Dakota-ultrasonics PR-82 Manuel d'utilisateur télécharger pdf (Page 17)

PR-8

Sonic Tester

At this point, the PR-8

has successfully calculated it's internal error

factor, and will compensate for this value in any subsequent

measurements. When performing a "probe-zero", the PR-8

will always

use the sound-velocity value of the built-in probe-disc, even if some other

velocity value has been entered for making actual measurements. Though

the PR-8

will remember the last "probe-zero" performed, it is generally a

good idea to perform a "probe-zero" whenever the tool is turned on, as well

as any time a different transducer is used. This will ensure that the

instrument is always correctly zeroed.

Calibration

In order for the PR-8

to make accurate measurements, it must be set

to the correct sound-velocity for the material being measured. Different

types of material have different inherent sound-velocities. For example, the

velocity of sound through steel is about 0.233 inches-per-microsecond,

versus that of aluminum, which is about 0.248 inches-per-microsecond. If

the tool is not set to the correct sound-velocity, all of the measurements the

tool makes will be erroneous by some fixed percentage. The one point

calibration is the simplest and most commonly used calibration procedure -

optimizing linearity over large ranges. The two point calibration allows for

greater accuracy over small ranges by calculating the probe zero and

velocity. The PR-8

provides three simple methods for setting the sound-

velocity, described in the following pages.

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Dakota-ultrasonics PR-82 Manuel d'utilisateur Page 17