One for all – Selection of Mode of Safe Operation

There is no question that the future will bring stricter safety regulations for operating mode selection – for example when servicing or for setup operations. But Bihl+Wiedemann would not be Bihl+Wiedemann if there was no convenient solution existing here as well: a new certified module in the Safety Monitor of the company based in Mannheim enables selection of mode of safe operation up to Performance Level e just by using ASi via standard HMIs – and makes it easy for the user to benefit from the various system advantages of AS-Interface even in times of tightened standards.


The discussion has long been a lively one in the world of automation, and it is not getting any quieter, rather louder. In the meantime there are even a few standards that specify exactly what the topic of the dispute is: a safety-related assessment of the selection of mode of operation.


The reason for the tightening of regulatory requirements already implemented in some fields and already planned in others is clear: when switching over to certain special operating modes various safety-related components and functions such as safety doors, enabling switches or reduced speeds are turned off in an automated way. This of course not only increases the risk of machine damage, but mainly represents a risk of injury to the operator.

Fig. 1: By using the certified module in the Safety Monitor a total of six instances for various system parts can be freely configured with five different modes each.

Simplicity is the top priority in configuring operating modes

Among the most common reasons for selecting a special operating mode is for instance the new setup of a machine after changing tools. Commissioning can also be considerably facilitated if it is possible to select dedicated modes of operation for various system parts. And when service and cleaning work is required in large systems, valuable production time can be saved if only the segments actually being worked on run in maintenance mode, whereas all the other sections remain in automatic mode.


Thus, if using safe operating mode selection it is essential that the correct protective function is provided for any application case. Unintended switching over or simultaneous enabling of multiple modes of operation obviously needs to be prevented. When configuring the single modes of operation simplicity should always be the highest priority, and this begins already with the interface used for changing. An important goal of safe operating mode selection is to minimize the temptations for arbitrary manipulation of protective devices by machine personnel. And the best way to do this is to make operation as convenient as possible for the user by means of an HMI – with flexible language, easily understood characters and clear arrangement of the respective elements.


All this could be found in the specification sheet of the developers at Bihl+Wiedemann as they began their work. What resulted is a solution which, from the perspective of user and programmer alike, offers a maximum of flexibility and efficiency, by combining the complete intelligence of the safe operating mode selection in a single certified module for the AS-Interface Safety at Work Safety Monitor. With just this one module a total of six instances for various system parts with five different modes of operation each can be freely configured to cover virtually any possible application case. The Deutsche Gesetzliche Unfallversicherung (DGUV), Department of Wood and Metal, defines for example the following five ’Modes of safe operation’ (MSO): manual mode with open doors and manually controlled motion, automatic mode with fully enabled safety technology, setup mode with reduced speed plus enabling switch and E-Stop, automatic mode with manual intervention at full speed, and finally service mode, whose characteristics are defined by the manufacturer.

The concept makes life easier for users and programmers

With this solution from Bihl+Wiedemann the universal, standardized cross-platform interface OPC UA guarantees the programmer extremely simple integration and diagnostics of the selection of mode of safe operation. Life is made easier for users since by using this module a non-safe device such as a standard HMI can be sufficient for safe operating mode selection. Thanks to the graphical representation that can be created on such a display the procedure becomes a completely simple and intuitive function of the machine.

FIg. 2: Simple configuration of the safe operating mode selection in the settings of the Gateway

The Bihl+Wiedemann concept is also flexible when it comes to protection. Access to safe operating mode selection can be controlled in two different ways: either by using a 2-channel safe input, or by means of an electronic key system combined with a special procedure.


Whereas version 1 is typically implemented using a safe key switch, a transponder- technology based system such as EKS FSA from Euchner is typically used for version 2, consisting of a read station and one or more keys with programmable memory. This requires two defined signals: on one hand a non-safe “Chip inserted” signal and at the same time a valid code word which is read from the key and which grants authorization for the operating mode selection. There are a total of five valid code words that can be used for a simple means of implementing various authorization levels. This means that the module can be configured for example such that a maintenance staff with his electronic key is able to select different modes than the actual operator.


Moreover a system like this offers the possibility of storing additional information and data such as process parameters on the key and sending them to the controller.

FIg. 3: Assigning a safe operating mode to an instance as part of the module configuration

From now on the module is planned in all new devices

The innovative module for safe operating mode selection is already integrated into the new Bihl+Wiedemann ASi Safety Gateway with integrated Safety Monitor for PROFIsafe via PROFINET (BWU3823). This multi-talented Gateway with Double Master, the open communication protocol OPC UA, webserver and many other features, currently offers what is surely the most powerful platform for the future in the company’s range. “But this is of course just the beginning,” says Managing Director Jochen Bihl. “From now on the module is planned in all new devices – including versions that are not assigned high-end.”


Because in times of stricter safety standards one thing is sure for the co-founder of the AS-Interface Masters from Mannheim: “I see safe operating mode selection for AS-Interface not as something just nice to have, but rather as a must. We have always wanted to make things as easy as possible for our customers to profit from the many advantages of the system. Which is something we want today more than ever in the face of ever more complex applications.”

Fig. 4: The innovative module for safe operating mode selection is already integrated into the new Bihl+Wiedemann ASi Safety Gateway with integrated Safety Monitor for PROFIsafe via PROFINET (BWU3823)