- Email: [email protected]
Measuring turbulent flow characteristics using a multi-dimensional ultrasonic probe
Ultrasonics International 87 abstracts transverse velocity is 3200 m s - 1 ) , four different depths of focus, with an aperture of 16 transducers centered between two transducers, or centered in the middle of one transducer. These 512 shots enable us to build an image of 128 lines oriented at 45 ° . The information delivered by each shot is stored in an electronic memory of 128 x 156 pixels of 16 levels (4 bits) after classical echographic treatment, i.e. a time-gain control of the echographic signal, detection and logarithmic compression. The image is read and delivered with classical -IV scanning, Theoretical and experimental evaluation of the prototype is presented: measurements are carried out with defects in holes drilled in a steel block, parallel to the face of investigation. Several non-destructive testing applications are shown (fatigue cracks measurements or evaluation defects in welds). Results obtained from this imaging device seem competitive in comparison with other techniques. The quality of the image is guaranteed by a lateral resolution which remains as low as 3 mm, at 6 dB for any depth.
dynamic range up to high frequencies. However, a high resolution requires a large number of digital steps, i.e. many comparators with memories. For example, a 4-bit digital peak detector has 16 amplitude steps and, therefore, 16 comparators with 16 memories. That is why the DFVLR looked for another method allowing digital peak amplitude measurements with high resolution, which should not require a large number of electronic devices. The new method is based on a modified counting A/D-converter. The device consists of a w i n d o w comparator with outputs connected to a memory. The reference voltage is changed step by step until its value is as large as the peak amplitude of the signal within the gate. The reference voltage is produced by a logarithmic D/A-converter which is connected with a counter. The clock frequency of this up/down counter is equal to that of the gate pulses. The features of the new developed peak detector, HFUS 1050, are: frequency range, 1 100 MHz; resolution, 1 dB; dynamic range, 31 dB.
Measuring turbulent flow characteristics using a Depth characterization with radiation field theory
multi-dimensional ultrasonic probe
D.K. Mak and I.R. Somerville, Canada Centre for Mineral and Energy Technology, Ottawa, Canada
J. Y. Cheung, K.J. Dormer and A. Ashrafzadeh, University of Oklahoma, Norman, USA
Ultrasonic spectral analysis has been used to determine the size and shape of a scattering discontinuity. An appropriate theoretical framework has to be developed for analysing the spectrum of an ultrasonic echo. Theoretical understanding of the flaw response is limited to a highly restricted class of flaws. Frequency minima obtained from spectral analysis can be used to characterize the shape, size and orientation of the defect. It will be pointed out here that the equations of the orientational dependence of the ultrasonic spectrum of the discontinuity response used by previous workers were not correctly derived. A new set of equations are derived using radiation field theory based on Huyghen's principle. Flat circular voids were used as examples. The equations can apply to a single pulse-echo transducer or the more general case of two transducers acting as transmitter- receiver system. Computer polar plots were drawn for the sound pressure profile of the scattered signal for different orientation of the scatterer. Experimental data have been collected for the double transducer system. The spectrum data agree quite well with the results of theoretical calculation.
This study demonstrates the feasibility of turbulent flow characteristics measurement using a dual transducer ultrasonic probe and compares its performance in measuring flow volume rate with other conventional techniques in a bench mark test done in vitro. The use of a multi-dimensional pulsed Doppler ultrasonic probe was effective in eliminating the need to know the Doppler angle between the transducer axes and the flow direction. For a single transducer probe, the Doppler angle was usually assumed because it cannot be measured. For a dual or triple transducer probe, the Doppler angle can be directly measured resulting in more accurate estimation of the velocity data. Such a dual transducer probe was designed and made. Since instantaneous velocity measurements were obtained, other turbulent characteristics such as shear stress and friction factor were also computed. To calibrate the probe and to compare its performance with other techniques, an in vitro experiment is set up using a pulsatile pump. A section of a dog's vessel was connected to the pump through a narrow orifice that generated turbulence. On the vessel, the dual transducer probe, a pulse transit time probe, and an electromagnetic probe were also attached. Flow rates ranging between 0 to 200 ml min 1 were used. Both laminar flow (without the orifice), and turbulent flow (with the orifice) conditions were tested with varying flow rates and pulse rates. By changing the size of the orifice, varying degrees of turbulence were created. Results showed that the dual transducer probe consistently provided the smallest error (3 5%) over the range of flow rates, pulse rates, and varying degrees of turbulence tested when compared to the other techniques. Such a low error rate was expected and was consistent with theoretical analyses. The transit time probe and the single transducer probe gave acceptable performance with slightly larger error. The performance of the doctro-magnetic probe was less acceptable due to its sensitivity to environment and random flow especially in highly turbulent conditions.
A high frequency peak detector for u.s. test pulses
W. Hillger, DFVLR Institut, Braunschweig, FRG The proportional monitor used in standard commercial flaw detectors determines the peak value of the higher u.s.-echo within the gate. The passive peak measurement method is often not sufficiently accurate for the detection of defects, particularly if the data must undergo further computer processing. The problem can be restricted to fast amplitude detection and storage of the value until the next measurement. Due to the relatively short pulse duration of 10 - 5 10 8 s, it is unfortunate to use the standard active peak value measurement methods of electrical engineering where the diode curve is extensively linearized using operation amplifiers. The advantage of digital methods over analog ones is a fast response time and that there are no changes in the memory after data acquisition, such as would happen, for example, in the case of analog memories with capacitances. However, the application of fast A/D-converters also requires calculation of the peak value, since converters sample the whole u.s.-signal as a sequence of separate points and do not determine the maximum level directly. For peak detection a modified flash converter is suitable, which yields a high
Integrated processing with the JUKEBOX ultrasonic imaging system
G. Corneloup, B. Comu, M. Perdrix and I. Magnin, CEN Cadarache, Saint Paul-lez-Durance, France JUKEBOX is a system for displaying and interpreting ultrasonic measurements designed to ensure compatibility with
Ultrasonics 1987 Vol 25 November
381
dynamic range up to high frequencies. However, a high resolution requires a large number of digital steps, i.e. many comparators with memories. For example, a 4-bit digital peak detector has 16 amplitude steps and, therefore, 16 comparators with 16 memories. That is why the DFVLR looked for another method allowing digital peak amplitude measurements with high resolution, which should not require a large number of electronic devices. The new method is based on a modified counting A/D-converter. The device consists of a w i n d o w comparator with outputs connected to a memory. The reference voltage is changed step by step until its value is as large as the peak amplitude of the signal within the gate. The reference voltage is produced by a logarithmic D/A-converter which is connected with a counter. The clock frequency of this up/down counter is equal to that of the gate pulses. The features of the new developed peak detector, HFUS 1050, are: frequency range, 1 100 MHz; resolution, 1 dB; dynamic range, 31 dB.
Measuring turbulent flow characteristics using a Depth characterization with radiation field theory
multi-dimensional ultrasonic probe
D.K. Mak and I.R. Somerville, Canada Centre for Mineral and Energy Technology, Ottawa, Canada
J. Y. Cheung, K.J. Dormer and A. Ashrafzadeh, University of Oklahoma, Norman, USA
Ultrasonic spectral analysis has been used to determine the size and shape of a scattering discontinuity. An appropriate theoretical framework has to be developed for analysing the spectrum of an ultrasonic echo. Theoretical understanding of the flaw response is limited to a highly restricted class of flaws. Frequency minima obtained from spectral analysis can be used to characterize the shape, size and orientation of the defect. It will be pointed out here that the equations of the orientational dependence of the ultrasonic spectrum of the discontinuity response used by previous workers were not correctly derived. A new set of equations are derived using radiation field theory based on Huyghen's principle. Flat circular voids were used as examples. The equations can apply to a single pulse-echo transducer or the more general case of two transducers acting as transmitter- receiver system. Computer polar plots were drawn for the sound pressure profile of the scattered signal for different orientation of the scatterer. Experimental data have been collected for the double transducer system. The spectrum data agree quite well with the results of theoretical calculation.
This study demonstrates the feasibility of turbulent flow characteristics measurement using a dual transducer ultrasonic probe and compares its performance in measuring flow volume rate with other conventional techniques in a bench mark test done in vitro. The use of a multi-dimensional pulsed Doppler ultrasonic probe was effective in eliminating the need to know the Doppler angle between the transducer axes and the flow direction. For a single transducer probe, the Doppler angle was usually assumed because it cannot be measured. For a dual or triple transducer probe, the Doppler angle can be directly measured resulting in more accurate estimation of the velocity data. Such a dual transducer probe was designed and made. Since instantaneous velocity measurements were obtained, other turbulent characteristics such as shear stress and friction factor were also computed. To calibrate the probe and to compare its performance with other techniques, an in vitro experiment is set up using a pulsatile pump. A section of a dog's vessel was connected to the pump through a narrow orifice that generated turbulence. On the vessel, the dual transducer probe, a pulse transit time probe, and an electromagnetic probe were also attached. Flow rates ranging between 0 to 200 ml min 1 were used. Both laminar flow (without the orifice), and turbulent flow (with the orifice) conditions were tested with varying flow rates and pulse rates. By changing the size of the orifice, varying degrees of turbulence were created. Results showed that the dual transducer probe consistently provided the smallest error (3 5%) over the range of flow rates, pulse rates, and varying degrees of turbulence tested when compared to the other techniques. Such a low error rate was expected and was consistent with theoretical analyses. The transit time probe and the single transducer probe gave acceptable performance with slightly larger error. The performance of the doctro-magnetic probe was less acceptable due to its sensitivity to environment and random flow especially in highly turbulent conditions.
A high frequency peak detector for u.s. test pulses
W. Hillger, DFVLR Institut, Braunschweig, FRG The proportional monitor used in standard commercial flaw detectors determines the peak value of the higher u.s.-echo within the gate. The passive peak measurement method is often not sufficiently accurate for the detection of defects, particularly if the data must undergo further computer processing. The problem can be restricted to fast amplitude detection and storage of the value until the next measurement. Due to the relatively short pulse duration of 10 - 5 10 8 s, it is unfortunate to use the standard active peak value measurement methods of electrical engineering where the diode curve is extensively linearized using operation amplifiers. The advantage of digital methods over analog ones is a fast response time and that there are no changes in the memory after data acquisition, such as would happen, for example, in the case of analog memories with capacitances. However, the application of fast A/D-converters also requires calculation of the peak value, since converters sample the whole u.s.-signal as a sequence of separate points and do not determine the maximum level directly. For peak detection a modified flash converter is suitable, which yields a high
Integrated processing with the JUKEBOX ultrasonic imaging system
G. Corneloup, B. Comu, M. Perdrix and I. Magnin, CEN Cadarache, Saint Paul-lez-Durance, France JUKEBOX is a system for displaying and interpreting ultrasonic measurements designed to ensure compatibility with
Ultrasonics 1987 Vol 25 November
381