SCADA Communication to Underground Vaults

[jarnott]

I have a customer with equipment underground (in manholes with steel covers) that needs monitoring & control. The problem is that he cannot bring an antenna to the surface for various reasons. We are using a repeater on a nearby pole (about 100m away) with great success in the 900MHz range. We have a small omni antenna in the manhole mounted about 12" below the manhole cover. It communicates with the repeater which has a Yagi on the pole. I suspect that we are communicating with the RF that is leaking around the manhole cover through the concrete/asphalt.

We need to optimize the design by maximizing the amount of signal to and from the radio in the manhole (We will experiment with a polymer concrete cover, but there will be cases where we must use steel covers).

I have the following questions/thoughts:
Which frequencies work better for penetration through concrete/asphalt; VHF, UHF/900MHz?
Is there any research available on this topic?
What are the RF implications of embedding the antenna in the concrete next to the cover about 6" below the surface (by drilling a horizontal hole in the side of the manhole & epoxying an antenna in)?

Thanks

John

 

[SAR923]

No radio signals will penetrate concrete very well but the higher frequencies will do a better job. There's a company that I can't remember the name of off hand that makes antennas just for this purpose. The antenna is meant for 900 MHz and looks like a green hockey puck. You epoxy the antenna to the manhole cover and then run the cable through a hole in the cover to the radio in the manhole. The antenna can be driven over with no damage and will transmit and receive for about 300 feet. I'll post the manufacturer if I can find their site again.

Edit: I just remembered the name. It's Bluewave out of Canada. Their distributor is Allcan at http://www.allcan.com/antennas/index.asp

 

[jarnott]

Jim,

Thanks for your kind reply.

"No radio signals will penetrate concrete very well but the higher frequencies will do a better job" - Thanks, this gives me a path to follow regarding choosing the best freq to use.

"run the cable through a hole in the cover" - The vault contains High voltage equipment & the customer does not want any "wire" near the cover. We are stuck with an antenna below the surface of the ground.

John

 

[SAR923]

I've got a few years experience in the electric utility industry so maybe some more details would help. Are these underground vaults for high voltage transformers? If so, what's the voltage? What is the equiment used for? What functions does he need to monitor using the SCADA system?

I can't imagine that an antenna that buried in concrete as you propose is going to work at all, especially since I assume we're talking abut a flea power transmitter. What does the customer object to about coax being in the vault? You can use intrinsically safe coax like that used in mining operations. I'm quite surprised you're picking up anything from the vault now. As you say, this must be RF leakage but most underground vaults are well sealed against moisture intrusion. If RF is leaking out, water must be leaking in, which I would assume should be a big issue for your customer.

It seems like your customer need to give you a better set of specs so you know what parameters you are really dealing with. One thing he needs to understand is that you can't assure him of reliable SCADA operation without a decent antenna so some compromises really need to made.

 

[hesham_mems]

William J. Chappell puplications

hello

William J. Chappell from University of PURDUE publish several papers for the antenna used for metallic manhole cover, I do not know if this can help or not
The papers I have

1- "A City-Wide Smart Wireless Sewer Sensor Network Using Parasitic Slot Array Antennas"

2- "Urban Sensor Networking Using Thick Slots in Manhole Covers"