A flame detecting apparatus in which a detecting electrode is disposed in a flame, the base of a transistor is connected to the detecting electrode and biased with a predetermined DC voltage derived from a biasing circuit, the biasing circuit including a resistor and the impedance of the flame, an AC signal is applied to the emitter of the transistor, and an amplified AC signal is derived from the collector of the transistor as an output signal; the output signal being used as a control signal for a fuel supply control and/or an indicator.
An improved electrical circuit for controlling the operation of a gas solenoid valve which regulates the flow of gas to a burner. Field effect transistors, whose operation is controlled by a flame rectification circuit and/or a timing circuit, directly control the operation of a relay which, in turn, operates the gas solenoid valve, thus eliminating the need for much more complicated circuitry to effect actuation of the gas solenoid valve.
The invention relates to a control circuit for a semi-conductor power element, comprising a circuit generating a signal synchronous with the variable current supply signal of the semi-conductor power element, and a logic circuit with high input impedance to receive directly, on the one hand, the said synchronous signal and, on the other hand, the low strength detection signal and which is such that the delay circuit is combined to the high input impedance logic circuit to prevent the production of control pulses on the electrode controlling the semi-conductor or power element, if one of the components of the control circuit should become faulty. The invention finds an application in burner control and safety devices.
A circuit arrangement for utilizing the "flame (or hot gas) rectification" effect in an air gap is provided in which the air gap is defined between electrodes one of which is connected to a source of A.C. and the other of which is connected to earth or other suitable potential. A non-linear resistance device is connected in series with the air gap and a voltage sensing is provided for detecting a voltage across the non-linear resistance device, the arrangement being such that when no flame or hot gas is present in the air gap the air gap and the non-linear resistance device are virtually open-circuited so that the A.C's alternated by filter means to zero volts D.C. with a small ripple, superimposed thereon at the input to the voltage sensing circuit, whereas when flame or hot gas is present in said air gap the non-linear resistance produces a negatively predominant signal which after filtering provides a negative D.C. voltage shift with a small percentage A.C. ripple superimposed at the input to the voltage sensing circuit.
A flame measuring device, in particular for use in a regulating device for a burner, includes an ionization electrode which is arranged in a flame region of the burner. An ac voltage is applied to the ionization electrode whereby a dc voltage component is superimposed on an ionization current that flows through a resistor connected to the ionization electrode. The flame region influences the ac voltage and the dc voltage at a blocking capacitor unequally, and allows an ac voltage component to be separated from the dc voltage component by way of a first means. The separated ac voltage component can be compared to a separated-off dc voltage component by way of a second means in order to produce a pulse width-modulated signal.
A flame responsive control circuit means has been disclosed which responds to the flame in a burner. The response is to the sudden rate of change of the resistance or impedance of a photocell upon the loss of flame. The two embodiments disclosed both utilize a rate of change sensing means to determine that a loss of flame has occurred. If a loss occurs, ignition is reinstituted immediately and the system either operates normally or locks itself out in a safety shut down.
