The Principle of
Rebar Locator is that it can be worked either by utilizing Eddy current effect
or Magnetic induction effect.
In cover meters
using eddy current effect, current in the search coil set up eddy currents in
the reinforcement which in turn causes the measured impedance of the search
coil to change. Instruments using this principle operate at above 1 kHz frequencies.
They are thus sensitive to the presence of any conducting material in the
vicinity of the search head.
In cover meters
using magnetic induction effect, a multi coil search head is used with a lower
operating frequency of less than 90 Hz compared to the eddy current type
device. Here the principle used
is similar to that of a transformer. In that one or two coils (acting as
primary coil) carry the driving current while one or two further coils (acting
as secondary coil) pick up the voltage transferred through the magnetic circuit
formed by the search head and embedded reinforcing. Such instruments are less
sensitive to the presence of magnetic materials in the vicinity of search head This in
In both types of
instruments the meter reading is affected by both the orientation and the
proximity of the metal to the search head. Thus it can be used to locate
reinforcing bars and determine their orientation. The cover to a bar can also
be find out if a suitable calibration can be obtained for the particular bar
size and the materials under investigation. Most instruments have a procedure
to estimate both bar size and distance from the probe to the bar when neither
is known.
Equipment
Equipment mainly
consists of a number of suitable battery or mains operated cover meters. Each
cover meter is comprised of a Search head, meter and an interconnecting cable.
The concrete surface is scanned by keeping the search head in contact with it
while the meter indicates the proximity of reinforcement by analogue or digital
means.
Procedure
The Rebar
Locator equipment is switched on. Then start the main menu function and select
the single point test. Then select approximate diameter 16. After that fix the
probe in vacuum and scan the probe with 90 degree to rebar direction. Whenever
the beep sound comes, move the probe slowly and it means we are near the rebar .
When the scroll bar gets maximum points stop the probe and select the OK button.
The value shown is the total depth of concrete. Then move the probe slowly
again and get maximum point in scroll bar and press menu button. Here we get
two values. The first value is the diameter of rebar and second value is the rebar
thickness.
Applications
·
For quality control by ensuring
correct location and cover to reinforcing bars after the placement of concrete.
·
Investigation of concrete
members whose records are not available or need to be rechecked
·
Location of reinforcement as a
preliminary test to some other tests in which reinforcement should be avoided
or its nature taken into account.
·
Location of buried
ferromagnetic objects like water pipes, steel joints, lighting conduits etc.
