Use of web services in technological process control systems

The optimal control of technological objects and processes is usually implemented by computer control systems with complicated structure and relations between elements. On the one hand, it allows to perform the functions of automatic control and regulation, alarms, process status registration and visualization. On the other hand, this leads to a significant complication of the systems because of increased process intensity, speed, accuracy and quality requirements.Use of web services is the most popular approach to solve the problem of integration and coordination of system elements. It is based on the exchange of messages of a special (universal) format between parts of the system and processing the responses.The role of web service and its place in control system has been analyzed. The most appropriate place is between the levels of PLC - controllers and SCADA one. It allows you to receive current information about the state of the technological process and implement the following functions: data acquisition by controllers; storage data to the database; providing data to the operator on demand and it’s visualization in real time; monitoring and alarms of process parameters.The web service build with Microsoft ASP.NET has been proposed for use in computer control systems. The key benefit of this technology are: open-source, cross-platform, fast and scalable. The development of web-services in control systems is a universal approach that can be applied to a large class of objects or processes. In the article the web service for temperature control has been proposed. The key task of the system is temperature data acquisition from the control object, to save information to the database, visualize the temperature curve, notify when the temperature exceeds limits.Since the Microsoft technology stack is already in use, MS SQL has been chosen. To increase the speed of development the Entity Framework Core application has been used, which provides a way to interact with data. To provide the security of the database and prevent development errors, a library has been implemented to access the database. It provides two interfaces Repository and Unit Of Work. Repository is an interface for interacting with each object in the database. The advantage of this interface is abstraction that removes dependency of a specific class implementation.The hardware of control system consists of programmable platform Arduino and such modules: Arduino Uno – the platform on the Atmega 328 microcontroller with built-in interface SPI, I2C, UART, 5 analog inputs and 13 discrete built-in power lines 3.3 and 5 V; MAX6675 - signal conversion module (12-bit ADC); thermocouple type K; ESP8266-01 - module with Wi-Fi interface; DS3132 - real time clock module.The modules interact according to the following algorithm: Arduino calls the thermocouple module and remembers the value, then calls the time module and forms a data period in which it places the time and temperature value. The controller module transmits data to the ESP8266-01 via a programmed UART interface. The Wi-Fi module reads data on the UART bus, forms HTTP request headers and sends JSON text to the server.Thus, web service for SCADA-level has been developed. The control object based on the Arduino hardware platform has been simulated. The developed web service provides the necessary level of security, high indicators of convenience of the human-machine interface, allows to analyze the object and track the past state of the system.