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Pneumercator Non - Discriminating <br /> Liquid Float-Switch Sensors <br /> SECTION 4 . CALCULATIONS <br /> Statistical analysis <br /> The data was analyzed using the statistical procedures described in the EPA <br /> protocol for non -volumetric methods . The PFA was calculated from the equation : <br /> PFA = TL1 / N1 <br /> where TLS is the number of cases where the method indicated a leak when no sample <br /> was present and Ni is the total number of tests conducted . If no false alarms occur , the <br /> PFA is zero or 0 % . <br /> The corresponding Po was calculated from the equation : <br /> PD = TL2/ N2 <br /> where TL2 is the number of tests where a leak was detected when product was present <br /> at the threshold level and N2 is the number of tests conducted . If a leak is detected <br /> every time a test is conducted , the Po is 1 . 0 or 100 % . <br /> Detection and Fall Times <br /> Once the threshold was determined for the liquid float-switch sensor , it was <br /> reimmersed in the product a minimum of six times to measure the detection time and <br /> the fall time . The detection time is the amount of time the detector must be exposed to <br /> the product before it responds . The fall time is the amount of time before the detector <br /> stops responding after being removed from the product . <br /> Specificity <br /> The specificity defines the different products that the float switches will respond <br /> to . Normally , the specificity is defined as either 100 % ( responds 100 % of the time) or <br /> 0 % ( never responds) for a certain product . <br /> Threshold <br /> The minimum detectable liquid level (threshold ) for each liquid float-switch <br /> sensor/liquid combination was calculated from the equation : <br /> Threshold = Mean + 4 . 414 * Standard Deviation <br /> where the mean is the average level for each test set . The tolerance coefficient for six <br /> data points (95 % confidence ) is 4 . 414 . <br /> Page 4 of 8 <br />