Economizer/dcv controller with manual sensor calibration

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.

What is claimed is: 
     
         1 . A system for calibrating an economizer controller, comprising:
 a first system sensor configured to obtain a first value of a first control parameter of an HVAC system;   a first precision sensor configured to obtain a second value of a same type as the first value related to the first control parameter, the first precision sensor configured to obtain the second value at a same time as the first system sensor obtains the first value;   wherein the economizer controller is configured to compare the first value of the first system sensor is with the second value of the first precision sensor to obtain a first offset; and   wherein the first offset is stored in a firmware of the economizer controller and is used to compensate the first system sensor.   
     
     
         2 . The system of  claim 1 , wherein the first system sensor is configured to obtain a third value of a the first control parameter at a second time and the first precision sensor is configured to obtain a fourth value of a same type as the third value at the second time the first system sensor obtains the third value. 
     
     
         3 . The system of  claim 2 , wherein the economizer controller is configured to compare the third value of the first system sensor is with the fourth value of the first precision sensor to obtain a second offset. 
     
     
         4 . The system of  claim 3 , wherein the first and second offsets are combined to provide a curve of offsets versus values from the first system sensor, which is extrapolated for obtaining offsets for other values obtained by the first system sensor. 
     
     
         5 . The system of  claim 1 , wherein the first system sensor is a temperature sensor. 
     
     
         6 . The system of  claim 1 , wherein the first system sensor is a relative humidity sensor. 
     
     
         7 . The system of  claim 1 , wherein the first system sensor is a CO 2  sensor. 
     
     
         8 . A method for calibrating a system sensor in a demand control ventilation system, the method comprising:
 placing a demand control ventilation system controller into a calibration mode;   measuring a first control parameter of the demand control ventilation system with a system sensor to obtain a first reading at a first time;   measuring the first control parameter with a precision sensor to obtain a second reading at the first time and in a same ambient environment as the system sensor;   computing an offset from a difference between the first and second readings; and   entering the offset into a memory of an economizer controller.   
     
     
         9 . The method of  claim 8 , wherein:
 the absolute value of the different in the first and second reading is the offset;   if the first reading is greater than the second reading, then the offset is subtracted from a subsequent reading from the system sensor for compensation of the subsequent reading; and   if second reading is greater than the first reading, then the offset is added to a subsequent reading from the system sensor for compensation of the subsequent reading.   
     
     
         10 . The method of  claim 8 , wherein:
 the readings of the precision sensor and the system sensor are stored in the demand control ventilation system controller; and   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 are automatically processed.   
     
     
         11 . The method of  claim 8 , wherein 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 are automatically processed by the economizer controller. 
     
     
         12 . The method of  claim 8 , further comprising:
 measuring the first control parameter with the system sensor of the economizer controller to get a first reading at each of a plurality of times at a plurality of ambient temperatures; and   measuring the first control parameter with the precision sensor to get a second reading at each of the plurality of times and the plurality of ambient temperatures   
     
     
         13 . The method of  claim 12 , further comprising:
 computing an offset from a difference between the first and second readings of the first control parameter for each of the plurality of times and 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 control parameter obtained at the same temperature that the offset was computed.   
     
     
         14 . The method of  claim 8 , wherein the first control parameter is a temperature parameter. 
     
     
         15 . The method of  claim 8 , wherein the first control parameter is a non-temperature parameter. 
     
     
         16 . A method for calibrating a system sensor of an economizer controller, comprising:
 placing the economizer controller into a calibration mode;   taking a plurality of readings with a system sensor of the economizer controller at a plurality of times to obtain a first set of different values of a parameter;   taking a plurality of readings with a precision sensor at a same plurality of times as the system sensor to obtain a second set of values of the parameter;   determining a plurality of offsets wherein each offset is a comparison of a reading from the system sensor and a reading from the precision sensor at a same time; and   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 most closely corresponding to the certain value.   
     
     
         17 . The method of  claim 16 , further comprising:
 graphing the plurality of offsets versus readings of the system sensor; and   constructing a curve that fits on the plurality of points on the graph.   
     
     
         18 . The method of  claim 16 , wherein the plurality of offsets versus readings of the system sensor are entered in a look-up table. 
     
     
         19 . The method of  claim 16 , wherein the 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 is automatically performed by the economizer controller for each reading from the system sensor of the parameter. 
     
     
         20 . The method of  claim 16 , wherein the economizer controller is a digital controller with demand controlled ventilation.