Signal processing apparatus for ultrasonic flaw detection system

Apparatus (10) for processing a return waveform generated by directing an ultrasonic pulse at an object (S) under test. A signal converter (12) converts the return waveform from an analog to a digital signal. The analog-to-digital conversion rate is approximately four times the operating frequency of the ultrasonic pulse. A signal processor includes a plurality of digital signal processors (14,16,18) each of which is separately controllable to process the converted digital signal. A communications network (20) directs the analog signal, converted digital signal, and an output signal from the signal processor to a visual display (28) and to various peripheral equipment (A1,A2) connected to the apparatus. A process controller (22) controls routing of these signals to and from the signal processor over the communication network. By processing a return waveform, peak amplitude values representing flaws or imperfections in the object can be determined and the processed waveform, including peak values, displayed.

CROSS-REFERENCE TO RELATED APPLICATIONS 
None. 
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
Not Applicable. 
BACKGROUND OF THE INVENTION 
This invention relates to the ultrasonic, non-destructive testing of 
objects, and more particularly to apparatus employing digital signal 
processing and digital signal processing techniques for processing and 
displaying the results of such tests. 
In copending U.S. Pat. No. 5,596,508, issued Jan. 21, 1997 entitled, "High 
Resolution Measurement of a Thickness Using Ultrasound," there is 
described an apparatus and a method for making highly accurate 
measurements of a material thickness using ultrasound. This 
non-destructive testing technique involves propagating an ultrasonic 
waveform having defined characteristics at an object or test specimen, and 
evaluating a return waveform to determine the attributes of the object or 
specimen to the desired degree of accuracy. In performing ultrasonic 
testing to measure material thickness, it is known to use sampling rates 
on the order of 100-500 MHz to obtain an accuracy level of 10*10.sup.-6 
inches, and it is not unknown to use sampling rates in the gigahertz 
range. The electronic circuits typically used in processing test data to 
acquire these numbers for samples is emitter-coupled logic, or ECL. 
Further, it has heretofore been common to employ analog signal processing 
to generate a visual display of the return waveform which is then 
evaluated by an operator to determine whether or not the test specimen 
meets required specifications. 
As an alternative to conventional ultrasonic testers, it is now possible to 
employ digital signal processing to evaluate the response waveforms and to 
perform pass/fail evaluations. A major advantage of using digital signal 
processing is that the sampling rate can now be on the order of 50 MHz, 
and still provide highly accurate measurement information to the user. 
Further, employing digital signal processing techniques enhances the 
accuracy of the results. In addition, digital signal processing techniques 
allow the signal processor to be interfaced with existing test equipment 
such as that described in the copending application, as well as other 
types of test equipment. Further, the signal processor apparatus can now 
provide a waveform display and data storage features which enable the user 
to immediately ascertain if a test specimen is acceptable as well as 
perform post-test analysis of the data obtained. 
BRIEF SUMMARY OF THE INVENTION 
Among the several objects and features of the present invention may be 
noted the provision of an apparatus for use in the non-destructive testing 
of an object or test specimen; 
the provision of such apparatus for processing an ultrasonic return 
waveform to obtain pertinent information about an object under test, and 
in particular the presence of flaws or imperfections which would make the 
object unsuitable for use; 
the provision of such apparatus to process such waveform quickly and 
efficiently and to provide highly accurate test results from such 
processing, the results being visually displayed for viewing by test 
personnel, or supplied to peripheral equipment for further data processing 
and analysis; 
the provision of such apparatus to employ a lower frequency ultrasonic 
pulse rate than other, conventional processors employ; 
the provision of such apparatus to further employ digital signal processing 
and processing techniques which produce a desired level of accuracy which 
is at least comparable to results obtained using conventional test 
apparatus and signal processing techniques; 
the provision of such apparatus to utilize curve fitting techniques as part 
of the waveform processing whereby amplitude peaks in the return waveform 
which represent areas of interest to be evaluated are readily and 
accurately ascertained to a desired level of resolution; 
the provision of such apparatus to construct a waveform trace from 
processed data and present such a trace for observation by a user, the 
trace being generated using the curve fitting techniques employed by the 
apparatus; 
the provision of such apparatus to further provide test data obtained from 
waveforn processing to an internal memory storage which is accessible by 
test personnel for subsequent processing and evaluation to determine 
acceptability of the object; 
the provision of such apparatus to employ multiple signal processors for 
evaluation of return waveform data and to control their operation so as to 
quickly and efficiently process the data, ascertain waveform peaks, and 
provide an accurate visual representation, the waveforn processing 
required to determine acceptability of the specimen under test being 
independently performable by any of the signal processors or by a 
combination of processors; 
the provision of such apparatus to employ a multi-channel capability so to 
be used in performing parallel testing of a number of specimens or 
multiple probe testing on a single specimen; 
the provision of a method for signal processing anal for routing a variety 
of analog and digital signals within a processing apparatus so as to 
process waveforms and display the results of such processing, and to 
provide the results of the processing to the peripheral equipment; 
the provision of such a method to be readily employed by test equipment and 
provide necessary signal processing by which the user can readily evaluate 
a return waveform and determine whether or not a material or object under 
test meets standards of acceptance; 
the provision of such apparatus which is compatible with the apparatus 
described in copending U.S. patent application Ser. No. 08/350,956 to 
perform the return waveform processing required by the apparatus; and, 
the provision of such an apparatus and method to provides a relatively low 
cost, reliable, flexible, easy to use, and accurate signal processing 
capability for a user. 
In accordance with the invention, generally stated, an apparatus is 
provided for processing a return waveform generated by directing an 
ultrasonic pulse at an object under test. A signal converter converts the 
return waveform from an analog to a digital signal at a conversion rate 
comparable to the frequency of the ultrasonic pulse. A signal processor 
includes a plurality of digital signal processors each of which is 
separately controllable to process the converted digital signal or which 
are usable in combination to perform the requisite processing. A 
communications network moves the analog signal, converted digital signal, 
and an output signal from the signal processor to a visual display and to 
various peripheral equipment connected to the apparatus. A controller of 
the apparatus routes these signals to and from the signal processor over 
the communications network. By processing a return waveform and displaying 
the results or providing the results to other equipment for analysis, peak 
amplitude values representing flaws or imperfections in the object can be 
determined and the processed waveform, including the peak values, 
displayed. 
As a method, the invention includes converting the return waveform from an 
analog signal to a digital signal, this conversion being performed at a 
rate comparable to that of the frequency of the ultrasonic pulse. Next is 
processing the resulting digital signal by one of a plurality of digital 
signal processors each of which is separately controllable to process the 
digital signal or combining the operation of multiple processors to 
perform this task. Routing the analog signal, converted digital signal, 
and an output signal produced by the signal processing over a 
communications network enables the output signal to be directed to a 
visual display for displaying a reconstructed return waveform, and to 
peripheral equipment by which additional processing is performed. Finally, 
the method includes controlling the routing of the aforesaid signals to 
and from said signal processors over the communication network. Other 
objects and features will be in part apparent and in part pointed out 
hereinafter.

Corresponding reference characters indicate corresponding parts throughout 
the drawings. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1 of the drawings, an apparatus 10 of the present 
invention is for use in processing a return waveform produced by the 
generation and transmission of an ultrasonic waveform at an object under 
test. Reference is made to copending application Ser. No. 08/350,956, the 
teachings of which are incorporated herein by reference, with respect to 
the generation of an ultrasonic waveform directed at a tube or other test 
specimen. The tube, or any other test specimen (S) has certain 
characteristics such as wall thickness, for example, which must be 
determined to a high degree of accuracy. As indicated in the copending 
application, it is possible to measure this thickness to an accuracy of 
10*10.sup.-6 inches. 
As shown in FIG. 1, a test installation for ultrasonic, non-destructive 
testing of an object or test specimen (S) includes a test fixture (F), an 
ultrasonic transducer (T), and the signal processing apparatus 10 of the 
present invention. An electrical signal (E1) having defined waveform 
characteristics including a frequency is supplied to a transducer (T) from 
the signal processing apparatus 10. As is well-known in the art, the 
transducer converts the electrical signal to an ultrasonic pulse directed 
at the test specimen (S) and converts the ultrasonic pulse reflections 
from the test specimen (S) into an electrical return waveform (E2) relayed 
to the processing apparatus 10. 
Referring generally to FIG. 2, the electrical signal (E2) representing the 
return waveform is received by the signal processing apparatus 10 as one 
of two inputs to an analog-to-digital converter 12. The second input to 
the analog-to-digital converter 12 is a signal (F1) directly proportional 
to the rate at which test specimen (S) is subjected to ultrasonic pulses, 
approximately 50 MHz in the preferred embodiment, but as low as 10 MHz in 
alternate embodiments conforming to the teachings of copending application 
Ser. No. 08/350,956. The analog-to-digital converter 12 processes the two 
input signals to convert the return waveform signal to a digital signal 
representation (D1) of the original analog signal suitable for digital 
signal processing. The resulting digital signal (D1) is then routed from 
the output of the analog-to-digital converter 12 to three digital signal 
processors 14, 16, 18, of the signal processing unit 19 over a 
multi-channel data bus 20. Within the signal processing unit 19, the 
multi-channel data bus 20 has three branches, (B1, B2, B3) corresponding 
to each digital signal processor 14, 16, 18. The flow of digital data 
along branch (B1) is restricted by two unit-directional gates (G1a, G1b) 
whereby digital data on branch (B1) is only received by digital signal 
processor 14. In addition to routing the digital signal (D1), branch (B1) 
may route additional digital data from memory modules (M1a) and (M1b) to 
the digital signal processor 14 as needed. As is shown in FIG. 2, branches 
B2 and B3 are identical to branch B1, and have corresponding reference 
notations. In an alternate embodiment, the analog-to-digital converter 12 
is multi-channel, capable of converting multiple signals simultaneously. 
Hence, the multi-channel data bus 20 is capable of transferring either a 
single digital signal (D1) or simultaneous separate digital signals (not 
shown) obtained from a plurality of test specimens (not shown) to each 
individual digital signal processor 14, 16, 18. In turn, each digital 
signal processor 14, 16, 18, is individually controlled by process 
controller 22 through enable lines 23a, 23b, 23c, to process all or a 
portion of each individual digital signal (D1) received from 
analog-to-digital converter 12. Processing of the digital signal (D1) or 
portions thereof may proceed in parallel or serial, as directed by the 
process controller 22. Process controller 22 contains a memory module 
(PCM), a processor unit (PC), and a signal time calculator (TOFC). 
Digital signals received by the digital signal processors 14, 16, 18, are 
internally processed through pre-programmed curve-fitting algorithms and 
finite impulse response filters to derive digital data values 
representative of peak amplitude points for each ultrasonic return 
waveform. The peak amplitude points are representative of features of the 
test specimen S, such as flaws, cracks, or other discontinuities, and can 
be used to reconstruct the original analog return waveform (E2) for 
analysis and display. These digital data values representative of the peak 
amplitude points, are then provided as respective outputs (01, 02, 03) 
from the individual digital signal processors 14, 16, 18, as digital 
signals, and routed along the respective branches (B1, B2, B3) of the 
multi-channel data bus 20 to a data storage device 24. 
Data storage device 24 is preferably comprised of a 4-port random access 
memory (RAM) module of sufficient size and speed to store the digital 
output signals (01, 02, 03). Access to the data contained within the data 
storage device 24 is controlled by the process controller 22. In addition 
to receiving the output digital signals (01, 02, 03) from each individual 
digital signal processor 14, 16, 18, data storage device 24 receives and 
stores the unprocessed digital signal (D1) produced by the 
analog-to-digital converter 12 by means of the multi-channel data bus 20. 
As is standard practice with random access memories, each storage location 
within the data storage device 24 is assigned a unique storage address. 
These addresses are communicated between the various components of the 
signal processing apparatus 10 by the branches and subsections of a 
multi-channel address bus 25 which is separate from the multi-channel data 
bus 20. 
In addition to data storage device 24, the preferred embodiment of the 
claimed invention employs additional random access memory modules for data 
storage. These include a control RAM module (CM), a signal acquisition RAM 
module (AM), a peak segment RAM module (PSM), and an interface RAM module 
(IFM). Each of these memory modules is in data flow communication with the 
data bus 20 and the address bus 25, and is controlled for the storage and 
retrieval of digital data by the process controller 22. 
The processed digital data stored in data storage device 24 may be 
retrieved and routed by the process controller 22 over the multi-channel 
data bus 20 to a peripheral connection interface 26 for transfer to a 
display means 28 shown generally in FIG. 3, or to additional external 
devices (A1, A2) shown generally in FIG. 1 for additional data processing. 
The peripheral connection interface 26 is preferably a standard AT/PCI 
interface suitable for direct connection to the motherboard of a desktop 
computer system (not shown). 
The preferred display means 28 shown generally in FIG. 3 employs a software 
algorithm capable of receiving the output digital signals (01, 02, 03) 
from the peripheral connection interface 26, and calculating a waveform 
trace (WT) representative of the original analog waveform (E2) received 
from said ultrasonic transducer (T). The operator may select from a 
variety of options when viewing waveform trace (WT) on the display means 
28. These may include viewing the original radio-frequency signal, viewing 
a rectified signal half wave positive or negative, and viewing a rectified 
signal full wave. The various waveform traces are viewed without the use 
of specialized hardware to rectify the signals. 
In addition to controlling the operation of the analog-to-digital converter 
12, the digital 20 signal processors 14, 16, 18, and directing data flow 
over the data and address buses (20, 25), the process controller 22 
regulates the operation of all input and output features of the signal 
processing apparatus 10 by means of enable lines (E1-E6). An output means 
29 includes outputs 30 and 31 for an alarm signal and data validity 
signals. The alarm signal and the data validity signals are activated when 
the process controller 22 detects incoming data which exceed the operating 
parameters of the system. Data exceeding the operating parameters of the 
system is rejected by the process controller 22. Additional inputs and 
outputs to and from the process controller 22 such as timing signals and 
external analog controls shown generally at 36, are received and routed 
through a field programmable gate array interface circuit 34 to the 
various other components of the signal processing apparatus 10 over the 
multi-channel data and address buses 20, 25. 
As a method, the ultrasonic signal processing of the claimed invention 
comprises the following preferred steps. First, the return analog waveform 
signals received from ultrasonic pulses are directed at one or more test 
specimens are received and routed to the signal converter for analog to 
digital conversion. Within the signal converter, the return analog 
waveform signals are processed along with a second set of input signals 
proportional to the frequency of the ultrasonic pulses directed at the 
test specimens to produce digital signals representative of the original 
analog return waveforms. The second set of input signals are within the 
range of 10 MHz to 50 MHz, and is in accordance with the teachings of 
copending application Ser. No. 08/350,956. 
Next, the method includes routing the resulting digital signals a 
communications network consisting of multi-channel data buses to 
individually controlled digital signal processors. The digital signal 
processors process the received digital signals through preprogrammed 
curve-fitting algorithms to produce digital output signals representative 
of the original analog return waveforms peak amplitude values. The digital 
signal processors are controlled such that they may either process an 
individual waveform in parallel or may each independently process separate 
digital signals allowing for rapid analysis of multiple return signals. 
Upon completion of the digital signal processing, routing the digital 
output signals to appropriate data storage locations within a data storage 
means. 
Further routing by the process controller may retrieve the digital output 
signals from the data storage means for transfer to either a display means 
or to an interface mean. Prior to display by the display means, the 
digital output data is reconstructed into waveform traces representative 
of the original analog return waveforms. Displayed as waveform traces, the 
digital output data enables an operator to quickly ascertain the 
characteristics and properties of the test specimen being examined. 
Similarly, digital output data routed by the process controller to the 
interface means may be processed or stored externally by external 
peripheral devices. 
What has been described is a method and processing apparatus used in the 
ultrasonic testing of an object or test specimen for processing ultrasonic 
return waveforms reflected from a test specimen to obtain pertinent 
information about the specimen. It is a feature of the apparatus to 
process return waveforms quickly and efficiently, and to produce accurate 
test data as a result of the processing. A major advantage of the 
apparatus is the combination of a lower ultrasonic pulse rate than 
conventional processors employ and a lower sampling frequency, together 
with the use of curve-fitting techniques that allow the amplitude peaks in 
a return waveform to be readily ascertained at a desired level of 
resolution. The apparatus further can construct a waveform trace from the 
processed data and display the results for observation by a user. In 
addition, data derived from the waveform processing can be stored in an 
internal memory of the apparatus or directed to external equipment for 
subsequent processing and evaluation. The processing apparatus employs 
multiple signal processors for evaluating return waveforms and a process 
controller coordinates their operation for quick and efficient data 
processing. Each processor can process all or a portion of the return, and 
the processors can be used singly or in combination for this purpose. The 
apparatus has multi-channel capability and can be used for parallel 
testing of a plurality of specimens. Outputs from the processing are 
provided to display means and peripheral instrumentation for additional 
waveform analysis. The apparatus is compatible with existing ultrasonic 
testing apparatus and provides a signal processing capability by which a 
user can readily evaluate return waveforms to determine if a specimen 
meets standards of acceptance. Finally, the apparatus provides the user a 
greater degree of flexibility than existing equipment while still 
providing accurate results. 
In view of the foregoing, it will be seen that the several objects of the 
invention are achieved and other advantageous results are obtained. As 
various changes could be made in the above constructions without departing 
from the scope of the invention, and it is intended that all matter 
contained in the above description or shown in the accompanying drawings 
shall be interpreted as illustrative and not in a limiting sense.