Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-02-23
2001-10-02
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S587000, C073S609000, C073S620000, C073S660000, C367S035000
Reexamination Certificate
active
06295872
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an ultrasonic measuring instrument comprising a housing which contains a transducer for transmitting and receiving ultra-sound waves, and a rotatable mirror placed inside the housing for directing ultra-sound waves coming from the transducer through a tapering window comprised in the housing to an object of measuring outside the housing, and for directing ultra-sound waves which are reflected by the object of measuring and which enter the housing through the window, to the transducer, whereby a tube is provided around, and rotating with the mirror, comprising a recess for the passage of ultra-sound waves.
BACKGROUND OF THE INVENTION
Such a measuring instrument is known and is used for the internal investigation of pipes. With this kind of inspection the reflection is used for one thing to derive the wall thickness of the pipe and for another thing to derive possible defects in the wall of the pipe. The ultra-sound waves employed for this purpose have a frequency spectrum from 2.5-10 MHz. To this end the known ultrasonic measuring instrument is provided with a transducer beaming in the longitudinal direction of the instrument's housing and whose sound waves are directed at an acoustic rotatable mirror which is placed at an angle of 45° with respect to the longitudinal axis of the instrument, which mirror reflects the sound waves radially through the window to the outside of the housing. The rotatable arrangement allows the pipe to be investigated over 360°. To effectuate rotation the mirror is mounted on the shaft of a motor.
U.S. Pat. No. 4,255,798 discloses an ultrasonic measuring instrument in accordance with the preamble of claim
1
.
One problem of the known ultrasonic measuring instrument is that the window may produce reflections which under certain circumstances obscure the measurement at the object of measuring. The objective of the invention is to reduce the window's influence on the measuring result, and in general to make it possible to obtain a truer measurement at the object of measuring, in which interfering influences stemming from the measuring instrument as such, are greatly reduced.
SUMMARY OF THE INVENTION
To this end the ultrasonic measuring instrument in accordance with the invention is characterized in that the material for the window is polyoxylmethylene.
Generally the frequency with which the transducer beams at the object of measuring is selected in accordance with the pipe diameter to be measured, the type of wall, and the amount of dirt on the inside wall of the measuring object. The muffling effect provided by the window further reduces the amplitude of the fraction of the original transmission reflected by the window, which could otherwise have an unfavourable influence on the measurement at the measuring object.
The objective of the invention is also furthered in a method for ultrasonic measuring employing said instrument by selecting the thickness of the window material in correspondence to the thickness of the object of measuring from a group including thicknesses of about 2 mm and about 6 mm.
When measuring an object having a thickness of at least 7 mm, the recommended thickness of the window material is set at about 2 mm, and when measuring an object having a thickness of maximally about 7 mm, the thickness of the window material is set at about 6 mm. The advantages gained thereby can be explained as follows.
Compared with the reflection from an object of measuring having a relatively thick wall, a thin wall thickness means that the reflection time is much shorter and the amplitude of the reflection is higher. On the other hand, when measuring a relatively thin pipe, a thick window pane, i.e. the thickness of about 6 mm is preferable. Under these circumstances the ultra-sound waves have to travel a greater distance in the window material, as a result of which the reflection from the window is delayed, is reduced, and can consequently be distinguished more clearly from the reflection signal of the object of measuring.
Preferably the tube is provided with a second diametrically applied recess, so that the tube does not exhibit any imbalance during rotation.
REFERENCES:
patent: 3504759 (1970-04-01), Cubberly, Jr.
patent: 3747398 (1973-07-01), Rathburn et al.
patent: 3763694 (1973-10-01), Rathburn et al.
patent: 3914987 (1975-10-01), Bickel et al.
patent: 4255798 (1981-03-01), Havira
patent: 4361044 (1982-11-01), Kupperman et al.
A Hak Industrial Services B.V.
Akerman & Senterfitt
Saint-Surin Jacques
Williams Hezron
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