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Road Tunnel Ventillation

VisGuard Visibility Monitor - Road Tunnels Installation Alternatives

 


SIGRIST's VisGuard visibility monitor offers unique installation flexibility that makes it possible to achieve precisely the right concept for each user and each application. The fundamental alternatives are:

  • In-situ or extractive measurement
  • Single-point or multiple-point sampling
  • Local operation of each instrument or multichannel operation in the tunnel control room

This description of various applications explains the different alternatives with the aim of facilitating selection of the best possible system.


In-situ installation right in the tunnel

VisGuard In situ 1

The simplest and lowest-cost solution is to mount the VisGuard right on the tunnel wall (or in an SOS niche). The VisGuard's built-in fan draws in the surrounding ambient air and the instrument measures the visibility with the scattered light method. So: one sensor for each detection point. If humidity causes problems, an optional heater is available to eliminate its effects.


Three alternatives are available for instrument operation and data transmission:

  • Installation proposal 1: Control unit „SIREL Robust” mounted right next to the VisGuard in the tunnel. The fully enclosed housing contains a display, the keypad for operation, and the power supply for the VisGuard. Signals are transmitted with 4 .. 20 mA or using 2 switching contacts.

  • Installation proposal 2: Control unit SIREL placed as far as 100 m away, outside the tunnel cavity. Display and keypad readily visible.  Signal transmission with 4 .. 20 mA or using 2 switching contacts.

  • Installation proposal 3: Multichannel control of a number of VisGuards with SIBUS. As many as 8 VisGuards can be operated and signals processed centrally via a digital bus. Where the Visguards are installed right in the tunnel, it can be convenient to have not only the readings, but also status information, error reports, etc., easily accessible at any time. The power supply and bus connection are taken care of by a SITRA mounted right at each VisGuard. For troubleshooting or correction of problems at a given instrument, a SIREL can be connected to the SITRA.

Visguard Slide1

 

Visguard Slide2

Visguard Slide3


Extractive detection – installation outside the tunnel cavity 

visguard

For installations outside of the actual tunnel in the control room, cross tunnel, emergency exists, etc. The obvious advantage here is easier access to the instrument without ever having to interrupt tunnel traffic. This simplifies servicing and correction of malfunctions. The arrangement is identical to that used in the past for UP/KTN/CTN installations. Existing sampling systems can be used unchanged. The following sample extraction alternatives are available:

  • Installation proposal 4: Mounting in enclosed niche (such as SOS-niche). Extraction length 0 .. 0.75 m with VisGuard in-situ, no additional blower. Instrument operation and signal transmission same as installation proposals 2 and 3.

  • Installation proposal 5: Extraction length 0 .. 5 m with blower SE12. Instrument operation and signal transmission same as installation proposals 2 and 3.

  • Installation proposal 6: Extraction length 5 .. 30 m with blower SE12. Instrument operation and signal transmission same as installation proposals 2 and 3.

  • Installation proposal 7: Extraction length 30 .. 500 m with blower SD4n. Instrument operation and signal transmission same as installation proposals 2 and 3.

  • Installation proposal 8: Multiple sampling from as many as 8 detection points feeding one VisGuard via a valve unit with detection point switching. Extraction length up to 200 m. In the case of extractive systems, this arrangement is usually more economical. The SIBUS multichannel control unit serves as many as 8 detection points.

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