GB1376019A - Burner control systems - Google Patents

Abstract

1376019 Burner control assemblies HONEYWELL Inc 16 Feb 1972 [15 March 1971 (2)] 7262/72 Heading F4T A control assembly 12 for a gas or oil burner 13, which burner has an igniter 40, flame sensor 43 and a fuel supply 37, is adapted for connection to a condition sensor 23, and comprises energizing conductors 45, 55, a timing switch 61 having normally closed 63 and normally open 62 contacts, a first solid state controlled switch Q1 in series with the switch 61 between conductors 45, 55 and connected to contacts 62, 63 respectively via means 21 for operating a safety switch having normally closed contacts 17 and means 60 for operating switch 61, a biasing network 47, 48 to operate switch Q1 in the absence of burner flame, a second solidstate controlled switch Q2 connected between conductor 45 and igniter terminal 28 and having a control circuit 86, 87 connected to a junction 57, and a third solid-state controlled switch Q3 for operating the fuel supply and connected in series with a holding circuit 73 of a relay 70, the relay 70 when energized providing an operating signal for the switch Q3 and having operating means 71 connected in series between the switch Q1 and contacts 62 of switch 61 closing of thermostat 23 applies alternating current from supply 10, 11 to a fan 33 and to a main circuit and bias circuit of triac Q1 to trigger triac Q1 thereby energizing timer heater 60 of time switch 61, which is initially in the position shown, and triggering triac Q2 to conduct to produce a spark at gap 41 of spark igniter 40. After 10-20 seconds heater 60 causes bimetal 59 to act on switch 61 to charge position to connect terminals 64 to 62 thereby de-energizing heater 60 and providing current through triac Q1, held in conduction due to bias at point 50, to an incandescent light bulb 71 and starting heating of a heater 21 of a normally-closed safety switch 17. Bulb 71 acts on photoresistor 72 causing triac Q3 to conduct lighting neon bulb 73 to latch triac Q3 "on" and thereby energize solenoid 39 of fuel valve 36 to allow fuel flow to burner head 34 for ignition by sparking at gap 41. Photo-cell sensor 43 senses the flame at head 34 and then shorts the bias to triac Q1 which thus turns off turning off triac Q2 in turn. After ignition a circuit through terminals 62, 64 and diode 93 energizes winding 42 to continue sparking at gap 41. After heater 60 has cooled down switch 61 reverts to the illustrated position removing an effective short across solenoid 38 of valve 35 which thereby opens to provide a second stage of fuel flow. Safety features are provided in that if triac Q1 shorts heater 21 operates to open safety switch 17 to lock the control out with the fault is manually rectified. Shorting of triac Q2 merely provides a constant ignition spark. If triac Q3 shorts, current through diode 85 on conduction of triac Q1 heats heater 21 to open switch 21. Diode 85 also acts in the event of a flame failure when operating to open switch 17. A further safety switch 14 is provided which opens in response to an unsafe limit condition, for example it may be a boiler low water cut-out or a temperature responsive switch.