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Tel: (905) 670-9580
Fax: (905) 670-9204
GEONICS LIMITED
E-mail:geonics@geonics.com
1745 Meyerside Dr. Unit 8, Mississauga, Ontario Canada L5T 1C6
URL:http://www.geonics.com
EM38-MK2
GROUND CONDUCTIVITY METER
OPERATING MANUAL
GEONICS LIMITED
LEADERS IN ELECTROMAGNETICS
8-1745 Meyerside Drive, Mississauga, Ontario L5T 1C6
Tel: (905) 670-9580 Fax: (905) 670-9204
E-mail:geonics@geonics.com Web site:http://www.geonics.com
April 2016
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Summary of Contents for Geonics Limited EM38-MK2 Series
- Page 1 Tel: (905) 670-9580 Fax: (905) 670-9204 GEONICS LIMITED E-mail:geonics@geonics.com 1745 Meyerside Dr. Unit 8, Mississauga, Ontario Canada L5T 1C6 URL:http://www.geonics.com EM38-MK2 GROUND CONDUCTIVITY METER OPERATING MANUAL GEONICS LIMITED LEADERS IN ELECTROMAGNETICS 8-1745 Meyerside Drive, Mississauga, Ontario L5T 1C6 Tel: (905) 670-9580 Fax: (905) 670-9204 E-mail:geonics@geonics.com Web site:http://www.geonics.com...
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Page 2: Table Of Contents
EM38-MK2 GROUND CONDUCTIVITY METER OPERATING MANUAL TABLE OF CONTENTS INTRODUCTION EM38-MK2 OPERATING INSTRUCTIONS - Simplified Method ......3 Battery Test ......................3 Calibration Method for Instrument Zero..............3 OPERATING INSTRUCTIONS - Expanded Method ...........6 Battery Test ......................6 Initial Inphase Nulling .....................6 Instrument Zero ......................7 Final Inphase Nulling ....................9 Equipment Sensitivity Checks ................10 Automatic Calibration of EM38-MK2 ..............10... - Page 3 APPENDIX ........................20 Schematic Diagram of Vertical and Horizontal Dipole Positions ......21 Relative Response Curves..................22 iii) Cumulative Response Curves ................24 Two Layer Curves....................26 Automatic Calibration Set-up ................34 External Battery Components ................35 vii) Protective Housing ....................36 viii) Extender Arm ......................37 Communication Protocol ..................38 Gain Calibration Check..................41...
- Page 4 INTRODUCTION This manual supplies users of the EM38-MK2 with operating information and some theoretical results to assist in the planning and interpretation of geophysical surveys. Additional information can be found in Geonics Technical Note TN-5, which outlines the factors affecting soil and rock conductivity, and Technical Note TN-6, which describes the general theory of terrain conductivity mapping using inductive electromagnetic techniques.
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Page 5: Battery Test
EM38-MK2 OPERATING INSTRUCTIONS Operator should follow the steps outlined below or as an alternative, and more theoretical procedure follow Sections 2.2 to 2.5 1. EM38 OPERATING INSTRUCTIONS - Simplified Method The following procedures are used to prepare the EM38-MK2 for survey operation. The suggested time interval between the various procedures are typical values;... - Page 6 Step 1 With the instrument in the air and in the horizontal dipole mode of operation (Fig. 1), set the Q/P and I/P readings to zero. Step 2 Now adjust the Q/P zero control so that an arbitrary value (i.e H=10 mS/m) appears on the display, for Q/P reading.
- Page 7 Fig. A...
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Page 8: Operating Instructions - Expanded Method
2. EM38-MK2 OPERATING INSTRUCTIONS - Expanded Method The following procedures are used to prepare the EM38-MK2 for survey operation. The suggested time interval between the various procedures are typical values; under adverse conditions they may have to be carried out more often and under good conditions less often, as dictated by survey experience. -
Page 9: Instrument Zero
2.3 Instrument Zero This adjustment should be carried out at the beginning of each day at the first survey station and should be checked thereafter two times a day or more often when making measurements over ground of low conductivity. As referred to earlier, this adjustment is used to accurately set the instrument zero so that if the unit were taken to a great height above the earth (so as to no longer respond to terrain conductivity) it would actually read zero. - Page 10 An example will help to illustrate this procedure. Suppose that with the instrument at 1.5 m height the meter reads 12 mS/m in the horizontal dipole mode and 35 mS/m in the vertical dipole mode. Then H = 12 mS/m V = 35 mS/m and we calculate C = 35-2x12 = +11 mS/m...
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Page 11: Final Inphase Nulling
Particularly over resistive ground the operator must ensure that, when setting the instrument zero he is not near fences, cars or other large metallic objects. The reason for this is that the theory wherein V =2H applies only for a uniform or a horizontally layered earth. The presence of large metallic objects will usually affect H more than V, and will thus give an error in the zero setting. -
Page 12: Equipment Sensitivity Checks
On some occasions it may be quicker to perform the survey twice, first in one mode and then in the other. If minimal effect from any susceptibility variations is desired (for example in archaeological applications) then the inphase nulling procedure described above must be carried out before every measurement and the faster way is probably to perform the survey twice, once in each dipole. -
Page 13: Electrical Interference
end of the instrument) either when on survey or when the null or zero is being set. To check whether a metal object is giving a detectable response simply move the object a few meters away from the instrument and note whether the reading changes. No change -- no problem. How near can the operator approach a conductive object such as a pipe, fence, etc., and still ensure that the readings are accurate? In a laterally uniform ground the EM38-MK2 should read the same regardless of the azimuth of the long axis (i.e., whether it is pointing north/south or... -
Page 14: Multi-Layer Calculations
results for the EM38-MK2 are shown in Fig. 2A for 1 m coil separation and 2B for 0.5 m coil separation where the function gives the fractional response to the meter reading from a thin horizontal sheet of thickness dz buried at a depth z. We see that in the vertical dipole mode the relative sensitivity to near surface material is very low (being zero right at the surface), that the sensitivity increases with depth, becomes a maximum at about 0.4 (0.2 m for 0.5 m coil separation) meters and decreases slowly thereafter. - Page 15 instrument reading in the horizontal dipole mode is more sensitive to instrument height or conversely that in regions where the surface topography varies rapidly on the order of 10-20 cm we can expect some scatter in the horizontal dipole readings. In the event that the earth is two-layered it is possible to resolve this geometry by lifting the EM38 above the ground and making a sequence of measurements at various heights in both the horizontal and vertical dipole mode.
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Page 16: Simplified Two-Layered Earth Interpretation
5.3.2. Simplified Two-layered Earth Interpretation In general, a two-layered earth has three unknown quantities, , and t, whereas measurements made with the EM38-MK2 on the ground produce only two measured quantities, (the apparent conductivity in the vertical dipole mode) and (the apparent conductivity in the horizontal dipole mode). -
Page 17: Output Units
which was indicated at the height of 1.5 meters and finally increases to a larger apparent conductivity. The magnetic susceptibility (in RMKS units) is then given by ∆σ K=57 x 10 (mS/m) (for 1 m) ∆σ K=14.5 x 10 (mS/m) (for 0.5 m) or in CGS units by 57x10... -
Page 18: Communication With External Logger
for detailed sounding of conductivity with depth it gives very useful results when the earth can be approximated by a two-layer mode. 9. COMMUNICATON WITH EXTERNAL LOGGER EM38-MK2 is designed to communicate with an external logger in two different ways: a) through an RS232 serial port via cable connection or b) via a wireless Bluetooth connection. -
Page 19: External Battery Care
The fully charged battery will read above 13 V. Recharge the battery if its voltage is below 10.5 V. The battery can be charged by attaching the battery charger to the connector on the battery pack. Remember to connect the charger to the battery before applying power to the charger. Completely charging a full discharged battery takes about 8 hours. -
Page 20: Protective Housing
10.2 Protective Housing An optional protective housing (see Figure 10) is designed to give the instrument protection from dust, mechanical shocks, as well as to improve instrument stability (drift) as a result of sudden change in environmental temperature. The housing is especially useful when the instrument is in a cart operating mode. - Page 21 EM38-MK2 INSTRUMENT SPECIFICATIONS Measured Quantity Apparent conductivity of the ground in millisiemens per metre (mS/m) at each coil separation Inphase response in parts per thousand (ppt) of secondary to primary magnetic field at each coil separation Conductivity Ranges 0 to 1,000 mS/m (4 digit digital meter) In-Phase Range ±...
- Page 22 12. APPENDIX Schematic Diagram of Vertical and Horizontal Dipole Positions (ii) Relative Response Curves (iii) Cumulative Response Curves (iv) Two Layer Curves Automatic Calibration Set-up (vi) External Battery Pack and Charger (vii) Protective Housing (viii) Extender Arm (ix) Communication Protocol Gain Calibration Check...
- Page 40 EM38-MK2 RS232 DATA PROTOCOL February 2008 DESCRIPTION The data from EM38-MK2 is transmitted to a data logging computer via a RS-232 port. The conversion and sending are automatic and continuous, no trigger is needed. PORT AND CABLE PIN ASSIGNMENT The computer interface is provided via a 3-pin circular Lemo socket mounted on the EM38-MK2 panel.
- Page 41 Each data record string consists of 16 bytes detailed below: Byte 1 (ASCII) " T " -- start byte Byte 2 (information byte. See next section for marker, mode, Interpretation.) Byte 3 Channel 1 High Byte Byte 4 Channel 1 Low Byte Byte 5 Channel 2 High Byte Byte 6...
- Page 42 CHANNEL INFORMATION Channel 1 ------ Conductivity FOR 0.5M Channel 2 ------ In-phase FOR 0.5M Channel 3 ------ Conductivity FOR 1M Channel 4 ------ In-phase FOR 1M Channel 5 ------ Temperature FOR 1M Channel 6 ------ Temperature FOR 0.5M DATA INFORMATION (for Channel 1~4) –160mV=0000HEX;...
- Page 43 EM38-MK2 GAIN CALIBRATION PROCEDURE The following is the Gain Check and calibration procedure for EM38-MK2 using the test coil and test jig. 1. Set the EM38-MK2 in the jig with the test coil as per figure 12. Make sure that the test coil is switched off.
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