To ensure functional safety, systems must stop immediately if a safety gate to a hazardous area is opened. Safety sensors detect the status of these doors. The sensors are often connected in series in a standardized manner: OSSD outputs (Output Switching Signaling Device) of one sensor are connected to inputs of the following sensor. To find out which sensor has been triggered, all sensors previously had to be wired individually in a star cabling system. In addition, only 1 bit could be transmitted - and only the information as to whether a sensor had detected the actuator or not.

This is where the 'Safety Device Diagnostics' diagnostic solution from Pilz comes in. It can be used to query status information from safety devices as well as read out their configuration parameters and visualize actions.

Long distances despite single-cable solution

First of all, the status of the safety sensors and the status of their inputs and outputs can be recorded as diagnostic information. As the diagnostic solution can cover distances of up to 900 m, warnings regarding overvoltage or undervoltage can also be read out, which can occur in particular with long cables. For example, large high-bay warehouses, intralogistics applications or extensive systems in the steel industry can be connected via a single cable solution.

It is also possible to retrieve device properties such as the article number, product version number and serial number or to store equipment identifiers, which makes it easier to replace equipment in the event of a fault. This information can also be used to quickly determine where a defective safety sensor is located, even in complex systems. The diagnostic solution's fieldbus module also documents all status changes - even after a power reset - so that faults can be clearly identified, unlike via the LEDs on safety sensors. This is important because further faults can easily occur during repair work - for example, when plugs are removed, which may mean that the original fault can no longer be detected.

Last but not least, warning lights in a control cabinet can be activated directly if a safety sensor has opened a safety gate. This method is still widely used in safe automation. The engineering and programming effort for the visualization is reduced by the fact that the fieldbus module of the diagnostic solution supports the direct control of a maximum of six lights.

Guard locking can be executed individually

The safe safety gate system 'PSENmlock' from Pilz offers safe guard locking and safe interlocking in one device. Together with the diagnostic solution 'Safety Device Diagnostics', safety gates can also be controlled individually for the first time.

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Together with the safe safety gate system 'PSENmlock', the diagnostic solution makes it possible to control even widely distributed safety gates individually. If maintenance work or a tool change is due in a system, for example, it is possible to define which doors may be opened after shutdown (without the use of 'Safety Device Diagnostics', all of them would open) and who is authorized to access them. This ensures that only appropriately trained and authorized personnel can access the system.

Predictive maintenance

As diagnostic data can be recorded on site or remotely, the solution can also be used for predictive maintenance. This applies not only to the timely replacement of worn parts, but also to maintaining operational safety.

If an operator reports a problem years later, the manufacturer was previously unable to easily determine what might have been changed in the machine in the meantime. With the data stored in the diagnostic solution, however, the original status can be compared with the current status 'at the click of a mouse', without the need for additional hardware at control level. This helps to reduce downtimes.

The modular approach

'Safety Device Diagnostics' consists of a fieldbus module plus distributor and safe sensors. The diagnostic solution makes it possible to retrieve data easily and remotely.

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Another example of Industry 4.0 scenarios are intelligent solutions for the functional safety of modular systems. Thanks to the line cabling of the diagnostic solution, it is comparatively easy for machine manufacturers to add another module.

If, for example, a user not only wants to manufacture their products, but also to wrap and pack them, this does not require any new cabling, changes to the control cabinet and design plans or additional safety devices. In addition to the electrical circuit, only the safety sensors for the right and left safety door need to be installed for each module and connected to the last sensor in the line via a further distributor. An additional fieldbus module is only required if 16 sensors are already connected to the diagnostic solution. However, as no more than six, eight or a maximum of ten sensors are usually connected in series, this scope is sufficient.

Author:
Martin Bellingkrodt is Product Manager Sensors at Pilz in Ostfildern.