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CAUTION –
1. When scanning for under-cover, the display
does not measure
cover.
2. The unit may signal a bar of adequate cover but larger size.
3. The unit
may not
signal an under-covered bar of smaller diameter.
4. The unit
will not
signal a bar which is completely missing!
5.4 More about transverse bars
Reinforcing bars lying transverse to the bar being measured will produce some additional
signal, and hence will cause the depth of cover to be underestimated.
When the search head is moved along the longitudinal bar and towards a transverse bar,
the signal strength will increase to a maximum followed by a small minimum when the
center of the head is located over the transverse bar. As the head is moved away, the
signal strength will reach another maximum and then fall back to its previous value which
is related only to the longitudinal bar. The cover depth indication will show the reverse
behaviour – a minimum, a small peak and then a second minimum.
Figure 8 Response to a transverse bar
Figure 8 shows these characteristic double-humped responses, which should be
entirely predictable since the locations of all transverse bars should already have
been identified using the
LOCate
mode. Three simple rules show how to obtain
the most accurate cover measurements in these circumstances.
