26
field
calibration
instructions
Prior to each use of the Model 785 / 790 Pulse DC Holiday Detector it is
important to perform a Field Calibration to verify that the required voltage
setting for the coating thickness will accurately detect defects (holidays)
in the coating.
ADDING TEST DEFECTS TO THE COATING.
1. Prior to turning on and setting the voltage on the detector manually add
one pinhole size defect on the coating surface, make sure the defect
goes down to the substrate (bare metal).
2. Set the voltage on the detector to the minimum voltage based on the
coating type and thickness. Use equation 525 x sqrt (mils) from NACE
SP0490 for Fusion-Bonded Epoxy and equation 1250 x sqrt(mils) from
NACE SP0274 for thick coatings. Use the spring or brush electrode to
travel over the test defects. See voltage table on page 22.
3. If you see the spark jump the gap from the electrode to the substrate
in the defect and the horn on the detector changes from a running tone
to a loud signal horn and the light on the display turns off then you have
successfully detected defects (holidays) in the coating and verified the
detector operation.
4. If your test does not successfully detect the test defect then increase
the voltage by 10% and test again. If test fails again continue increasing
by 10% until the test is successful.
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