Recycling scheme is in the can thanks to P-NET

A Scandinavian recycling company has specified P-NET (IEC 61158/4) as the fieldbus of choice to network thousands of retail outlets for the purposes of controlling the return of bottles and cans.

A Scandinavian recycling company has specified P-NET (IEC 61158/4) as the fieldbus of choice to network thousands of retail outlets for the purposes of controlling the return of bottles and cans for recycling.

"Green" legislation in Denmark dictates that drinks containers include a levy on purchase, which is refunded on return by the consumer.

The logistics of such a process warrants the use of automation to identify each container type and source, and to credit the shopper with the cumulative deposit.

It also involves the sorting of bottles and cans for return to the supplier.

To do this, each container must be identified with a bar code.

The process is known as "Reverse Vending".

The enormity of the project is tempered by the fact that all Reverse Vending machines (the unit into which the shopper puts the empty bottles and cans), sorting machines, and other "behind the scenes" equipment, have their own local control units each with a P-NET communication interface.

All units are structured around a cluster of P-NET control modules (called a CS-box), which have been developed and manufactured by Proces-Data A/S.

The CS-box, which holds a database of all the legitimate bottles and can types that will be accepted and records all the transactions that have been made on this unit, can also communicate with a central depot for database transfer via P-NET and GSM modem.

Each I/O module and programmable controller is clipped together on a single DIN rail and they communicate between each other by means of built-in IR light pipes using the multi-master P-NET protocol.

Local control and monitoring is provided by a keyboard/display unit, which is also connected to the P-NET Fieldbus.

Because of this common fieldbus structure, it is possible for a shop to choose between a number of competing equipment suppliers to achieve an optimum solution, considering price, as well as functionality.

For example, a shop can buy a Reverse Vending machine from one company, and a sorting machine from another, and still be certain that the complete system will work.

The Dansk Retursystem company has been granted the sole right to appoint systems integrators to manufacture and install such machines.

Following an EU wide tendering process, a systems integration company has been made responsible for the hardware implementation, and another company for the data collection, maintenance and service software for the project.

The first contract involves some 2500 shops and supermarkets in Denmark, although it is anticipated that some 10,000 outlets will potentially be fitted with these recycling systems.

The system has been fully operational for some time in nearly 2500 shops, and has now been proven to be completely reliable and robust, even during peak load periods.

This was demonstrated recently, when the deposits required for all types of bottles and cans were reduced.

This meant that the quantity of returned bottles and cans increased dramatically in the days before the change.

In addition, the central database servers had to call all the shops via the GSM interface to update the local databases with the new rates.

This was all done overnight while the shops were closed, and caused very little disruption or problems.

One odd exception was that it was found that a number of aerials from the GSM modems had been stolen!.

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