Use the following process to measure cover:
1. Connect and Calibrate the probe
2. Set the measurement range
3. Set the bar size
4. Locate the bar
5. Read the cover depth
Connect and Calibrate the probe.
Calibration must be performed every time you
switch the instrument on.
To remind you, the Cover depth display will show
0 mm (0.00 in) until calibration is performed.
Connect the probe cable to the connector on the
right hand side of the MC8022+. Align the white
index marks on the connectors, push the plug onto
the instrument connector, then turn the locking ring
in the direction of the green arrow. Press the red
button to switch on the MC8022+.
Calibrate the instrument by holding the probe
in the air at least 1m away from metal objects
and magnetic fields, such as keys, rings or coins,
fluorescent lights, mobile phones or computer
screens.
Press and release the left hand yellow button
(CAL). The instrument will beep when the button
is pressed and beep again when calibration is
complete. The display changes to show a value
around 160 mm (Lo) or 220 mm (Hi) depending on
the range and bar size selected.
“Cover depth at limit” is shown to indicate that
the reading is outside the specified measurement
limits of the instrument.
Move the probe towards a metallic object and note
that the cover depth display gradually changes to a
lower value.
These simple checks confirm that the instrument is
functioning and ready for use. If required, a sample
rebar of known diameter can be used for a more
complete confirmation of operation.
To get the best possible results, calibration should
also be performed periodically if you are making
large numbers of measurements and especially
before making measurements of deep cover.
Set the measurement range
The MC8022+has two measurement ranges – High
and Low. Change range by pressing the right hand
yellow button (Range).
An indicator on the right-hand side of the screen
shows Hi or Lo.
The High range is more sensitive so it can measure
greater cover depths. When locating a bar or
measuring cover, you should normally use the
High range to avoid missing deep bars. However,
when trying to find the orientation of bars that are
closely spaced, try the Low range because it is less
affected by nearby bars.
Set the bar size
Cover measurement is only accurate if the bar size
is known reasonably precisely.
If you know the bar size, press the middle yellow
button (BAR) to set the value shown on the Cover
depth page. Pressing (BAR) selects the next
available bar size. In the picture, the bar size has
been set to 16 mm.
To locate a bar and estimate its size automatically,
see “Automatic bar sizing” below; this will set the
current bar size to the measured value.
Quick bar location
To quickly find the approximate position of a bar,
look at the top of the probe whilst slowly sweeping
the probe over the search area.
The red bar indicator light flashes briefly when the
signal detected from a bar is near its peak and this
can be used as a quick guide to bar location.
For more precise location follow the procedure
below.
Precise bar location and cover measurement
Hold the yellow face of the probe flat against the
concrete surface. Move the probe over the surface
whilst watching the cover depth display. The probe
is positioned roughly over a bar when the cover
depth reading is at its lowest.
Keeping the probe over the same spot, rotate it
around its centre. When the lowest cover reading
is seen, the probe body has been aligned with the
direction of the bar.
Now the bar orientation is known, slowly sweep
the probe, keeping it parallel to the bar. The lowest
cover reading will now correspond to the centre
line.
Once you have found a bar and aligned the probe
to it, you can read the cover depth from the display.
If you want to log this cover reading, press the
yellow button on the probe. This will record the
cover depth, bar size, time and date and can be
viewed on the MC8022+or downloaded to a PC
later if required. (See Data logging, below)
For maximum precision follow the same procedure
but instead of watching for minimum cover, look for
maximum signal strength reading.
Signal strength is shown below the main cover
depth readout, in smaller numbers – 1854 in the
picture.
The signal strength reading is at its greatest when
the probe is aligned with the centre line of a bar.
When this position and alignment is found, read
the cover as before.
In some situations an alternate method is useful
to map out the orientation of bars. First sweep
the probe in a straight line until you find a bar (bar
indicator light / lowest cover / maximum signal).
Mark this position. Now perform a second sweep
in the same direction but some distance from
the first and again mark the bar position. A line
drawn between these marks gives the orientation
of the bars. Keeping the probe parallel to the bar
orientation, perform a third sweep to find the
centre of the bar. The location of parallel bars can
now be marked by extending the sweep either side
of the first bar.
Audio cover mode
MC8022+has an audible indication of detection
strength which helps to locate bars without having
to watch the display. To use Audio cover indication,
go to Settings, select Audio and set Mode to
“Cover”. You can also adjust the volume from this
menu.
Now when you sweep the probe over the search
area, you will hear a tone that increases in pitch
as you get closer to a bar and reaches its highest
pitch when the probe is aligned with the bar.
Set the audio Mode to “Off” to stop the tone.
MEASURING COVER4
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Bar size Hi range Lo range
6 mm 110 mm 70 mm
40 mm 185 mm 90 mm
Maximum cover
