CANNON Instrument Company | Calibration
Figure 15: Load Unit Calibration
Compliance
During BBR load cell calibration, the data obtained is used to automatically generate a correction
factor for the LVDT measurement. This factor is defined as device compliance, and is displayed by
the BBR software at the conclusion of the calibration. The correction factor compensates for slight
changes in the reading of the LVDT which are not a function of the beam deflection. A slight but
significant part of the deflection reading is due to compression of the load cell itself. By making a
correction to the deflection reading with each load, a more accurate measurement of the actual
deflection of the sample is obtained. The value for this correction has been found to be between
two and nine µm/N, depending on the physical characteristics of the load cell, and should be stable
within 1.5 µm/N.
Run the Confidence Test
While not a part of the calibration procedure, a measurement of the stiffness modulus of a thin steel
beam is made to confirm the calibration.
The confidence test should be performed immediately prior to BBR asphalt binder testing and after
the instrument has reached the desired test temperature. A good confidence test result (yielding
results in GPa of ±10 percent of the value on the certificate) will provide greater assurance of
accurate results with subsequent testing.
To run the confidence test, select Run a Confidence Test from the Calibrate menu. Follow the
screen prompts to complete the test. A thin (approximately 1.20 mm) steel beam is needed, as well
as two to four 100-gram weights, depending on the laboratory calibration protocol.
If the test fails repeatedly, recalibrate the instrument and rerun the confidence test.
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