Checkline TI-25S - Manual (Page 10)

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7.0 D OWNLOADING C USTOM C ALIBRATIONS TO THE TI-25S
In addition to the eight (8) preset calibration (material types), the TI-25S is s
upplied with two custom calibrations (Custom1 and Custom 2) which are set
using the free Datacomm Software and then downloaded to the TI-25S using
the option Data Cable p/n N-306-0010. To utilize one or both of these User-Set
Calibrations, follow the procedure outlined below. Approximate sound velocities
for common materials can be found in Appendix B.
1. Connect the serial cable (Part No. N-306-0010) to a COM port on a
computer and to the RS232 connector located on the bottom of the
TI-25S. Remove and replace the rubber plug before and after
programming.
2. Assuming that PC software is installed and running, select the TI-25S
icon from the gauge selector icons. A window will appear with the
title “TI-25S Velocity Upload Utility.”
3. Under the Preset Velocity heading are two options. The first option is a
test box with a velocity number displayed. The text box is editable. To
change the velocity, click in the text field and type in the appropriate
velocity number. The second option is a list box with a material type
displayed. To change the material type, click the down arrow located to
the right of the list box. Use the arrows or slider bar to scroll through
the available material types. Click on a material to select it.
4. To select the units (english or metric), click on the radio button located
to the left of the units title. A black dot will appear in th button when
selected.
5. Click on the Program Gauge button located in the top right of the
window. A pop up window will be display with the following message
“Turn on gauge power.” Press the ON/OFF button on the TI-25S to
download the velocity. The TI-25S will display the new velocity.
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8.0 T RANSDUCER S ELECTION
The TI-25S 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 measurements. 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 ultra-
sonic energy into the material being measured such that a strong, stable echo is
received by the TI-25S. Several factors affect the strength of ultrasound as it trav-
els. 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 trans-
ducer. A large emitting area will send more energy into the material being meas-
ured 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 it travels has any grain structure, the sound waves will also
experience scattering. Both of these effects reduce the strength of the waves,
and thus, the TI-25S’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 contact-
ing 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.