Checkline TI-MVX - Manual (Page 25)

4.7 Glossary of terms
Repetition Rate & Display Update
The repetition rate is how often the TI-MVX generates a burst of ultrasound.
The TI-MVX has a fixed repetition rate of 1 kHz, or 1000 times per second. The
TI-MVX updates the display 4 times per second in regular measurement mode
and 32 times a second in hi speed scan mode. Therefore, the scan mode is
most suitable for fast scans of a test piece at a lower resolution.
Variable Pulser Width
Transducers have a center frequency where they are most efficient at transmit-
ting sound (i.e. they are resonant). The TI-MVX has a variable width pulser with
three setting options (spike, thin, wide). These settings determine the period of
time the pulser turned is on. High frequency applications, where resolution is a
requirement, may require the spike or thin settings to achieve optimal results.
Low frequency applications, where more penetration is a needed, may require
the thin or wide settings, offering increased penetration. The variety of transduc-
er frequencies and diameters used in conjunction with the pulser settings,
enable users to fine tune the TI-MVX for their application needs.
Gates
Gates control the time measurement process. They enable the user to select
measurement regions and threshold levels (sensitivity). The TI-MVX is equipped
with two gates. In pulse-echo mode a single gate can be used to eliminate noise.
In echo-echo mode both gates are used. In this mode the second gate starts
automatically after a signal is detected during the gates region, and after a user
adjustable delay, sometimes called a hold-off.
-25-
8.2 Setting Up Thru Paint Mode
The first thing to note in this section, is that by selecting the transducer type
from the list of probes stored in the TI-MVX, a basic echo-echo thru paint config-
uration is recalled from memory. Each of the transducers in the list contain pre-
configured echo-echo settings. However, fine adjustments may be necessary in
order to be suitable for your specific applications. These configurations are gen-
eral setups only. Once the transducer type has been selected and the appropri-
ate calibration procedure completed, the TI-MVX can toggle between pulse-echo
(flaws & pits), and echo-echo (thru paint) modes by simply pressing the MULTI
MODE key located on the keypad. Refer to page 19 for additional information.
When configuring the TI-MVX for specific thru paint applications, all of the scope
parameters will potentially be needed. The delay, width, gain, threshold, gate1,
and gate2 features will be subject to change. For this reason, they have all been
added to Hot Menu fields located directly beneath the A-Scan display for quick
and easy access. Note: Once the values of the fields have been changed or
modified, these changes must be saved to a setup location prior to powering the
TI-MVX off. Failure to do so will result in losing your changes.
THRU-PAINT (INCORRECT) THRU-PAINT (CORRECT)
Refer to the incorrect diagram above. Point (A) represents the detection on the
first back wall echo. The true, second back wall, reflection should be detecting at
point (D). However, the hold-off (C) is setup incorrectly and the TI-MVX is detect-
ing the ring down noise of the transducer, on the first reflection, rather than the
true second back wall reflection shown at (D).
Before we look at the diagram with the correct configuration, let’s consider all
of our options on how to fix the problem beforehand. Our delay and width will
simply change the view options of the screen – not needed in this example.
Will a gain or threshold adjustment fix the problem? Unfortunately, not. Why?
Notice the amplitude of the cycle just to the left of (B). If we tried to increase the
threshold level above the height of the cycle, we would lose our detection for
both echoes resulting in no reading at all, If we decrease our gain, reducing the
-56-