Xref: utzoo rec.boats:4191 sci.physics:13784 sci.electronics:13138 Path: utzoo!attcan!uunet!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!samsung!umich!sharkey!cfctech!teemc!fmeed1!cage From: cage@fmeed1.UUCP (Russ Cage) Newsgroups: rec.boats,sci.physics,sci.electronics Subject: Re: St Elmo's Fire - 100 v/m ? Summary: You can measure this gradient with good contacts. Message-ID: <7307@fmeed1.UUCP> Date: 24 Jul 90 16:12:30 GMT References: <1990Jul18.111525.5749@ioe.lon.ac.uk> <5498.26aba906@cerritos.edu> Followup-To: rec.boats Organization: Ford Motor Co., Electronics Div., Dearborn, MI Lines: 20 In article <5498.26aba906@cerritos.edu> yoshinaga@cerritos.edu (Michael Yoshinaga) writes: >> chapter 9). Away from thunderclouds, the earth has a negative charge >> relative to "the sky." The potential difference is quite incredible: >> about 100 volts per meter. > >Why can't this be measured with a DVM? Because the source impedance is incredibly high; a 100K ohm/V DVM won't see enough current to move it. Using better contacts (radioactives, which ionize the air slightly and make it conduct, bringing the contact to the same potential as the air for small but reasonable currents), you can measure this gradient quite simply. Wing-leveler autopilots for model airplanes have been made with a couple of such contacts and some op amps. -- Russ Cage Ford Powertrain Engineering Development Department Work: itivax.iti.org!cfctech!fmeed1!cage (Business only) Home: russ@m-net.ann-arbor.mi.us (Everything else) I speak for the companies I own, not for the ones I don't.