Reducing Errors When Orthogonal Sizing - Elcometer 331 SH Operating Instructions Manual

M
EASURING SIZE OF REINFORCEMENT BARS

9.4 Reducing errors when orthogonal sizing

This technique improves the accuracy of orthogonal sizing of bars where the nearest parallel bars
appear to be adequately distant, but the transverse bars are closer together
illustrated in Figure 18 where position X is the measurement position.
The technique involves zeroing the Covermeter with the search head held close to the concrete:
1. Hold the search head in contact with the concrete surface. The centre of the search head
should be in the centre of the space between the bars as shown in Figure 19.
2. Press the ZERO softkey to zero the Covermeter.
3. Move the search head to the measurement position and then carry out orthogonal sizing as
previously described in section 9.2 on page 27.
The aim of this technique is to subtract the 'background metal' signal; but it only provides an
estimate of that background. As a result, it tends to over-compensate for the errors and therefore
may result in an under-estimate of bar size (and cover).
Nevertheless, comparison with results from orthogonal sizing conducted with a standard zeroing
technique can be used to get a slightly pessimistic estimate of the probable error (or degree of
confidence) in the result.
v. In this situation, accuracy may also be improved by using a Narrow Pitch search head.
30
R
Figure 18. Measurement position
Figure 19. Zeroing
( )
ORTHOGONAL
Transverse bars are close
together
v
. This situation is