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Two - Point calibration
1. Conduct a one point calibration routine as described previously in this section. You should
conduct this routine at the high end of the measurement range
2. Repeat the routine with another sample at the low end of the measurement range, except this
time enter the thickness into the TWO POINT area in the CAL menu.
Note: CHECK YOUR CALIBRATION. Place the transducer back on both calibration points. If the
thickness is out of tolerance repeat the steps above.
8 TAKING READINGS
Disclaimer: Inherent in ultrasonic thickness measurement is the possibility that the instrument will
use the second rather than the first echo from the back surface of the material being measured. This
may result in a thickness reading that is TWICE what it should be.
Responsibility for proper use of the instrument and recognition of this phenomenon rests solely with
the user of the instrument.
Other errors may occur from measuring coated materials where the coating is insufficiently bonded
to the material surface. Irregular and inaccurate readings may result. Again, the user is responsible
for proper use and interpretation of the measurements acquired.
8.1 BEFORE YOU START
•
Prepare the surface.
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Ensure the correct transducer is selected and set in the gauge.
•
Select the correct measurement mode - see 'Measurement - Modes" on page 10.
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Set the zero point of the transducer - see:
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'Transducer - Zeroing" on page 11 and
•
Calibrate the gauge - see:
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'Calibrating - for a Material" on page 11 and
•
Choose the measurement view (DIGITS, RF or RECT, or B-SCAN) - see 'The Measurement
Screen" on page 6.
8.2 PROCEDURE
1. Apply couplant
For the gauge to work correctly there must be no air gap between the transducer and the
surface of the material to be measured. This is achieved using a couplant.
Before the transducer is placed on the surface, put a small amount of couplant supplied with
the gauge on the surface of the material. Typically a single drop is sufficient.
2. Place transducer onto the surface of the material to be measured
Press the transducer wearface into the couplant. Only moderate pressure is necessary to
keep the transducer stationary and the wearface seated flat against the surface of the
material.
3. Read display
If six or seven bars of the stability indicator are showing, the display will be reading the correct
thickness of the material directly beneath the transducer.
If the stability indicator has fewer than five bars showing, or the numbers on the display seem
erratic, 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:
•
adjust the gain, or
•
select a different transducer (size or frequency) for the material being measured.
13
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