Gossen MetraWatt SECULIFE UP, Руководство по эксплуатации, Страница: 9 / 22

GMC-I Messtechnik GmbH
9
SECULIFE UP
Water as a Measurement Medium*
The measurements are to be performed in water because ultrasound propagation in water
closely approximates that in tissues. The ultrasonic attenuation in water can be taken as a lower
limit on the attenuation that will be encountered in the body. Large areas in the body can consist
of low attenuating material such as urine and amniotic fluid. The use of water prevents
measurements in a more highly attenuating material, such as liver equivalent gels, from
representing the highest possible intensities that might be encountered in the body.
* Ultrasound propagation in water closely approximates human tissue and degassed water is
the generally accepted test medium for ultrasound transducers.
Degassed Water
Ultrasound Power measurement accuracy is affected if the water contains more than 5-10 PPM
of air. To degas, boil distilled water for 30 minutes, then seal the container tightly and place it in
a refrigerator. An alternate method of degassing water is to heat the water to the boiling point,
then pull a vacuum on it for five to ten minutes. The degassed water storage container should
be made of glass or plastic. Polystyrene containers should not be used since they allow oxygen
to permeate and degrade the water quality. Before testing, pour water into tilted test tank with
minimum amount of turbulence. The test tank water surface will absorb oxygen, therefore a
change of degassed water is recommended before each test. Water temperature affects
accuracy, so it is recommended to use an ambient testing temperature of 24.0 ±3.0 °C (75.2
±5.4 °F). Sonic energy agitates the water surface through heating and scattering
The time duration of each test should be limited to a few minutes. Prolonged testing, particularly
at higher power levels, will show visible signs of air bubbles on the transducer, target, and the
absorbing rubber surface.
OPERATING INSTRUCTIONS