Terminology
Used terms

In the area involved in the control of machines are used shortcuts that characterize the machine control. Abbreviations used are taken from the English terminology, these include:

- CNC
- PLC
- PAC
- HMI
- DCS

## Numerical control - CNC (Computer Numerical Control)

Development of industrial production has brought with it the need for increased production of machine tools and forming machines. Machine control that was classic manual or cam was replaced by digital control. The first numerically controlled machines appeared in the 40th and 50 20th century. Servo control instructions for these machines were on punched tape (NC machines). With the development of computer technology, the machines were equipped with this information technology (CNC machines).

In modern CNC systems are highly automated component design using CAD programs (Computer-Aided Design) and CAM (Computer-Aided Manufacturing). These programs create a computer file that lists the sequence of commands needed to operate a particular machine, which can be equipped with various machine tools - machining centers.

## PLC (Programmable Logical Controller)

Programmable logic controller (PLC) or programmable controller is a digital computer, which is used to control the operation of machinery and production processes. PLCs are used in many industrial sectors. Unlike general purpose computers, the PLC is designed for processing information from multiple inputs, is more resistant to temperature changes, to electrical interference and vibrations and shocks. Programs for the control of the device are typically stored in battery-backed or non-volatile memory. PLC operates in real-time system, because the output commands must respond to changing input conditions.

## PAC (Programmable Automation Controller)

PLCs are gradually supplemented by new features that are no longer simple functions of logical type. They are complemented not only by regulatory roles, but a whole range of tasks in which there are also very demanding numerical algorithms and algorithms of artificial intelligence. For their designation is sometimes abbreviated PAC (Programmable Automation Controller), which can be translated as "programmable automation system."

## HMI (Human Machine Interface)

Meaning this acronym describes the user interface. This is a place where there is an interaction between people and machines. The aim of the interaction between man and machine in the user interface is effective operation and control of the machine, and feedback from the machine. This is the information about the state of the machine or its components and the values of measured quantities ongoing technological process. This information helps the operator in taking operational decisions in the control of machines and processes.

The user interface is a system that includes hardware (physical) and software (logical) components. There are different systems of user interfaces from simple mechanical to computer systems. Currently, industrial process control use SCADA visualization programs (supervisory control and data acquisition), enabling the data to be displayed with animations.

## DCS

These systems (Distributed Control System) is a large process control systems (PCS Process Control Systems - sometimes abbreviations are used as synonyms), which began to be used in the 60 years with the advent of the first control computers, which represented the numerical solution of the centralized control of large technological systems such as chemical processes, power plants, etc. They were built as suitable centralized solution. The 70 years there have been the first control minicomputers, which, while allowing partial decentralization. These solutions were used throughout the 70 summer and the beginning of the 80 years. These systems are generally divided into DCS: for power, for the nuclear program, for other technological processes, control systems for buildings.

Some DCS systems are specialized, some are, however applicable in more areas. Exceptions are control systems, where extremely high demands on safety and reliability of the control system. Highly secure and reliable systems are very expensive and therefore not deployed where it is not absolutely necessary.

DCS system is characterized by strict hierarchical construction with three levels of control that is bottom-up:

- sensors level - sensors, actuators,
- the level of the first control (technology control and regulation),
- operator level,
- Superior level.

In any case, however, still represent a large DCS control system with only a high degree of reliability in areas where it is necessary to treat a large number of inputs and outputs of various types and where reliability and security is absolutely categorical requirement. Their advantage is also the compactness of the system.