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mvip@mitech-ndt.com
3.2 Condition and Preparation of Surfaces
In any ultrasonic measurement scenario, the shape and roughness of the test surface are of
paramount importance. Rough, uneven surfaces may limit the penetration of ultrasound through the
material, and result in unstable, and therefore unreliable, measurements. The surface being
measured should be clean, and free of any small particulate matter, rust, or scale. The presence of
such obstructions will prevent the transducer from seating properly against the surface. Often, a wire
brush or scraper will be helpful in cleaning surfaces. In more extreme cases, rotary sanders or
grinding wheels may be used, though care must be taken to prevent surface gouging, which will inhibit
proper transducer coupling.
Extremely rough surfaces, such as the pebble-like finish of some cast iron, will prove most difficult
to measure. These kinds of surfaces act on the sound beam like frosted glass on light, the beam
becomes diffused and scattered in all directions.
In addition to posing obstacles to measurement, rough surfaces contribute to excessive wear of
the transducer, particularly in situations where the transducer is “scrubbed” along the surface.
Transducers should be inspected on a regular basis, for signs of uneven wear of the wearface. If the
wearface is worn on one side more than another, the sound beam penetrating the test material may
no longer be perpendicular to the material surface. In this case, it will be difficult to exactly locate tiny
irregularities in the material being measured, as the focus of the sound beam no longer lies directly
beneath the transducer.
4 Operation
4.1 Power On/Off
The instrument is turned on by pressing the
key.
The gauge can be turned off by pressing the
key while it is on. The tool has a special memory that
retains all of its settings even when the power is off.
4.2 Probe Zero
The
key is used to “zero” the instrument in much the same way that a mechanical micrometer
is zeroed. If the gauge is not zeroed correctly, all the measurements that the gauge makes may be in
error by some fixed value. When the instrument is “zeroed”, this fixed error value is measured and
automatically corrected for all subsequent measurements. The instrument may be “zeroed ” by
performing the following procedure.:
1. that the wearface of the transducer is clean and free of any debris.
2. Press the
key to activate the probe zero mode.
3. Use the
key and the
key to scroll to the probe model currently being used. Be sure to set
the right probe model to the instrument. Otherwise, there will be erroneous.
4. Apply a single droplet of ultrasonic couplant to the face of the metal probe-disc.
5. Press the transducer against the probe disc, making sure that the transducer sits flat against the
surface.
6. Remove the transducer from the probe disc.
