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This simulation represents a water tank with two fluid inlets (Fluid A and Fluid B) and one manual outlet. Two PID controllers are used:

• Level PID Controller: Adjusts the overall inflow into the tank to achieve a desired tank level. The error is calculated as the difference between the target tank level and the actual tank level. The PID (Proportional–Integral–Derivative) controller then computes a correction that is added to the steady-state outlet flow to determine the net desired inflow.
• Mixture PID Controller: Adjusts the distribution of the net inflow between Fluid A and Fluid B to achieve a desired mixture (percentage of Fluid A in the tank). It calculates the error between the target mixture and the actual mixture and computes a correction. This differential correction is used to split the net inflow between the two inlets.

The net inflow is split as follows:

• Fluid A inflow = (Net inflow + Mixture correction) / 2
• Fluid B inflow = Net inflow - Fluid A inflow

Tuning the PID parameters (Kₚ, Kᵢ, and K_d) is critical:

• Kₚ (Proportional Gain): Determines the reaction to the current error. Higher values result in a stronger reaction.
• Kᵢ (Integral Gain): Eliminates steady-state error by considering the accumulation of past errors.
• K_d (Derivative Gain): Predicts future error based on the rate of change, helping to reduce overshoot.

Use the sliders on the left panel to adjust the setpoints and PID parameters. The live diagrams show how the setpoints (red lines) compare with the actual measured values (blue lines) over time.

The physical simulation on the right shows the tank with a blended color indicating the mixture (blue for Fluid A and red for Fluid B), valve gauges representing the current valve openings, and a display of the current tank level and total volume in liters.

Experiment with the parameters and observe how the regulators adjust the inlets to maintain the desired level and mixture.

Kjell-Ove Mickelsson LKAB