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To measure the displacement of an irregular sensor , immerse the sensor in a <br /> graduated cylinder to the alarm depth . The volumes before and after immersion should <br /> be recorded . The difference in volume (VD ) is the displacement of the sensor at the <br /> threshold level . This displacement volume should be added to the test volume obtained <br /> from the burette before the calculations are conducted . <br /> The alarm level can then be calculated from the equation : <br /> L = (VB +VD) * C <br /> where L is the level at which alarm first occurs , VB is the volume of the burette , VD is the <br /> displacement volume of sensor at alarm level , and C is the conversion factor to convert <br /> volume to height (e . g . , ml/ in ) for the test cylinder. <br /> The threshold is calculated from the equation : <br /> Threshold = Mean + 4 . 414 *STD <br /> where the mean is the average alarm level for each test set , and STD is the standard <br /> deviation for each data set . The tolerance coefficient for six data points (95 % <br /> confidence) is 4 . 414 . <br /> Liquid-Float Switch Sensors Page 2 of 2 <br />