Welded Mesh And Joined Bars - Elcometer protovale P330 Operating Instructions Manual

Because the CM9 CoverMaster is unaffected by the nature of the material
covering the reinforcing bars, the easiest way to practice location
technique is to use uncovered bars which you can see. A block of wood or
plastic of 20 to 45mm thickness can be held between the search head and
the bars to simulate the depth of concrete cover.
Start from the simplest situation, a single straight bar, and progress
through parallel bars, lapped bars, and crossing bars. As you develop skill
and confidence with uncovered bars, move on to locating bars in more
realistic situations.

Welded mesh and joined bars

With isolated reinforcing bars, the eddy currents are induced within the
individual bars. Welded mesh reinforcing creates current loops which
produce additional strong indications.
Very strong signals are obtained when the search head is across the
centre bar of a double or 'figure-of-eight' loop but these locations must not
be used for cover measurements. Minimum signals are obtained as
before when the search head is over the centre of a single loop, and
ordinary-strength indications when the head is accurately aligned with the
middle of a side. Only the last kind of indication is suitable for measuring
depth of cover.
In any situation where signals are very strong, the audible indication may
be driven towards its highest pitch and the LED on the head to its
maximum brightness, and no longer increase in proportion to the signal.
To avoid this, back off the AUDIO control counterclockwise until the sound
and LED are again responding readily to changes.
CAUTION – Backing off the AUDIO control does not reduce the overall
sensitivity of the instrument, but will silence the audible and LED
indications when the search head is removed from the region of high
signal strength. This may cause deeply covered bars to be missed.
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