Coupled Tank gadget/system (CTS) is extensively used particularly in chemical process industries. In procedure industries the controlling of tanks is important. Whenever we talk about controlling it means that we need a closed loop system. In industries liquid is pumped into tanks and after certain processing the output of the tank is pumped into another tank at a certain desired level. It is important to maintain a level of the tank and regulate flow between tanks. There are many solutions for controlling the liquid level of (CTS). In this project we have developed a PI controller for (CTS) when there are three tanks and each have separate input and output and they are also coupled, then controlling of this sort of system becomes more difficult. In recent past the level measuring approaches was very traditional. Most of the project uses probes to measure the level in each tank. This method has problem that you have to use many probes for level measuring in the tank and if any probes or wire got short with other wire than level is automatically lost. So in order to resolve this issue we proposed a new approach of level measuring that is measuring level without in contact with tank. The approach we propose is different from the recently proposed approach in the research paper written by Vishal Vaisastha in IJMET in 2015. 
The project is divided in two sections, first one is software and second one is hardware. The software section is main part of this project because it contains the PI controller for CTS. In recent past as we look at vishal vaisistha work and Yeshudas Muttu work we can easily see that digital controller has easy to implement and can easily be replaced with any other controller. So in our project we also prefer to use digital PI controller because this reduces the circuitry that we have to make and only to design the interface and hardware section.
In recent past, Yeshudas uses NI DAQ card between software and hardware. This card need a multiple other circuits or to buy modules to be implemented or connected in order to work properly, this increases the cost of this project. If we look at Yeshudas paper we reach on solution that he had not designed the hardware he on . So we have to proposed another solution regarding this problem. We are proposing new way of interface between software and hardware which is arduino. Arduino is cheap and can easily be bought from local market. Arduino has a feature of compatibility with matlab and can easily receive PWM signals and can easily write level measurement to matlab for Analysis of data and performance of the system.
There are many tuning methods for PID controller such as Auto tuning, Z-N method, Trial and error method and C-C method. These methods have their own benefits and losses. The best method is Z-N method because this method produce stable output.