Control Station is software for process control training, tuning and analysis . The gravity drained tanks, shown below, is two non-interacting tanks stacked one above the other.
Liquid drains freely through a hole in the bottom of each tank.
As shown, the controller output signal manipulates the flow rate of liquid entering the top tank. The measured process variable is liquid level in the lower tank. The disturbance variable is a secondary flow out of the lower tank from a positive displacement pump. Thus, the disturbance flow is independent of liquid level except when the tank is empty. This is a good process to start your studies because its dynamic behavior is reasonably intuitive.