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Likewise, Micromotion mass flowmeters are used extensively in our facility, for example, on chromatography skids. From one fieldbus connection to the device, we can realize all four process variables measured or calculated by the mass flowmeter. These include mass flow, volumetric flow, fluid temperature, and fluid density. Typically, volumetric flow is the primary value of interest, and is a calculated value from the device (mass flow/density). Volumetric flow is used as the process variable for the flow control loop on the chromatography skid. Initial running of the skid requires priming the inlet buffer lines.
While executing the prime phase, weíve noticed that when two-phase flow is introduced through the meter, the density will drop in proportion to the two-phase mixture, causing the volumetric flow to read high. Since we prime the various buffer lines based on passing a certain liquid volume, itís important to only totalize liquid flow and not two-phase flow. To prevent totalizing of two-phase flow, we use the density input, detect when itís no longer that of a liquid, and then turn off the totalizer. In this case, the host controller is actually writing to a parameter in memory in the fieldbus device. This ensures that all buffer lines have had the predetermined liquid volume transferred, and shows the two-way communication available with fieldbus devices.
In addition, Gemu manufactures valve actuators for on/off diaphragm valves. These valve actuators communicate to the host by way of AS-i bus . The valve actuators have a solenoid valve and open/close limit switches in the actuatorís topworks. Itís not unusual to find diaphragm valves open for SIP, and then indicate valve not closed when commanded closed at the end of SIP. This is due to the diaphragm being more malleable when heated, which allows the actuator stem to drive the diaphragm slightly deeper into the weir of the valve body past the previously set or cold diaphragm closed position. This device includes a programmable hysteresis for the open and closed limit switch that allows for process condition. Typically, itís the closed limit switch weíre interested in confirming in the case of sterile boundary valves.
Genzyme reports that fieldbus helped it achieved its technology objectives in five areas:
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