Flow Indicators and Transmitters

There are flow meters in the reflux line, distillate line and bottoms lines. The meters all operate by displacement and magnets in dual rotors cause a reed switch to close once evei7 rotation. This provides a pulsing signal that is interpreted by a display unit mounted on the main instrumentation panel. A selector switch determines which flow reading is displayed. The distillate and bottoms flow meters are identical. Each is accurate to ±1.0% of the actual flow over the range 0.08-5.0 L/min and is pressure rated to 520 kPa. However, the construction of the meters has been modified to permit operation at higher pressures and they have been located downstream of the control valves to avoid exposure to the full column pressure. The reflux flow meter is accurate to ±0.5% of the actual flow over the range 0.5-30 L/min and is rated to 8500 kPa. The volume per pulse from the reflux meter differs from the other two meters so that the displayed reading must be multiplied by a factor of 1.24 to indicate the actual flow rate. The display unit transmits a 4-20 mA signal that can be used as a controller input. Note that changing the selector switch will affect the signal to the controller so that this should only be done when the controller is in manual (open-loop).

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