Abstract: An electrostatic air cleaner has at least one hole in one of the plates over which air with charged dirt particles is passed. A light source is mounted adjacent to the hole so as to direct its light through the hole. A light sensor detects the level of light passing through the hole. As dirt particles deposit on the plate, they fill in the hole over a period of time, reducing the amount of light passing through the hole. It is possible by measuring the amount of light passing through the hole, to determine the amount of dirt deposited on the plate. In a preferred embodiment, each of the plates contain a hole in alignment with each of the other plates' holes so that light from a single light source can pass through each of the holes. Such a configuration allows both the light source and the light sensor to be located outside of the entire group of plates.

Abstract: A manufacturing method for control devices which incorporate potentiometers whose resistance characteristics other than linearity are subject to unit-to-unit variations, and in which a wiper positioning knob in cooperation with a fixed scale indicates the set point for the controlled parameter, the method involving mounting the potentiometer in its theoretically ideal orientation in the device, affixing the knob to the potentiometer so that a pointer thereon points to the desired location on the device for a predetermined point on the scale when the wiper is positioned to control the parameter to the set point corresponding to the predetermined point on the scale, and marking the scale on the device so that the predetermined point on the scale is at its desired location on the device.

Abstract: A microprocessor watchdog circuit in which a voltage less than a reference voltage is supplied to a comparator substantially only in response to a pulse train status signal having a predetermined repetition rate. Repetition rate sensitivity results from a charge pump connected to receive the status pulse train through a series connected resistor and capacitor having a suitable time constant. The comparator output terminal, at which a reset signal is produced, provides a low impedance path to ground if the charge pump removes charge from a second capacitor more slowly than charge is supplied thereto through a charging resistor, thereby increasing the voltage supplied to the comparator.

Abstract: A digital control system, for a gas-fired, forced combustion air heating appliance, controls operation of a combustion air blower and a gas valve as a function of essentially square wave input signals derived from a thermostat, a combustion air proving sensor switch, and a gas valve control relay. When a first input signal from the thermostat demands heat, the control system first checks for the presence of a second input signal (which indicates the status of the combustion air sensor switch) before starting the combustion air blower. If the second input signal indicates that combustion air is being delivered before the combustion air blower has started, the control system immediately halts the ignition sequence. If the combustion air sensor switch is functioning properly, the ignition sequence continues and the control system checks a third input signal to determine the status of the contacts of the gas valve relay.

Abstract: A control system, for a gas-fired, forced combustion air heating appliance, controls operation of a combustion air blower and a gas valve as a function of signals from a thermostat, a combustion air proving sensor switch, and a gas valve control relay. When the thermostat demands heat, the control system first checks the status of the combustion air sensor switch before starting the combustion air blower. If the combustion air sensor switch indicates that combustion air is being delivered before the combustion air blower has started, the control system immediately halts the ignition sequence. If the combustion air sensor switch is functioning properly, the ignition sequence continues and the control system checks the status of the contacts of the gas valve relay.

Abstract: A control circuit for controlling the speed of a tapped winding motor that includes a set of motor speed selection relays, and a normally open relay connected in series with the set of motor speed selection relays. The motor speed selection relays are connected to the tapped windings of the motor for varying speed of the motor. A microprocessor controls energization of the relay windings upon request for a change in motor speed so that the normally open relay is open before and during any change of state of the motor speed selection relays corresponding to the requested change in motor speed.

Abstract: A control circuit for controlling the ignition time of a control system for a gas-fired combustion air heating appliance comprising a set of potentiometers and a controller for detecting failures in the control circuit. The set of potentiometers are used together to select the ignition time of the control system. The potentiometers are set to produce analog input signals which, when converted to digital signals, have a predetermined complementary relationship (such as one's or two's complement). The controller is connected to the set of potentiometers and includes an analog-to-digital converter which receives the analog input signals from the set of potentiometers and converts them into digital signals. The controller compares or analyzes the digital signals derived from the first and second potentiometers to detect failures in the control circuit and halts operation of the control system if the digital signals do not have the predetermined complementary relationship.

Abstract: A control circuit for a fuel valve in a gas fired furnace controlled by an electronic thermostat is disclosed. The thermostat requires a load current to properly operate, and a pickup and hold circuit along with a time delay circuit are integrated to control a load current circuit to provide the correct load current for the thermostat.

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.