What is the control ratio?
Under a budgetary control system, actual performance is compared to budgeted performance to enable the identification of variances. When deviations or variances are expressed in terms of ratios, these ratios are referred to as control ratios.
What is ratio control write its importance with examples?
Ratio control is used to ensure that two or more process variables such as material flows are kept at the same ratio even if they are changing in value. In industrial control, examples of ratio control that come to mind are: Burner air/fuel ratio. Mixing and blending two liquids.
Which controller is used for flow control?
A mass flow controller (MFC) is a device used to measure and control the flow of liquids and gases. A mass flow controller is designed and calibrated to control a specific type of liquid or gas at a particular range of flow rates.
Why the controller used for ratio control is normally PI type?
The controllers in ratio control are usually P-I type. This is in order to achieve zero steady state error for maintaining the desired ratio. Derivative action is avoided because the flow is always noisy. The ratio of these two streams affect the quality of the output of the process.
Where is the ratio control?
The ratio control architecture is used to maintain the flow rate of one stream in a process at a defined or specified proportion relative to that of another. A common application for ratio control is to combine or blend two feed streams to produce a mixed flow with a desired composition or physical property.
How do you calculate ratio control?
In this design, the ratio is calculated by dividing the one flow by the other. This calculated ratio is then used as the process variable for a ratio controller. This design creates a highly nonlinear control loop of which the process gain is inversely proportional to the flow rate in the denominator.
What is the function of flow controller?
Flow controllers are electric devices which monitor and maintain flow-rate variables, typically in process applications. They can be used in conjunction with pumps and valves in fluid flow systems, in order to provide better control of flow variables.
What is P gain and I gain?
Gain is the ratio of output to input—a measure of the amplification of the input signal. The three primary gains used in servo tuning are known as proportional gain, integral gain, and derivative gain, and when they’re combined to minimize errors in the system, the algorithm is known as a PID loop.
What are the drawbacks of P controller?
The primary drawback of P-Only control is its propensity for Offset. Offset is a sustained difference between a loop’s Set Point and its input. It typically results when the Set Point is changed without re-baselining or when the process encounters a sustained disturbance.
How is the flow rate maintained in ratio control?
The controller maintains the flow rate of the the controlled flow at a ratio to the wild flow. The desired ratio is set by adjusting ratio the setpoint. Ratio control then monitors the value of one variable and sets the value of the second variable at a specific ratio to the first.
How is ratio control used in a second controller?
The same transmitter signal is used as a set point for a second controller which controls the flow in a second line. The ratio of one flow rate to the other can be changed by adjusting the gain (or proportional band) of the secondary controller. Figure shows a typical ratio control system.
How does a flow controller control the flow?
A standard flow controller then controls the flow according to this set point. If required, you can divide the controlled flow by the wild flow to display the actual ratio to the operator, but don’t use it to control the ratio. The figure below shows the two ratio-control designs.
How are sensors used in a ratio control loop?
Ratio control loop has one sensor and transmitter in the wild flow and another set in the controlled flow.Both sensors transmit signals representing the respective flow rates to the ratio controller. The controller maintains the flow rate of the the controlled flow at a ratio to the wild flow.
