C. MAINTENANCE
✓ Ensure that the source rod opening on the gauge bottom is
completely closed or covered by the tungsten sliding block. If
any opening is visible, the sliding block should be cleaned.
Refer to page C-11 for instructions. If the sliding block still
does not close completely, contact the nearest Troxler Service
Center (see page C–17).
ASPHALT READINGS ARE HIGH/LOW
✓ Take magnesium (Mg) reference block readings. When taking
Mg block reference readings, place the 1-inch Mg reference
block on top of a uniform 4 in. (10 cm) thick asphalt or concrete
layer. Place the gauge on top of the Mg reference block. Set the
count time to 4 minutes and the layer thickness to 1 in. (2.5 cm).
Place the source rod in the measurement position. Take a count.
If the readings are high or low, proceed to the next step.
✓ Check the thickness and count time parameters.
✓ Incorrect special calibration and/or incorrect offset should be
disabled.
✓ Check calibration constants against the factory calibration sheet.
✓ If all of the above parameters are correct, use the special
calibration to calibrate the gauge for the job.
GAUGE READS REFERENCE BLOCK HIGH/LOW
(Perform a Mg Reference Block reading as described above)
✓ Check thickness parameter.
✓ Check standard counts.
✓ Check source rod measurement position (see page 3–8).
✓ Special calibration disabled?
✓ Offsets disabled?
✓ Surface under the reference block should have at least 4 in.
(10 cm) of homogenous material such as asphalt or concrete.
✓ Surface under the reference block must be smooth, flat and dry.
✓ The gauge may need to be sent back for re-calibration.
Model 4640-B Appendix C–3
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