Radiodetection rd7000+, Руководство по эксплуатации

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© 2014 Radiodetection Ltd 22
6.2 Verifying depth
measurements
Check a suspect or critical depth reading by lifting the
locator 50mm (2”) above the ground and repeating the
measurement. If the measured depth increases by the
same amount it is a good indication that the depth
reading is correct.
When locating for a conductor or sonde, depth
measurements should be accurate to ±5% if conditions
are suitable. However, you may not always know if the
conditions are suitable so the following techniques
should be used to check critical readings:

Check that the route of the line is straight for at least
2 meters (6½ft) to either side of the measurement
point.

Check that the signal response is reasonably
constant over the 15 meter distance to the
transmitter and make depth measurements to either
side of the original point.

Check that there are no adjacent lines carrying a
significant signal within 1 to 2m (3 to 6½ft) of the
target line. This is the most common source of error
of depth measurements as a strong signal coupled
to an adjacent line can often introduce ± 50% error.

Make several depth measurements at points slightly
displaced from the line’s apparent position. The
shallowest indication will be the most accurate and
will also indicate the line’s position most accurately.
6.2.1 Rough depth calibration check
This paragraph describes several quick and easy ways
of verifying that the depth reading on the locator when
used for markers or conductors and sondes is within
acceptable limits.
Please refer to this if you are getting inaccurate depth
readings from a cable or pipe for which you know the
approximate depth. Inaccurate depth readings could be
the result of the locator picking up a stronger signal
such as another cable or pipe running in close parallel
to the target pipe or cable.
When locating for RF Markers
1 Set the locator to marker mode and select the
correct marker type.
2 Place the marker on top of a non-metallic object,
such as a cardboard box, on the ground and away
from any buried lines or other sources of
interference.
3 Place the locator horizontal, at a distance equal to
half the maximum depth range distance for the
marker you are using (for example 700mm / 27½
”
for the center of the marker ball to the bottom of the
locator).
4 Note the depth as indicated on the locator LCD.
5 Compare this reading with the depth reading on the
locator.
Refer to appendix 12.9 to verify if the Locator is
operating within specification.
When locating for conductors or sondes
There are two ways of checking the calibration of the
locator in the field. Both methods require the use of a
transmitter:
Method 1
Place the transmitter on top of a non-metallic object,
18”/500mm in height or more, on the ground and away
from any buried lines. Switch the transmitter on in
induction mode. Hold the locator with the blade
horizontal and pointing towards the front of the
transmitter and approximately five meters from the front
of the transmitter.
1 Switch the locator on.
2 Select the same frequency as is selected on the
transmitter but make sure that this frequency is in
the sonde mode.
3 Move the locator from left to right and when the
bargraph reading is at its peak note the depth as
indicated on the locator. Measure the distance from
the base of the locator to the center of the
transmitter using a tape measure.
4 Compare this reading with the depth reading on the
locator.
The locator can be considered accurate if the difference
between the depth reading on the locator and the
distance measured with the tape is less than 10%.
Method 2
1 Apply a signal to a cable or pipe of known depth.
2 Locate the cable or pipe; the locator will display
depth on the LCD automatically.
3 Compare the depth reading on the locator with the
actual depth.
NOTE: The accuracy of depth measurement is subject
to a number of factors and is meant as a guide only.
Exercise caution when performing any excavation.
6.3 Current Readings
6.3.1 Identification using current
measurements
Measuring current value on a line helps confirm the
identity of the line and may provide information about
the condition of cable insulation or pipe coating.