Hello my friends.
In the pic below, you can see that the water company and the gas company made some markings.
They use a metal detector like device to locate the under ground pipe.
My question is, how did the water company person know that the beeping indicated a water pipe and not a gas pipe?
On the same note, how did the gas company person know that the beeping indicated a gas pipe and not a water pipe?
The pipes are so close to each other that one can be mistaken for the other.

What is the electronic detection technology used that can discriminate between different pipes?
In other words, if you are a gasman, how do you know that the beep signal is a beef from the gas pipe and not from the water pipe.

Thank you friends!

 

Well here in Philly most of the underground systems are mapped, so there is that.

 

I'm not sure they would tell you if they even know.

 

They attach a signal generator to the metal pipe (or cable) and search for the buried signal.

 

They attach a signal generator to the metal pipe (or cable) and search for the buried signal.

Yes, but, if you are a gasman, then how do you know that the signal is a gas pipe signal and not a water pipe signal.

 

My guess: they don't know. They know approximately where they both are from a map, then they find the exact location with the metal detector. Those look like "dig safe" markings. They mark the location of any pipes so people don't hit and break them when digging.

 

Yes, but, if you are a gasman, then how do you know that the signal is a gas pipe signal and not a water pipe signal.

They attach the signal transmitter at a known node like a valve or the meter.

 

Yes, but, if you are a gasman, then how do you know that the signal is a gas pipe signal and not a water pipe signal.

Because if you attach a signal to a water pipe, only the water pipe will Ping. If you attach to a gas pipe, only the gas piple will Ping. In my neighborhood, the gas pipes don't touch the water pipes so we don't have a problem with cross-talk.
Also, a tracer wire is wrapped around the plastic gas "pipes" so they can be found with the detector. The technology is usually a 455kHz radio signal and the piple becomes a long antenna - similar to the invisible fence used to keep dogs inside a an area defined by a wire with a 455kHz signal. The dog beeps when its collar gets too close and detects the wire - if you know what I mean.

 

Yes, but, if you are a gasman, then how do you know that the signal is a gas pipe signal and not a water pipe signal.

Because he attached the signal to the gas pipe!

 

In addition to the explanations already given, which are correct, the gas person knows where the pipes should be, and that helps quite a bit.. And when they were using the machine to push through the ground to pull in new gas lines, that underground portion had a quite advanced transmitter that sent data to the worker with the receiver up above. That system would also tell the depth quite closely.