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Dakota Ultrasonics DFX-8 plus MANUAL2 User Manual

Page 109

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DFX-8

Ultrasonic Thickness Gauge

105

Known Thickness

Sometimes the sound velocity of a coating material is unknown. In this case a
sample with a known thickness can be used to determine the sound velocity of the
coating. As previously discussed, the DFX-8 offers a one point calibration option for
coating in PECT measurement mode. It is also import to reiterate that the coating
sample must be coupled to a metallic material in order to perform the calibration.
The calibration should also consider calibrating on high side of the intended
measurement range, when using the one point option, minimize overall error. For
example, if the measurement range of the coating will be from .040” - .080” (1.0mm
2.3mm), a coating closest to .080 (2.0mm) should be used. Note: It’s always handy
to carry a set of mechanical calipers to use in conjunction with the DFX-8 for
calibration in the field:

One Point Calibration

Note: Be sure that the probe zero procedure has been performed prior to

performing this calibration procedure.

1) Physically measure an exact sample of the coating using a set of calipers or

a digital micrometer.

Note: The coating sample must be coupled to a metallic material in order to be

calibrated.

2) Apply a drop of couplant on a piece of metal and place the coating sample

on the metal over the couplant. Apply a drop of couplant on the transducer

and place the transducer in steady contact with the coating and sample or

actual test material. Be sure that the reading is stable and the repeatability

indicator, in the top left corner of the display, is fully lit and stable. Press the

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