The model function played by the automobile industry is one of the reasons why all other branches in industry fall back on the fast and uncomplicated bus. The field-bus system is gaining increasing influence in the food and beverages industry as well. It has already become established in all major fields and primarily those where innovative management focuses on efficiency as well as lower costs.
Project planning
The basic conditions shall first of all be defined when planning extensions to the plant, new equipment or modifications to installations are already in service:
What are the quantities of data to be transmitted, what distances are involved, what other physical influences are to be expected, etc.
Seeking professional advice as early as in the planning phase is to be recommended and the Interbus Club can be of assistance here, in particular in that attention shall be paid to those details that have been overlooked as well as to the benefits that Interbus can offer.
Why Interbus?
One major advantage of Interbus is the structure of this field-bus system: Interbus is a closed-loop system whereas all other bus systems have a line structure. It can be said without going too deeply into the technical details of the characteristics that only Interbus realises a constant processing time (cycle time). This is important for a predictable behaviour by machinery and sections of the plant. Interbus transmits 4096 I/O data in less than nine milliseconds and this for a low, and hence insensitive, clock-pulse rate of 500 kBaud. Commercially available cables are used for the transmission.
Extensive installation often requires branching into several sub-levels. Interbus offers the possibility of creating a tree structure with up to sixteen levels to meet all requirements. As many as 255 bus nodes can thereby be realized.
Interbus allows individual areas in sections of the plant to be shut down without causing any detrimental effects in the remainder of the system. Thus only that section of the plant in question needs to be shut down in order to carry out repairs in the event of a fault or inspection work.
Cost-saving as early as during installation
The costs that can be saved by using Interbus as the field-bus system become apparent as early as in the planning and commissioning phases. There are considerable savings to be made in cable racks, the holes through masonry walls are much smaller than for parallel cabling and the number of switching-cabinet meters is considerably less. The commissioning time for the Interbus closed-loop system is significantly shorter than for line-structured systems. Whereas in line-structured systems, each segment (intermediate section between two bus participators) has to be put into operation separately, the Interbus master automatically puts the sub-routes into operation and without needing the user for this. Should the master not find the participator, for instance in the event of wiring being incorrect, then an appropriate message is given on the integrated display together with information of the location for this (Figure 1).
Figure 1
The display is intergrated in the master module
The extensive experience in commissioning acquired throughout the world confirms that with Interbus, the times required for commissioning amount across the board to only some 20% of the time and effort otherwise needed. For the plant operator, this plays an important role in two respects: The commissioning costs are lower and production can be started up sooner.
The programming tool “CMD” (Configuration, Monitoring, Diagnostics) includes diverse protocol functions. The plant operator can carry out modifications and extensions himself thanks to the straightforward operation of the Interbus system with the help of CMD.
Diagnostics possibilities
Most of the plants in the food and beverages industry reach an efficiency exceeding 90% by the end of the commissioning phase. According to experience, this then falls as early as after 6 months to between 80% and 75%. How can Interbus as the field-bus system contribute to maintaining the efficiency of the plant? This essentially depends on how quickly faults are detected, localised and rectified. As system failures are extremely seldom, those faults that occur more frequently should be diagnosed thoroughly. Interbus can detect and localise faults in the plant. One example is the failure by a fuse caused by a damaged cable or a defective sensor. The fuse used in the input and output modules would burn-though and generate a message on the display for the module. At the same time, the fault message can be forwarded over a register to the control system for further processing in the programmable controller and generates an entry in the table at a higher-level system for the acquisition of operating data.
In the same manner, all anomalies occurring are registered and signaled. Even faults difficult to isolate, such as for example, sporadically occurring faults attributable to EMI (electromagnetic interference), can be localised and recorded. Such a failure analysis is not possible for conventional cabling or with other bus systems.
Preventive maintenance (here for once without high costs) provides the possibility of detecting faults before these occur and hence of being able to react in good time. An interruption in individual wires is an early warning for a pending cable rupture. The cables used for Interbus are highly flexible and exhibit a low bending radius, and thus are less sensitive than other types of cables. Should damage however result, then this is manifested in the form of intermittency in the transmission path. This leads to discrepancies in signals without the whole system shutting down. Such a cable rupture can be detected in good time with Interbus in service, and longer system downtimes can be avoided. The often quoted keywords here of “Preventive Maintenance” have become reality with Interbus.
Special products
One example is the motor control switch (Figure 2) specially developed for the food and beverages industry. This component is available both as a mechanical version up to 4 kW as well as the electronic variation up to 1.5 kW in IP67 stainless steel housings. A version as a frequency converter rounds off the product range. These devices can withstand splashing water, acid, lye and aggressive detergents and are controlled via Interbus in the plant installed in the immediate vicinity of the motor. The signals from neighboring initiators can be collected over the four integrated digital inputs. Control is possible at all times because the momentary current flow can be read off via the bus by the programmable controller. Deviations beyond the programmed limiting values can be assessed. A terminal for manual operation is available in the event of an operational fault, and hence the drive system can be controlled independently of the bus.
Figure 2 The motor control switch in the IP67 protected stainless steel housing (in This case opened) is a special development for the food and beverages industry
This is just one of the diverse developments available to the market that merge together in the Interbus Club from more than 600 companies. The complete list of suppliers together with the products available is available free-of-charge from the Interbus Club.
Outlook
Continuously further-developing engineering requires on-going expansion of the range of products that are Interbus-compatible. Interface modules for Simatic S7 control systems are available, as are Interbus masters for products from all the other prominent manufacturers of programmable control systems (Figure 3).
Figure 3 Interbus interface modules in the S7-400 control system
Forward-looking is also the trend to PC-based control-system solutions based on worldwide standardized software such that the classic stored-program control system may no longer be available in the foreseeable future. Plug-in cards for the PC slots will take over automation tasks in future, and the efficiency of these will be upgraded to the most up-to-date processor generation on the market. A wide program of such products is already available today.
Control-system logic, bus control systems and visualisation can be united in a simple way in one unit by this means.
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