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Optional LARGE HEAD.
To fit the large head, unplug the head lead from the small head by releasing
the bayonet lock, and plug into the large head.
It is not necessary to switch the instrument off when exchanging heads.
It is recommended that you return to the "Main Menu" and then re-enter a
measuring mode; and it will be necessary to re-zero the instrument.
In Depth mode, the screen display will be similar to the display shown when
using the small head; but for indicated covers greater than 99mm, the two
jumbo digits will be preceded by a vertical bar to their left, representing
"1"(hundred).
AutoSizing still operates in both Locate and Depth modes. As a different
head is being used, and different look-up tables for the calculations, the
deduced bar diameter may differ slightly from that deduced by the standard
head; and the instrument is factory-calibrated for best results from the
standard head.
The large head therefore may exhibit up to ±1 size absolute error and ±1
size random error; but the accuracy will still usually be the same ±1½ bar
sizes.
The internal tables for the Orthogonal Sizing mode are not designed to be
applicable to the large head. However, orthogonal sizing is still possible,
but the tolerance of diameter determination increases from ±½ bar size to
±1 bar size.
Note that the large head should only be used for covers too great to be
measured by the standard head (e.g. covers of 80mm or more); and only
resolves bars if they are adequately spaced (centres-pitch more than about
1½ times their cover). For covers shallower than 70mm, the standard head
should be used in preference.
UNDERCOVER mode
This is not actually a separate mode, but a feature which can be activated
whenever the CM9 is in either LOCATE or DEPTH modes.
It enables you to preset a minimum cover in millimetres, and then the CM9
will signal, audibly and on the head LED, all those bars whose cover is less
than that minimum.
Firstly, you should be in either the LOCATE or DEPTH mode.
The diameter of the bars to be investigated should be set using the
and
buttons. The normal sound system should be muted by turning the
AUDIO knob to the
position.
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