Checkline TI-25S - Manual (Page 8)

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5.0 Z EROING T HE P ROBE
Setting the Zero Point of the TI-25S is important for the same reason that setting
the zero on a mechanical micrometer is important. If the gauge is not “zeroed”
correctly, all of the measurements the gauge makes will be in error by some fixed
number. When the TI-25S is “zeroed,” this fixed error value is measured and
automatically corrected for in all subsequent measurements. The TI-25S may be
“zeroed” by performing the following procedure:
1. Make sure the TI-25S is on.
2. Plug the transducer into the TI-25S. Make sure that the connectors are fully
engaged. Check that the wearface of the transducer is clean and free of any
debris.
3. On the top of the TI-25S, above the display, is the metal
probe-disc. Apply a single droplet of ultrasonic couplant
to the face of this disc.
4. Press the transducer against the probe-disc, making sure
that the transducer sits flat against the surface of the
probe-disc. The display should show some thickness
value, and the Stability Indicator should have nearly
all of its bars illuminated.
5. While the transducer is firmly coupled to the probe-disc,
press the PRB-0 key on the keypad. The TI-25S will
display “Prb0” while it is calculating its zero point.
6. Remove the transducer from the probe-disc.
At this point, the TI-25S has successfully calculated itsinternal error factor,
and will compensate for this value in any subsequent measurements. When
performing a “probe-zero,” the TI-25S will always use the sound-velocity value
of the built-in probe-disc, even if some other velocity value has been entered for
making actual measurements. Though the TI-25S will remember the last
“probe-zero” performed, it is generally a good idea to perform a “probe-zero”
whenever the gauge is turned on, as well as any time a different transducer is
used. This will ensure that the instrument is always correctly zeroed.
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9.0 T AKING M EASUREMENTS
In order for the transducer to do its job, there must be no air gaps between the
wear-face and the surface of the material being measured. This is accomplished
with the use of a “coupling“ fluid, commonly called “couplant.” This fluid
serves to “couple” or transmit, the ultrasonic sound waves from the transducer,
into the material, and back again. Before attempting to make a measurement, a
small amount of couplant should be applied to the surface of the material being
measured. Typically, a single droplet of couplant is sufficient.
After applying couplant, press the transducer (wearface down) firmly against the
area to be measured. The Stability Indicator should have six or seven bars dark-
ened, and a number should appear in the display. If the TI-25S has been properly
“zeroed” (see page 8) and set to the correct sound velocity (see page 9), the
number in the display will indicate the actual thickness of the material directly
beneath the transducer.
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 trans-
ducer (size or frequency) for the material being measured. See page 10 for
information on transducer selection.
While the transducer is in contact with the material being measured, the TI-25S
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 TI-25S 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.