Abstract:
An economizer controller with sensor calibration. A controller sensor may be used to measure a parameter. At the same time at the same location of the measurement with the controller sensor, a measurement of the same parameter may be made with a precision sensor. The difference between the two measurements may be saved to a controller memory as an offset. The offset may be used to compensate future measurements of the same parameter by the controller sensor. Additional offsets at various magnitudes may be obtained between the precision and the controller sensors for compensating subsequent measurements by the controller sensor. Measurements with the compensated sensor may be used for calibrating sensors in other economizer controllers, for example, at remote locations in the field.

Description:
BACKGROUND 
       [0001]    The present disclosure pertains to controllers and particularly to economizer controllers. More particularly, the disclosure pertains to compensation of sensors for economizer controllers. 
       SUMMARY 
       [0002]    The disclosure reveals an economizer controller with sensor calibration. A controller sensor may be used to measure a parameter. At the same time, at the same location of the measurement with the controller sensor, a measurement of the same parameter may be made with a precision sensor. The difference between the two measurements may be saved to a controller memory as an offset. The offset may be used to compensate future measurements of the same parameter by the controller sensor. Additional offsets at various magnitudes may be obtained between the precision and the controller sensors for compensating subsequent measurements by the controller sensor. Measurements with the compensated sensor may be used for calibrating sensors in other economizer controllers, for example, at remote locations in the field. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1  is a diagram of obtaining a setting from a precision sensor; 
           [0004]      FIG. 2  is a diagram of compensating the system sensor; and 
           [0005]      FIG. 3  is a schematic of a representative economizer system. 
       
    
    
     DESCRIPTION 
       [0006]    Energy savings and precise environmental control are continually gaining importance as energy costs rise. In the effort to better control, and optimize energy use for environmental controls, the accuracy of the individual sensing elements in the system become more and more important. This drives an ever increasing commercial need for accurate sensing solutions. 
         [0007]    This disclosure may solve the need by allowing precision sensors to be calibrated for accuracy when coupled with an economizer controller. This may be a digital economizer/DCV (demand controlled ventilation) controller that has a capability for manually calibrating individual sensors in the field. 
         [0008]    The invention may be implemented in economizer firmware. When a customer would like to calibrate an individual sensor in an economizer/DCV system, the controller may be placed in calibration mode. Then the customer is able to calibrate each sensor to a reference. This calibration offset may then be stored in the firmware and used to compensate sensor data before submitted to the next level of firmware. 
         [0009]      FIG. 1  is a diagram of obtaining a setting from a precision sensor. A calibration start  11  may begin by going to read a system sensor at symbol  12 . A precision sensor may be brought in and a value of the precision sensor may be obtained at symbol  13 . With the value of the precision sensor, the system sensor offset may be computed at symbol  14 . With the sensor offset at symbol  15 , then one may be at a calibration end  16 . 
         [0010]      FIG. 2  is a diagram of compensating the system sensor. A sensor compensation start  18  may begin by reading the system sensor at symbol  19 . With the sensor offset at symbol  15 , a compensated value of the system sensor may be computed at symbol  21 . Then one may be at a sensor compensation end  22 . 
         [0011]      FIG. 3  is a schematic of a representative economizer system  50 . A thermostat  51  may be connected to an economizer logic module  52 . A demand control ventilation sensor  53  may be connected to module  52 . Return air  54  may come in through a recirculation damper  55  into a mixing air chamber  56  where air  54  may be mixed with outdoor air  57  coming through an intake damper  58 . Mixed air may be discharge air  59  which is drawn by an indoor fan  61  through a direct expansion coil  62  and provided to a space being conditioned via a supply duct  68 . Dampers  55  and  58  may be controlled by an actuator  63  which is connected to module  52 . Damper  58  may close as damper  55  opens and vice versa. A portion of return air  54  may taken from return air duct  64  and drawn through a damper  65  by an exhaust fan  66  through an exhaust duct  76  to outside the system as exhaust air  67 . Exhaust fan  66  may be connected to module  52 . The position of damper  65  may be determined at least in part by module  52 . The proportions of outdoor air  57  and recirculated air  54  taken into supply duct  68 , as well as the amount of air  67  from return air duct  64 , may be controlled by intake damper  58 , recirculation damper  55  and exhaust damper  65 . An enthalpy sensor  71  situated in an intake or outdoor air duct  73  may be connected to module  52 . For differential enthalpy, a second enthalpy sensor  72 , along with enthalpy sensor  71 , may be connected to module  52 . 
         [0012]    A mixed air sensor  74  may be situated in chamber or duct  56 , or a discharge air sensor  75  may situated in chamber or duct  68 , but not necessarily both. One or the other of or both sensors  74  and  75  may be connected to logic module  52 . There may be situations where there would be both a mixed air sensor in the mixed air chamber and a separate discharge air sensor in the discharge chamber or duct. There may also be situations where there is not a discharge air sensor but that a mixed air sensor is mounted in the discharge chamber or duct. 
         [0013]    Economizers may save energy in buildings by using cool outside air as a means of cooling the indoor space. When the enthalpy of the outside air is less than the enthalpy of the recirculated air, conditioning the outside air may be more energy efficient than conditioning recirculated air. When the outside air is both sufficiently cool and sufficiently dry (depending on the climate), the amount of enthalpy in the air is acceptable to the control, no additional conditioning of it is necessarily needed. This portion of the air-side economizer control scheme may be referred to as free cooling. 
         [0014]    Economizers may reduce HVAC energy costs in cold and temperate climates while also potentially improving indoor air quality, but they might often not be appropriate in hot and humid climates. With the proper controls, economizers may be used in climates which experience various weather systems. 
         [0015]    When the outside air&#39;s dry-bulb and wet-bulb temperatures are low enough, economizers may use water cooled by a wet cooling tower to cool buildings without operating a chiller. Often a plate-and-frame heat exchanger may be inserted between the cooling tower and chilled water loops. 
         [0016]    To recap, the present calibrating mechanism for an economizer controller may have a precision sensor of a first kind and a first system sensor of the first kind of an economizer controller. The first system sensor may be read to obtain a first value in a first ambient environment at a first time. The precision sensor may be read to obtain a second value in the first ambient environment at the first time. The first value may be compared with the second value to obtain a first offset from a difference between the first and second values. The first system sensor may be read to obtain a third value at a second time. The third value of the first system sensor may be adjusted by incorporating the first offset to obtain a compensated third value of the first system sensor. 
         [0017]    The calibrating mechanism may further have a second system sensor of the first kind of a second economizer controller. The second system sensor may be read to obtain a fourth value in a second ambient environment at a third time. The first system sensor may be read to obtain a fifth value in the second ambient environment at the third time. The fifth value of the first system sensor may be adjusted by incorporating the first offset to obtain a compensated fifth value of the first system sensor. The fourth value may be compared with the compensated fifth value to obtain a second offset from a difference between the fourth and compensated fifth values. The second system sensor may be read to obtain a sixth value at a fourth time. The sixth value of the second system sensor may be adjusted by incorporating the second offset to obtain a compensated sixth value of the second system sensor. 
         [0018]    The first system sensor may be read to obtain a fourth value in the first ambient environment at a third time. The precision sensor may be read to obtain a fifth value in the first ambient environment at the third time. The fourth value of the first system sensor may be compared with the fifth value of the precision sensor to obtain a second offset from a difference between the fourth and fifth values. 
         [0019]    The first and second offsets may be combined to provide a curve of offsets versus values from the first system sensor, which can be extrapolated for obtaining offsets for other values obtained by the first system sensor. The curve may be extrapolated for obtaining offsets for compensating various values from the first system sensor. The first system sensor may be read to obtain a sixth value at a fourth time. An offset may be determined from the curve for compensating the sixth value. 
         [0020]    A sensor of the first kind may be a temperature sensor, a relative humidity sensor, a CO2 sensor, or the like. 
         [0021]    The approach for calibrating a system sensor in an economizer controller may incorporate measuring a first parameter with a system sensor of an economizer controller to get a first reading, and measuring the first parameter with a precision sensor to get a second reading. It may further incorporate computing an offset from a difference between the first and second readings, entering the offset into a memory of the economizer controller, and using the offset for calibrating other readings from the system sensor. 
         [0022]    The first reading from the system sensor may be an X. The second reading from the precision sensor may be a Y. |X−Y| may be the offset. If X is greater than Y, then the offset may be subtracted from a subsequent reading from the system sensor for compensation of the subsequent reading. If Y is greater than X, then the offset may be added to a subsequent reading from the system sensor for compensation of the subsequent reading. 
         [0023]    The readings of the precision sensor and the system sensor may be stored in the economizer controller. A determination for the offset from the readings of the precision sensor and the system sensor, and compensation of a subsequent reading of the system sensor may be automatically processed by the economizer controller. 
         [0024]    The approach may further incorporate measuring the first parameter with the system sensor of the economizer controller to get a first reading at each of a plurality of ambient temperatures, and measuring the first parameter with the precision sensor to get a second reading at each of the plurality of ambient temperatures. Also, the approach may incorporate computing an offset from a difference between the first and second readings of the first parameter for each of the plurality of ambient temperatures, and using an offset, computed at a temperature of the plurality of ambient temperatures, for calibrating another reading from the system sensor of the first parameter obtained at the same temperature that the offset was computed. The first parameter may be a non-temperature parameter. 
         [0025]    An approach for calibrating a system sensor of an economizer controller, may incorporate taking a plurality of readings with a system sensor of an economizer controller at a first set of different values of a parameter, and taking a plurality of readings with a precision sensor at the first set of different values of the parameter for the first set of different values. Then a plurality of offsets may be determined where each offset is a comparison of a reading from the system sensor and a reading from the precision sensor at a same time, of the parameter for the first set of different values. A reading from the system sensor of a certain value of the parameter may be compensated with an offset from the plurality of offsets for a value, of the first set of different values, most closely corresponding to the certain value. 
         [0026]    The approach may further incorporate a graphing the plurality of offsets versus readings of the system sensor. Each offset of the plurality of offsets and each corresponding reading of the system sensor may be plotted as a point on a graph resulting in a plurality of points on the graph. A curve may be constructed that fits on the plurality of points on the graph. The plurality of offsets versus readings of the system sensor may be entered in a look-up table. 
         [0027]    Compensating a reading from the system sensor of a certain value of the parameter with an offset from the plurality of offsets for a value corresponding to the certain value may be automatic by the economizer controller for each reading from the system sensor of the parameter. 
         [0028]    The economizer controller may incorporate a user interface for placing the controller in a calibration mode for compensating a reading with an offset determined by a reading from each system sensor relative to a reading from the precision sensor. Offsets determined for readings of each system sensor may be stored at the controller for availability for compensating a reading from a system sensor at the controller in absence of the precision sensor. 
         [0029]    The economizer controller may be a digital controller with demand controlled ventilation (DCV). 
         [0030]    U.S. Pat. Nos. 6,161,764, 4,570,448, and 7,434,413 may be relevant. U.S. Pat. No. 6,161,764, issued Dec. 19, 2000, is hereby incorporated by reference. U.S. Pat. No. 4,570,448, issued Feb. 18, 1986, is hereby incorporated by reference. U.S. Pat. No. 7,434,413, issued Oct. 14, 2008, is hereby incorporated by reference. 
         [0031]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0032]    Although the present system has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.