Chapter 2. Instrument Setup
68
DMS Go Operator’s Manual
2.5.4 Adjusting Temperature Compensation (PROBE & CAL - TEMP COMP)
Temperature variations change the sound velocity of materials and transducer delay lines and, therefore calibrations. All calibrations should
be performed onsite, and with calibration blocks at the same temperature as the test piece, to minimize errors due to temperature variations.
When it is not possible to heat the calibration block, the use of a temperature compensation formula can be used to calculate the test piece
thickness back to ambient temperature.
Temperature Compensation: As the temperature of a test object increases, the ultrasonic velocity of the material will slightly decrease.
When this occurs, the wall thickness will read thicker than the actual temperature when measured at ambient. To compensate for this factor,
the DMS Go has the ability to calculate a compensated thickness value based upon the inputted test piece temperature and a compensation
factor.
1.
In the
MAIN
menu, scroll to the
PROBE & CAL
submenu using the joystick (
).
2.
Use the joystick to
ENABLE
or
DISABLE
temperature compensation. If you
ENABLE
temperature compensation, three other functions
appear:
•
CAL TEMP
- The temperature of the calibration block (typically ambient temperature).
•
CUR TEMP
- The current temperature of the material.
•
TEMP COEF
(Temperature Coefficient) - The change in material velocity per degree, adjusted from a user table. (A typical value for
carbon steel is -0.0002 in/us/°F or -0.###mm/m/C). The value input should be obtained from the company level III UT manager or
corporate NDT guidelines.
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