ESTABLISHING A SYSTEM FOR AUTOMATIC MONITORING AND 

 CONTROL OF A CA STORAGE 



Katrin Kaminsky and William J. Bramlage 

 Department of Plant and Soil Science 



and 



Ernest A. Johnson 

 Department of Food Engineering 

 University of Massachusetts 



The Orsat gas analyzer is used almost exclusively in New England to 

 determine the concentrations of oxygen (O2) and carbon dioxide (CO2) within a 

 controlled atmosphere (CA) storage. Control of these levels is performed 

 manually by the storage operator. Although the Orsat method is inherently 

 accurate, the procedure itself for sampling and measuring the atmosphere in the 

 rooms contains much opportunity for human error. Also, since this operation is 

 time-consuming, atmospheres are generally measured and adjusted no more often 

 than once per day. Under this type of management considerable fluctuation of 

 the storage atmosphere can occur, and problems can go unnoticed or uncorrected 

 for some time. To compensate for these potential problems, significant margins 

 of error are incorporated into standard CA recommendations. Even so, serious 

 errors in atmosphere maintenance are still common. 



There are alternatives to the Orsat method of measuring storage atmosphere 

 composition. Electronic devices for measuring O2 and CO2 are widely available. 

 A system using these devices to frequently and automatically measure O2 and CO2 

 levels was developed in England, and quickly was expanded to provide automatic 

 adjustment of O2 and temperature when they exceeded set tolerance levels. More 

 recently, automatic adjustment of CO2 has also been developed. These systems 

 are controlled by a programmed computer, and can be purchased as "package" 

 units. However, the costs of such units is discouraging for operators of the 

 relatively small storages that are typical of the New England apple industry. 



Another alternative is the "user-built" system, in which a user assembles 

 his own system from available components, developing a system to meet his needs 

 and to stay within his financial resources. Such a system employs separate 

 components which are available for O2 and CO2 analysis, a personal computer for 

 data handling and initiation of sampling, measuring, and controlling devices, 

 and the necessary pump, valves, and relays to facilitate the whole process. 

 This approach has been applied successfully to both research and commercial 

 systems at a cost less than that of a package system. 



It is our conviction that automatic monitoring and controlling of CA 

 storage atmospheres can significantly improve operation of New England apple 

 storages. To establish a demonstration, "user-built" system for use with the 

 storage rooms at the Horticultural Research Center, Belchertown, last year we 

 received a grant from the Massachusetts Society for Promoting Agriculture. 

 During the 1986-87 season, we assembled and operated this system. It is the 

 purpose of this article to describe the system and provide an initial 

 assessment of its operation. 



