With no flow through the meter, the two tubes oscillate completely out of phase with one another. As product flows through the meter, the oscillating tubes are delayed or advanced due to Coriolis forces. As a result, a variable phase differential is developed between the two tubes that is proportional to the mass flowing through the unit and measured by the sensors located on the tubes. There are significant design features of the sensor that set this meter apart from other meters. Those features include: • Patented torsion rod designto minimize tube stress and eliminate tube-stress fractures. The design is unique in that the Coriolis force is produced by a very slight torsional twisting motion of the tubes about an axis. This motion places very low fatigue stress on the tubes and contributes to the long service life that is a characteristic of the design • High mass dual cross bar support of oscillating flow tubes to drastically reduce susceptibility to “noise” or external vibrations that may interfere with the accuracy of other meters • Increased tube-wall thickness relative to other Coriolis mass flow meters ensures that meter accuracy is unaffected by changes in pressure, and permits operation at high working pressures up to 11,600 psi. The increased tube-wall thickness also eliminates the need for secondary containment around the meter. Pressure rating of the flow tubes is equal to or greater than the ANSI flange rating. • Tube construction of 316 Ti stainless steel, which is a superior grade to “L” series stainless steel and compatible with a wider range of liquids. Other tube materials, such as Hastelloy and even Tantalum are available for highly corrosive media. Each of these features contributes to superior performance and long service life, and makes the RHM Flow Sensor design unique in the industry. Mechanical Construction Features The oscillating structure and all its parts, including a base plate, are vacuum-brazed. The stainless steel housing covering the sensor is bolt-connected and O-ring sealed to the base plate. Hydraulic connectors are also screwed against the base plate where O-ring seals seal against the flow tubes. This construction provides a significant advantage in cleaning and changing process fluids because the connectors can easily be removed. In addition, this consruction is ideal for fluids that have a tendancy to coat the inner walls of the tubes or to solidify at ambient temperatures. The standard material for all wetted parts is 316 Ti stainless steel, with Hastelloy and Tantalum available for highly corrosive media. Units supplied with Hastelloy and Tantalum include flanges that are directly welded to the tube ends to eliminate seals inside the flow path ( Type F, Version 3). The same is true for sanitary fittings to meet clean in place (CIP) standards. Electrical Construction Features The coils are of thermoplastic-insulated wiring (polyimide-coated) molded in epoxy resin. Starting at the coils, the wiring is fixed onto the tubes and routed via the most secure route to a connection board (see illustration at right). From the connection board, the wiring is routed directly into the terminal box, which has a terminal block for cabling. The RTD temperature sensor which is attached to the flow-tube is similarly connected. Specifications and dimensional data are provided on pages 4 through 11. 3
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