With safety to the top

Two maintenance lifts at the Austrian Gleinalm Tunnel were modernised with ABB AC500-S safety controllers to ensure state-of-the-art functional safety. Using the Structured Text programming language, the safety functions in the lifts can be reliably implemented.

The Gleinalm tunnel on the A9 Pyhrn motorway in Austria connects the districts of Leoben and Graz-Umgebung. Two exhaust shafts are distributed over a length of 8.3 km, reaching more than 300 m down into the mountain. In order to be able to maintain them and inspect the condition of the shafts, lifts were built into the shafts in 1980. After a good four decades of operation, the shaft lifts were to be retrofitted 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 modernise the lifts in the two maintenance shafts. Thanks to the good cooperation with ABB in other tunnel projects, SISS decided to upgrade the lifts 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 lift - in a dark, cold place without mobile 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 according to 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 fulfil this, 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 lift speed is above a certain limit, the control system causes a hydraulic brake to be activated, which throttles the speed to a safe level or makes a safe stop.

Since the PLC was mounted on the steel cable drum, but the lift movement is controlled from the car, safe decentralised peripherals are located in the car. Therefore, a connection between the PLC and the peripherals had to be created that would also function reliably 360 m into the mountain and process safety-related data. With the AC500-S and the integrated PROFINET/PROFIsafe fieldbus, this is achieved via a redundant WLAN connection and directional radio.

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. With the help of a special sheet metal construction on the lift, the icicles can be broken. ABB's Eden (IP69K) non-contact safety sensors were used for this purpose. The sensors indicate when the shaft lift 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 with the Structured Text (ST) programming language. With ST, programming can be done very flexibly and quickly. Any programming errors can be counter-checked with ABB's Safety Code Analysis (SCA) tool. This safety code analysis tool can be used to verify safety-relevant programming rules according to IEC 61508-3 for the languages ST, FBD (Function Block Diagram) and LD (Ladder Logic). 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 efforts after implementation. The SCA tool was also used in this project during acceptance by the expert.

Control supports complex arithmetic functions

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