Abstract: In a distributed logic control system, two duplicate analog I/O boards are provided to provide redundancy for the analog I/O boards. The analog I/O boards serve the function of applying analog output signals corresponding to received digital signals from a data processor to analog signal responsive units. Each analog I/O board has a microprocessor and two digital-to-analog converters and a analog-to-digital converter. The microcomputer determines whether the analog output signals generated by the digital-to-analog converters are within limits and, if they are not, it generates a fail signal applied to a programmable array logic circuit. Each analog I/O board includes a watch dog timer to indicate the sanity of the analog I/O board. The programmable array logic circuits respond to the failure conditions indicated by the watch dog timer and the microcomputer to select one of the analog I/O boards to be the operating analog I/O board to provide analog signals to analog signal responsive units.

Abstract: In a sequence-of-events system for a distributed process control system, unfiltered changes in process element status are initially stored at each remote site along with a time tag. Each remote site has an I/O manager board to which are connected a number of individual I/O boards. Each I/O board in turn has connected to it process signal inputs from a number of process elements (e.g., 16), which can be in an "on" or "off" state. Each I/O board includes a change-of-state detector to which the process signal inputs are coupled. The change-of-state detector detects a change of state of any process input and generates an interrupt signal, which is coupled to a microprocessor also located on the I/O board. The microprocessor reads the status of all the process element inputs coupled to the scanner and also the output of a local clock on the I/O board.

Abstract: In a low NOx burner, oil and gas are distributed into the combustion zone from within a central tube, surrounded by an outer tube to define an annular channel between the central tube and the outer tube. A windbox surrounds the inner and outer tubes to introduce air into the annular channel and through openings in the inner tube into the central tube. The central tube and outer tube are sized so that the velocity of air through the outer tube is substantially greater than the velocity of air flow through the inner tube to the combustion zone so that an axial recirculating air flow is generated in the combustion zone. The difference in the velocity of the air streams is maintained small enough so that minimum turbulence is generated in the combustion. The air flow paths are constructed so that no angular rotation in the air flow occurs in the combustion zone.

Abstract: In a triac power switching system, two triacs are connected in series between an AC power source and a load. Each time power is applied to a load, the triacs are tested by first turning on one of the triacs while maintaining the other triac turned off, then turning on both triacs to apply power to the load for a set time interval and then turning off one of the triacs and determining whether power is still applied to the load. If power is applied to the load while either one of the triacs is supposed to be off, an alarm is sounded. In addition, if power is not applied to the load when both triacs are turned on, an alarm is sounded.

Abstract: In a pilot light igniter for a burner, an inner tube for receiving fuel gas is concentrically positioned within an outer tube for receiving air in the annular space between the inner tube and the outer tube. Apertures are formed in the inner tube to impart angular momentum to the fuel gas as it flows from the inner tube into the annular space so that the mixture of air and gas swirls as it flows to the open distal end of the outer tube. A spark disk is provided on the end of the inner tube and a flame rod extends axially from the spark disk. The air and fuel mixture is ignited by a spark produced by high voltage applied between the spark disk and the outer tube. A low voltage source applied between the flame rod and the outer tube causing current pulses provides an indication of the presence of a flame.

Abstract: In an infrared flame detector system an infrared photodetector is positioned to receive infrared radiation from the flame to be detected. The output of the infrared flame detector is amplified with a gain readily switchable between two different gain values. The amplified output signal is filtered by a programmable high pass filter, in which the corner frequency can be selected to have different values and is readily switchable between two different values to correspond with different fuels generating the flame being detected. The output of the programmable filter is full wave rectified to provide a DC signal level corresponding to the AC signal generated across the photodetector. This DC signal level is compared with a reference signal voltage selected to correspond with the signal voltage produced when no flame is present, to provide an indication of the presence or absence of a flame.

Abstract: A damper assembly for closing a duct carrying hot gases. The assembly comprises a damper frame mountable in the duct, a plurality of damper blades supported by parallel blade shafts rotatably mounted in the frame, the shafts having shaft ends projecting from the frame at least one side thereof, blade operating arms secured to the projecting blade shaft ends, and linkage means operatively coupling the blade arms to each other and to an actuating device for opening and closing the damper.