Measuring with the Gauge
42
Other reasons for difficulty in getting readings
¾ Is the Probe-frequency correct for the Gauge ?
Ö Cygnus 1 ROV Gauge is always supplied with the Gauge and Probe correctly
configured to operate together - check that the Gauge is still being used with the
original Probe
Ö If this is not the case the Gauge and Probe should be returned to Cygnus, to be
configured to work together
¾ Measuring in Air : is there adequate couplant applied to the material being measured,
and is the surface properly prepared ?
See : Preparing to take Measurements
, page 38
Check that there is plenty of couplant applied, and that there are no air-gaps between
the Probe and the material when measuring in air
GENERAL POINTS ON THICKNESS GAUGING
¾ On very rough surfaces, and especially if both sides are badly corroded, it is often
necessary to move the Probe around to locate a reflector. Sometimes a slight rocking
movement can help find reflectors which are otherwise impossible.
¾ Measuring in Air : always ensure that there is plenty of couplant present for good
contact, but beware that on a pitted surface the Gauge may just measure the couplant-
filled pit – always avoid measuring directly over external pits.
¾ Beware that in extreme conditions, or if the plate is of poor quality and contains many
inclusions, the ultrasound will be scattered to such an extent that measurement may not
be possible.
¾ Beware that the multiple-echo technique will not work if the front and back surfaces of
the material being measured are not close to parallel; also note that long narrow bars
cannot be gauged along their length with the multiple-echo method.
¾ The instrument should not be used near arc-welding equipment, as this affects the
performance of the Gauge.
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