A SYSTEM FOR GREENHOUSE CLIMATE CONTROL USING HP EQUIPMENT

A series 200, Model 9920S controller and 3497A digital acquisition/control unit, manufactured by Hewlett-Packard, was installed November 1984, for controlling climate in four identical greenhouses. The system hardware and software were configured to: 1) Measure aspirated air temperature at three locations in each house with thermocouples. 2) Measure air temperature with an RTD, platinum unit at a central location. 3) Accumulate total, global solar radiation in each house. 4) Determine humidity with both wet bulb and capacitance-type probes. 5) Analyze CO₂ levels at the controller location with a continuous purging sampling system. 6) Sense canopy temperature with remote, 30° FOV infrared thermometers. And 7) accumulate natural gas consumption for night and day periods. Similar measurements are made outside, including wind velocity.

The system controls air temperature according to the average of the three thermocouple units, humidity, CO₂ level, shading and irrigation frequency. Vapor pressure is expressed in millibars and CO₂ concentration in Pascals, corrected for elevation. Additional software provides capacity to accumulate data on disc for summary printouts of maximums, minimums and averages of all inputs; and to record instantaneous values of all parameters at a rate decided by the operator.

The controller can be eventually configured to 7 Megabytes central memory (950 K-bytes presently), and the acquisition/control unit expanded in excess of 10 "extenders" (one presently used).