Components in a Ratio Control Loop
Ratio control systems are installed to maintain the relationship between two variables and to stop a third variable from arising. The correct method of control depends on an understanding of the components in an effective ratio control loop. Although the control can lead to complex loop systems, ratio control loop components are conceptually simple.
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The Loop
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A ratio control loop is established to divert an uncontrolled element, known as "wild" flow. Think of it as a river or an electrical current which flows at a rate that needs to be regulated by a certain ratio. A second element, known as "controlled" flow, is also diverted into the loop for the purpose of establishing a specific ratio balance. Once the two elements are in the loop, they are regulated by valves, pump or circuits. The deployment of processes inside the loop depends on the variables and the needs of the designer.
Processing the Wild
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Successful ratio control depends heavily on the presence of a regulating component to set the necessary ratio of wild flow. In its simplest form, this could be a "ratio station," a circuit or valve which sets the wild flow level for subsequent mixing. Although different systems can be designed for the placement of this regulation, wild flow regulation must occur for ratio to succeed. Wild flow can be sent directly to the ratio station, regulated there and fed into the next stage in the loop.
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Processing the Controlled
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Processing the controlled element is equally regulated. Although it is controlled, an effective ratio control loop must still contain a mechanism which checks the integrity of a controlled flow. In a more complex model produced by Emerson Process Management, the controlled flow contains the same regulatory element as wild flow. The difference is that controlled flow is ensured at this stage to confirm that the ensuing mix contains the appropriate ratio.
Blending the Processed Elements
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The ratio "mixer" is a conceptual meeting point for controlled and wild flows. Ratio control loops must combine manipulated flows to work. This applies to anything from water or electrical flow to home amplifiers. In a laboratory, a ratio mixer might be the beaker into which a scientist pours rationed quantities of variable liquids. An amplifier may contain a circuit which balances variant electrical signals. Elements which are first separated must ultimately converge in order to be successfully routed beyond a ratio control loop.
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