Capacity Increase Leads Mineral Water Company to Go Underground
APPLICATION OVERVIEW
A mineral water company specializing in supplying high-quality products has implemented a new loading terminal building which is set up beyond the previous filling systems as part of a capacity increase. A 320-foot long (100 meters) underground conveyor line links the new building and existing production facility. The new line was specified to handle a total transport distance of more than 1,300 feet (400 m), with throughput of 5,400 crates per hour.
INTERBUS was chosen to network the system’s frequency converters as well as the digital inputs and outputs from PLCs used as control elements. Thirty-nine converters were assembled in the central switch cabinet near the conveyor loader and unloader, while another 76 were distributed and mounted along the conveyor line.
INTERBUS is the network for all devices, including the two converters and one digital I/O module which is continuously accommodated in subdistribution boards.
All information is stored centrally in the INTERBUS controller or in the PLC, enabling the system to boast almost 100% availability. While service is being performed to the system, each device on the bus can simply be replaced without any required adjustments to the devices or the system. A simple command incorporates the device into the system.
CONTROL SYSTEM
Process Data
Process data flow includes control word data as well as nominal or actual values. Typical data length in this application is 16 or 32 bits, and the data must be provided with up-to-date information in a matter of milliseconds.
If parallel wiring were to be used in place of INTERBUS, signals would have to be connected individually to the converter.
The conveyor transport system sees “Control Word 1” as “Process Data Word 1”, and “Speed” as “Process Data Word 2”. This word controls the converter as familiar I/O commands. Depending upon the command used, the converter can supply status information about its condition. INTERBUS makes it possible to process both fault and operational messages in a straightforward manner.
Parameter Data
Parameter data includes the device-specific data structure. It is possible to occupy up to 230 bytes in the
converters. Parameter data can be specified for particular uses such as acceleration ramps. Parameter data has different demands on the bus system since it is not time-critical, though it must be possible to send this data to individual converters at any time without interfering with process data transmissions.
“Total Frame Protocol”
While the above requirements may be seemingly contradictory, INTERBUS has enabled the efficient transfer of both process and parameter data. In the system’s “total frame protocol,” data from individual devices occupies a certain number of words. The intelligent controller prepares a data message for all stations. The time-critical process I/O data are read or written in a single cycle. This data message also incorporates parameter data, assigned to a different area of the message destined to the converters.
RESULTS/BENEFITS SUMMARY
- The conveyor belts can be viewed as a single unit comprising both mechanical and electrical components. The designer simply copies the conveyor portion of the system’s design as often as required, considerably reducing the number of required circuit diagrams.
- The facility’s electrician can fully test system functions in advance.
- The system is set up by simply connecting the supply cables and the bus cable; local device settings are not required. Upon system power-up, the INTERBUS controller automatically detects and stores both functions and specific ID coded addresses of all devices connected to the network. The system recognizes any device meeting the INTERBUS DIN 19258 standard, making it easy to mix-and-match devices from different manufacturers.
- Cabling complexity is reduced to a minimum, saving on both cable and installation costs.
