Electric and electronic equipment is used in tunnels for ensuring traffic safety or as part of other functions critical for safe operation. In tunnels, rapidly moving trains and other vehicles cause big and sudden changes in the prevailing conditions. Pressure and temperature changes caused by air currents, as well as dust and water may be harmful to the reliable operation of equipment.
Sabik Oy wanted to ensure the functionality of two different types of railway signals in the demanding metro tunnel conditions. The signals are mounted on tunnel walls and they steer train traffic with the help of LED signal units of different colours.
Testing with a view to vibration, temperature changes, dust and water
"Sabik provided us with precise information on the signals to be tested, the conditions in metro tunnels and the requirements of EU standards on railways. We drew up a comprehensive testing programme on the basis of this data. The tests conducted included vibration testing, testing of changes in climate conditions and tightness testing," relates Olavi Nevalainen, Leading Expert, Testing of Electronics.
Vibration testing was used for simulating the vibrations in the product structure that strong pressure changes may cause. Vibration tests reveal potential weaknesses in the mechanics and electrical connections in electronic structures.
Metro railway signals in vibration testing.
"In addition to vibration testing, we also tested how the products functioned when facing rapid temperature changes, with temperature changing rapidly from frost to warmth, and we conducted a cyclical humidity test with a view to potential condensation of moisture on and in the product."
Metro railway signals in a climate testing cabinet.
Due to dust and water occurring in tunnel conditions, the signal housings were tested in accordance with the tightness class IP54 applied to enclosures. The housing must be dustproof and splash proof.
Impact resistance is tested as well
On the basis of shock testing, the product's IK rating can be defined for the product to classify the impact resistance of the housing.
In this case, shock testing was needed to ensure the durability of the LED signal units and signal housings in case they are hit by loose stones or other particles.
Metro railway signals, impact testing.
Testing proved the functionality
"At Sabik's request, the tests were carried out on a tight schedule. The products did well in testing, and at the end of the testing programme it was possible to state that Sabik's railway signals were functional and durable in demanding tunnel conditions," says Nevalainen, summing up the results.
With this testing, Sabik can now prove the functionality of its products and their suitability for metro tunnel use.