Figure 142

Signal flow diagram for column material balance

(wrOmax = top-product flow-meter span, lbm/min Kjn = controller gain, psi/psi Gchtis) = controller dynamic gain K„hr = receiver level transmitter gain, psi/ft

Note that we have ignored the dynamics of level measurement and of the flow control loop. For averaging level control, this introduces little error.

We can now prepare the partial signal flow diagram of Figure 14.3. From this we can see by inspection that:

ATpTK^d

For pneumatic instruments:

(l\Mt)t where (AHT)T is the level transmitter span, in feet, for a 3-15-psig output. We can now define a characteristic time constant:

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