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0 <br />J <br />Iii <br />F7 <br />'i <br />J <br />Line Pressure Probes - These devices sense line pressure (usually by use of an <br />electronic strain gauge) to detect leaks. Critical factors are precision, sample <br />time, thermal stability, operating range, etc. <br />Line Volume Probes - Varies by manufacturer but generally consist of a device of <br />known volume which empties during a leak. By timing this event a leak rate <br />® is projected. The device is large in size, and has had difficulty in EPA <br />certification. <br />Float Switch - The switch described previously is used in double wall steel tanks. <br />A smaller float switch is required for double wall fiberglass tanks. <br />Thermal Absorbtion - Same as described previously, used in annular space of <br />double wall fiberglass tanks. <br />Product Soluble - Same as described previously. <br />Light Refraction/Conductivity - Same as described previously. Explained in detail <br />later. <br />Magneto-Strictive Gauge - Currently the most accurate and popular technology <br />used for gauging tanks. Explained in detail later. <br />Capacitive Gauge - Measures capacitive effect created by product contact with the <br />probe shaft and interpolates level. This probe requires regular maintenance <br />to keep product film from building on probe shaft.. <br />Float Switch - Installed at a fixed position within the tank to indicate an overfill <br />condition. <br />Control1 ' ' 'Page 8 <br />