17
en
specification is because the physical temperature of the probe zero calibration standards has changed. If
the accessory temperature sensor is being used, the sensor will automatically adjust the physical
temperature and the gauge should be within specification and displaying an elongation value of 0.0000” +/-
0.0001”.
To verify probe zero:
1.
Open the group in which you previously stored the probe zero data - see “Opening an Existing Data
Logger Group File” on page 32.
Note: You should always use this group for the zero verification procedure, as it contains the original
settings and measurement data of the probe zero calibration standards.
2.
Place the transducer with couplant on the calibration standard.
3.
Press MEAS to return to the measurement screen.
4.
Press MEAS again and then highlight LOC in the hot menu.
5.
Press ENTER.
The Group View Box is displayed.
6.
Scroll the cursor to the next blank cell for the System Zero bolt.
Note: This will always be a cell located in columns B to ZZ. Since this is the
first verification following the initial measurement of the Probe Zero
Calibration Bars, the cursor should be located on a calibration standard in column B. It is also
important to note that the L-REF stored in column A also contains all the gauge settings when the L-
REF was initially measured. These settings will automatically be copied to all the columns B to ZZ, for
each individual bolt. Therefore, no adjustments to the gauge should be necessary.
7.
If the elongation is +/- 0.0001” (and therefore within specification) press ENTER to save the current
reading in the highlighted cell location, storing all the current probe zero verification data.
If the elongation is greater than +/- 0.0001” (and therefore out of specification) proceed to step 9.
8.
Repeat steps 2 to 7 for the other probe zero calibration standards.
If all the elongations are within specification, the probe zero verification procedure is complete.
9.
If an elongation is out of specification, press MEAS to return to the measurement screen and then
complete steps 10 to 12 below for all elongations out of specification.
10. Press MEAS again and then highlight TEMP in the hot menu.
11. Press ENTER.
The Group View Box is displayed. The ELONGATION value is now within specification.
12. Press ENTER to save the current reading in the highlighted cell location, storing all the current probe
zero verification data.
9 TEMPERATURE COMPENSATION
9.1 INTRODUCTION
The temperature of a fastener affects both its physical length (due to thermal expansion) and the velocity
of sound in the fastener. As the temperature of a fastener increases, the ultrasonic length increases at a
rate greater than the physical change in length.
If you intend to measure the same fastener at different time intervals over the service life of the bolt, it is
therefore very important to compensate for changes in temperature in order to produce accurate results.
If, however, a fastener will only be measured once, never to be measured again, temperature compensation
is not needed, as long as the reference length and elongation are measured at the same temperature and
time.
Although the thermal expansion of the fastener and the ultrasonic change in velocity as a result of
temperature are two separate effects, within the gauge, they are combined in a single factor known as the
Temperature Coefficient (Tc).
The sections that follow outline the procedures for selecting and using the temperature compensation mode
with the accessory temperature sensor when using the BG80TDL. There are three temperature
compensation modes:
