Dynalog C-SCAN 2000 Series - 4.6 Direction Change within a Survey

Leaders in Pipeline Survey Systems
OPERATOR’S MANUAL
Issue 4.04 - 1207 29
NOTE: We may freely switch between CHAINAGE and DISTANCE. When we enter a distance, the
chainage is automatically stored (it is displayed on the attenuation display).
The chainage start point is used to start a new survey. This point does not have to be zero. As
an example, consider a survey of four points. The first point is at CP marker 10 which has a
distance marker of 3678m (3.678km) and the last point is at CP marker 11 which has a distance
marker of 3978m (3.978km). The two intermediate points are 100m apart.
Point CP number Line distance distance chainage
#00 10 3678 3678
#01 - - 100 3778
#02 - - 100 3878
#03 11 3978 - 3978
Point #00 is entered as a chainage start point with a value of 3678m
Points #01 and #02 are entered as distance from previous point as 100m
Point #03 is entered as chainage 3978m.
Select CHAINAGE
Press this key to go to Select DISTANCE
Press this key to go to START POINT CHAINAGE start point.
4.6. Direction change within a survey
There are occasions where a survey is proceeding and every point surveyed is producing good
results i.e. attenuations less than 1 mB/m. But then a section is encountered that has a high
attenuation (say 10 mB/m). If the gap between each point has been 100m we do not know
where the fault that has caused the high attenuation is within the last 100m. So we need to go
back to a point half way. Remember that going towards the generator is a negative distance.
The diagram below explains the method.
As the attenuation reading between points #03 and #04 is back to a normal level (0.73mb/m) we
know that the fault must lie between points #02 and #04
If GPS is being used, remember to enter a minus for the distance (GPS has no concept of
direction). If chainage is being used, just enter the chainage (no sign). Chainage inherently
works out the position correctly.
But what is the attenuation value between #02 and #04? To see this we need to look at the
graphs in more detail. Choose the attenuation graph.