A ratio control system is a type of control system used in industrial processes to maintain a specific ratio between two or more process variables. The goal of ratio control is to ensure that the relationship between these variables remains constant, regardless of changes in other process conditions.

In a ratio control system, the controller continuously adjusts the manipulated variables (such as flow rates or speeds) of two or more interconnected control loops to achieve and maintain the desired ratio between the controlled variables (such as flow rates, levels, temperatures, or compositions). The ratio can be fixed or dynamically adjusted based on process requirements.

Here's how a typical ratio control system works:

1. Measurement of Process Variables: Sensors or instruments measure the values of the process variables involved in the ratio control system. For example, flow meters may measure the flow rates of two different fluids.

2. Calculation of Ratio: The controller calculates the ratio between the measured values of the process variables. This calculation can be based on a predefined setpoint ratio or dynamically adjusted based on process conditions or requirements.

3. Comparison with Setpoint: The calculated ratio is compared with the desired setpoint ratio. If the actual ratio deviates from the setpoint, the controller generates an error signal.

4. Control Action: The controller adjusts the manipulated variables of the control loops to correct the error and bring the ratio back to the desired setpoint. This adjustment may involve increasing or decreasing the flow rates, speeds, or other process parameters as needed.

5. Feedback Control: Feedback loops continuously monitor the process variables and provide feedback to the controller to ensure that the desired ratio is maintained over time. The controller makes ongoing adjustments to the manipulated variables to compensate for any disturbances or changes in the process.

Ratio control systems are commonly used in various industrial processes where maintaining a specific proportion between process variables is critical for product quality, process efficiency, or safety. Examples of applications include:

• Mixing processes in chemical processing and pharmaceutical manufacturing.
• Blending processes in food and beverage production.
• Fuel-to-air ratio control in combustion systems.
• Proportioning of raw materials in batch processes.
• Dilution and concentration control in water treatment and wastewater management.

Overall, ratio control systems help optimize process performance, reduce waste, and ensure consistent product quality by accurately controlli