Reaching Montmartre Safely

Legitimate Faith

What a courageous step was adventured in 2006 by RATP (Regie Autonome des Transports Parisiens), operator of the passenger inclined lift leading to Sacre Coeur on Montmatre, in Paris. Operation of the inclined lift with its two independent routes was switched to state-of-the-art F-safety technology via wireless communication. It was aimed at the highest possible operational reliability under manless operation. At the same time, the goal was to increase driving speed and thereby also increase transport capacity. Until then, capacity had been limited due to inductive data transmission and outdated safety technology.

The new control concept was based on a Siemens 315F control in the upper station and Siemens F ET200 components in the cabins for monitoring critical components such as doors and for actuating an emergency stop. Wireless communication between the cabins and control unit is realized via PROFIBUS/PROFIsafe in synergy with two radio modules. The DATAEAGLE 3712 (via Schildknecht) radios with appropriate directional antennas were placed at the cabins and in the top station for radio communication via 200 m line of sight.

All automation components were safety approved. Even back then, the still young PROFIsafe technology via wireless transmission  had already proven itself at some ski resorts for controlling the lifts. For example in Oberstdorf or at the ski jump stadium of Courchevel. However, in the lively metropolis Paris at Montmartre, thousands of WLAN access points directly adjacent to the lift provided too much interference. Thanks to experience gained from earlier implementations, Schildknecht succeeded in reliably excluding these interfering sources by selecting appropriate antenna variations and their deliberate placement.

As previously mentioned, it was a courageous step by RATP, since installation – after more than twelve years of rail operation – not a single failure of communication or any actuation of the safety function by the radio link has occurred. So looking back on the radio and communication technology applied at that time, until now has been worthwhile.

PROFIsafe and DATAEAGLE – a Reliable Pair

PROFIsafe is the historically first international safety standard according to IEC61784-3-3. PROFIsafe is capable of being completely implemented in software. Combined with PROFIBUS or PROFINET, it covers the complete range of safety applications in process and manufacturing automation. PROFIsafe is also permitted for wireless transmission technologies such as WLAN and Bluetooth, due to its Black Channel Principle. Such an F-communication between two stations aims to transmit unadulterated data (integrity) to the defined recipient (authenticity) at the right time (timeliness). Within the classification system of the ISA SP 100 committee regarding compliance with the requirements for radio technology, PROFIsafe is categorized class 0 (the highest class) and PROFIBUS is rated class 1.

The DATAEAGLE radio modules are available for different radio technologies. The opinion of Schildknecht is that Bluetooth 2.1 is the presently most stable radio technology. It utilizes the 2.4 GHz Band which does not require approval and thanks to its freqency hopping function provides for particularly reliable communication.

A great challenge in the application at Montmartre was the high cyclical data rate required for guaranteeing operational safety. For this purpose, a PROFIBUS interface equipped with a patented software was integrated into the radio system. It enabled a cyclical data rate of the PROFIsafe-transmission at 1.5 Mbit/sec without any amendments to the fieldbus or the application program. The cabins were installed with “emergency stop circuits” which sent a signal to the control unit via PROFIBUS/PROFIsafe every 50 ms. In case the signal is missing for a time interval of 500 ms, this is immediately interpreted as an emergency stop and the cabin is automatically stopped. The DATAEAGLE pre-processing function was set to 600 ms and thereby subordinate to the PROFIsafe function. This adjustable filter time avoids emergency stops of the rail which might be caused by external interference and interrupted radio communication. 

Safe Wireless Solutions for All Areas of Automation Technology

Within the framework of current IoT or IIoT applications, wireless communication is increasing in importance. In this context it is good to know that the solution described above is suitable for all automation tasks – even and especially in the industrial environment – and constantly proves its value. This has been demonstrated with many examples of PROFINET/PROFIBUS/PROFIsafe safety communication combined with DATAEAGLE radio modules and Bluetooth radio technology, not only at Montmartre.

Thomas Schildknecht
Schildknecht AG