controls the contact arm 10B which varies resistance 45 and restores the balance of the bridge. The galvanometer pointer is restored to the " null " position in which it is out of the range of action of the contacts 49, 50 so that the condition of the motor circuits is restored to normal and the motor stopped. The motor also positions index arm 10 relatively to a scale 11 and produces a record on a clock driven chart 12. Similar balancing and recording apparatus driven by a motor 17 is provided in association with the thermocouple 5. In a modification, both arms 10, 18 operate over a common scale and recording chart. A motor 26 is connected in parallel with the motor 9 and operates a valve 3 to regulate the fuel supply. Variations in the temperature of the cold junction of the thermocouple are compensated by a variable resistance 47B the contact 47A of which is controlled by a bi-metallic strip. The bridge circuit is periodically standardized by a standard cell 95. A cam switch 76 periodically disconnects the thermocouples and connects the galvanometer in a bridge circuit including the standard cell 95 and the battery 43. If adjustment is necessary the galvanometer operates a motor 92 which regulates resistance 93. In a further modification, a single motor controlling balancing, indicating and recording is alternately operated by the thermocouples 4, 5.