The safety functions in the elevators can be reliably implemented using the Structured Text programming language. The Gleinalm tunnel on the A9 Pyhrn highway in Austria connects the districts of Leoben and Graz-Umgebung. Over a length of 8.3 km, there are two ventilation shafts that descend more than 300 m into the mountain. Elevators were installed in the shafts in 1980 in order to maintain them and inspect the condition of the shafts. After a good four decades of operation, the shaft elevators were to be refitted and brought up to the latest technical standard - also in terms of functional safety.

The Austrian infrastructure company ASFiNAG commissioned Strabag Infrastructure & Safety Solutions (SISS) to modernize the elevators in the two maintenance shafts. Thanks to the good cooperation with ABB on other tunnel projects, SISS decided to upgrade the elevators with the AC500-S safety PLC.

Bernhard Heinzel, Group Manager Technical Support at SISS, is satisfied with the result: "Before the retrofit, the maintenance workers often got stuck with the elevator - in a dark, cold place with no cell phone reception. Now everything works smoothly."

Performance level c as a requirement

The AC500-S can be used for safety functions up to Performance Level (PL) e in accordance with ISO 13849-1. As part of a risk analysis, PL c was defined as a requirement for some functions in this project. In order to fulfill this requirement, a rotary encoder is evaluated via the control system, which supplies the signals for the functions "safely limited speed" and "safe brake control/safe stop". If the encoder indicates that the elevator speed is above a certain limit value, the control system triggers the activation of a hydraulic brake that reduces the speed to a safe level or performs a safe stop.

As the PLC was attached to the steel cable drum, but the elevator movement is controlled from the car, safe decentralized peripherals are located in the car. It was therefore necessary to create a connection between the PLC and the peripherals that would also function reliably 360 m into the mountain and process safety-related data. With the AC500-S and the integrated PROFINET/PROFIsafe field bus, this is achieved via a redundant WLAN connection and radio relay.

Due to the extreme climatic conditions, icicles up to 3 m long can form in the shaft, especially in winter, which can endanger personnel and equipment. The icicles can be smashed using a special sheet metal construction on the elevator. ABB's non-contact Eden safety sensors (IP69K) were used for this purpose. The sensors indicate when the shaft elevator is in a predefined position from which the icicles can be safely broken by a predefined movement.

Programming safety functions with ST

The main argument for using the AC500-S was the possibility of programming the safety functions using the Structured Text (ST) programming language. ST allows very flexible and fast programming. Any programming errors can be counter-checked with the Safety Code Analysis (SCA) tool from ABB. This safety code analysis tool can be used to verify safety-relevant programming rules in accordance with IEC 61508-3 for the ST, FBD (Function Block Diagram) and LD (Ladder Logic) languages. The SCA tool is certified by TÜV SÜD for applications up to SIL 3 (IEC 61508) and PL e (ISO 13849-1). The resulting code with a clear structure not only speeds up commissioning, but also significantly reduces certification and maintenance work after implementation. The SCA tool was also used in this project for acceptance by the expert.

Control unit supports complex arithmetic functions

The possibility of trigonometrically controlled safety applications is another advantage of the AC500-S. The controller supports complex safety arithmetic functions (SIN, COS, TAN, LOG, LN, SQRT etc.) with floating point calculations. For elevators, this allows the safely limited speed to be monitored dynamically and very precisely for the application.