DeFelsko PosiTector 100 v.4.0 - Manual (Page 24)

Page 24 100 Series
Calibration and Optimization
The Model 100 is factory aligned and does a self check each time it takes a
measurement. Periodically calibrate the Gage against known thickness
calibration standards to verify correct operation and determine if the Gage is
within tolerance.
Calibrate
⇒
Optimize
⇒
Measure
Overview
The operation of an ultrasonic coating thickness Gage is based on the transit time of
an ultrasonic pulse through a coating. The Gage measures this time and multiplies it
by a sound velocity constant for the type of coating material being measured. The
resulting value is displayed on the LCD as thickness.
To obtain optimum accuracy it is necessary to use the correct sound velocity
constant for the material being measured. The Model 100 has internally stored
constants that are set at the factory using NIST or NPL traceable reference materials.
To verify that the Gage is operating correctly make measurements of standards that
have a known thickness and are made of a material with a known sound velocity
constant. This allows you to verify that the Gage can measure accurately.
Calibration is the act of measuring known Thickness Calibration Standards and
verifying that the results are within the tolerance of the Gage. The Gage is calibrated
using the specific sound velocity constant for the reference standard material.
The actual sound velocity in materials often varies significantly from the values
found in published tables. A selection of coatings and substrates are programmed in
at the factory. At times it may be necessary to optimize the Gage to the material
being measured.
Optimization is the act of changing the Gage’s thickness reading or sound velocity
constant to match that of a known sample to compensate for the different velocity of
sound of the material being measured. Optimization does not effect the Calibration
of the Gage.
The Model 100 has an optimization mode (
Optimize Reading) to allow for
matching the sound velocity constant used in the Gage to that of the actual material
being measured. To accomplish this, a measurement is made of a known thickness
of the material and the display is adjusted to the correct thickness reading. If a
known thickness is not available, factory settings can be used.