Abstract: A method and apparatus detect a faulty air switch in a heating system which has an operation cycle comprising a plurality of operating periods. The air switch senses air flow in the heating system and causes air flow limit contacts to open when the air flow is outside a predetermined limit. The air flow is outside the predetermined limit during a first operating period of the operation cycle. A series circuit comprises the air flow limit contacts, coupled in series with other limit contacts between a limit sense terminal and an energized input terminal. The other limit contacts should be closed during the first operating period of the operation cycle. The limit sense terminal is sampled during the first operating period to determine whether the limit sense terminal is energized. Based on whether the limit sense terminal is energized, the air switch is determined to be faulty or operating properly.

Abstract: The present invention is a method and apparatus for changing fuels used in a heating system without substantially recycling the heating system where a main flame burns fuel supplied to the heating system. A fuel changeover signal is received from a fuel selector. Flow of a first fuel to the heating system is regulated in response to the fuel changeover signal to achieve a low fire state in the heating system. A pilot flame is established in the heating system and flow of the first fuel is shut off. A fuel indicator signal is received from the fuel selector indicating a desired fuel. The main flame in the heating system which is burning the first fuel is extinguished. The pilot flame is monitored for stability and the main flame is re-established in the heating system burning the desired fuel in response to the fuel indicator signal.

Abstract: Empty component locations are detected on an assembled circuit board where the component locations are marked with spots of a fluorescent substance before assembly. The circuit board is exposed to stimulating radiation by a radiation source causing luminescence from the spots of fluorescent substance on which the stimulating radiation is impinged. The circuit board is then examined for the luminescence to determine whether the components are between the spots and the radiation source.

Abstract: A burner control system has a microprocessor for testing parameters of operation and for indicating deviations from a preset range for each. The sensors monitoring the parameters provide their outputs as analog voltages to analog to digital (A/D) converters which provide the parameters in digital form. Tests using preset voltage standards increase the likelihood of A/D converter accuracy. In addition, as operating conditions for the burner change, different preset ranges are used for each sensor output when testing them so as to provide maximum confidence of proper burner operation.

Abstract: A method and apparatus monitor fuel pressure in a heating system where a controller controls actuation of fuel valves. A fuel pressure limit signal is provided to the controller for determining if the fuel pressure crosses predetermined thresholds. In order to avoid nuisance shut-downs, the fuel pressure limit signal is ignored by the controller for a predetermined time interval after the controller has actuated a fuel valve.

Abstract: A fail-safe electronic position monitoring system for a motor is specifically described in a flame safeguard system. The same fail-safe system could be used more generally in any type of positional monitoring system using a potentiometer. The potentiometer and its wiper are monitored by a microcomputer which has stored in its memory a profile of at least three critical parameters. The parameters are a low voltage parameter, a high voltage parameter, and a parameter that deals with the rate of the voltage level change. The rate voltage level change includes monotonocity function.

Abstract: An anti-bounce system for control of critical loads is provided. A control system contains two subsystems. The first subsystem functions for normal control of the critical loads, but has a relatively long information processing time. This long time might prevent the system from controlling the loads in a safe manner. The system has a second subsystem that has a very rapid processing time. Both of the subsystems are connected to the load by coupling means to monitor as a feedback signal the exact state of the loads. The second subsystem overrides the first, and disconnects power whenever there has been an interruption of power for a short period of time.

Abstract: A flame safeguard control system using a microcomputer is disclosed. The microcomputer responds to the flame signal as provided from a normal flame amplification chain and an analog-to-digital converter. A safety backup circuit in the form of a redundant flame signal detection circuit analyzes the analog signal being provided to the analog-to-digital converter. In the event that the microcomputer is unable to shut the main fuel valve off, the redundant flame detection circuit becomes operative to deenergize part of a series circuit including the relay for the main fuel valve.

Abstract: A microcomputer control utilizes a nonvolatile memory with an interlock. The interlock functions upon the removal of the microcomputer control from a base or from a mounting surface, and its reinstallation. The removal and reinstallation deletes memory and requires reprogramming. This prevents the removal of a microcomputer control that is protected by battery backup without reprogramming the memory. This safety function is particularly useful in flame safeguard or burner control equipment where the interchange of microcomputer fuel burner controls without reprogramming for the particular burner could create a hazard.

Abstract: A purge time hold circuit is provided in a flame safeguard sequencer to in turn provide a safe start check of a burner control system. If a flame is indicated during a prepurge period, the purge time hold means will reset to a zero status and the timer will hold until the signal clears itself. If the flame signal does not clear itself within a preset time, a safety shut down will be commanded.

Abstract: A flame safeguard sequencer incorporates an interlock checking means that verifies the proper status of the start or preignition interlocks in the burner system and the run interlocks of the burner system. In the event that an interlock opens during a period of time when it should not be open, the system can limit the operation of the sequence to a short time period (typically 30 seconds) to allow the interlock to reestablish a normal running state. If the correct state is reestablished, the system continues normal operation. If the correct state is not reestablished, the system is shut down on safety and a coded fault-hold indicator advises a serviceman of where to find the problem.

Abstract: The high fire and low fire switches normally operated by a damper in a fuel burner installation are verified by a switch test function. In the event that the switches are malfunctioning, the fuel burner sequence is extended to compensate, or the sequence is terminated and annunciated. The extension of the sequence is accomplished by a time sequencer alteration means that is part of a flame safeguard sequencer.

Abstract: A safety circuit which connects a condition responsive circuit to a cyclic signal detecting circuit. In order to provide the cyclic signal detecting circuit with a continuous cyclic input, the condition responsive circuit and a cyclic redundancy checker is provided. The cyclic redundancy checker identifies a specific series of logic bits from the condition responsive circuit and responds favorably only to that series of logic bits. If any other series of logic bits occurs, the cyclic redundancy checker of the system ceases to function, thereby causing the cyclic signal detecting circuit to cease to function and it in turn opens a series contact to deenergize a critical load in a control system.

Abstract: A flame detection circuit means that is responsive to an ultraviolet responsive tube is provided with a safety circuit. The safety circuit encompasses a pulse responsive circuit that is responsive to the characteristic conduction pattern of an ultraviolet responsive type of tube and will not respond to a shunt resistance. The circuit relies on the normal conductivity of a shorting field effect transistor that must be gated into a nonconductive state for an output means to be activated.

Abstract: An electronic network for safe operation of an infrared flame flicker burner control system is disclosed. The network is placed across the infrared flame detector and modifies the detector's action in the event of a flameout so that a refractory shimmer effect is reduced to avoid falsely causing the burner control system to indicate the presence of flame.