Patent GB-388773-A (GB)
Title: Improvements in and relating to heating installations
IPC: G05D23/24
Filed: 1931-05-20
Abstract: 388,773. Electric selective control systems. BARON, H., 231, Strand, London.-(Soc. pour le Perfectionnement de la Chaufferie ; 4, Rue de Mondovi, Paris.) May 20, 1931, No. 14916. [Class 40 (i).] Apparatus for controlling and regulating heating installations or industrial furnaces comprises a plurality of like sources of direct current potential connected together at a common point, one or more resistance elements connected in series with each of these sources of potential to form a plurality of branch circuits, these branch circuits being connected together at a common point at their ends remote from the sources of potential, and a bridge connection comprising regulating apparatus connected between the common point of connection of the sources of direct current potential and the common point of connection of the branch circuits. The values of the resistance elements and current sources are so chosen that normally no current flows in the bridge connection. At least one of the resistance elements is variable with temperature and is exposed to a temperature determining the heating control whereby an unbalance of the resistance elements due to temperature variation causes a current to flow in the bridge connection which operates the regulating apparatus to effect the heating apparatus control. Preferably two like sources with two branch circuits are employed. Resistances variable with temperature exposed to the external, interior, and/or heating temperature may be connected in one branch circuit. The regulating apparatus may effect the heating control in a variety of known ways. for example by controlling the draught or the admission of fuel to the furnaces of the boiler supplying hot water or steam to the heating installation, the mixers regulating the proportions of hot and cold water supplied, or the operation of pulsator mechanism which intermittently circulates the heating fluid at a variable frequency. According to Figs. 1 and 2 two like sources of potential 29 are connected at 31. In series with one of the sources there are resistances 32 exposed to the external temperature, 33 kept at the temperature of the radiators and 34 exposed to the temperature of the place being heated. The other branch' circuit comprises 'a resistance invariable with temperature but capable of manual variation. Between the point 30 of 'connection of the branch circuits and the point 31 is connected a galvanometer 36, the needle of which as shown in Fig. 2 is provided with a screen 37 moving between a light source and two like photoelectric cells 38, 39 connected in series with two like batteries 29a. According to the direction of movement of the screen 37, a relay 42 is influenced in one direction to lower the heating temperature or in the opposite direction to raise it. The resistance 34 or the resistances 32, 33 may be omitted. The resistances 32, 33, 34 may alternatively be connected in parallel. According to a modification for controlling hot water or steam systems, Fig. 3, the regulating apparatus comprises a sensitive electric motor 44 connected in series with a rectifier 55 between a point of connection 45 of two sources of potential comprising the secondaries of transformers 51, 52 and associated rectifiers 53, 54 and a point of connection 46 of two branch circuits, one comprising a resistance 47 exposed to the atmospheric temperature and a resistance 48 exposed to the temperature of the place to be heated or the heating fluid, the other comprising fixed and variable resistances 49, 50. Normally the working of the boiler furnace is at its maximum. When the internal temperature rises above the balancing value the motor rotates at a proportional speed and closes a contact 65 exciting thereby an electromagnet 63 and actuating a mercury interrupter 62. An electromagnet 60 thereby excited attracts a pawl 59 and puts in operation a clockwork commutator 58. The conducting sectors of the commutator establish for a determined time a current in a heating resistance 56 of a thermally sensitive device which acts in known manner to reduce the temperature of the boiler. At the same time a cam 69 and contact 68 short-circuit the resistance 49 and rectifier 55 causing the motor 44 to reverse and break the contacts 65, 68. The cycle of operation repeats until equilibrium is attained. If the boiler lacks fuel a current flows through a rectifier 72 and apparatus 73 which records the time during which the boiler remains underfed. According to another modification, Fig. 4, the resistance 49 is omitted. When too much heating is being provided, the motor 44 by clockwise rotation of a cam 89 closes a contact 90 and heats a resistance 92. This closes contacts 94, 95 and operates an electromagnet 60 which reduces the heating as in Fig. 3. If the heating temperature becomes too low the cam 89 rotates in an anticlockwise direction closing a contact 91 and stopping the motor by the abutment of the edge 96 against the blade 87. This heats a resistance 98, closes contacts 99, 100, and opÚrates an alarm through a relay 101. Additional' controlling means are provided comprising a mercury thermometer 108 exposed to the temperature of the place to be heated and provided with a series of contacts 102, 103, 104, &c., which are connected through parallel resistances 105; 106, 107 and the mercury column of the thermometer across the secondary of the transformer 52. Variations in the temperature of the thermometer cause a variation of load on the transformer 52 and appropriate regulation by means of the motor 44. Alternatively the resistances 105, 106, 107 may be mounted in parallel with the resistance 50. An indicating galvanometer 109 the central zero of which is hidden by a screen 110 may be placed in parallel with the motor 44. Apparatus may also be so constructed that it accelerates the working of the boilers when the temperature relations are disturbed. A device may then be provided which maintains the apparatus in an accelerated condition until the boilers reach a predetermined pressure, for example the actuation of the regulating apparatus may close a holding circuit which operates through contacts closed by a mercury manometer when the boiler pressure is too low.