Elcometer Protovale CoverMaster CM52 Operating Instructions Manual page 10

Depth measurements MUST be made using the orientation of the search head that
produces the strongest signal. Section 3 of this manual is devoted to techniques for
locating buried reinforcing bars and placing the search head in the correct position for an
accurate depth measurement. Do not attempt depth measurements until the techniques
in section 3 have been fully mastered.
The material covering the reinforcing bar does not affect the ability of the CM52
CoverMaster to locate reinforcing bars and measure the depth of cover.
One exception is if the cover material itself is magnetic. For example, the CM52 cannot
detect bars which are covered by steel sheet, and depth measurements may become
distorted in areas where there is a high congestion of bars. However, the CM52
CoverMaster can still make accurate depth measurements on reinforcing bars covered
by magnetic aggregates such as 'Lytag' (see section 5.11).
When used correctly, the CM52 CoverMaster is capable of measuring cover depths to
better accuracy than required by British Standard 1881 Part 204, up to depths of at least
90mm (Figure 5). Compliance with BS1881:204:1988 is maintained over the entire
usable range.
Figure 5. Accuracy of the CM52 CoverMaster exceeds BS1881:204
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