A microcontroller controlling a fuel valve (35) allows for more than one trial time in a furnace system, while using only one pin of the microcontroller. An alternating current signal at an input port (20) of the microcontroller causes the microcontroller to allow a first long trial time period. Any direct current signal at the input port causes the microcontroller to allow only a second shorter trial time period. The trial time input port (20) of the microcontroller is placed between two other ports (15, 25) which either receive or send direct current signals.

Microcontroller and system for controlling trial times in a furnace system

A solid-state fail safe gas valve system in which first and second gas valves are arranged in series in a gas passageway, the valves being actuatable by first and second solenoid operators respectively, the second operator requiring a voltage greater than the operating voltage supplied to the valve system to achieve actuation. The operators are separately energized through microprocessor controlled switches so that a capacitor connected across the second operator and its switch is pumped to a voltage above the supplied voltage by voltage induced by interrupted energization of the first operator.

Fail-safe gas valve system with solid-state drive circuit

A microprocessor-based power switching circuit responds to a common form of noise by disconnecting power from the controlled apparatus. The microprocessor provides an alternating voltage when power is to be provided, and the alternating voltage is converted by a detector circuit to a voltage close to ground which cuts off a transistor. When the transistor is cut off, an interface circuit places a thyristor which performs the actual power switching, into conduction. Noise on the base of the transistor can only drive it into conduction which then puts the thyristor into non-conduction.

Interface circuit for low power drain microprocessor-based thermostat

A fail-safe gas valve driver circuit controlling the gas supply line of a gas burner, which circuit in its essential circuit elements (FIG. 1) includes an appropriate switching means (S1) effectively feeding a pulsed DC wave form into the rest of the valve relay driver circuit, operatively consisting only of a capacitor (C1) in series with a gas valve relay (K1), which in turn is in parallel with a diode (D1). In operation, the valve relay coil is energized by charging the capacitor with the switch connected to a positive DC voltage source (V dc ; FIG. 1A), and then grounding the positive end of the capacitor (switch connected to ground) applying a negative voltage across the coil of the relay (FIG. 1B). When the capacitor is again connected to the positive DC voltage source by the switch, the current in the relay coil is sustained by the diode (FIG. 1C). The switch is operated at a sufficiently high rate so the current in the relay coil has insufficient time to decay significantly during the charging cycle of the capacitor before being replenished during the capacitor discharge cycle. With this circuitry the gas supply valve (G.V.) will always go to, or be maintained in, a closed position, regardless of what component(s) of the valve relay driver circuit might fail or deteriorate. Any inadvertent supply of gas to the burner due to any component failure is avoided without any component redundancy. Two exemplary, transistor switching circuits are described (FIGS. 2 & 3).

Fail-safe valve relay driver circuit for gas burners

An arrangement for driving actuator coils for two or more driven devices employs a microprocessor or similar controller and an actuator driver circuit The actuator driver circuit controls two or more relay actuator coils from a single microprocessor output terminal This output terminal can provide a high, low, or pulse output signal An amplifier switching device, such as a transistor, whose base is coupled to the output terminal of the microprocessor, drives the first relay actuator coil as its load A rectifying diode is connected to one end of a capacitor and thence through a negative resistance device to a second relay actuator coil or other driven device The coil impedances are selected so that the second coil has a significantly higher impedance than the first coil When output pulses appear at the microprocessor output terminal, the transistor switch pulses on and off, and thus energizes the first coil Flyback voltage pulses pass through the rectifier diode to charge up the capacitor until its voltage exceeds the threshold voltage of the negative resistance device Then current flows to energize the second relay actuator coil By selecting the appropriate pulse rate, the microprocessor can energize either or both actuator coils

Energy preservation and transfer mechanism

A fail safe drive circuit for enabling the relay which in turn opens the valve for supplying gas to a burner is disclosed and includes a pair of field effect transistors both of which must be operating properly to enable the relay. One transistor receives an enabling input from a rectifier circuit and will be enabled only if the alternating input signal is of sufficient magnitude and repetition rate. The other transistor is turned on and off by the alternating input signal and the gas valve will be turned on only when each of the transistors is operating in its intended mode. The circuit thus discriminates against false enabling signals such as a direct current signal, line voltage signal, a non-repetitive alternating current signal, or other spurious signal.

Victor F. Scheele

Papers

Fail safe gas valve drive circuit