Checkline TI-CMXDL - Manual (Page 28)

7. Press the OK key to complete the probe zero function, or ESC key to cancel the probe
zero function.
8. Remove the transducer from the probe zero disk, and proceed to the calibration section.
NOTE: The value that is displayed will change depending on the current velocity setting
in the TI-CMXDL. Disregard the number that is displayed. It is not important. What is
important is accurately performing the steps outlined above to insure reliability of the
probe zero
calculation.
6.3 Material Calibration
In order for the TI-CMXDL to make accurate measurements, it must be set to the correct
sound velocity of the material being measured. Different types of materials 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 method—
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-CMXDL
provides four simple methods for setting the sound-velocity outlined below:
Using A Known Velocity
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 CAL menu is highlighted and displaying
the submenu items.
2. Use the UP and DOWN arrow keys to scroll through the sub menu
items until VELOCITY is highlighted.
3. Press the ENTER key to display the Digits Edit Box.
4. Press the UP and DOWN arrow keys to scroll the highlighted value.
5. Press the LEFT and RIGHT arrow keys to scroll the digit locations.
6. Repeat steps 4 & 5 until the velocity number is correctly displayed.
7. Press the OK key to set the velocity and return to the menu screen,
or ESC to cancel entering the velocity.
8. Finally, press the MEAS key to return to the measurement screen
and begin taking readings.
Using A Known Thickness
Sometimes the sound velocity of a material is unknown. In this case a sample with one or
two known thicknesses can be used to determine the sound velocity. As previously dis-
cussed, the TI-CMXDL has a one or two point calibration option. The one point calibration
option is most suited for linearity over large ranges, as noted above. The user should also
consider calibrating on high side of the intended measurement range, when using the one
point option, minimize overall error. For example, if the measurement range is .100”
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9.3 Coating Calibration (PECT)
Known Velocity
If the coating velocity is known, the user may wish to simply enter the velocity number
into the TI-CMXDL, rather than have the TI-CMXDL calculate the velocity value using
known thickness on a coating sample(s). The steps for entering the velocity are outlined
below:
Using a Known Material Velocity
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 CAL menu is
highlighted and displaying the submenu items.
2. Use the UP and DOWN arrow keys to scroll through the sub
menu items until COATING VEL is highlighted.
3. Press the ENTER key to display the Digits Edit Box.
4. Press the UP and DOWN arrow keys to scroll the highlighted
value.
5. Press the LEFT and RIGHT arrow keys to scroll the digit
locations.
6. Repeat steps 4 & 5 until the velocity number is correctly
displayed.
7. Press the OK key to set the velocity and return to the menu
screen, or ESC to cancel entering the velocity.
8. Finally, press the MEAS key to return to the measurement screen and begin taking
readings.
Known Thickness
Sometimes the sound velocity of a coating material is unknown. In this case a sample w
a known thickness can be used to determine the sound velocity of the coating. As previo
ly discussed, the TI-CMXDL offers a one point calibration option for coating in PECT
measurement mode. It is also import to reiterate that the coating sample must be coupled
a metallic material in order to perform the calibration. The calibration should also consid
calibrating on high side of the intended measurement range, when using the one point
option, minimize overall error. For example, if the measurement range of the coating wi
be from .040” - .080” (1.0mm 2.3mm), a coating closest to .080 (2.0mm) should be used
NOTE: It’s always handy to carry a set of mechanical calipers to use in conjunction wit
the TI-CMXDL for calibration in the field:
One Point Calibration
NOTE: Be sure that the probe zero procedure has been performed
prior to performing this calibration procedure.
1. Physically measure an exact sample of the coating using a set
of calipers or a digital micrometer.
NOTE: The coating sample must be coupled to a metallic material
in order to be calibrated.
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