CRITICAL FACTORS TO BE CONSIDERED IN AUTOMATING 

 CONTROL OF THE ATMOSPHERE IN C-A STORAGE OF APPLES 



Recently, there have appeared on the market, at least two units designed to 

 generate or to control the atmosphere for C-A storages. In evaluating these units 

 for possible installation in existing C-A rooms or in new construction, the 

 following critical factors may provide basis for a decision. 



The potential advantages of automating the control of the C-A process are 

 mainly: a savings in labor costs; an increase in reliability; and an operating 

 advantage, in being able to open the C-A room, unload a portion of the produce 

 stored, and then close the C-A room and operate again. The control pattern with 

 these new units may show less variation than with manual control, but the 

 quantitative improvement in fruit quality as a result has not been established. 



CA PROCESS HAS BEEN BIOLOGICAL. WITH MANUAL CONTROL 



With the CA process, as it is known today, generation of the atmosphere 

 has been achieved primarily by biological means, with chemical absorption towers 

 to aid in the control of the excess CO2 *nd nitrogen gas as an aid in reducing 

 •xygen level to operating conditions. The atmospheric composition has been con- 

 trolled manually by the operator on the basis of an Orsat analysis. 



DIFFERENCE BETWEEN MECHANIZATION AND AUTOMATION OF CA 



Application of time clocks to program CO2 towers or to program addition 

 •f nitrogen or outside air, represents some mechanization but no t automat ion 

 since self control of the process is not possible by simple mechanization. 



Indicator-controllers or recorder-controllers with sensing and control 

 capabilities for humidity, oxygen level, and CO2 level have been available for 

 some time but their application to automatically control the CA process has been 

 slew due to high initial cost. However, these instruments require periodic 

 calibration, which is usually against an Orsat analysis or a mixture of purchased 

 gases of known composition. 



LIMITED AUTOMATION OF CA PROCESS ALREADY ACHIEVED 



Of the variables that require control for the CA process (CO2 level, O2 

 level, humidity and temperature), temperature control has already been automated 

 and in a well designed refrigeration system humidity control is inherent. 

 Therefore, any further automation of control must deal with the variables of 

 CO2 and O2 levels. 



"COME-DOWN" AND "OPERATING" PERIODS IN CA 



There are two distinct periods in the operation of a CA storage; the period 

 commonly referred to as the "come-down" when the O2 level drops from approximately 

 217, to 3% and the CO2 level increases to 5% (for Mcintosh); and the period 

 commonly referred to as the "operating" period, when the atmosphere is maintained 



