Checkline TI-MVX - Manual (Page 22)

0.010 inch to 9.999” in steel. However, the maximum attainable thickness is
much less for more attenuative materials (materials that absorb sound).
Accuracy, is determined by how consistent the sound velocity is through the
sound path being measured and, is a function of the overall thickness of the
material. For example, the velocity in steel is typically within 0.5% while the
velocity in cast iron can vary by 4%.
4.4 Couplant
All ultrasonic applications require some medium to couple the sound from the
transducer to the test piece. Typically a high viscosity liquid is used as the medi-
um. The sound frequencies used in ultrasonic thickness measurement do not
travel through air efficiently. By using a liquid couplant between the transducer
and test piece the amount of ultrasound entering the test piece is much greater.
4.5 Temperature
Temperature has an effect on sound velocity. The higher the temperature, the
slower sound travels in a material. High temperatures can also damage trans-
ducers and present a problem for various liquid couplants.
Since the sound velocity varies with temperature it is important to calibrate at the
same temperature as the material being measured.
Normal temperature range: Most standard transducers will operate from
0
∞ F to 180 ∞ F.
High temperature measurements: Special transducers and couplants are
available for temperatures above 180
∞ F up to 650 ∞ F with intermittent contact. It
is necessary to cool the transducer, by submerging the transducer in water
between readings, when measuring high temperatures.
Modes and temperature errors: In addition to errors caused by velocity chang-
ing with temperature, some modes (measurement techniques) are affected more
than others. For example, dual element mode has larger errors due to changes
in temperature of the delay line. However, multi-echo techniques help to mini-
mize these errors.
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Using Auto Find
1) Press the MENU key once to activate
the menu items tab. Press the MENU key
multiple times to tab right, and the ESC key
multiple times to tab left, until the UTIL
menu is highlighted and displaying the
submenu items.
2) Use the UP and DOWN arrow keys to scroll through the sub menu items until
AUTO FIND is highlighted.
3) Place the transducer on the test material and obtain a reading.
4) Press the ENTER key to automatically adjust the display settings and bring
the waveform into view.
5) Once the signal is displayed, press the MEAS key to return to measurement
mode.
9.3 High Speed Scan
The High Speed Scan feature of the TI-MVX increases the overall sample rate
from the standard 4 measurements a second to 32 measurements a second.
This feature enables a user to make scanned passes over an arbitrary length of
the test material, while still maintaining a reasonable representation of thickness
over the scanned area or region. The display will continue to be updated during
the scan process, and when the transducer is removed, the TI-MVX will display
the minimum reading found. The procedure to use the SCAN MODE feature is
outlined below:
Using the Scan Mode
1) Press the MENU key once to activate
the menu items tab. Press the MENU key
multiple times to tab right and the ESC key
multiple times to tab left until the UTIL
menu is highlighted and displaying the sub-
menu items.
2) Use the UP and DOWN arrow keys to scroll through the sub menu items until
SCAN MODE is highlighted.
3) Use the LEFT and RIGHT arrow keys to toggle the SCAN MODE on/off.
4) Press the MEAS key to return to the measurement screen.
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