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Achieving the highest protection for man and machine

03 July 2013

Safety is a major topic in the automation industry. With Murrelektronik's fieldbus module MVK Metal Safety, you have the best possible solution for active safety technology and also achieve the highest standards for your installation. Michael Greiner reports.

The automation industry is constantly looking for solutions to improve the production processes while focusing on efficiency and cost-effectiveness. In addition, there is the vital obligation to ensure that all staff  involved in the production process are protected from injury or potential dangerous situations, as well as protecting the machines from damage. Legislation requires intensive efforts to comply with all aspects of safety technology.  

Safety technology is imperative and requires a distinction between passive and active safety technology. In passive safety technology, safe installations are created by combining passive safe fieldbus modules with safety relays. If a guard door is opened or someone reaches through a light curtain, the module's outputs are switched off by the relays and the machine's components are safely and quickly shut down.

Passive safe fieldbus modules keep air and creepage distances.  The circuit boards have spaces wide enough to eliminate cross circuits. This ensures that no external power can interfere with the system after it has been switched off and after the safety function has been released.

Murrelektronik offers passive safe fieldbus modules (MVK Metal, Cube67 and MASI) and MIRO Safety relays. In passive safety technology, the existing safety technology (MIRO Safe) is combined with standard passive safe fieldbus modules. This facilitates machine installations so you can maintain quality concepts and principles in your system.

Active safety technology, on the other hand, is different. Here, the basic principle is that the complete fieldbus solution has to comply with safety technology requirements. Affected out-puts are not only passively shut down by disconnecting voltage, but they are deactivated by the control. These systems require individual components to meet the requirements of safety technology, a safe control (F-PLC) to transfer safe signals reliably.

Murrelektronik offers the MVK Metal Safety fieldbus module that is available as a pure input module and as mixed module with safe inputs and outputs. MVK Metal Safety is the component necessary to create fieldbus solutions that meet the requirements for active safety technology.

Safety sensors, guard door applications, emergency stop buttons, light curtains and more are connected to the inputs and integrated into the safety system. On the safe outputs, actuators (up to 2A) e.g valves or low power motors, are connected and these can be safely deactivated, if necessary.

To ensure safe data transfer, MVK Metal Safety uses the transfer protocols PROFINET/PROFIsafe or PROFIBUS/PROFIsafe. These are safety-related extensions of the proven PROFINET and PROFIBUS protocols that are standard in industrial applications. The PROFIsafe extension was developed by the companies that are involved in the PROFIBUS user organization PNO, it is vendor independent and open.

It is listed in the in-ternational standard IEC 61784-3-3. By linking these protocols with the existing ones, the current communication technologies can be used. With PROFIsafe, fail safe data and stand-ard data are transferred with the same bus cable.

This avoids incalculable, additional efforts for engineering and installation. Furthermore, it is possible to integrate standard modules into the individual lines of safe fieldbus solutions which saves wiring costs. And it is also possible to upgrade the fieldbus solution to a safe system without making any substantial changes. 

MVK Metal Safety consists of a solid metal housing with surface finishing.  This makes it suitable for soldering applications. Because of its excellent vibration resistance (vibration 15 g and shock 60 g), MVK Metal Safety is perfectly suitable for applications in rugged and extreme environments, for example in forming and sheet metal working. The modules are fully potted, therefore they are resistant to cooling lubricants that are often used in cutting production - metal lathing, milling and drilling. MVK Metal Safety meets IP67 protection requirements.

The modules are very compact and feature an integrated fieldbus connection. Therefore, no additional bus node has to be installed. Another benefit is that both fieldbus cable and supply voltage can be daisy chained from one module to the next. Each M12 input port features two inputs.

They can also be used for two single channels or one two-channel safety circuit. In two-channel applications, the channels can be configured as equivalent or antivalent. It is also possible to adjust the discrepancy time. This is important, if two sensors with different reaction times have to be precisely synchronized.

The easy-to-read labels on the module and ports are yellow so that the user can see at a glance that this is a safety product. Yellow is also used for the light rings and the contact carriers at the ports.

Cross circuit monitoring is another important feature of the modules. Each input of MVK Metal Safety has a separate, parametrical clock signal. Cross circuits caused by pinched cables or ground faults are immediately detected and reported. However, you can also deac-tivate this pulsing, for example in applications with light curtains that are checked for cross circuits by their own internal logic.

The parameters of the individual modules are stored in the control. Therefore, you don't have to set the parameters with additional programming devices and you don't need software tools when exchanging a module.  The advantage is that the modules can be easily exchanged during service and the relevant data can still reach the module through the control without any problems.

The key to cost-effectiveness in machine and system installation is reducing unplanned down time. Which is why MVK Metal Safety's thorough diagnostic functions are an excellent feature. Failures such as overloads, sensor short circuits and cable breaks are separately monitored on each channel; an LED indicates which port is affected and the failure is report-ed to the control. This ensures that adjacent channels are not influenced.

Michael Greiner is product manager, automation & safety at Murrelektronik GmbH, Germany

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