Specifications

Important Notice
USN52 L Operating Manual Page 3
Specifications and Procedures
The customer must understand and provide
for interpretation and compliance with the
specifications covering its work, generated
by such groups as in-house Quality Assur-
ance, Technical Societies, Industry Groups,
or Government Agencies.
Ultrasonic Thickness Measurements
Ultrasonic thickness measurements are the
result of the mathematical product of the
velocity of sound in a material and the tran-
sit time of the soundwaves through the
material. The transit time is the data ob-
tained by the ultrasonic equipment.
Velocity of Sound
The accuracy of ultrasonic thickness mea-
surements and of flaw location depends to
a major degree on the velocity of sound
through the material. This velocity value is
dependent on characteristics of the mate-
rial being tested, and is generally indepen-
dent of the operation of the test instrument.
This manual describes means for calibrat-
ing the instrument and its internal calcula-
tions for the velocity of sound value of the
test material when it is known, or for finding
the velocity of sound empirically using test
blocks of the test material which are ac-
cessible for concurrent mechanical thick-
ness measurement. No claim, explicit or
implied, is included as to the uniformity of
the velocity of sound throughout any given
part or batch of parts. Any non-uniformity
of velocity of sound in the test material may
result in erroneous thickness measure-
ments.
Temperature Dependence
Velocity of sound is affected to varying de-
grees by the temperature of the material
through which the sound travels. When tem-
perature variables are expected, frequent
checks must be made to maintain instru-
ment calibration for the changing test con-
ditions. Velocity changes due to tempera-
ture variation may affect the material being
inspected, transducer delay lines and other
equipment components.
Doubling of Thickness Readings
When measuring relatively thin walls, with
thicknesses below the minimum thickness
specified for a particular instrument/probe
combination, down to about half the speci-
fied minimum thickness, the first echo may
occur while the instrument is electronically
blocked to prevent false triggering. When
this occurs, under certain combinations of
thin wall dimensions, surface conditions, in-
strument, probe parameters, etc., the sec-
ond echo or other echo signal combinations
may produce a readable signal. The instru-
ment reading and apparent thickness are
up to about twice the actual value, resulting
in a condition that is sometimes called “dou-
bling”.
Krautkramer instruments have conservative
specifications in this regard, which in most
cases will prevent misreadings. When us-
ing a A-scan readout, the condition is usu-
ally apparent to the trained operator. Read-
ings using instruments with only analog or
digital meter indicators, in this thinner range,
should be further evaluated when the read-