shuts down the furnace in the event of any one of a number of possible sensed faults self testing occurs automatically before an attempt at ignition and during furnace operation proper functioning of the sensor which senses for induced air flow through the burner combustion chamber is tested prior to enabling a fan which causes that induced air flow air flow is confirmed by sending to and receiving back from the sensor a sequence of pulses should air flow not be sensed during a combustion period combustion is terminated a flame sensor is provided for determining the presence of a flame in the combustion chamber during times when a flame should be present pulse sequences are sent to and received back from the flame sensor to confirm that a flame is present when it is known that no flame is present if sent pulses are received back a fault has occurred and the system locks out if at any time any pulses are received when none were sent the system also locks out application_number US 34929689 A description referring first to fig2 an integrated burner control for a gas burner is illustrated the system includes a gas valve control relay 11 which is operable upon command from the integrated burner control microprocessor 13 to open a gas valve and supply gas to a burner combustion chamber the microprocessor issues a command to open the gas valve on line 15 which passes through driver transistor 17 to energize the relay coil 19 closing normally open contacts 21 and opening the normally closed contacts 23 the furnace or burner includes an inducer fan for supplying air to the burner combustion chamber and a pressure sensor of a conventional diaphragm type for sensing air flow caused by operation of.