– 11 –
5. Press the transducer against the probe-disc, making sure that the transducer
sits flat against the surface. The display should show some thickness value, and
the Stability Indicator should have nearly all its bars illuminated.
6. While the transducer is firmly coupled to the probe-disc, press the PRB-0 key
on the keypad. The TI-25M-MMX will display “Prb0” while it is calculating its
zero point.
7. Remove the transducer from the probe-disc.
At this point, the TI-25M-MMX has successfully calculated it’s internal error
factor, and will compensate for this value in any subsequent measurements. When
performing a “probe-zero”, the TI-25M-MMX will always use the sound-velocity
value of the built-in probe-disc, even if some other velocity value has been
entered for making actual measurements. Though the TI-25M-MMX will remem-
ber the last “probe-zero” performed, it is generally a good idea to perform a
“probe-zero” whenever the gauge is turned on, as well as any time a different
transducer is used. This will ensure that the instrument is always correctly zeroed.
4.3 Calibration
In order for the TI-25M-MMX to make accurate measurements, it must be set to
the correct sound-velocity for the material being measured. Different types of
material have different inherent sound-velocities. For example, the velocity
of sound through steel is about 0.233 inches-per-microsecond, versus that of
aluminum, which is about 0.248 inches-per-microsecond. If the gauge is not
set to the correct sound-velocity, all of the measurements the gauge makes will
be erroneous by some fixed percentage. The one point calibration is the simplest
and most commonly used calibration procedure -optimizing linearity over large
ranges. The two point calibration allows for greater accuracy over small ranges
by calculating the probe zero and velocity. The TI-25M-MMX provides three sim-
ple methods for setting the sound-velocity, described in the following pages.
Note:
Although the TI-25M-MMX has a thru-paint/coating feature, one and two
point calibrations must be performed on material with the paint or coating
removed. Failure to remove the paint or coating prior to calibration, will result in
a multi material velocity calculation that may be different from the actual material
velocity intended to be measured.
Calibration to a known thickness
Note:
This procedure requires a sample piece of the specific material to be meas-
ured, the exact thickness of which is known, e.g. from having been measured by
some other means.
1. Make sure the TI-25M-MMX is on and switched to P-E (pulse-echo) mode.
Press the Dual-Multi key to toggle modes.
– 18 –
9 .0 RS2 3 2 S
ERI AL
P
ORT
The TI-25M-MMX is equipped with an RS232 serial port. Using the accessory
cable (part# N-306-0010), the TI-25M-MMX has the ability to connect to a com-
puter, or external storage device. The following section outlines the procedure for
connecting the TI-25M-MMX to a computer, and how to collect data using any
standard communications program:
Connecting To a Computer
1. Connect the accessory cable (part# N-306-0010) to the 2 pin jack located on
the bottom of the TI-25M-MMX, and the 9 pin connector to a serial port on
the computer.
2. Start the communications software that will be used to collect the
measurements (i.e. Microsoft Windows 3.1 -Terminal, or 95, 98,
Me, XP -HyperTerminal).
3. Setup the communications software using the following parameters:
Data Bits -8, Parity -None, Stop Bits -1, Baud Rate 1200.
4. Set the communications software COMM port to the port number that the
TI-25M-MMX is connected.
5. After taking a measurement, press the SEND key to send the measurement
to the computer. The measurement will be displayed on the computer screen.
NOTE:
Communications software packages generally have the ability to capture
the screen data to a common text file. This text file, containing the measurements,
can then be imported into any common spreadsheet program (i.e. Excel, Quattro
Pro, Lotus123) for further reporting requirements.