Red Lion PCU - Manual (Page 75)

APPENDIX “A” - APPLICATION EXAMPLES
CHEMICAL MIXING APPLICATION
A customer wants to control the ratio of one liquid flow to the other in a
chemical mixing application. Each flow is monitored with a flow transducer
that provides a 4 to 20 mA output signal. The PCU monitors the flow of
liquid “A” via the optional Remote Setpoint Input. Liquid “B” is monitored
by the main input. Both inputs are scaled independently during initial setup
and programming. The only task left to the operator is to enter the desired
ratio of B to A.
The 4 to 20 mA output of the PCU controls the position of a proportional
valve. Thus controlling the flow of B. As disturbances cause the flow of A to
vary, the PCU ensures that the proper ratio is always maintained. The flow of
“A” is shown in the secondary display simultaneously with the flow of
“B”(main display).
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Figure 38, Chemical Mixing, Flow Ratio Application