System Diagnosis Technology Based on PROFIBUS

For a long time, PROFIBUS technology has provided excellent products and solutions for a large number of users. However, with the further development of automation technology, users have higher and higher expectations for automation systems. They are not only satisfied with using automation products to construct an automation system and implement an automation task, they expect automation products and technologies to play a greater role and generate greater value throughout the life cycle of the project.

Value engineering drives the development of diagnostic technology

From this chart, if we use the value engineering method to evaluate the life cycle of an automation system, we can divide it into the equipment installation stage, system debugging stage, equipment commissioning stage and aging maintenance stage. Generally speaking, end users and owners can only benefit from the automation system after the equipment is put into production and operation, and the user's investment is the largest in the early stage of installation, and decreases as the number of equipment purchased decreases. After entering the system debugging stage, the main expenses are the commissioning engineering and technical personnel and the use of production time. Among them, the longer the debugging cycle, the later the production will be put into operation, and the greater the loss and investment will be. The cost of entering the equipment aging and maintenance stage has increased, which is mainly due to the aging of the product and the expenditure of accessories. We look forward to using fully integrated automation technology, especially SIMATIC's PROFIBUS-based system diagnostic technology, to create more profits and benefits for users and owners in the installation stage, debugging stage and equipment aging stage. From the perspective of the equipment installation stage, if the installation cycle can be effectively shortened and the installation quality can be improved, the installation cost can be reduced by up to about 8%. If the debugging progress can be effectively accelerated during the debugging stage, the entire construction period can usually be shortened by 10%, which means that production can be carried out in advance. Of course, reducing downtime during the equipment production phase is the most important concern for users, especially front-line maintenance personnel. After entering the aging maintenance phase, our goal is to eliminate hardware failures within 5 minutes, which can greatly reduce the workload of on-site maintenance and improve the production efficiency of the automation system.

Diagnostic technology must serve the entire project life cycle

SIMATIC's PROFIBUS-based diagnostic technology can optimize the value engineering of automation systems and provide support for the entire project life cycle. From equipment installation, system commissioning, and system operation and maintenance, system diagnostic technology can provide installation engineers and commissioning engineers with rich and detailed system diagnostic information; it can provide accurate and detailed equipment diagnostic information to equipment operators, front-line electrical maintenance personnel, and production equipment management personnel. In addition, due to the characteristics of fully integrated automation, this diagnostic information can be easily and effectively displayed on the human-machine interface in a graphical manner.

We know that PROFIBUS is a low-voltage, high-frequency time-differential signal system. Therefore, the connection quality and signal quality of the communication cable are particularly important. According to our experience, 95% of system installation errors and communication problems are caused by improper connection of the communication cable. Therefore, Siemens provides a complete set of fast and effective connection solutions. These include specially designed quick-connect cables, quick-connect connectors, and quick stripping tools. In this picture, we can see that according to the selected model of the quick-connect connector, we can easily measure the length of the stripping tool to be stripped, and then because the built-in multi-layer blades in the stripping tool can very accurately strip the protective layer, shielding layer and support layer of the cable at one time, in this way, electromagnetic compatibility problems caused by insufficient shielding layer length or too long communication line can be eliminated.

The most important task during the debugging phase is how to quickly and effectively optimize the communication relationship between on-site devices and eliminate the source of errors.

The handheld bus physical tester BT200 is specially designed for the evaluation of the quality of PROFIBUS field connection. The design object of BT200 is the electrical construction personnel on site. Therefore, through the simple LED display and clear button design, general electrical personnel do not need very professional PROFIBUS communication and network knowledge background to independently evaluate and check the connection quality of the field network, and transmit the test results to the computer through offline mode. The BT200 handheld bus physical tester can easily complete the inspection of the bus cable disconnection fault, short circuit fault, and voltage fluctuation. At the same time, the cable length can be determined by locating the cable reflection technology, so that most field connection errors can be solved. For single devices connected to the PROFIBUS bus, the tester can also test their PROFIBUS interface circuits. Inside the tester, an RS485 driver has been integrated, with a built-in 5 volt voltage and RTS signal. The handheld bus physical tester can automatically detect all accessible sites on site and generate a list of active sites. Currently, the tester supports multiple language versions.

All test results can be easily transmitted to a PC via point-to-point cables. The dedicated software package included with BT200 can effectively analyze and process the data.

The test report can include the test results of the system's main cable and a single communication node, as well as the cable connection quality report. These reports can serve as a technical basis for project acceptance and quality control.

In addition to the handheld tester, we can also use the diagnostic function integrated in STEP7 to analyze the project. First, we can upload the current bus configuration through STEP7. Its working process is as follows: STEP7 automatically detects all accessible stations connected to PROFIBUS, then confirms the status of each active station and reads the actual configuration information of the active station. This information is stored in the buffer area of ​​STEP7, and engineers can access all the information by connecting online. Since the above work can be completed without starting the PROFIBUS master station, engineers can selectively diagnose various process sections and automation systems of the entire project.

STEP7 can also access the diagnostic buffer of the PROFIBUS master. Since each device connected to the site will send a corresponding diagnostic message to the PROFIBUS master, engineers can find the details of all diagnostic events they want to know in the buffer. These diagnostic events are divided into two categories, one is external events caused by signals stored on the site, and the other is internal events stored in the system. All events are accompanied by time tags (including month, day, year, hour, minute, second and millisecond). Each diagnostic event contains a certain length of detailed information description, so engineers can accurately analyze the cause and location of the diagnostic event through time and formulate corresponding countermeasures. Users can also define some user events themselves, and send diagnostic messages to the PROFIBUS master when certain conditions are met.

Through engineering software such as STEP7, engineers can easily complete project debugging. During the operation phase of the equipment, for end users and front-line operation and maintenance personnel, the system diagnostic function is mainly to quickly locate faults and reduce downtime.

The demand for advanced diagnostic functions has led to the emergence of professional fieldbus diagnostic equipment

The newly developed repeater with diagnostic function can perform continuous expert-level diagnosis on the entire production automation system. The function of the standard repeater is mainly to solve the attenuation and delay problems caused by the signal during long-distance transmission. The standard repeater can effectively amplify and regenerate the signal, thereby expanding the scale of the network and ensuring good communication quality. The repeater with diagnostic function integrates all the functions of the standard repeater and has powerful diagnostic functions. The diagnostic repeater appears as a separate slave in the system configuration. This device can be easily configured in STEP7 and other standard PROFIBUS network configuration tools. So, what functions does the diagnostic repeater have?

The diagnostic repeater can implement expert diagnostic functions, such as name resolution of PROFIBUS segments, system fault location, distance measurement between stations, and generation of detailed fault type reports (such as sensor disconnection and short circuit).

The diagnostic repeater starts the diagnosis of the PROFIBUS network from the topological logic detection of the system bus. By calling the SFC103 diagnostic repeater, the actual topology of all networks and the list of currently accessible stations can be easily obtained. Since three PROFIBUS interfaces are integrated, the repeater can realize the single-sided connection of the PROFIBUS master station and connect two subnets. Two measurement systems are integrated inside the diagnostic repeater to complete the reflection calculation of the cable, thereby effectively improving the measurement accuracy and reliability. The integrated function of the ordinary repeater can connect up to 62 PROFIBUS stations. The communication rate of the adaptive network can reach up to 12 megabits per second. Up to 9 cascaded repeaters can be deployed in one system.

The diagnostic repeater can even perform graphical diagnosis of the PROFIBUS network. Engineers can access any connected network segment through online connection. The diagnostic repeater can graphically display the specific location of the fault, such as between nodes X and Y, and can calculate the specific location (accurate to meters). At the same time, the diagnostic repeater can also report the possible causes of the fault and give technical advice. The diagnostic repeater can also graphically display the topological logic of the current PROFIBUS network. The test results can be displayed in STEP7 or stored in the user's data area. The diagnostic buffer is also integrated in the diagnostic repeater. For each connected network segment, it can store the last 10 diagnostic events that occurred, and for each diagnostic event, detailed information based on timestamps and graphical display are provided.

The diagnostic repeater can also generate a communication quality assessment report based on the time axis. We can see that since the diagnostic repeater has a built-in oscilloscope function, the horizontal axis is based on time marks, and the vertical axis shows the number of communication conflicts and communication errors that occurred in the current network. Therefore, we can easily determine the operating status and quality of the current network through this chart and thereby find the reasons for the decline in network communication quality and effectively improve it. This statistical result can be used as a technical basis for project acceptance quality control and system evaluation.

Display of on-site diagnostic information

For front-line operators and maintenance personnel, intuitive, fast and clear display is their main requirement for system diagnosis. Within the framework of fully integrated automation, all active stations in the system will regularly send diagnostic messages to the PROFIBUS master, and the PROFIBUS master will automatically and regularly transmit the diagnostic messages to the human-machine interface system. Therefore, engineers can get detailed and clear information on the human-machine interface without intervening and programming this process.

In STEP7, the variable definitions and labels in the control system are completely consistent with those in the human-machine interface system and share a unified database. Therefore, users do not need to intervene and program the transmission of information between the automation control layer and the human-machine interface layer. In short, this process is automatically triggered and implemented by the framework of fully integrated automation.

At the human-machine interface of Totally Integrated Automation, users can get a predefined and designed diagnostic screen for free. On this diagnostic screen, the PLC automatically completes the diagnostic data packet function call (FB125), and the on-site personnel can directly see the diagnostic screen of the entire automation system. And they can selectively access a single node. In the single-station browsing interface, the system will report the node status, affiliation, the slot where the fault occurred, and the channel number, and can even clearly indicate the fault information and type caused by external wiring and sensors.

Promotion and application of diagnostic technology

The large-scale promotion of diagnostic technology will inevitably drive the improvement of the overall level of automation technology and will become a new hot spot in the market in the future.