GB1412495A - Flame guard - Google Patents

Abstract

1412495 Flame sensors ELESTA AG ELEKTRONIK 18 Jan 1973 [26 Jan 1972] 2632/73 Heading F4T A flame sensor for a burner provides for an initial external luminosity test at a higher sensitivity than is used for flame sensing during operation, the sensor including a voltage operated switch S, and resistors R2, R3 and the coil RV 1 of a motor or solenoid operated fuel valve connected together or a voltage divider across the supply rails Ph, O, the junction of resistors R2 and R3 being connected to a light detector F and to switch S and the junction of resistor R3 and coil RV 1 being connected to a contact tr1, operated by an electrically heated actuator TR, to provide for a first and a second mode of operation when contact tr1 is open and closed respectively, the voltage developed at the junction of R2 and R3 in the first mode in response to any signal from the light detector being sufficient to operate switch S and prevent the burner from operating should detector F provide a signal before actuator TR heats sufficiently to close contact tr1, and the voltage developed at said junction in the second mode being sufficient to operate switch S only when the burner is producing a flame. On closure of a thermostat Th, a burner motor M, the heater TR and an igniter ZT are energized and if detector F senses that ambient luminosity is below a predetermined level a relay R of switch S remains initially de-energized, and heater TR subsequently closes contacts tr1 to energize fuel valve RV1 and place the circuit in its second mode, and also releases a member (33), Fig. 4 (not shown), initially blocking operation of a contact al by relay R. If a flame is produced, photoresistor detector F causes ignition of a cold cathode tube Ro thereby energizing relay R which then opens a contact a2 and changes over contact al to de-energize heater TR and maintain the valve open, igniter ZT remaining energized via al, trl until TR cools to move contact trl back to a terminal 49 which may be used to energize a further fuel valve for two-stage operation; contact al is also effective in this state to maintain the circuit in the second mode with R3 in parallel with R2. If the flame goes out, relay R drops out and a new start-up cycle, including ambient light sensing, is initiated. If during any startup the ambient luminosity is such that relay R is immediately energized, contact a2 opens whereby igniter ZT is de-energized and valve RV1 is not energized, but, since in this condition member (33) prevents relay R from operating contact al, heater TR is energized to operate contacts (tr2), Fig. 4, to effect shut-down. Contacts (tr2) also cause shut-down if ignition is not effected within a predetermined period following opening of valve RV1.