The process plant's measurement and control tasks can be completed by fieldbus technology, while the plant using fieldbus technology will benefit. Intelligent field devices can provide higher accuracy. Only one conversion is needed from analog to digital, and the transmission of digital data can be guaranteed by parity check and other methods, thus ensuring the high precision of the control loop and the high stability of the output.
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Today's field devices can transmit additional status information such as normal operation or fault information, or other status of field devices. The purpose of preventive maintenance is achieved through some regular status information of field devices. DCS manufacturers call it an asset management system. These functions can have a multiplier effect for equipment maintenance in many cases.
In addition, if the field device is replaced during the batch process or when the plant is in operation, the remote configuration function through the fieldbus can greatly improve its working efficiency, and the above advantages can be integrated in the process automation industry, even in relatively conservative applications. Occasionally, field buses have undoubtedly established their status.
Advanced diagnostic tools unveil the mystery of fieldbus communications <br> Many people who first come into contact with fieldbus networks always see it as a "black hole" or an obscure channel. Data is input into the channel through the DCS and is Received by a field device, and vice versa, this process is more or less mysterious. In fact, the reason is simple: When multiple devices are connected in parallel by the same cable, the communication signal has a more complicated degree. This is especially true when comparing 4-20mA technology. When a cable is connected to only one field device, its load current can reflect all the information: measured values, short-circuit conditions, and the degree of cable damage.
The advanced diagnostic module automatically monitors the physical layer status of the fieldbus during device operation. Its monitoring value can be read in the control room. Its general alarm information can be easily integrated into the plant control system via the OPC interface. Operation and maintenance personnel sometimes have very ambiguous descriptions of operational behaviors, such as: "The equipment is running well all day - only suddenly the signal has disappeared for several hours, but then it appears again" or "the LCD of the field equipment" There is electricity, but the device exists only momentarily in the segment activity list." In most cases, because the handheld tool cannot interpret the fieldbus cable data signal, the necessary information cannot be reported to the user, which in turn causes the above-described recording to describe the occurrence of ambiguity.
Today's fieldbus diagnostic tools make the fieldbus physical layer and its communication transparent — such as the advanced diagnostic modules used in FieldConnex® Power Hub. The module can measure the power supply unit outside the supply voltage, network segment load current, bus signal amplitude, line noise or signal distortion. The diagnostic module can monitor the bus communication process and can distinguish between network segment information and individual field device information. Diagnostic Manager can display simple and clear information for the user to read - this transparently obscures the already obscured factory environment.
Abnormal situation <br> Every day, many situations that cause damage to the fieldbus physical layer and communications occur, but we cannot detect:
Use substandard cables,
Use a non-enclosed cabinet that may enter the water. Corrosion can cause attenuation of signal transmission in field devices.
Due to vibrations, burrs that may loosen the aging shield of the cable or field device may cause the fieldbus to be pole-balanced or short-circuited to the ground. Incorrect shield grounding will introduce more induced noise into the loop.
The reasons leading to the user's above-described ambiguous description are manifold. Any kind of condition can cause the fieldbus physical layer parameter to exceed the warning value, but it does not cause communication interruption. Fieldbus is a fault-tolerant system, but a variety of small faults add up and seriously affect its operation. At this time, any additional interference is enough to completely exceed the limit of the entire fieldbus system parameters, thus interrupting the communication. For example: Start the variable frequency motor near the main line of the bus and introduce the interference signal so that the field bus will be interrupted instantaneously.
The fieldbus physical layer is not really mysterious; it just needs to be clearly pointed out by the right tool, such as using advanced diagnostic modules. All of the above conditions can be detected and processed in a timely manner. During the debugging process, the higher the installation quality, the higher the fault-tolerant level of communication. However, this does not allow the user to satisfy: what the user needs is to be monitored before the disturbance is severe and early warning can be provided.
Warning and alarm functions for easy preventive maintenance.
The advanced diagnostic module monitors the fieldbus communication online in real time. Operation and maintenance personnel can view all data in the control room. There is no need for operators to operate in hazardous areas. No need to open the control cabinet or field junction box to get all the necessary information directly.
Communication: The communication signal is modulated on the power supply. The bit signal is the rising and falling edge of the rectangular wave and the peak-to-peak value is 1V. This makes fieldbus communication very stable and resistant to interference.
During commissioning, a warning value with a dead zone can be set for all measured values. As soon as the warning value is exceeded, a warning is triggered and transmitted to the operator station. At this point, the operator can use the advanced diagnostic module to diagnose: signal noise, signal grounding, etc., whether the situation shows signs of deterioration. The device operator can then make a decision based on these diagnostic information to determine if immediate repairs are needed, wait until the next shift for repairs, or wait until the unit is overhauled and treated again—all without compromising the factory's high-quality production levels.
Optimized production - peace of mind <br> If you can reduce the number of stoppages or unplanned losses, everyone should be rewarded. Even in the best state of the field bus, there may be transmission errors and bus cycle increases. Reducing system response time also helps improve product quality. Well-run fieldbus systems and equipment not only increase the reliability of the entire system and improve product quality, but also reduce the workload of plant managers, operations, and maintenance staff—monitored using the Pepperl+Fuchs FieldConnexTM advanced diagnostics module. The "black hole" fieldbus installation became clear.
Fieldbus: debug with advanced diagnostic tools
　　 Process plant with fieldbus technology