Ratio control system

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. 1

2. INDEX Introduction Block diagram Description of loop Advantage Disadvantage. 2

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). 3

4. 4 RC Flow 1 Flow 2 Pv Set Point output CV Process line 2 FT 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. 5

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. 6

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. 7