DMTA-10004-01EN, Rev. D, November 2016
Chapter 10
156
10.7 Using Temperature Compensation
The 38DL PLUS can compensate for changes in sound velocity due to temperature
variations. This function is useful for example when the test block may be at room
temperature while the actual material can be at an elevated temperature.
Using the temperature compensation function, you can input the temperature of the
calibration standard in °F or °C units. You can manually enter a fixed elevated
temperature, manually enter a temperature for the current ID location, or
automatically read the temperature from an optional temperature probe.
The sound velocity of most steel changes about 1 % for every 55 °C (100 °F) change in
temperature. The following equation is used to compensate for the change in sound
velocity due to temperature.
Where:
MTI = Measured time interval
V
0
= Calibrated test block velocity
T
1
= Actual material temperature
T
0
= Temperature at calibration
k = Temperature coefficient (normally –0.00018 for °C or –0.0001 for °F)
A temperature coefficient of 0.00018 for °C (or 0.0001 for °F) assumes a 1 % change in
velocity per 55 °C (100 °F) change in temperature.
To use the temperature compensation
1. Press [SETUP MENU].
2. In the menu, select the TEMP COMP.
3. In the TEMP COMP screen (see Figure 10-18 on page 157):
a) Set TEMP COMP ENABLE to ON to activate the temperature compensation
function.
b) Set DEGREE UNITS to the desired temperature units (FAHRENHEIT or
CELSIUS).
c) Set CALIBRATION TEMP to the temperature of the test block used to
perform the calibration. The allowable range is –10 °C to 500 °C or 14 °F to
932 °F.
Temperature corrected thickness MTI V
0
× 1 kT
1
T
0
–()×()+()×=
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