Hilti PS 200 Mode D'emploi page 62

Diameters given for bars that do not conform to one of
these standards may not fall within the accuracy spec-
ifications.
-WARNING-
en
The diameter calculation is an estimate and intended to
indicate probable diameter only. If the bar diameter must
be known with 100 % certainty, concrete must be removed
from the structure and the bar measured physically.
-WARNING-
Never attempt to determine the diameter of a bar by mea-
suring it on the image. Whilst the center of the bars in the
image correspond with those in the structure, the image
is not a scale drawing of the bars. The width of the bars
shown is representative of the signal strength received
by the scanner. Small bars close to the surface may thus
appear similar in size to larger bars at greater depth.
-NOTE-
The most accurate and reliable diameter and depth values
are obtained at points on the bar as far away from other
bars as possible and away from edges of the scan that are
parallel to the bar in question. Effects at the edges of the
scan may affect bars lying parallel typically up to 100 mm
from the edge.
Depth and diameter calculations should not be made along
the grid lines and not at points where bars cross.
Other factors influencing depth and diameter accuracy
are rough scanning surfaces, ferrous or magnetic sub-
stances in the concrete mix, a smooth scanning technique
starting at the correct point on the grid and following
the grid lines exactly and an adequate ratio between cov-
er and bar spacing.
Please refer also to section 7.5 for further advice on how
to get the most out of the system.
-NOTE-
If the bar diameter is known, it can be entered under Fix
Diameter. See below.
Fixing the diameter
If the diameter is known, the value should be entered as
this improves the accuracy and reliability of depth deter-
mination. Press Fix Diameter.
60
Printed: 07.07.2013 | Doc-Nr: PUB / 5070389 / 000 / 00
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Set the diameter to On using the left or right arrow but-
tons. Move to the diameter input field using the up or
down arrow buttons and select the diameter.
Press Done to confirm the selection and return to the
scan. The Fix Diameter symbol appears in the status bar
to the right of the display.
Calibrating the image
This option is intended for measurements of the high-
est accuracy and can be used when the depth and diam-
eter of a bar at a certain point are already known. It should
be used with caution as improper use can lead to incor-
rect depths being displayed. The image will be calibrat-
ed depending on the information given and the depth
around the point calibrated will be given with the utmost
accuracy. It is normally only of use to manufacturers of
precast concrete components.
Depths and diameters of bars in a different part of the
scan may lie outside the specification if the calibration
function is applied.
After moving the cursor to the point where the depth
and diameter are known, select Calibrate.
Set Calibration to On and enter the depth and diameter
values for this point on the image. Press Done to con-
firm and return to the scan. The system checks whether
the values entered are plausible based on the informa-
tion it has for that point. If this is not the case, calibra-
tion will be rejected.