Abstract: A networked air measurement system includes a sensor capable to measuring a characteristic of an air sample, the sensor having an air inlet port; a backbone tube in communication with the air inlet port of the sensor; a plurality of air intake valves in communication with the backbone tube, air admitted through one of the plurality of air intake valves communicated into the backbone tube; an air flow induction device in communication with air in the system, air moved by the air flow induction device from the plurality of air intake valves through the backbone tube, to the sensor; and a controller connected to the sensor and to each air intake valve, the controller executing a control sequence which opens and closes air intake valves to admit air and form air samples communicated to the sensor. The system controller may use time intervals or measurements of air samples to determine proper times at which to open individual ones of the air intake valves.

Abstract: A resonator as disclosed that has a plurality of resonating chambers having a predetermined size that attenuate sound in a conduit. The resonator may be disposed along the inner periphery of the conduit. Alternatively, it may be disposed on the outside periphery of the conduit so that flow through the conduit may be unrestricted. Additionally, the resonator may include a honeycomb fairing to attenuate sound at higher frequencies. Also disclosed is a system in which a resonator may be located within the conduit of an HVAC system to attenuate the sound.

Abstract: Precision gas flow control is provided utilizing a first coarse gas flow control element and a second fine gas flow control element. The second element is selected and operated to pass only a fraction of the flow passed by the first element. The elements may be connected either in series or in parallel so that at least a portion of the gas flow passes through each flow control element. Control circuitry is also provided which may be responsive at least in part to an indication of desired gas flow through the device for controlling the first element to provide a coarse gas flow adjustment and for controlling the second element to provide a fine gas flow adjustment. In some applications, only fine flow adjustment may be provided. Where the elements are being utilized for example as the tracking flow control elements for a sealed enclosure, either the fine flow control element or both elements may also be made responsive to pressure errors in the enclosure.

Abstract: A system is provided for detecting presence and/or motion of a person or other movable entity within a selected space. Detection is accomplished by detecting reflected light or other radiation from the space, presence being signified when detected radiation differs from an established background, either up or down, by an amount exceeding a predetermined threshold. Blending of the entity with the background is avoided by viewing the entity at at least two different angles with different background, for example by use of two spaced detectors, and variations in background are automatically compensated for when a presence indication persists for a selected period of time after the last motion indication is received. The background is updated to the current level when this occurs.

Abstract: A system for maintaining a desired pressure (either positive or negative with respect to surrounding) in a sealed room or other substantially sealed closed space has a gas supply and a gas exhaust connected to the space through a supply flow control element and an exhaust flow control element, respectively. A tracking one of the two control elements has its flow controlled in response both to the measured pressure in the space and to an indication of flow through the other, driving flow control element. The flow control elements are adapted to provide a designed, at least nominal effective leakage for the space with changes in the pressure differential between the space and at least one of the gas supply and gas exhaust. For preferred embodiments, the effective leakage is achieved by either mechanically or electronically modifying the flow/pressure characteristic of at least one of the valves to have a designed, at least nominal change in flow for changes in pressure across the element.

Abstract: A method and apparatus for controlling a fluid flow valve with a linear control loop such that the error signal utilized to actuate a variable rate controller for moving a valve control element or for controlling another valve control parameter is the same for a given control parameter change regardless of the current control parameter value or the current or desired fluid flow through the valve. A non-delayed indication of current fluid flow is also generated.

Abstract: This invention relates to a fume hood controlling method and apparatus which reduces the amount of replacement air required to operate a fume hood by permitting the fume hood to operate at a relatively low face velocity in the absence of a containment affecting condition, but which is capable of detecting the occurrence of a containment affecting condition, such as the presence or movement of a user within a selected area of the face of the fume hood, and of increasing face velocity to a selected level in response to such detection. When the detected condition no longer exists, the control automatically returns the fume hood to the lower face velocity, preferably with a time delay. Maximum replacement air volume and minimum replacement air volume may also be controlled in response to such detection.

Abstract: An apparatus for sensing the extent to which the sash or sashes covering the access opening of a fume hood are open. The apparatus includes a source of electromagnetic energy at a selected AC frequency below 10.sup.6 MHz, with a preferred frequency range being from 10 KHz to 100 KHz. The source preferably includes a wire coil connected to an oscillator of the selected frequency with the detector for the AC signal also preferably including a wire coil. Suitable elements are also provided for controlling the amount of electromagnetic energy from the source wire coil which reaches the detector wire coil as a function of sash opening.

Abstract: An apparatus for sensing the extent to which the opening of a fume hood is uncovered by the hood sashes, and is particularly adapted for use with hoods having sashes which are moved horizontally. Radiation from a radiation emitter, such as an optical or a magnetic emitter, are sensed by corresponding detectors. For some embodiments of the invention, there is relative movement between the emitters and detectors as the sashes are moved to cover or uncover the opening, the movement between the emitter and the detector being such that the amount of radiation detected by the detectors is proportional to the uncovered portion of the opening. The relative movement may be accomplished by, for example, having the detectors fixed and having the emitters mounted to the sashes or by having the detectors mounted to some sashes and the emitters mounted to other sashes. A unique magnetic emitter is also provided with enhanced flux throw.

Abstract: Method and apparatus for varying the make-up air volume of an HVAC system used in conjunction with a laboratory fume hood. The invention maintains a constant difference in air volume between the total air volume exhausted from the laboratory, including the variable fume hood exhaust volume and the make-up and supply air provided by the HVAC system. The invention provides a continuous modulation of the make-up air volume which tracks the exhaust volume to maintain a constant preset differential between the makeup and exhaust volumes. The invention includes a preferred embodiment in which a signal from a sash height transducer is used to control the volume of make-up air.

Abstract: A fume hood controller system in which the sash position is monitored by a transducer which provides a signal indicative of the area of the hood opening. A variable speed motor controller is responsive to the sash position signal to provide a fan speed which varies in a substantially continuous and linear manner as a function of the sash opening. In an alternate embodiment, the air flow through the hood is controlled by a damper or similar device. Several embodiments are shown in which the present invention may be used to control a fume hood system in which a blower exhausts a plurality of fume hoods while maintaining a substantially constant face velocity in each hood.

Abstract: A fume hood controller system in which the sash position is monitored by a transducer which provides a signal indicative of the area of the hood opening. A variable speed controller responsive to the sash position signal to provides a fan speed which varies as a function of the sash opening. An optional circuit monitors the power drawn by the motor and compares the actual power drawn by the motor with the expected power for the present sash position. If the actual power falls below the threshold, an alarm signal is generated indicating a reduced air flow in the fume hood. Additionally, motor overload may be detected by comparing the motor speed control signal with the actual motor speed. An alternate embodiment is shown in which the present invention may be used to control a single blower which exhausts a plurality of fume hoods while maintaining a substantially constant face velocity in each hood.

Abstract: A PWM, controlled current, voltage source inverter controls an induction motor in response to signals from a power factor control circuit. The power factor control circuit receives signals related to motor terminal voltages and multiplexes them to a comparator. The inverter and multiplexer are sequenced each time the comparator input reaches a reference level. The frequency of the inverter is thus self generated. The power factor of the system can be controlled to implement a variety of control strategies.

Abstract: An inverter controls an induction motor in response to signals from a power factor control circuit. The power factor control circuit receives signals related to motor terminal voltages and multiplexes them to a comparator. The inverter and multiplexor are sequenced each time the comparator input reaches a reference level. The frequency of the inverter is thus self generated. The power factor of the system can be controlled to implement a variety of control strategies.