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EM31-SH

MANUAL

Page

19

increasing or decreasing, and possibly negative values or
some combination of each.

NOTE: It is always advisable, when surveying for buried metal

to record both the inphase and quad-phase components.
While the inphase, in general, is a better detector of
metal, the quad-phase is more sensitive to long, extended
targets (eg. pipelines) which are, at least partially, in
electrical contact with the ground.

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Summary of Contents for EM31-SH

Page 1: ...Unit 8 Mississauga Ontario Canada L5T 1C6 URL http www geonics com EM31 SH OPERATING MANUAL GEONICS LIMITED LEADERS IN ELCTROMAGNETICS 8 1745 Meyerside Drive Mississauga Ontario Canada L5T 1C6 Tel 90...

Page 2: ...om NOTE TO EM31 AND EM34 USERS Through the normal course of operation it is possible that the battery contacts will become contaminated with dirt and grit To clean these contacts use fine sand paper 4...

Page 3: ...nd Conductivity Measurements 10 2 1 1 Initial Set up Procedure 10 2 1 2 Equipment Functional Checks 14 2 1 3 Operating Procedure 16 2 2 Buried Metal Detection 18 2 2 1 Set up and Operating Procedure 1...

Page 4: ...UREMENT ACCURACY NOISE LEVELS OUTPUT PORT FOR REAL TIME LOGGING DIMENSIONS WEIGHT Self contained dipole transmitter Self contained dipole receiver 2 0 meters 9 8 kHz 8 disposable alkaline C cells appr...

Page 5: ...id and accurate measurement of terrain resisitivity Since the EM31 does not require electrical contact with the ground it fulfils this objective The basic principle of operation of EM31 is simple With...

Page 6: ...ach layer of different conductivity the instrument will read an intermediate value as discussed in more detail in Section 5 2 The unit of conductivity used is the millimho per meter the same as millis...

Page 7: ...ayered raising the instrument from the surface of the earth to the normal operating position can result in a reading which stays constant or even increases slightly with height In general readings mad...

Page 8: ...EM31 SH MANUAL Page 4 Table 1A Resistivities of Igneous and Metamorphic Rocks...

Page 9: ...EM31 SH MANUAL Page 5 Table 1B Resistivities of Consolidated Sediments...

Page 10: ...EM31 SH MANUAL Page 6 Table 1B cont d Resistivities of Consolidated Sediments...

Page 11: ...EM31 SH MANUAL Page 7 Table 1B cont d Resistivities of Consolidated Sediments...

Page 12: ...EM31 SH MANUAL Page 8 Table 1C Resistivities of Unconsolidated Formations...

Page 13: ...EM31 SH MANUAL Page 9 EM31 SH FRONT PANEL FEATURES...

Page 14: ...e switch to the OPER position and rotate the Range switch counter clockwise to the BATT position Turn data logger on and run polycorder program EM31 MK2 as per EM31 MK2 data logger manual If the displ...

Page 15: ...er s operating system completely protects you from losing data because the battery has run down Here s how it works as the Polycorder operates drawing from the main supply it monitors the batteries so...

Page 16: ...when they are only slightly discharged you will get less and less use out of each recharging Obviously you will need to balance this with the risk of being forced to suspend data collection because t...

Page 17: ...the old one Plug in the two pin connector Place the bracket around the battery pack and align the six holes with the holes in the case Drop the six outer screws in place and tighten them down Reload p...

Page 18: ...ductivity Q reading and rotate the COARSE control one step clockwise If the conductivity reading remained the same tolerance 0 2 the phase is already correct return the COARSE control to its original...

Page 19: ...lockwise one step The conductivity reading should change between 78 to 82 mS m It is unlikely that the sensitivity of the instrument will vary however it may be useful to record the actual reading for...

Page 20: ...ly in mS m and full scale reading minus 99 of overage is indicated by the Range switch Normal Operating Position Vertical Dipoles b The instrument can be operated in either of two dipole modes vertica...

Page 21: ...l turn on before the measurement is recorded Alternatively the operator may choose to leave the instrument on and watch for anomalous reading between data points The instrument however has a time cons...

Page 22: ...field to the primary magnetic field in parts per thousand ppt The inphase display reads directly in ppt and it has same sensitivity regardless of the range switch positon b Experience has shown that t...

Page 23: ...TE It is always advisable when surveying for buried metal to record both the inphase and quad phase components While the inphase in general is a better detector of metal the quad phase is more sensiti...

Page 24: ...be readily set by following the procedure described in Section 2 1 1 3 2 Absolute Calibration Absolute instrument calibration is easily achieved if any area of ground is available of known and constan...

Page 25: ...EM31 SH MANUAL Page 21 Figure 2 Conductivity Correction Instrument on the ground surface For 2 m unit...

Page 26: ...stivity anomaly To ensure the correct spacing it is useful at the start of the survey to continuously observe the conductivity values that are encountered as the operator moves alone the survey line T...

Page 27: ...shown in Figure 3 The negative going peak indicates the location of the pipe It is then possible to accurately determine the location and strike the direction azimuth of the conductor axis as follows...

Page 28: ...the operator has satisfied himself as to their possible effect In every case this is determined by rotating the instrument and determining whether there is maximum and minimum which appears to be rel...

Page 29: ...tely reflect the true terrain conductivity In any circumstance where the apparent conductivity varies significantly in a distance which is short compared with the intercoil spacing the possible presen...

Page 30: ...e to observe the spatial variations of terrain conductivity rather than the absolute value of conductivity itself Figure 2 shows that even at the higher values of terrain conductivity the instrument w...

Page 31: ...e multiply this function by one hundred to yield percent all of the ground below a depth z of two meters yields 45 of the response the ground below three meters yields 32 the ground below four meters...

Page 32: ...EM31 SH MANUAL Page 28 Figure 4 Multi Layer Response Diagram...

Page 33: ...4 1 00x0 14 7 21 mmho m Fig 7 CROSS SECTION GRAVEL DEPOSIT 1 000 R Z1 k2 R Z1 k2 0 0033 Z1 5m a 30 1 00 0 20 24 0 mmho m Z1 3m a 30 1 00 0 32 20 4 mmho m Z1 1m a 30 1 00 0 71 8 77 mmho m Fig 6 CROSS S...

Page 34: ...apparent conductivity becomes relatively independent of the actual value of the conductivity of the lower layer For k2 1 the apparent conductivity simply becomes a function of the thickness of the upp...

Page 35: ...n ground difficulties associated with generating sufficient current in the ground The use of inductive electromagnetic techniques avoids both problems since ground probes are not required This allows...

Page 36: ...physical applications down to depths of the order of six meters The intercoil spacing is fixed at twelve feet 3 66 meters The effective penetration referred to above is an average value in those regio...

Page 37: ...ta was only recorded with one exception at every 100 feet The exception occurred at station 7 50 where it was noted that a local resistivity high occurred this was of course not observed on the Wenner...

Page 38: ...t to read off scale 6 5 Example D Lake Scugog EM31 Measurement Interval 50 feet This survey illustrates the extremely high resolution achievable with the EM31 or the EM34 systems since neither techniq...

Page 39: ...conductive that it was not possible to take readings The second sheet illustrates the application of the two layer curves to interpret the survey results in terms of depth 6 7 Example F Discontinuous...

Page 40: ...hereas an average value for the conductivity of the infilling glacial till is of the order of 8 to 12 millimhos per meter Thus the EM34 at either intercoil spacing yields approximately 30 to 34 millim...

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