The article presents developed method and general principles of creating ladder diagrams, which are commonly used for systems with programmable logic controllers (PLC). Ladder diagrams are created for sequential control systems of technological processes, which are described by a connection pattern, time diagrams of the executive elements` operation. The executive elements are double-acting pneumatic or hydraulic actuators controlled by bistable electrovalves. A method of designing sequential systems enabling the creation of a ladder electro-pneumatic system is presented. The ladder diagram consists of two parts. One is responsible for controlling the valve coils, the other for the implementation of the memory block. The signals that control the transition to the next state are the signals described on the boundaries of the graph division. The synthesis of control systems and their verification was carried out using the computer aided program FluidSim by Festo.

There exist numerous modelling techniques and representation methods for digital control algorithms, aimed to achieve required system or process parameters, e.g. precision of process modelling, control quality, fulfilling the time constrains, optimisation of consumption of system resources, or achieving a trade-off between number of parameters. This work illustrates usage of Finite State Machines (FSM) modelling technique to solve a control problem with parameterized external variables. The structure of this work comprises six elements. The FSM is presented in brief and discrete control algorithm modelling is discussed. The modelled object and control problem is described and variables are identified. The FSM model is presented and control algorithm is described. The parameterization problem is identified and addressed, and the implementation in PLC programming LAD language is presented. Finally, the conclusion is given and future work areas are identified.