Automatic flame detector and ignition controller for gas burner - uses programmable unijunction transistors driving thyristors and relays to provide flame detection and controlled delays before re-ignition

摘要

The power stage is connected to the AC mains and includes the solenoid valve and the ignitor, which are connected through relay contacts. The validation stage is supplied via transformer from the AC mains. A programmable uni-junction transistor is used to detect the flame using electrodes in the flame. The transistor removes the trigger voltage from a thyristor, releasing two AC supplied relays, thus closing the solenoid valve. Simultaneously, contacts on one of the relays initiate a timing circuit comprising a second transistor, whose anode is grounded viaa capacitor which requires a set time to charge, triggering another thyristor and activating two relays which open the solenoid valve and attempt re-ignition.