Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-08-15
2002-11-05
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S626000, C073S628000
Reexamination Certificate
active
06474164
ABSTRACT:
SUMMARY OF THE INVENTION
Add-on units are attached to standard analog or digital ultrasonic flaw detector instruments for either suppressing noise spikes that clutter up the flaw detectors' screens or enhancing very weak, barely detectable signals. The add-on units may do both simultaneously as well. Each unit includes an adjustable filter so that a user may tune the filter bandwidth to a specific range within the overall transducer band that coincides with the signal to be either suppressed or enhanced.
Each adjustable filter may use a variable filter circuit. The filter has independent controls for frequency, bandwidth and null/gain adjustments. The unit also includes a pre-amplifier for boosting weak signals prior to filtering. The unit may be added to any ultrasonic non-destructive inspection/evaluation (UT NDI/E) equipment and operates independently of that equipment. The unit operates in any of the three UT NDI/E inspection modes: pulse-echo, pitch-catch and through-transmission. The unit operates on single signals and in real-time. The unit has a small enclosure so that it may be portable and operated by a battery or an ac adapter.
The new Noise Suppressor II (NSII) system combines three independent functions, two tunable filters and one pre-amplifier, into one unit that provides a means for either suppressing noise signals (spikes or background noise) or enhancing a signal of interest by increasing the signal
oise ratio, or both.
The system is used as an add-on module to ultrasonic pulser/receiver instruments. These instruments may be either analog or digital devices that are components in an overall ultrasonic (UT) non-destructive inspection/evaluation (NDI/E) system, or they may be stand-alone self-contained UT instruments, usually called flaw detectors, that are commonly used in either manual, semi-automated or fully automated UT NDI/E applications. Even though these UT instruments may have some built-in noise suppression and/or signal enhancement capabilities, these are usually fairly rudimentary and hard-wired such that the user has no choices other than those supplied by the instrument manufacturer. As an add-on module, the NSII system's purpose is to enhance the function of the UT instrument by giving the user a set of signal filtering controls that are tunable to the particular needs of each application. As such, the NSII provides a significant increase in noise suppression and/or signal enhancement capabilities, all under user control.
The primary purpose of the NSII is to enhance signals returned from UT transducers being used as part of the NDI/E process. One of the main problems associated with UT flaw detector instruments is discriminating the response (either pulse-echo, pitch-catch or through-transmission) of a flaw from the background noise. Flaw detectors operate normally in a very wide band mode, whereas the signal returned from the transducer is much narrower in bandwidth. A simple narrow band filter may be used to substantially lower the noise floor and to enhance the signal
oise ratio.
One of the problems, however, is that the returned echo is not always centered on the same frequency as the built-in bandpass filter. The signal returned from the transducer is typically fairly wide band and different types of defects (i.e. targets) are represented in different bands of the incident signal. Also, UT transducers themselves may resonate at different frequencies and this varies with the type of transducer being used.
It is therefore highly desirable that the filter be tunable (i.e., adjustable) so that the user may “tune” the filter band to the specific range within the overall transducer band that coincides with the signal to be either suppressed or enhanced. This is similar to tuning a stereo receiver to find the optimal frequency position that delivers the best signal for a broadcasting station of interest. The NSII provides three functions that permit the user to tune either of the two filters' bands: (1) center frequency of at least 0.5 MHz (preferably ranges between 0.5 to 1.3 MHz and between 1.5 MHz to 7 MHz), (2) width of the band (narrow, medium, wide), and (3) amplification, either positive or negative, in the band (Gain=+15 dB or Null=−20 dB). Frequency ranges of about 0.15 to about 25 MHz are provided by embodiments of the invention.
Noise suppression is desirable when the noisy signal(s) is(are) induced by the material or the flaw detector itself. Noise from external sources (i.e., environmental noise) can also present problems due to their superposition on the small return responses from defects and the subsequent need for high amplification in the UT instrument to detect these small signals. External noise can sometimes literally mask the signal of interest or at least make its detection very difficult. Examples of high-amplitude external noise sources include electrical noise from positioning motors of a scanning system and welding machines.
It is therefore desirable that the filter be able to remove certain frequency bands as well as enhance the main frequency. It is also necessary to vary the bandwidth of the filter to match the bandwidth of the desired signal or noise source to obtain optimal signal enhancement.
The NSII does all of these things over a frequency range compatible with most ultrasonic NDI/E testing: at least 0.5 MHz with preferred ranges of about 0.5 to 1.3 MHz and 1.5 MHz to 7 MHz, or about 0.15 to about 25 MHz. The effectiveness of the NSII is increased by including two filter elements that permit combinations of noise suppression, signal enhancement or both. In theory, more stages may be added until the filters start interfering with one another due to bandwidth considerations.
The NSII contains a pre-amplifier as a third independent function. The preamp is adjustable by the user over a 0 dB to 30 dB range, in steps of 10 dB. The preamp's purpose is to boost weak signals (up to 30 dB) prior to any filtering operation(s) or to act as a stand alone additional amplification boost when no filtering is desired. This latter condition is commonly encountered when running long cable lengths between the UT transducer and its receiving UT instrument. The total gain of the system, therefore, is equal to 60 dB which derives from +30 dB in the preamp and +15 dB in each of the two filters if both filters are being used for signal enhancement.
The preferred Noise Suppressor II™ is an add-on unit to ultrasonic pulser/receivers and flaw detectors. The unit can be set to either suppress noise (spikes or background) or to enhance the signal
oise ratio of weak desirable signals, or both.
The preferred Noise Suppressor II™ combines three independent functions that can be used in any combination—preamp (up to 30 dB in 10 dB steps) and two tunable bandpass filters. The unit incorporates novel circuitry that enables the inspector to tune each filter anywhere in the 1.5-7.0 MHz band, the ultrasonic band most commonly used for inspection. The width of the band is also adjustable (low, mid, high) and each filter can either be set to null out a noise signal (−20 dB attenuation applied in the tuned band) or to enhance a desired signal (+15 dB gain applied in the tuned band). One filter can be used to null noise while the other is set to simultaneously enhance a desired signal, or both filters can be set identically to effectively “double up” on either noise cancellation (via −40 dB total attenuation) or signal enhancement (via +30 dB total gain).
The NSII is connected between the transducer(s) and the pulser/receiver or flaw detector. It is housed in a small (4″×7″×1.5″) enclosure weighing less than two pounds and is powered by either a 9 v battery or AC. It operates in both pulse-echo or pitch-catch/thru-transmission modes. All settings are via detented rotary dials so that the user is assured of repeatable inspections. The unit interfaces with any type of analog or digital ultrasonic unit to provide an add-on enhancement.
The Noise Su
Mucciardi Anthony N.
Tilden Thomas J.
Creighton Wray James
Larkin Daniel S.
Narasimhan Meera P.
Saint-Surin Jacques
SLX, Inc.
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