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METHODOLOGY <br />AES SYSTEM II is a computerized, constant level, precision <br />tank testing system capable of testing three tanks simultaneously <br />with an accuracy of 0.05 gph in three to five hours. SYSTEM II <br />uses a calibrated pressure weight sensor to sample product volume <br />variances every six seconds for a minimum of one hour up to a <br />maximum gf three hours. Using this data and a least squares fit <br />equation , the computer calculates a total product volume variance <br />rate for the tank, stated as a gallon per hour value. <br />A temperature array is used to sample thermal trends of the <br />product (See Figure 2). The sensors are mounted at a specific <br />vertical spacing to give an indicative sampling of the thermal <br />trend of the product. <br />Pretest: The AES SYSTEM II testing procedure requires that <br />a stability "pre-test" be performed. The pre -testing period allows <br />the technician to see when temperature trends in the tank <br />stabilize. During pre -testing, the technician will monitor noise <br />levels from the temperature array and level sensor to determine <br />trends. These sensor readings are monitored and recorded. If <br />erratic results are obtained, causes are investigated and <br />eliminated. The technician evaluates the following criteria, which <br />must be met prior to performing a precision test. After <br />stabilization, a calibration period is initiated. <br />A known amount of product is added to the tank so the computer <br />can determine system accuracy and liquid -to -air surface area. This <br />value is the combined surface area of the tank piping and any vapor <br />pockets which may exist. The technician subtracts the actual <br />surface area value from the calculated value to deter -mine vapor <br />pocket size. The vapor pocket must have a surface area of less <br />than 100 square inches before testing can proceed. <br />After venting all lines and inspecting for visible leaks, the <br />initial product variance rate is calculated and must be less than <br />one gallon per hour. If the product loss is greater than one <br />gallon per hour, a leak is indicated and the level is <br />2Statistical equation using the slope of the data to determine <br />a rate per hour value for the computer calculations. <br />4 <br />