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0 <br />The Magneto-Strictive Tank Level Gauge is the most widely used in the U.S. It <br />consists of a probe head, containing the electronics, a shaft (brass or <br />stainless steel), which extends across the diameter of the tank, two floats, <br />one for product and one for water, and temperature sensors, usually 3 to 5 <br />located within the shaft. This probe continuously transmits to the SOC the <br />current level of the product, level of water, and the temperature of each <br />sensor. <br />The operation of the probe is as follows: <br />The probe electronics sends an electrically induced wave down the shaft (wave <br />guide). A magnet located within the product float reflects part of this wave <br />back up the shaft to the probe head. By recording the time required for the <br />wave to travel to the float and back, the distance to the float (level) is <br />calculated. The portion of the wave not reflected by the product float <br />magnet continues down the wave guide and is similarly reflected by the <br />water float. <br />The temperature sensors are volumetrically spaced along the shaft and are wired <br />to the probe head electronics. <br />Level precision is 0.001 inch; temperature precision is 0.1 degree F. <br />The gauge is connected to the SOC via a special cable. The SOC continuously <br />monitors the gauge to record product inventory and deliveries. The SOC <br />also can use the gauge information to run a statistical test on the tank to <br />detect leaks. These tests usually require approximately 2 hours of no <br />product movement, depending on tank level. New SOC units automatically <br />abort tank tests when a sale is begun and re-initiate the tests when the <br />pump stops. This ensures that on every occasion of sufficient "quiet time" a <br />tank test will be accomplished. <br />Control Engineers, U -SA. Page <br />u <br />