Senin, 15 Agustus 2016

TECHNICAL SPESIFICATION FOR WENNER ELECTROD ARRANGEMENT IN RESISTIVITY 1-D DAN 2-D

ABSTRACT


Currently, the geoelectric survey is developed so rapidly. It is caused development of electronic and computer so fast with high precision and accurate  performance. The development of resistivity meter for multy channels has been created for resistivity 2-D. Those equipments are so expensive, however handy to use in the field. The explanation and using the one channel resistivity meter could be use for the resistivity 1-D and 2-D. The sample will be taken with for the Wenner electrode arrangement only and it will be applied to other array.


1. INTRODUCTION

The meaning of resistivity one channel is the equipment has been existed before appeared the resistivity 2-D. Those equipments are OYO OHM Type 2115, Yokogawa Resistivity meter type 3244, ABEM SAS 300, and NANIURA NRD 300 HF. The equipment for survey geoelictlric 2 D (2 Dimensi)  had been development such us ABEM SAS 4000, GEORES, OYO PROFILER 4 in 10 years ago.

The resistivity meter could be used for resistivity 1-D and 2-D. The sample of the survey will be applied to Wenner Electrode Arrangement.  The procedure for exc cution is explain in the following items.

2. THE BASIC THEORY OF ELECTRICITY


The principle of resistivity survey is to inject electric current trough 2 ( two ) electrode current ( ∆ I ) , so there is influence the differences of a pair inner potensial electrode ( ∆ V).  If we knows the diferences current and potensial , so we can get the resistance ( R ) from OHM LAW  :

  R =  (∆ V)/(∆ I) in ohm.                                             ( 1 )

If the electric current trought the homogeneus sylinder of bar , so the value R depend on the lenght of bar ( L ) and the sylinder area ( A ).

R ­­= L / A (ohm-m)                                                                 ( 2 )
The equation above has the fixed value  in unit of ohm-m. To know the resistivity of material the equation became :

r = AV/ L I ( ohm-m)  or r = K R                                         ( 3 )
where K= A./L is  the geometric factor, which is depend on the position of the current electrode and potential elctrode.  The geometric factor are different from the each of electrodes arrangement as shown in Figure 1.


Figure 1. The geometric factor from various electrode arrangements.

The geometric factor for electrode arrangement Of WENNER is K =  2pa and r = 2pa R in unit ohm-m, where  a or  L is the distance of electrode WENNER.
In electrode arrangement of SCHLUMBERGER m the geometric factor as follows :

K = 2 p/(1/AM – 1/AN) – (1/BM – 1/BN)  or

K = p{(AB)2 – (MN)2 } , where  AB=current electrode and MN=electrode  pot.
                    4 MN

  ρ =     KR = p{(AB)2 – (MN)2 }  R                                                   ( 4  )
                               4 MN



Figure 2. The electrode arranggement of SCHLUMBERGER     

In the SCHLUMBERGER methode the electrode potensial is fixed and will be change at certained distances. The maximum distance of AB/2 is not more than  5 x  MN/2.
  
3.     RESISTIVITY 1 D FOR WENNER ELECTRODE ARRANGEMENT

The first attempt to measure electrical resistivity of soils was made at the end nineteenth century with the two-electrode technique. Whitney et.al.(1887), Gardner (1898), and Briggs (1899 ) developed relationships between soil method measures the sum of both electrical resistivity and soil water content, temperature, and salt content, The two-electrode  method measures the sum of both soil resistivity and the contact resistivity between the electrode and soil. The latter is very eratic and unpredicted.

Wenner  (1915 ) based on the work of Schlumberger suggested that a linear array of four equally spaced electrode would minimize are separated contact problems if potential measuring and current – induced electrodes are separated in space. Since then all electrical resistivity methods applied in geophysics and soil are based on the standards four electrodes principles. The Wenner Electrode Arrangement devided into Wenner α , Wenner β  , and Wenner γ shown on Figure 1. The procedure for theWenner Electrode Arrangement is as follows :

1.     Determine the point O on the ground surface.
2.     The four electrode arrangement set on the ground and measure the deferent of current ( ∆ I ) and different of potential ( ∆ V ). The data is write  on the field data sheet
3.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 1.0 meter.
4.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 1.5 meter.
5.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 2 meter
6.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 3 meter.
7.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 5 meter
8.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 7 meter.
9.     The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 10 meter.
10.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 12 meter.
11.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 15 meter.
12.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 20 meter.
13.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 25 meter.
14.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 30 meter.
15.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 40 meter.
16.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 50 meter
17.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 60 meter
18.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 75 meter
19.  The first Wenner  Electrode Arrangement set on C1 P1 = P1 P2 =C2 P2 = a = 100 meter
20.  In the field plotted data on double log paper.
21.  The resistivity curve could be intrepreted using RES 1D, VESPC, RESINT 53, IP2Win and GRIVEL.
                                               

                                               Figure 3. Three Types Wenner Electrod Arrangement



  
Figure 4. The equipotential lines , current line and datum points on the four electrod array ( Wenner and Schlumberger ).



Figure 5. Field Data Sheet For Wenner Array Resistivity 1-D



Figure 6. Interpretation resistivity curve with software IP2Win

Figure 7. The Geological Profile based on Resistivity Values


3.     RESISTIVITY 2 D FOR WENNER ELECTRODE ARRANGEMENT

An example of the electrodes arrangement and measurement sequence that can be used for a 2-D electrical imaging survey shown in Figure 6 . The procedures to get data resistivity 2-D with Wenner α electrode arrangement with 20 electrodes and electrode spacing a with level 6. Firstly, mark the peg on the ground with numbering from 1 to 20.
The first step is to make all the possible measurement with the Wenner array with electrode spacing “1a”.  For the first measurement electrodes number 1,2,3. and 4 are used. Notice the electrode 1 is used as the first current electrode C1 , electrode 2 as the first potential electrode P1 , electrode 3 as the second potential electrode P2 and electrode 4 as the second current electrode C2. for the second measurement, electrode number 2, 3, 4 and 5 are used for C1 , P1 , P2 , C2  respectively. This repeated down the line of electrodes until electrodes 17, 18, 19 and 20 are used for the last measurement with “1a” spacing. For a system with 20 electrodes , note that there are 17 ( 20-3) possible measurements with “1a” spacing for the Wenner array.
After completing the sequence of measurements with “1a” spacing, the next sequence of measurement with “2a” electrode spacing is made. First electrodes 1.3.5 and 7 are used for the first measurement. The electrodes are chosen so that the spacing between adjacent electrodes is “2a”. For a system with 20 electrodes , note that there are 14 ( 20-2x3) possible measurement with “2a” spacing.
The same process is repeated for measurements with “3a”, “4a”, “5a” and “6a” spacings. To get the best results with the equipment one channel, the measurement in the field survey should be measurements one step by one step and record data on the field sheet. The field sheet is shown on Appendix 2 and the program resistivity 2-D as shown on Fig   .The sample of Wenner Electrode Arrangement is shown on the RES2DINVx32  program on the folder of LANDFILL.DAT. The LANDFILL.DAT is an example field data for the Wenner array obtained by survey with 50 electrode.


Figure 8. Multy – Channel Digital Resistivity Meter


Figure 9. Program RES2DINV for LANDFILL SURVEY


Figure 10. Sequence of measurement to build up a pseudosection in resistivity 2-D



3.     CONCLUSSION AND RECOMMENDATION

1.        The resistivity meter one channel can be used for measuring survey on resistivity 1-D and      resistivity 2-D.
2.        The measurement of resistivity 1-D is very fast and for 1 (one) day works could be finish 5 or 6 sounding points.
3.        The measurement of resistivity 2-D is take time then the equipment 1 (one ) channels. It is caused to many datum points ( 334 datums ) and required  1 (one ) or 2 (two days ) measure








REFERENCES :

1.     Geoelectrical Imaging 2-D 3-D GEOTOMO SOFTWARE, Agust 2004, RES2DINV ver.3.54 for Windows 98/Me/2000/NT/XP. Rapid 2-D Resistivity & IP inversion using the least – squares method.
2.      Loke, M.H. Dr. Electrical imaging surveys for environment and engineering studies. A practical guide 2 D and 3-D surveys. Copyright (1997,1999,2000) email:mhloke@pc.jaring.my.
3.     University of Moscow. 2000 IP2Win. A program for resistivity interpretation.
4.     Wenner F. 1955. A method of measuring earth resistivity. US Dept. Com.Bur. Standard Sci.Paper 258.
5.     Briggs,L.J. 1899. Electrical instrument for determining the moisture , temperature, and soluble salt content of soils. U.S. Dept, Agr. Bul,15,
6.     Gadners, F.D., 1898 The electrical metod of moisture determination in soils: results and modifications in 1897, U.S. Dept. Agr. Bul,12,
7.     Whitney, M,F.F.D. Garned. And L,J. Briggs, 1897., An Electrical Methodof determining the moisture content of arable soil.U.S. Depth. Agr.Bul.6.



















Appendix 1

Single Channel Resistivity Meter
Naniura NRD 300 HF

































Appendix 2


Field Data Sheet For Resistivity 2D



















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