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Title: Humidity controller
Claims: I claim: 1. In an environmental control system, a humidity controller responsive to a humidity sensing means for controlling apparatus of the system to provide compensation for changes in the humidity within a given area relative to a set point as sensed by a sensing means, said humidity controller comprising a sensing network including said humidity sensing means and set point means for establishing said set point, said sensing network being operable to provide a differential output indicative of the relative humidity within the area, and control means including first and second threshold detecting means and threshold means including said setpoint means for establishing different turnon thresholds for said first and second threshold detecting means to enable said control means to provide a first control for said system apparatus in response to a differential output of one polarity provided by said sensing network and a second control signal for said system apparatus in response to a differential output of the opposite polarity provided by said sensing network. 2. An environmental control system as set forth in claim 1 wherein said set point means is adjustable to permit selection of the set point value and wherein said threshold means establishes a detection differential for said first and second threshold detecting means which remains constant for different set point values. 3. An environmental control system as set forth in claim 2 wherein said threshold means includes means for adjusting the detection differential for said first and second threshold detecting means. 4. An environmental control system as set forth in claim 2 wherein said set point means establishes a set point voltage at an output thereof which is indicative of the selected set point value, and said threshold means includes circuit means connected to said output of said set point means for supplying a reference voltage derived from said set point voltage to inputs of said first and second threshold detecting means to establish said detection differential for said first and second threshold detecting means. 5. An environmental control system as set forth in claim 2 wherein said first threshold detecting means includes means for increasing the differential output of said sensing network whenever said first threshold detecting means is enabled and wherein said second threshold detecting means includes means for increasing the differential output of said sensing network whenever said second threshold detecting means is enabled. 6. An environmental control system as set forth in claim 1 wherein said humidity sensing means comprises a resistance-type humidity sensing element having a resistance characteristic that varies non-linearly with changes in relative humidity and wherein said sensing network includes means for adjusting the differential output to compensate for the non-linearity of the sensing element. 7. In an environmental control system, a humidity controller responsive to a humidity sensor which monitors the humidity within a given area for controlling apparatus of the system to provide compensation for changes in the humidity within the monitored area relative to a set point value as sensed by the humidity sensor, said humidity controller comprising a sensing means including said humidity sensor and set point means, said humidity sensor establishing a sensor voltage indicative of the relative humidity within the monitored area at an output of said sensing means and said set point means establishing a set point voltage indicative of the desired humidity for the monitored area at a second output of said sensing means, detector means including first and second threshold detecting means having inputs connected to said outputs of said sensing means, and threshold means for deriving a reference voltage from said set point voltage which is extended to inputs of said first and second threshold detecting means to establish a first turn on threshold for said first threshold detecting means and a second turn on threshold for said second threshold detecting means whereby said first threshold detecting means is enabled to provide a first control signal whenever the sensor voltage increases relative to said set point voltage by an amount greater than the first threshold value and said second threshold detecting means is enabled to provide a second control signal whenever the sensor voltage decreases relative to said set point voltage by an amount greater than said second threshold value, first switching means responsive to said first control signal to effect energization of a first apparatus of the system to effect a decrease in the humidity in the monitored area, and second switching means responsive to said second control signal to effect energization of a second apparatus of the system to effect an increase in the humidity in the monitored area. 8. An environmental control system as set forth in claim 7 wherein said sensing means comprises a bridge network having said humidity sensor connected in a first branch of said bridge network and said set point means connected in a second branch of said bridge network, and means for applying an energizing potential to said bridge network to enable said sensor voltage and said set point voltage to be provided at first and second outputs of said bridge network. 9. An environmental control system as set forth in claim 8 wherein said bridge network includes means connected in a further branch of said bridge network for balancing the bridge network to permit the sensor voltage to equal the set point voltage when the humidity in the monitored area is at the set point value. 10. An environmental control system as set forth in claim 7 wherein said threshold means includes circuit means connected to said second output of said sensing means for deriving said reference voltage from said set point voltage and for extending said reference voltage to inputs of said first and second threshold detecting means. 11. An environmental control system as set forth in claim 10 wherein said circuit means includes means for adjusting the amplitude of the reference voltage to thereby vary the range of the differential thresholds for said first and second threshold detecting means. 12. An environmental control system as set forth in claim 8 wherein said first threshold detecting means includes feedback means for extending a portion of said first control signal to an input of said first threshold detecting means to maintain said first switching means enabled until said sensor voltage decreases to the value of said set point voltage and said second threshold detecting means includes further feedback means for extending a portion of said second control signal to an input of said second threshold detecting means to maintain said second switching means enabled until said sensor voltage increases to the value of said set point voltage. 13. An environmental control system as set forth in claim 10 wherein said first and second threshold detecting means comprise first and second operational amplifier means, respectively, each connected for operation as an open loop switching circuit. 14. An environmental control system as set forth in claim 13 wherein said detector means includes input network means having means for extending the setpoint voltage to an inverting input of said first operational amplifier means and to a non-inverting input of said second operational amplifier means and means for extending the sensor voltage to a non-inverting input of said first operational amplifier means and to an inverting input of said second operational amplifier means. 15. An environmental control system as set forth in claim 14 wherein said threshold means includes resistance means having potentiometer means connected between said second output of said sensing means and a point of reference potential to provide said reference signal at a wiper of said potentiometer means, and means for connecting said wiper of said potentiometer means to said inverting inputs of said first and second operational amplifier means. Other info: Inventors: Young, Geoffrey Allen (Bridgeport, TX, US) Application Number: 551097 Filing Date: 1975-02-20 Publication_date: 1976-05-18 Assignee: Johnson, Controls, Inc. (Milwaukee, WI) Primary Class(es): 236/44R 62/176.1, 165/223 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Wayner, William E. Assistant Examiner: Attorney: Johnson, Dienner, Emrich & Wagner |
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