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around and existing drawings, dependency on the user a variety of means such as
investigation and field observation.
2. Blind test method
Pre-test preparation: before the blind test, the receiver should be placed within a
certain distance from the transmitter, generally between 5 and 10 meters, preferably
about 7 meters. One person holds the transmitter as close as possible to the ground (as
close to the ground as possible). Do not connect to any line, turn on the transmitter,
frequency select high frequency or rf (recommended radio frequency), power choose
high grade. The other person holds the receiver, the head points to the transmitter's
panel (front), and the two machines are about 7 meters apart. At this time, open the
receiver, frequency selection and transmitter, then the gain, the receiver as far as
possible from the transmitter radiation air out of the influence of the magnetic signal,
usually drop gain (about 50 db) causes receiver signal strength to display at around
$500, according to the signal strength base, the gain unchanged, keep the distance,
then blind test work. Note: the two machines are close to each other. The receiver gain
drop is very low, the detection depth is lost, and the blind area is reduced. The
distance between the two machines is far away, the receiver is far away from the
receiver, the receiver gain is reduced, and the test depth can be guaranteed, but the
secondary signal of the radiation is relatively weak, and the blind area increases.
A) blind test method 1: surface measurement
(1) Operation: on the basis of pre-test preparation, the two sides of the machine are
facing each other, parallel to each other, and can not move fast enough to move slowly,
so that the instrument has sufficient reaction time. The transmitter is active, the
receiver is passive, and the receiver's head is always pointed to the front of the
transmitter and the two machines are in a consistent state. When the signal intensity of
the receiver increases suddenly (the gain is constant, greater than the base before the
test). There is a metal pipeline between the transmitter and the receiver. At this point,
the receiver can be lifted up a bit, and the signal intensity will be reduced to the
ground to see the signal strength.
Whether it increases or not, if so, it is certain that there is a pipeline underneath. In
this way, it can be perpendicular to the direction of movement (the deviation Angle is
plus or minus.10 °) within a depth of 2.5 meters of all metal pipe are all measured, can
use inductive method to measure the distance to the known point, the gold
The path of the pipe is measured, and then another moving direction can be detected,
and the vertical line of the moving direction can be detected, so that the pipeline in
this operation surface can be found out.