Dakota Ultrasonics PX-7 DL - Manual (Page 15)

PX-7 DL Ultrasonic Thickness Gauge
11
If the Stability Indicator has fewer than five bars darkened, or the numbers
on the display seem erratic, first check to make sure that there is an
adequate film of couplant beneath the transducer, and that the transducer
is seated flat against the material. If the condition persists, it may be
necessary to select a different transducer (size or frequency) for the
material being measured. See page 28 for information on transducer
selection.
While the transducer is in contact with the material that is being
measured, the PX-7 will perform four measurements every second,
updating its display as it does so. When the transducer is removed from
the surface, the display will hold the last measurement made.
IMPORTANT
Occasionally, a small film of couplant will be drawn out between the
transducer and the surface as the transducer is removed. When this
happens, the PX-7 DL may perform a measurement through this couplant
film, resulting in a measurement that is larger or smaller than it should be.
This phenomenon is obvious when one thickness value is observed while
the transducer is in place, and another value is observed after the
transducer is removed.