System setup

Acoustic tunnel Monitoring system

The acoustic tunnel monitoring system consists of the following main components:

  • Microphone
  • Connection box
  • signal transmitters (optical or copper)
  • Analysis computers with ring buffer and alert log

The microphones withstand the prevailing climatic conditions in tunnels and provide high quality signals. The higher the quality, the more robust the analysis algorithms. The microphones can be mounted on a separate fixture on the sidewall of the tunnel or directly on the connection box. The connection boxes provide the power supply to the microphones and are responsible for the amplification and A/D conversion of signals into digital audio signals, which are then transmitted as digital signals via optical fibre or copper cables.
The analysis computer analyses and classifies the microphone signals in realtime. The first step is to reliably differentiate the acoustic signals into "normal" and "Alarm" classes. The second step is to then automatically classify in more detail and assign individual alert classes such as crash, tyre burst, door banging, etc.The analysis computer is also connected to a ring buffer, which stores the data from all microphones for defined period of time (e.g. 48 hours). The alert log also stores all incidents detected, including the start and end time, the classification, the microphone channels involved, the detection parameters and the audio data.

Tunnel microphones

Special microphones were developed which are able to withstand the rough conditions in tunnels. The microphones were subjected to comprehensive splashing water and ageing tests, the results of which were validated by acoustic measurements.

Features of the tunnel microphones

  • Linear frequency response
  • Resistance to temperature, dirt and corrosion
  • Protection against splashing water and water jets
  • Simple mounting, maintenance and cleaning

Hydrophobic dust-proof membranes provide additional protection against ingress of water and dust. Despite these protective characteristics, the membrane is acoustically transparent across the entire frequency range. The membranes are fitted in protective caps and can be easily replaced during periodic maintenance.

Connection to the traffic mangement system

The AKUT system can be connected to each tunnel control centre and traffic management system both using a standardized or proprietary interface. All of the monitored information is transmitted to the control centre, which is also responsible for system control.

During maintenance, individual microphones or tunnel tubes or even the entire system can be set to
maintenance mode.

The respective audio signal is retrieved from the alert log and played back over the loudspeaker in the control centre. The dialog box also allows the user to start live audio streams from a specific microphone to provide the tunnel operator with a real-time overview of the current situation in the tunnel.

Examples for incidents & alarms