For the gas lines in the city to your house they use a "Thumper" to detect the metal pipe. When they lay plastic pipe they bury wire along with the pipe. I think the gas guy said that they hook something to the line and then follow the signal with a thing that looks like a metal detector. The metal pipes do have a slight current going through them due to electrolysis. To keep the pipes from being eaten by this they hook a zinc bar as a sacrificial "goat" every so often on the line and this is what the current uses as it's cathode in its natural plating process. Think you might have to hook some kind of a signal to the line in order to detect the pipe/wire.. Bill ----- Original Message ----- From: "rad0" To: "picsters!" Sent: Friday, October 22, 2004 5:10 AM Subject: [PIC]: Sensing a current > I was chatting with a gas pipeline man, > and he told me that gas lines have a > slight current running through them, > and they use this to locate the position > and depth of the pipe. > > Can someone go over how you might > build a sensor to do this? > _______________________________________________ http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist