Data Communication Between Industrial Control Instrument And Monitoring Configuration Software

1. Introduction
At present, intelligent instruments used in industrial field usually have data communication function. For the measurement and control equipment using fieldbus technology and standard communication interface, when they are configured through the configuration software, because the configuration software is for open measurement and control equipment, it is generally easy to establish the communication between industrial control PC and equipment. However, the industrial measurement and control instruments widely used in the industrial field still mainly use RS232 or RS485 communication mode. Compared with the fieldbus technology, RS232 and RS485 can only represent the physical medium layer and link layer of communication. If you want to realize the two-way access of data, you must write your own communication application program. Most of these programs can not meet the ISO / OSI specification, can only achieve a single function, suitable for a single device type, and the program is not universal. In view of this situation, this paper introduces how to realize the data communication between the instrument and the industrial computer system through windows OLE technology, using other third-party application development tools to generate ActiveX controls for data communication, and using ActiveX controls for real-time database interface provided by configuration software.
2. Structure of industrial control configuration system
Industrial control configuration system is mainly composed of industrial field control instruments, detection instruments and industrial control computers. The system configuration is carried out through monitoring configuration software. Industrial field instruments realize field control, monitoring, display and real-time data transmission. The operation data of each control or detection point on the site is transmitted to the upper industrial control computer in real time by RS-485 communication interface. The industrial control computer calculates, analyzes, processes and stores the operation data of each point on the production site, and generates the real-time operation process curve, operation parameter data sheet, diagnosis and alarm of each fault condition, etc.
3. ActiveX control for data communication
The I / O device driver of industrial control configuration software is a bridge for the interactive communication between configuration software and I / O devices such as PLC and intelligent instrument. It provides a good data communication environment for I / O devices with standard communication interface. However, instruments with non-standard communication interfaces usually need to be specially developed by the manufacturer's special development software, which is difficult and inconvenient. However, industrial control configuration software is usually a standard control container, which supports ActiveX controls based on Component Object Model (COM) technology of windows that can be automatically called by the outside. Therefore, data communication ActiveX controls for control instruments can be generated with VB, VC + + or other third-party application development tools and packaged in the form of OCX. The configuration software registers and inserts the data communication activcx control through the control manager, directly references the properties and methods of the data communication AC tiveX control in the built-in program language script program, calls the special data communication function, sends data to the field instrument or returns the field data directly to the configuration software. So as to realize the data communication between configuration software and industrial field instruments.
4. Real time database interface control
The industrial control configuration software itself also provides many ActiveX controls, among which the real-time database interface control Dbcom is specially provided for external third-party programs. The real-time database db of the configuration software is an open data platform, and Dbcom has various standard interfaces, Users can call Dbcom in various common development environments (such as VB, VC +, C "etc.) to access the data in the configuration software database db. Users can access real-time data, historical data and setting data in the DB through Dbcom. The accessed data can be local database or database on other remote computers on the network [1] 。 First, the data communication program between the industrial control computer and the on-the-spot instruments is compiled by VC+. Then the DBCOM control is invoked, and all variables that need to exchange data with the field instruments are defined by attribute Tag-Pars in the DB database. In the data communication program, once the communication with the field instrument is successful, the specific control method provided by Dbcom can be used to access the database in the configuration software to realize the data communication between the field instrument and the configuration software. Dbcom also has the event processing function. When the data changes, the event ondatachanged will be automatically generated to notify the variable sequence number or variable name defined by the attribute tagpars, and refresh the changed data value. This will simplify the programming of data communication program and improve the real-time data communication between field instruments and industrial control configuration software.
5. Conclusion
For industrial field instruments whose data communication interface does not comply with ISO / OIS specifications, it is generally difficult to program their data communication through the I / O device driver of the configuration software when they are configured by the industrial control configuration software. The method of realizing data communication between industrial field instruments and industrial control configuration software by using OLE technology and control programming is introduced in this paper. It is a relatively simple and effective method in practical engineering application.

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