Variable dead band pressure control system

Automatic temperature and humidity regulation – Thermostatic – Expanding solid

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Details

236 14, 165 31, 62186, B64D 1300

Patent

active

043924174

ABSTRACT:
A pressure control system for an air distribution system which includes a supply blower (10), a distribution duct network (20) and a plurality of air outlets (22a, 22b), includes a plurality of pressure sensors (25a, 25n) positioned at various points in the air ducts to measure pressure therein. Controls are provided for selecting the lowest of the sensed pressures (42) and the low pressure signal becomes one input to a variable dead band controller (44). Another input is an adjustment (45) for commanding the desired system pressure. The controller compares the pressure to a dead band threshold established about the set point and delivers appropriate signals to an actuator (31) which operates through a linkage (32) to control the inlet vortex vanes (33) and hence the air flow of the supply blower. A wide dead band is used to avoid hunting of the system, but when a response is required a narrow dead band is used to ensure that the system drives to the set point. Controls are provided (47 ) to periodically reset the controller to its narrow dead band position to prevent drift of the system. For systems also including a return blower (11) an additional controller (54) is provided to operate its actuator (35) to control its inlet vanes (37). Controls are provided (31b, 35b) for developing feedback signals indicative of air flow in the supply and return blowers, and these signals are applied to calibration circuits (52, 56) to the controller (54). The calibration circuits are specially designed to provide independent adjustment of maximum and minimum air flow tracking between the supply and return blowers.

REFERENCES:
patent: 2112520 (1938-03-01), Crawford
patent: 2282210 (1942-05-01), Plum
patent: 3591077 (1971-07-01), Alton
patent: 4011735 (1977-03-01), Martz et al.
patent: 4044947 (1977-08-01), Spethmann
patent: 4089462 (1978-05-01), Bradford
patent: 4108375 (1978-08-01), Keeney
patent: 4189093 (1980-02-01), Schnaibel et al.
Johnson Control Apparatus Bulletin and Installation Instruction PC-4000 Electronic Static Pressure Controller.
Johnson Control Apparatus Bulletin and Installation Instruction HQ-3000 High Signal Discriminator.
Johnson Control Installation Instruction LQ3000 Low Signal Discriminator.

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