6
mvip@mitech-ndt.com
2.2 Keypad Definitions
Turn the instrument
on/off
Sound
velocity
calibration
Turn on/off the EL
backlight
Enter
Probe-Zero
operation
Plus;
Turn on/off Scan
mode
Unit switch between
Metric and Imperial
system
Minus;
Turn on/off the
beep mode
Data Save or Data
Delete
3 Preparation
3.1 Transducer Selection
The gauge is inherently capable of performing measurements on a wide range of materials, from
various metals to glass and plastics. Different types of material, however, will require the use of
different transducers. Choosing the correct transducer for a job is critical to being able to easily
perform accurate and reliable measurement. The following paragraphs highlight the important
properties of transducers, which should be considered when selecting a transducer for a specific job.
Generally speaking, the best transducer for a job is one that sends sufficient ultrasonic energy
into the material being measured such that a strong, stable echo is received by the gauge. Several
factors affect the strength of ultrasound as it travels. These are outlined below:
Initial Signal Strength. The stronger a signal is to begin with, the stronger its return echo will be.
Initial signal strength is largely a factor of the size of the ultrasound emitter in the transducer. A large
emitting area will send more energy into the material being measured than a small emitting area. Thus,
a so-called “1/2 inch” transducer will emit a stronger signal than a “1/4 inch” transducer.
Absorption and Scattering. As ultrasound travels through any material, it is partly absorbed. If the
material through which the sound travels has any grain structure, the sound waves will experience
scattering. Both of these effects reduce the strength of the waves, and thus, the gauge’s ability to
detect the returning echo. Higher frequency ultrasound is absorbed and scattered more than
ultrasound of a lower frequency. While it may seem that using a lower frequency transducer might be
better in every instance, low frequencies are less directional than high frequencies. Thus, a higher
frequency transducer would be a better choice for detecting the exact location of small pits or flaws in
the material being measured.
Geometry of the transducer. The physical constraints of the measuring environment sometimes
determine a transducer’s suitability for a given job. Some transducers may simply be too large to be
used in tightly confined areas. Also, the surface area available for contacting with the transducer may
be limited, requiring the use of a transducer with a small wearface. Measuring on a curved surface,
such as an engine cylinder wall, may require the use of a transducer with a matching curved
wearface.
Temperature of the material. When it is necessary to measure on surfaces that are exceedingly
hot, high temperature transducers must be used. These transducers are built using special materials
