ULTRASONIC FAULT DETECTION SYSTEM USING A HIGH DYNAMIC RANGE ANALOG TO DIGITAL CONVERSION SYSTEM

• US 20090223294A1
• Filed: 03/25/2009
• Published: 09/10/2009
• Est. Priority Date: 10/14/2005
• Status: Active Grant

• Current Assignee: Olympus Ndt
• Original Assignee: Olympus Ndt
• Inventors: THOMAS, Andrew
• Granted Patent: US 7,963,166 B2
• Time in Patent Office: Days
• US Class Current: 73/627
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/262 by electronic orientation or focusing, e.g. with phased arrays phased arrays per se G10K11/34
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/44 Processing the detected response signal , e.g. electronic circuits specially adapted therefor digital signal processing per se G06F17/00
• CPC Class Codes: G01N 29/4463 Signal correction, e.g. distance amplitude correction [DAC], distance gain size [DGS], noise filtering
• CPC Class Codes: H03M 1/188 Multi-path, i.e. having a separate analogue/digital converter for each possible range

Abstract

A method and apparatus for effecting ultrasonic flaw detection of an object processes an echo signal received from the object being tested in at least three signal channels, wherein the echo signal is scaled to different degrees along each channel to increase and extend the dynamic range of an associated A/D converter system, in a manner which dispenses with the need for using numerous analog high pass and low pass filters and a variable gain amplifier. This reduces complexity and avoids performance limitations. The digital to analog converters sample the differently scaled input signal and a selection circuit selects the output of the digital output obtained from that analog to digital converter which has the highest gain, but which has not overflowed. The digital outputs are seamlessly merged to produce an output that can be displayed as a scan display which shows the location of faults.

Claims

1. An object inspection system, comprising:

a transmit and receive section to generate a test signal and to receive a responsive echo signal,

a transducer that converts a test signal to an ultrasonic signal, applies the ultrasonic signal to a target object to be tested, receives an ultrasonic echo signal and produces the echo signal for the transmit and receive section;

a signal processing circuit coupled with the transmit and receive section for receiving and processing the echo signal, the signal processing circuit including at least one signal processing channels, each channel including a respective preamplifier that scales the echo signal to a different degree;

an analog to digital converter coupled to the preamplifiers via amplification circuits, in a manner that passes to the analog to digital converter only a non-saturated output of at least one of the preamplifiers; and

an automatic gain control circuit which is coupled to the outputs of the preamplifiers and is capable of detecting the magnitudes of the outputs of the preamplifiers and to provide gain settings for the multiplier circuits which are selected to assure that the non-saturated output is provided to the analog to digital converter.

2. The system of claim 1, including an acquisition logic circuit which is coupled to and receives an output from the analog to digital converter and an additional output which is derived from the automatic gain control circuit.

3. The system of claim 2, wherein the additional output is produced by at least one analog to digital converter provided between the acquisition logic circuit and the automatic gain control circuit.

4. An object inspection system, comprising:

a transmit and receive section to generate a test signal and to receive a responsive echo signal;

a transducer that converts the test signal to an ultrasonic signal, applies the ultrasonic signal to a target object to be tested, receives an ultrasonic echo signal and produces the echo signal for the transmit and receive section;

a signal processing circuit coupled with the transmit and receive section for receiving and processing the echo signal, the signal processing circuit including at least two signal processing channels, each channel scaling the echo signal to a different degree, and each channel having a respective analog to digital converter;

a selection circuit which selects that output of that analog to digital converter which provides the largest amplification of the echo signal without having overflowed; and

a channel blender responsive to the selection circuit and operable to blend outputs of said analog to digital converters to produce a blended analog to digital output.

5. The system of claim 4, wherein the selection circuit is coupled to a plurality of magnitude comparators which are respectively coupled to respective ones of said analog to digital converters, wherein each of said magnitude comparators is structured to compare an output of its respective analog to digital converter to a respective predetermined reference, said selection circuit being responsive to said magnitude comparators to determine, in advance, whether one or more of said analog to digital converter is tending toward an erroneous reading.

6. The system of claim 4, wherein each of the analog to digital converters has a respective overflow output, and the selection circuit including a channel select logic circuit which receives the respective overflow output and selects the output of that analog to digital converter which provides the largest amplification without having overflowed.

7. The system of claim 4, further comprising a respective frequency trim circuit for at least one of said signal processing channels, the respective frequency trim circuit causing the frequency responses of the filters to match one another.

8. The system of claim 4, including first and second analog digital converters each having a respective clock input, the clock inputs being synchronized with one another with a phase adjustment between activating clock edges thereof to compensate for signal path delays in each channel.

9. The system of claim 4, further comprising an exponent generator for scaling the output of a selected analog to digital converter output and storing the same in a random access memory.

10. The system of claim 4, including a DC offset circuit which applies a digital DC offset correction at signal location located after said selection circuit, wherein the DC offset circuit includes a baseline capture circuit coupled to at least one of the first or second analog to digital converters to produce a correction signal, and including a baseline corrector which is capable of subtracting the correction signal from an output signal derived from one of the first or second analog to digital converters.

11. The system of claim 4, including at least first and second signal channels which include, respectively, first and second preamplifiers which respectively provide first and second scaled outputs of the echo signal, wherein the analog signal delay module comprises a delay line with taps, wherein a desired tap is selected by a switch to obtain a desired delay.

12. An object inspection system, comprising:

a transmit and receive section to generate a test signal and to receive a responsive echo signal;

a transducer that converts the test signal to an ultrasonic signal, applies the ultrasonic signal to a target object to be tested, receives an ultrasonic echo signal and produces the echo signal for the transmit and receive section;

a signal processing circuit coupled with the transmit and receive section for receiving and processing the echo signal, the signal processing circuit including at least two signal processing channels, each channel scaling the echo signal to a different degree, and each channel having a respective analog to digital converter;

a selection circuit which selects that output of that analog to digital converter which provides the largest amplification of the echo signal without having overflowed; and

a delay circuit constructed as one of;

a first delay facility for delaying outputs of at least one of the analog to digital converters in response to a condition when saturation of one of the analog to digital converters is foreseeable, prior to processing of said outputs at said selection circuit; and

a second delay facility which is effective to cause the selection circuit to refrain from selecting an analog to digital converter output which has overflowed, until after the overflowed analog to digital converter has recovered from a saturation condition.

13. The system of claim 12, wherein the delay circuit provides a delay which is at least one clock period for the system.

14. The system of claim 13, wherein the delay circuit is further effective to delay a respective overflow output of the analog to digital converters.

15. An object inspection system, comprising:

a transmit and receive section to generate a test signal and to receive a responsive echo signal;

a transducer that converts the test signal to an ultrasonic signal, applies the ultrasonic signal to a target object to be tested, receives an ultrasonic echo signal and produces the echo signal for the transmit and receive section;

a signal processing circuit coupled with the transmit and receive section for receiving and processing the echo signal, the signal processing circuit including at least two signal processing channels, each channel scaling the echo signal to a different degree, and each channel having a respective analog to digital converter;

a selection circuit which selects that output of that analog to digital converter which provides the largest amplification of the echo signal without having overflowed; and

an auxiliary circuit constructed as one of;

a respective frequency trim circuit for at least one of said signal processing channels, the respective frequency trim circuit causing the frequency responses of the channels to match one another;

a preamplifier associated with each channel, and a saturating preventing circuit associated with each preamplifier and effective to prevent saturation of a respective input stage of each preamplifier, to prevent signal distortion from affecting inputs to other channels; and

a reference voltage circuit respectively applicable to each of said analog to digital converters in each signal channel to adjust a full scale range thereof.

16. The system of claim 15, wherein the reference voltage circuit includes a respective digital to analog converter associated with each respective analog to digital converter.

17. A method for ultrasonic object testing comprising the steps of:

providing a test signal to a transducer to generate an ultrasonic signal capable of being propagated and reflected in a target object to be tested;

receiving an ultrasonic echo signal and producing an echo signal to be processed;

processing the echo signal in at least two signal processing channels with the echo signal being scaled to different degrees in each processing channel and thereafter being converted to a digital output utilizing a respective analog to digital converter in each processing channel;

selecting an output from that analog to digital converter which provides the largest amplification of the echo signal without having overflowed; and

enabling a full dynamic range of sampled data of the echo signal to be processed on every sample clock cycle, in a manner which allows the sampled data to be rendered on a linear scale or on a logarithmic scale.