According to industry insiders – whether it‘s wafer fingers, rolls, or cones – every second wafer manufactured industrially worldwide is baked using a Franz Haas wafer machine developed in the Lower Austrian town of Leobendorf. Production lines for the most diverse wafer varieties – flat and hollow wafers, wafer rolls, ice cream cones, waffles, and wafer snacks – are developed at the Wafer Innovation Center there. As well as being highly flexible as a result of the automation side being modular, these customised plants must in particular satisfy country-specific safety standards in order to meet the applicable norms and directives of the respective target markets. With its new base unit PNOZ m B1 Burner, part of the safe small controller PNOZmulti 2 and specially developed for use in furnaces – including the TÜV-tested burner software module – the automation expert Pilz has created a solution for the safe control and monitoring of the gas burners in the Austrian wafer machine manufacturer‘s ovens. It’s an ideal solution for Bühler because global certification means it can be used as standard. 

As a result, the wafer machine specialist is able to implement functional safety as well as burner control, and so all of the safety technology for its automatic baking ovens, using a single, flexible, configurable and safe small controller. What’s more, with sophisticated diagnostic opportunities and a variety of communication options it is easily incorporated into the automation environment, which is usually specified by the customer. 

Safety Tasks of the Burner Control System

Company founder Franz Haas invented the first wafer machine as early as the end of the 1940s. In the decades that followed, the plant and machine manufacturer significantly shaped ongoing development of industrial wafer production with numerous other innovations. Since 2018, the company has belonged to the Swiss Bühler Group, with subsidiaries around the globe. 700 people are employed in the wafers area of the Consumer Foods division at the Leobendorf site, working in development, design, and production, as well as sales, service, maintenance, and spare parts management. Customers from all over the world come to the Wafer Innovation Center in Leobendorf to test and optimise production processes for their wafer products.
At the heart of every wafer production line is the oven. This may be up to 35 m long depending on the product and plant configuration. The heating is generally provided by gas-fired long tube burners. “The dough is poured on to individual baking plates, which circulate through the oven at up to 0.5 m/s. The typical baking time for a wafer depends on the product but is around 2 minutes,” says Wolfgang Grassberger, outlining the baking process. He’s responsible for machinery safety in the wafer division at Bühler. “The burner controller‘s most important task is to monitor the extinguishing of the flame and if necessary to interrupt the gas supply safely and immediately. In this way we can prevent the escape of unburned gas and, in the worst-case scenario, an explosion.” What supposedly sounds simple turns out on closer inspection to be a complex control sequence. It begins back at the ignition process, which already comprises almost 20 individual steps. “Each burner has two redundant, diverse main gas valves, which undergo a tightness test even before the actual ignition process,” says Wolfgang Grassberger, quoting an example. An ionisation current sensor detects the flame and therefore successful ignition – UV flame monitors may be used as an alternative. “The minimum and maximum gas pressure, the suction function, compliance with the permitted maximum temperature and many more are monitored during firing,” says Wolfgang Grassberger, listing a few more of the burner controller‘s safety tasks. 

Burner Controls and Monitors up to Six Burners Independently of Each Other

Bühler has been using the safe SIL 3 / PL e compliant small controller PNOZmulti from Pilz to implement functional safety on its machines since the early 2000s. The list of safety tasks ranges from emergency stop and safety gate monitoring through to the SLS function (Safely Limited Speed) for setup mode. “We maintain an excellent working relationship with Pilz and are already using the second generation PNOZmulti. We particularly appreciate the flexibility that the configurable small controller has to offer, with its numerous expansion modules, wide range of configuration and communication options and outstanding diagnostic functionalities,” says Wolfgang Grassberger, not sparing in his praise. “Of course, it‘s a real benefit to us that Pilz has developed its own, TÜV certified burner software block, which is flexible for us to use with our various, customised machine configurations.” That’s because the PNOZmulti 2 at Bühler now also carries out the tasks previously performed by separate burner controllers – and in keeping with the multi it is more compact and has greater functionality: one base unit PNOZ m B1 Burner controls and monitors up to six burners independently – previously a separate controller was required for each one. “The biggest advantage for us is that we can now standardise all the safety technology for our machines, i.e. functional safety and burner control, with a single system,” says Wolfgang Grassberger in a nutshell.

For Uniform Global Use

PNOZmulti 2 can easily be connected to higher-level automation environments via the communication modules available for all common fieldbus and Ethernet systems – another important aspect for Bühler given that the production lines are supplied worldwide and so must be appropriately diverse to consider the requirements of the different markets. The status and diagnostic data generated by PNOZmulti can easily be incorporated into the respective visualisation system. As a result, the current actual state of the burner can be displayed in individual steps and analysed in great detail. All information and, above all, error messages are visualised in plain text on the operator panel. “That is a real milestone for us and represents clear added value for our customers. So, the days when you had to read and interpret codes from flashing LEDs are well and truly over,” Wolfgang Grassberger explains. Bühler doesn’t rely on the often-preferred integrated safety technology but sees advantages in uniting the standard and safety controller in one system environment. Wolfgang Grassberger: “Using Pilz technology to implement all of the safety technology, completely independent from the standard automation, has many advantages for us. But what’s most important is that we can standardise use of the technology worldwide, because Pilz takes care of international certification, including for the burner management.” 
 

Retrofit Burners Also Included

The new burner version opens up another application area in the retrofit sector, as a replacement for older burner controllers without bus capability. PNOZmulti 2 is suitable here too because, as a modular system with wide-ranging configuration software, the configurable, safe small controller is flexible and adaptable in both hardware and software. This is confirmed by Bühler – some outdated burner controllers on existing installations have already been replaced by PNOZmulti 2: “Our systems often operate for decades. So, the availability of spares is just as much an issue as safety. In this respect it makes total sense to modernise using up-to-date safety technology and so this is an ever-increasing field for us.”
The Austrian wafer machine manufacturer is already working with Pilz on further modularisation of its burner controllers with PNOZmulti: up to 24 single burners are to be controlled individually – for even greater flexibility with regard to the product diversity of users worldwide.
 

Author
Karl Haderer, Regional Sales Manager, Pilz Österreich