RATIO CONTROL SYSTEM USED IN VARIOUS PROCESS DEPENDS UPON APPLICATION

1. Ratio control System
by
Ashvani shukla
Dy.Manager (C&I)
BGR ENERGY SYSTEMS LTD.
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2.  INDEX
 Introduction
 Block diagram
 Description of loop
 Advantage
 Disadvantage.
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3.  Introduction.
 A ratio controller is a special type of feed forward
controller where disturbances are measured and
their ratio is held at a desired set point by
controlling one of the streams. The other
uncontrolled stream is called wild stream. Fig
shows the schematic of a ratio controller. The
ratio of flow rates of two streams are being held
at a desired ratio by controlling the flow rate of
one stream. The flow rates are measured
through flow transmitters (FTs).
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4. 4
RC
Pv
Set
Point
output
CV
Process line 2
FT
RC
Process line 1
Ratio

5.  SYMBOLS
 FT, Flow transmitters.
 PV, Process variables.
 SV, Set variables.
 RC, Ratio controller.
 CV, Control valve.
 Ratio controls are used where we have to
control one physical quantity with the
ratio of two different physical quantity as
shown in figure.
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6.  In ratio control we are measuring the flow
in two different lines one is called wild
flow and second is called controlled line.
 After measurement of steam flow we
divide the each other and create the ratio
for measured value for ratio controller.
 We provide the set point for ratio control
and error generated by ratio controller
converted in output and fed to valve
depends upon the ratio of both value of
flow.
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7.  Advantages
 Allows user to link two streams to produce
and maintain a defined ratio between the
streams.
 Simple to use.
 Does not require a complex model.
 Disadvantages
 Often one of the flow rates is not measured
directly and the controller assumes that the
flows have the correct ratio through the
control of only the measured flow rate.
 Requires a ratio relationship between
variables that needs to be maintained.
 Not as useful for variables other than flow
rates.
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