abem Terrameter LS, Instruction Manual

Page: 47 / 114

ABEM Terrameter LS
37
The available settings on the Receiver View (Figure 39):
Measure mode
Measuring mode options include SP, resistivity (RES), IP, and a
combination of RES and IP
Minimum # of
Stackings
Maximum # of
Stackings
The number of stackings needed depend on site conditions,
electrode spread size and the type of electrode array used. It is
recommended to start out a task with stacking, and if very
favourable signal-to-noise ratio is at hand the maximum number
of stackings value may be reduced even as low as to one
Error limit
The error limit is equivalent to the standard deviation between
repeated measurements (stackings) divided by the mean value
for a data point, also known as variation coefficient. Measuring
will be repeated the minimum number of stackings requested.
Measurement for the current data point will stop if the variation
falls within the specified limit. If not it will continue until either
the variation drops to the limit or the maximum number of
stackings have been reached
Delay Time The delay time setting defines the interval from switching on
current transmission until signal integration for the resistivity
measurement starts. Integration time defines for how long signal
averaging lasts for each part of the measuring cycle. Delay time
plus integration time defines the total duration of a current
transmission pulse. In the case of resistivity mode measuring,
however, double integration time is used for the negative part of
the current pulse (see Appendix B. Measurement Modes)
Acq. Time
The acquisition time should always be set to a multiple of the
power line frequency period time in order to suppress power line
noise. In areas with 50 Hz power line system the period is 20
ms, and for 60 Hz it is 16
2
/
3
ms, which means that any multiple
of 100 ms is ok. It should be noted, however, that in some
countries the railway system uses a frequency of 16
2
/
3
Hz,
which means that multiples of 60 ms are required (note that such
noise may be observed many kilometres or even tens of
kilometres away from railway lines)
Number of IP
Windows
The number of IP windows only applies to measurements in IP
mode, and the timings are defined in the “Measure/IP Windows
Settings” View (Figure 41)
Record Full Wave
Form
If “Record full waveform” is checked all measured full
waveform data will be saved to disk with a time resolution of 1
millisecond. See chapter 6.11 Full Waveform Data for more
information on this issue (page 64)
Power line
frequency
The power line frequency should be set to 50 Hz or 60 Hz
depending on the system used in the area of investigation