Return-Path: Received: (qmail 18650 invoked from network); 17 Dec 2002 14:38:31 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 17 Dec 2002 14:38:31 -0000 Received: (qmail 24119 invoked from network); 17 Dec 2002 14:38:27 -0000 Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 17 Dec 2002 14:38:27 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 18OIqi-0003bi-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 17 Dec 2002 14:37:32 +0000 Received: from [212.159.14.225] (helo=murphys.services.quay.plus.net) by post.thorcom.com with smtp (Exim 4.10) id 18OIqi-0003bZ-00 for rsgb_lf_group@blacksheep.org; Tue, 17 Dec 2002 14:37:32 +0000 Received: (qmail 23009 invoked from network); 17 Dec 2002 14:36:58 -0000 Received: from unknown (HELO hugh) (62.60.120.51) by murphys.services.quay.plus.net with SMTP; 17 Dec 2002 14:36:58 -0000 Message-ID: <003901c2a5d9$49b6d3c0$0504210a@c.scope> From: "g6tmk" To: rsgb_lf_group@blacksheep.org References: <5.1.0.14.0.20021217141612.02c7cbc8@pb623250.kuleuven.be> Date: Tue, 17 Dec 2002 14:33:14 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4133.2400 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: Re: LF: EARTH RESISTANCE Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, hits=-0.3 required=5.0tests=QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_00_01, USER_AGENT_OEversion=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Hi Rik, If one uses the four probe method of measuring ground resistivity, the problem of contact resistance with the ground is overcome. Current is injected into the soil through the outer two electrodes, and a voltage is measured between the inner two electrodes. Use a constant current source on the outer two probes, and a high impedance voltmeter on the inner pair. You have to use a.c. because otherwise you get electrolytic effects. If there is a poor connection the voltage on the constant current source rises to force the same current through the soil. There is no volt-drop at the voltage probes because there is negligible current here. There are a variety of different arrangements of probes advocated for different purposes, but basically the wider the spacing the deeper the current flows in the soil. There is a diagram, and the equation to calculate the resistivity at this location: http://www.mines.edu/fs_home/tboyd/GP311/MODULES/RES/NOTES/2estres.html Commercial equipment for measuring this (the sort of thing you see on time team) uses about 1mA of current, and a frequency between 50 and 200 Hz that avoids mains harmonics (I seem to have used 132Hz in my design). Sometimes this sort of activity is called "geophys" - but I think if one uses mains for the current source, one should call it "Geofizz" ! 73 Hugh M0WYE ----- Original Message ----- From: "Rik Strobbe" To: Sent: Tuesday, December 17, 2002 1:19 PM Subject: Re: LF: EARTH RESISTANCE > At 09:50 17/12/2002 +0000, you wrote: > > >Has anyone measured earth resistance alone under different conditions? If I > >recall correctly, this can be done with three earth stakes and Kirchoff's > >laws. > > > >Mike, G3XDV > > I am wondering about that for years now. > Apart from the fact that the measurement will be frequency dependent I > would expect that it also depends on how deep the stakes are driven into > the soil (maybe unless you have a uniform soil). > Anyone ever tried this (with or without success) at frequencies of 136kHz > (or 180kHz) ? > > 73, Rik ON7YD > > > >