Elcometer Protovale CoverMaster CM52 Operating Instructions Manual page 20

Thus the possibility of errors due to adjacent bars is greater when the bars are further
away from the search coils. This also applies when the head is turned over to use the
white face in congested situations– the extra 30mm separation will make the measurement
more susceptible to errors caused by adjacent bars. When measuring very shallow cover
in congested situations, it is better to use thinner spacers (10 or 20mm) under the black
face of the search head.
Figure 10 shows the relationship between the performance of the CM52 CoverMaster and
the performance standards given in BS1881:204:1988, for various depths of cover and bar
to bar pitches. The CM52 CoverMaster meets the British Standard of performance at all
pitches greater than 40mm, and significantly surpasses the British Standard limit of ±15%
for multiple bars.
Figure 10 Effect of pitch upon accuracy of cover depth measurement
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