pulseEKKO PRO
4-Running in Scope Mode
67
Figure 4-3: Timezero or the first break is the first large deflection in the trace. Ideally, timezero needs to be shifted to the start of
the second vertical division as shown in Figure 4-2. Use the
Auto <>
button to try and automatically locate timezero and set it to
the correct position. The
Shift >
and
Shift <
buttons can be used to move timezero to the right and left respectively. When a Shift
button has been pressed, it changes to reverse video and timezero will keep moving in that direction until Shift is turned off by
pressing it again. The percentage button indicates the percentage of the shift in each step, a larger percentage indicating a larger
shift. Locating timezero further to the right reduces the amount of data collected from the subsurface (left). Locating timezero fur-
ther left affects the data collected and should be avoided.
The location of timezero is affected by a number of factors. These include: various system hardware
components, length of fibre optic cables, separation of transmitter and receiver antennas, and the total
time window.
To set 'timezero', the transmit and receive antennas should be set to the antenna separation being used for
the survey (Section 3.2.4: P37). This assures a large first arrival with minimal propagation delay. The start
of the second division represents the ‘ideal’ location for timezero (see Figure 4-2). The purpose is to adjust
the ‘timezero’ location so that it falls near the start of the second division. There are 4 menu options along
the bottom of the screen to assist with adjusting timezero: Auto <>, Shift <, Shift > and a percentage.
Pressing
Auto <>
initiates an automatic search and adjust to bring the timezero location within the ideal
region. The automatic search and adjust, while not perfect, should work get timezero close to the ideal
region most of the time. It is based on the assumption that the first break (first signal to arrive) is strong
compared to the surrounding background noise. If antennas are at a large separation, or there is a large
amount of external noise then this automatic adjustment may not function correctly.
Figure 4-4: If the transmit pulse is not visible on the Scope screen, use Auto <> to shift the pulse closer to the ideal region shown
in Figure 4-2.