GE PT878GC 用户手册
April 2004
C-4
Ultrasonic Thickness Gauge Theory of Operation
Remember that an ultrasonic test measures thickness at only one
point within the beam of the transducer, and that in corrosion
situations wall thicknesses often vary considerably. Test
procedures usually call for making a number of measurements
within a defined area and establishing a minimum and/or average
thickness. Ideally, data should be taken at increments no greater
than half the diameter of the transducer, to insure that no pits or
other local variations in wall thickness are missed. It is up to the
user to define a pattern of data collection appropriate to the needs
of a given application.
point within the beam of the transducer, and that in corrosion
situations wall thicknesses often vary considerably. Test
procedures usually call for making a number of measurements
within a defined area and establishing a minimum and/or average
thickness. Ideally, data should be taken at increments no greater
than half the diameter of the transducer, to insure that no pits or
other local variations in wall thickness are missed. It is up to the
user to define a pattern of data collection appropriate to the needs
of a given application.
It is possible that on some severely corroded or pitted materials
there will be spots where readings cannot be obtained. This can
happen when the inside surface of the material is so irregular that
the sound energy is scattered rather than being reflected back to
the transducer. The lack of a reading may also indicate a
thickness outside the range of the transducer and instrument
being used. Generally, an inability to obtain a valid thickness
reading at a particular point on a test specimen could be a sign of
a seriously degraded wall which may warrant investigation by
other means.
there will be spots where readings cannot be obtained. This can
happen when the inside surface of the material is so irregular that
the sound energy is scattered rather than being reflected back to
the transducer. The lack of a reading may also indicate a
thickness outside the range of the transducer and instrument
being used. Generally, an inability to obtain a valid thickness
reading at a particular point on a test specimen could be a sign of
a seriously degraded wall which may warrant investigation by
other means.
C. Calibration - The accuracy of measurements are only as good
as the accuracy and care with which the gauge has been
calibrated. It is essential that the thickness gauge be calibrated (as
described on page 9-12) whenever the transducer is changed or
you have a reason to doubt the accuracy of the readings. Periodic
checks with samples of known thicknesses are recommended to
verify that the gauge is operating properly.
as the accuracy and care with which the gauge has been
calibrated. It is essential that the thickness gauge be calibrated (as
described on page 9-12) whenever the transducer is changed or
you have a reason to doubt the accuracy of the readings. Periodic
checks with samples of known thicknesses are recommended to
verify that the gauge is operating properly.