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- - 1 <br /> • <br /> f� <br /> The induction mode is also used as a metal detector to detect buried near surface metal objects <br /> such as rebar, manhole covers, and various metallic debris including UST's This is done by <br /> holding the transmitter-receiver unit above the ground and continuously scanning the surface The <br /> electromagnetic signal (primary magnetic field) generated by the transmitter induces current flow <br /> in the earth In the presence of any nearby subsurface objects that are electrically conductive, the <br /> induced current produces a secondary magnetic field Tnis secondary field is detected by the <br /> receiver which then produces an audible tone The larger, mcre conductive, and shallower the <br /> object, the higher pitched the tone The maximum response is produced when the instrument is <br /> directly above a conductive object <br /> We used two different instruments to locate ar=d confirm positions of underground utilities a <br /> RadioDetectien RD-400 and a Fisher iVII-E "111-Scope " We also usea the "M-Scope" in the <br /> induction mode as a specialized metal detector to locate other ouned metallic oojects <br /> i• <br />