En «analog mann» endrer mening

The two Eaton controllers provide us with a costefficient solution with which we can cover all the required interfaces. We can now also ensure a considerably more even flow of the grain and thus improve plant utilization.
- Frank Zimmermann Elektro Dittus

The Zechlesmühle production plant is located in Ditzingen, a town northwest of Stuttgart. It produces cereal products such as wheat flour, wheat semolina or wholemeal flour, some of which is sold in the company's own mill shops. The company also processes summer barley for beer making. The cereal is stored in 47 storage cells, of which 17 are located in a separate building complex which was equipped with a new automation system. The cereal is supplied by the local farmers who tip the grain during harvest time in the so-called feed chute in the mill yard. From here it is transported on several conveyor lines to two scales. These measure the quantity of supplied cereal and assign it to the appropriate storage cells. 47 drives and around 100 sensors ensure that the cereal finds its way to one of the 17 silo cells.

The maximum storage capacity of the mill is around 3,000 t of cereal – a quantity that can be processed in the plant within 48 hours. In order to achieve this level of output, the silo area was extended in 2013 and the automation architecture extensively modernized. The contract for upgrading the control technology was awarded to Elektro Dittus, a wellestablished and traditional company from Ditzingen, offering a wide range of services, from conventional home installations right through to solutions for renewable energy. Frank Zimmermann, electrical engineer and managing director of Elektro Dittus GmbH, has worked for several years for the Zechlesmühle and has been responsible for building services management projects, as well as maintenance work for the drive and controller technology of the mill plant.

“Up to now, the plant was not really automated,” Zimmermann says. “You see, I'm an analog man,” Thomas Siegle, general manager at the Zechlesmühle, added tongue in cheek. Some of the technology used in the mill still comes from the sixties. An upgrade in the nineties hardly changed anything. The plant continued to be conventionally wired. This had real disadvantages in daily routine operation, as Zimmermann explains: “In order to start up the installation, every drive and every function had to be connected manually in the correct sequence. Each individual system here was an island solution in a separate switch cabinet.”

This is now no longer the case: Zimmerman has now combined four switch cabinets distributed in the plant and has housed them in a single cabinet. This combination of different systems in a single automation solution presented a specific challenge. In order to automate the silo plant, a relatively large number of different interfaces are needed to implement the communication with the peripheral systems in place. The scales, for example, requires a Profibus interface, whilst the temperature sensors in the storage cells can only be connected via an RS485 interface. The CAN bus, on the other hand, is required for the communication inside the switch cabinet and to connect variable frequency drives. Last but not least, the system also requires an Ethernet interface to connect the visualization and the network, as well as for programming.

“Finding a controller that combines all these interfaces in one was impossible. We could naturally have used a controller with an additional gateway providing the interfaces I need,” Zimmermann explains, “however, it would have been a relatively expensive solution.”

with Eaton: “We have already been using switchgear from Eaton for a relatively long time and have had a good experience with it,” Zimmermann adds. "The new generation of XV and XC controllers makes the implementation of a visualization easy.” The XV-152 HMI/PLC with touch display combines PLC functionality with HMI technologies. It is also available with an RS485 interface and comes standard with an additional Ethernet interface. This controller was installed in the door of the switch cabinet. Its main task is to implement the visualization and to communicate with the temperature measuring system, in which data is called acyclically and displayed. For the control of the actual process, i.e. the drives, gates and above all the scales – Zimmermann installed an XC-152 inside the switch cabinet. This is responsible for the sequential control of the drives and communicates with the scales via a Profibus interface.

The majority of the Eaton automation components installed in the plant, such as RMQ Titan control circuit devices, DIL contactors, PKE motor-protective circuit-breakers, DS7 soft starters and various switchgear components, are interconnected via SmartWire-DT. This means that, instead of connecting the individual switchgear, sensors and drives with the controller via point-to-point connections, all stations can be connected quickly and simply to the “green” eight-pole ribbon cable using device plugs. SmartWire-DT provides the connected devices with power and at the same time implements the data communication. The Zechlesmühle even uses two SmartWire-DT lines: One line serves all components fitted in the door; the second one connects all contactors fitted inside the cabinet. This eliminated the need for a possibly fault susceptible SmartWire-DT connection between the cabinet interior and the door, as this could be implemented with just an Ethernet connection between the two controllers.

“In this case, an important requirement for us was the possibility to transfer all switch states, process data and motor status messages from the Eaton circuit-breakers to the controller without any additional equipment. This enables the load on the drives to be monitored and if necessary the quantity of the conveyed grain reduced,” Zimmermann explains. One example he mentions is an elevator or bucket conveyor which transports the grain vertically. Once this reaches its performance limit, the product flow has to be reduced. “This is still carried out manually,” Zimmermann continues. “However, in a second step we wanted the data of the circuitbreakers to flow into the controller, so that the product feed can be metered automatically. In this way we can run the entire plant continuously close its optimum rate.”

Zimmermann's summary of the integrated automation solution based on Eaton technology is entirely positive: “The controllers provide us with a cost-efficient solution with which we can cover all interfaces. The price/performance ratio of the Eaton controllers is very attractive, particularly if you take the cost of the programming systems into account. We can now also ensure a considerably more even flow of the grain and thus improve plant utilization.” Thomas Siegle, the former devotee of an analog world, is now also impressed: “Whilst you previously had to think which switch to trip, I now just have to press a button. Previously there were also always problems when the gate of a silo had not closed properly, resulting in different grain types mixing. Today the plant detects this automatically and triggers an alarm.” Siegle already has other automation tasks in mind that he wants to implement with Zimmermann: The flour silo control and the flour mixing machines need to be upgraded. “I have now got the taste for it and I'm done with the analog world,” says Siegle.