Elcometer Protovale CoverMaster CM52 Operating Instructions Manual page 14

Very strong signals are obtained when the search head is across the centre bar of a
double or 'figure-of-eight' loop (Figure 7: left) but these locations must not be used for
cover measurements - see section 4. Minimum signals are obtained as before when the
search head is over the centre of a single loop (Figure 7: centre), and ordinary-strength
indications when the head is accurately aligned with the middle of a side (Figure 7: right).
Only the last kind of indication is suitable for measuring depth of cover.
More complex situations, such as congested reinforcing, partially connected mesh and
reinforced pipes, are dealt with in section 5 – ADVANCED TECHNIQUES.
In any situation where signals are very strong, the audible indication may be driven
towards its highest pitch and the digital indication may no longer increase in proportion to
the signal. To avoid this, back off the ZERO control counterclockwise until the indicators
are again responding readily to changes.
CAUTION – Backing off the ZERO control reduces the overall sensitivity of the
instrument, and will silence the audible indication when the search head is removed from
the region of high signal strength. This may cause deeply covered bars to be missed.
11