Abstract: A flame rod inserted in a flame created by the secondary air supplied to a burner is used to generate a flame signal voltage. This flame signal voltage fluctuates with the amount of secondary air available and with the fuel supplied. These fluctuations are relied upon by an integrated control system that utilizes a microprocessor or microcomputer to safely control an induced draft-type of furnace.

Abstract: A combustion control apparatus which controls combustion in a combustor which is a heat source of a hot-water boiler or a hot-air heater includes a memory circuit which generates an alarm signal and also a signal for stopping the operation of the apparatus and which maintains the apparatus in the shutdown state, when an abnormal condition such as abnormal heating or ignition failure is sensed. This memory circuit is protected from malfunction due to noise generated from external output units in the combustion control apparatus by a circuit which detects an abnormality signal with timing other than the timing of generation of noise from the external output units, and the output of this circuit is applied as an input to the memory circuit. The detection circuit is arranged to detect the abnormality signal while receiving clock pulses from a timer as its input, and the phase of its detection timing is selected to be out of phase with the noise generation.

Abstract: A safety device for a gas burner comprises a first ignition nozzle 31 in a pilot burner 3, an inflammable gas guide tube 32 facing the first ignition nozzle, a second ignition nozzle 33 at the end of the guide tube oriented toward a main burner 2, a pressure sensing tube 6 coupled between the guide tube portion near the first ignition nozzle and one diaphragm chamber of a differential pressure sensing device 7, and an automatic valve 4 actuated by the pressure sensing device to close a main gas pipe 1. If the flame at the first ignition nozzle is extinguished the pressure near the beginning of the guide tube increases sharply, which actuates the pressure sensing device 7 to close the valve 4 and terminate combustion.

Abstract: A thermostat is arranged to be responsive to the temperature of flue gases from an oil burning heater and actuates switches when the temperature of the flue gases reaches either a predetermined high value or a predetermined low value. The switches are effective, when actuated by the thermostat, to cut off flow of oil to the burner, either by stopping operation of a pump or by effecting closing of a valve in the oil supply conduit. The thermostat is provided with a latch that holds it in the high temperature position, when that position has been reached so that cooling of the flue gases thereafter will not result in resumption of oil flow to the heater. In one form of the invention the same circuit arrangement can be adapted to control either a pump-fed heater or a gravity-fed heater.