Geonics Limited EM38-MK2, Operating Manual

11 

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 
east/west).  Any significant difference in the reading in two directions at right angles is an 
indication of a significant lateral disturbance.  To check whether a pipe or fence is producing an 
erroneous reading make two measurements of the ground conductivity, one reading with the long 
axis pointing to the object and a second reading at right angles.  If the two readings differ by 
more than 10% a significant disturbance is being felt and the measurement point must be located 
further away from the object. 
 
It should be noted when traversing a pipe on a survey line perpendicular to the pipe direction in 
the vertical dipole mode that the reading over the pipe may decrease and attempt to go negative.  
If the goal is to locate the pipe one should again rotate the instrument 90

o

 so that the long axis is 

parallel to the pipe in which case the apparent conductivity reading becomes a maximum when 
(a) the instrument is directly over the pipe and (b) also pointing in the same direction as the pipe.  
These remarks apply in the vertical dipole mode, which should be used for the detection of pipes 
since the exploration depth is greatest.  It is, of course, assumed that the pipe is conductive i.e., is 
made of iron, steel or copper. 
 

4. ELECTRICAL INTERFERENCE

 
Occasionally electrical interference will be encountered, either from cultural sources (50/60 Hz 
power lines, industrial noise) or from atmospheric electricity (spherics).  Noise from cultural 
sources will often manifest itself as slow or rapid semi-periodic oscillations of the output meter 
reading which must be averaged out by the operator.  The amplitude of these excursions may be 
a function of the coil orientation and will also be largest on the most sensitive (low conductivity) 
range. 
 
Atmospheric noise will usually show itself as sporadic changes of the meter reading, usually 
most severe in the horizontal dipole mode.  In this case the receiver operator must again average 
out the noise, or restrict himself to the vertical dipole mode of operation, or wait until the 
spherics have decreased. 
 

5.

NOTES ON SURVEY INTERPRETATION

 
5.1  

Linearity of Response

 
The indicated apparent conductivity measured with the EM38-MK2 is accurate over most of the 
range of the instrument. 
 
5.2  

Relative Response with Depth 

 
TN-6 discusses in detail the fact that it is possible to calculate the relative response from material 
at different depths for both the vertical and horizontal dipole mode coil configurations.  The