Hi all
I am currently planning on a tunnel instrumentation project and considering combinedly using Campbell 3G modem and radio as our wireless communication option.
Briefly, we have some VW instruments both inside and outside the tunnel. Since the farthest instrumented location from tunnel portal is about 200 m, so I don't think 3G modem gonna work. I am thinking about using spread spectrum radio for the data acquisition boxes inside the tunnel and the 3G modem for the boxes outside the tunnel. So the signal from inside the tunnel will be relayed via radio to the box equipped with 3G modem (let's call it main box) and then we from a remote office (in a different city) will have direct connection to the main box. For such a network configuration, do we need both a RF 401 and 3G modem for the main box? We may also have some data acquisition boxes outside the tunnel with wireless avw 206 communicating to the main box as well.
Am i missing something important here? Any comments and suggestions would be appreciated
Thanks!
Your "main box" will probably need a datalogger (CR1000 or CR800) to make the connection between the RF401 network and the 3G/Cell network. That main box would also need to be within radio range of both the stations inside the tunnel and also stations outside the tunnel that will also link back to the main box.
Your antenna may not be able to pull in both "tunnel AVW206s" and "outside 206s" at the same time (in theory it is possible, but a suitable antenna location may not emerge, and using two antennae is a pretty advanced proposition). A repeater station might be needed if that
turns out to be the case.
Another thing to consider is that the radio environment inside the tunnel may not be favorable for RF401/AVW206 communications. There are at least two other options you would have available:
1. Use RS-485 wiring instead of radios inside the tunnel.
2. Just run the VW sensor cables the 200m to the main box, and put an AVW200 device there that can read them. Most VW sensors can still work with the AVW200 even if their cable lengths are 1000m (in some cases even up to 1600m).
If you want to go with RS-485 wiring (Option 1), you would place an MD-485 device in the tunnel right next to your
AVW200. Then the "main box" would have an MD-485 device also. The cable connecting them would be co-ax.
Option 2 seems simpler than Option 1 if you can do it, and also simpler than using AVW206s inside the tunnel.
If you feel you need to use radios in the tunnel, it may be worthwhile to take a temporary set of 2 RF401s into the tunnel to test out how the radios work, get some signal levels, etc.
Appreciate it! I will try to share in the forum what we finally come up with.