UT Testing-Add01b-Equipment Calibrations

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ASNT UT Level III pre-exam preparatory course note


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Addendum-01b Equipment Calibration My ASNT Level III UT Study Notes 2014-June.

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Pulse-Echo Instrumentation

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The Circuitry:  Voltage activation of the PE crystal  Ultrasound formation  Propagation  Reflection  Charge formation of crystal  Processing  Display

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Transmitter TGC Receiver Amplifier Detector Scan Converter Display TRX Pulse-Echo Instrumentation TGC – Time Gain Compensation Circuit

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Pulse-Echo Instrumentation Pulser Components 1. HV pulse generator 2. The clock generator 3. The transducer

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TIME TIME ++ - P Generated Wave Applied Voltage V - Pulse-Echo Instrumentation

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The Pulser rate is known as the pulse repetition frequency PRF. Typical PRF 3000 – 5000. PRF automatically adjusted as a function of imaging depth. Pulse-Echo Instrumentation

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Switch that controls the output power of the HV generator is the attenuator. Pulse-Echo Instrumentation

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PULSER ATTENUATOR TRX Pulse-Echo Instrumentation

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CLOCK GENERATOR Controls the actual number of pulses which activate the crystal. Responsible for sending timing signal to the 1. Pulse generator 2. TGC circuitry 3. Memory Pulse-Echo Instrumentation

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Sensitivity refers to the weakest echo signal that the instrument is capable of detecting and displaying. Factors that determine sensitivity are 1. Transducer frequency 2. Overall and TGC receiver gain 3. Reject control 4. Variable focal zone on array real-time instruments. Pulse-Echo Instrumentation

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Increasing the voltage causes 1. Greater amplitude – greater penetration 2. Longer pulses – degrades axial resolution 3. Increase exposure Pulse-Echo Instrumentation

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Transducer has dual roles transmitting and receiving signals. The transducer is capable of handling a wide range of voltage amplitude. The Receiver is capable of handling only smaller signals Therefore it is desirable to isolate the pulser circuit from the receiver circuit. Pulse-Echo Instrumentation

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The Transmit Receive Switch TRS – positioned at the input of the receiver and is designed to pass only voltages signals originating at the transducer by the returning echoes. Pulse-Echo Instrumentation

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The Receiver Unit consist of 1. Radiofrequency Amplifier 2. Time gain compensation TGC unit 3. Demodulation Circuit 4. Detector Circuit 5. Video Amplifier Pulse-Echo Instrumentation

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Radio-Frequency Amplifier • Amplify weak voltage signals. •This is called GAIN Pulse-Echo Instrumentation

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Electric signals generated by the transducer are weak and needs amplification. The gain is the ratio of the output to input Voltage or Power. Gain Voltage Out Voltage In Pulse-Echo Instrumentation

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The Imaging effect of adjusting gain are: 1. Increasing the gain - increased sensitivity better penetration 2. Decreasing the gain – decreased sensitivity less penetration 3. Too high a gain – overloads the display loss or spatial resolution Pulse-Echo Instrumentation

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Saturation Level Distance Amplitude Normal Gain Pulse-Echo Instrumentation

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Saturation Level Distance Amplitude Excess Gain Pulse-Echo Instrumentation

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Primary objective of grayscale pulse-echo imaging is to make all like reflectors appear the same in the Image regardless where they are located in the sound beam. Pulse-Echo Instrumentation

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Time Gain Compensation TGC TGC - electronic process of adjusting the overall system gain as a function of the transmit time. Pulse-Echo Instrumentation

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TGC Controls •Near Gain • Slope Delay •Slope • Knee •Far Gain •Body Wall Pulse-Echo Instrumentation

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Gain dB Depth cm DELAY SLOPE KNEE MAX GAIN NEAR GAIN Pulse-Echo Instrumentation

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Gain dB Depth cm SLOPE KNEE MAX GAIN NEAR GAIN Body wall Pulse-Echo Instrumentation

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Gain dB Depth cm DELAY SLOPE KNEE CUT-OFF Pulse-Echo Instrumentation

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The slide potentiometer allows adjustment of receiver gain for small discrete depth increments. Pulse-Echo Instrumentation

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Gain dB Depth Time Slide Potentiometer Pulse-Echo Instrumentation

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Frequency Tuning of the Receiver The frequency band width of the receiver refers to the range of ultrasound signal frequencies that the receiver can amplify with a maximum gain. Pulse-Echo Instrumentation

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Types of Amplifiers •Wide-Band • Narrow-Band Pulse-Echo Instrumentation

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Frequency MHz Gain Gain Frequency MHz Wide-band amplifier Narrow-band amplifier Pulse-Echo Instrumentation

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Receiver B Receiver A Receiver C Receiver D TRX Output To System Frequency Selector Switch Receiver Unit Pulse-Echo Instrumentation

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DYNAMIC RANGE The dynamic range is a measure of the range of echo signal amplitudes. The dynamic range can be measured at any point. The dynamic range decreases from transducer to receiver to scan converter and finally to display. Pulse-Echo Instrumentation

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Large range in signal amplitudes is due to: 1. Normal variation in the reflection amplitude. 2. Frequency dependent tissue attenuation. Pulse-Echo Instrumentation

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RF amplifier can handle a wide range of signal amplitude at its input – but cannot accommodate the corresponding output using linear amplification. Pulse-Echo Instrumentation

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Linear amplification - all voltages amplitudes regardless of size at the point of input are amplified with the same gain factor. Pulse-Echo Instrumentation

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LOGARITHMIC AMPLIFICATION In Logarithmic amplification weak echoes amplitudes are amplified more than strong echoes. This can reduced the dynamic range by as much as 50. The process of reducing the signal DR by electronic means is called COMPRESSION Pulse-Echo Instrumentation

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Input signal Gain A B Linear Amplification Logarithmic Amplification Pulse-Echo Instrumentation

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R-F amplifier can also set the electronic level in the machine. S-N level – compares real echo signals the system can handle versus the non-echo signals presents Noise. The Higher the SN ratio – better the operation of the system. Pulse-Echo Instrumentation

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Pre-amplification is a technique to reduce system noise. Positioning of part of the amplifier circuitry in the transducer housing reduces system noise. Pulse-Echo Instrumentation

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REJECTION Rejection is the receiver function that enables the operator to systematically increase or decrease the minimum echo signal amplitude which can be displayed. Alternate names Threshold Suppression. Pulse-Echo Instrumentation

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Noise Level Dynamic Range Saturation Level Rejection Level Zero Signal Level Pulse-Echo Instrumentation

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SIGNAL PROCESSING RF waveform – oscillating type of voltage signal AC First Step in processing the signal is Demodulation. Demodulation is the process of converting the electric signal from one form to another. Pulse-Echo Instrumentation

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DEMODULATION  Rectification  Detection Pulse-Echo Instrumentation

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RECTIFICATION • Rectification results in the elimination of the negative portion of the RF signals • Half Wave Rectification • Full wave Rectification Pulse-Echo Instrumentation

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Half-Wave Rectification Pulse-Echo Instrumentation

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Full-Wave Rectification Pulse-Echo Instrumentation

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DETECTION The main effect of detecting the rectified RF signal is to round out or smooth the signal as to have a single broad peak. The rectified RF signal following detection is referred to as a Video Signal. Pulse-Echo Instrumentation

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Smoothing Pulse-Echo Instrumentation

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The video signal is then further amplified by the VIDEO AMPLIFIER. The output from the video amplifier is forwarded to 1. CRT or 2. Scan converter Pulse-Echo Instrumentation

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DIGITAL SCAN CONVERTER The device that stores the echo signal is called a Scan converter. Pulse-Echo Instrumentation

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All Scan Converters are designed to 1. Store echoes in appropriate location 2. Encode echoes in shade of gray 3. Read out echoes in a horizontal raster format Pulse-Echo Instrumentation

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4. Digital Memory is divided into small squares Pixel. 5. The Pixels form the Image Matrix 6. Total of storage location rows x columns 7. x and y location ADDRESS Pulse-Echo Instrumentation

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Matrix Rows x coordinates

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Matrix Columns y coordinates

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Matrix Pixel

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1x 1y 3x 3y 5x 5y 8x 7y 10x 10y X Y ADDRESS

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In the Scan converter the echoes are processed on a first- come first-in basis. Pulse-Echo Instrumentation

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50 50 50 50 50 50 50 50 50 50 50 50

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50 50 50 50 50 50 50 50 50 50 50 50 Raster Process

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DIGITAL SCAN CONVERTER • Convert echo voltage signal into a numerical value. • Each numerical value corresponds to a shade of gray. Pulse-Echo Instrumentation

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The number of shades of gray is determined by the BIT CAPACITY. of shades of gray 2 Pulse-Echo Instrumentation

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Echoes dB Pulse-Echo Instrumentation

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2 1 4 2 8 3 16 4 32 5 64 6 128 7 256 8 Shades of Gray Bit Pulse-Echo Instrumentation

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Gray Scale Resolution dynamic range dB of gray shades Pulse-Echo Instrumentation

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Operator can select different A/D conversion scheme Preprocessing. Each preprocessing curve is called an algorithm and assigns a specific percentage amount of shades of gray to regions of the echo amplitude. Pulse-Echo Instrumentation

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100 50 0 Available Shade of gray Echo Strength 1 2 3 4 Pulse-Echo Instrumentation

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POST PROCESSING Assignment of specific display brightness to numerical echo amplitudes read out of the digital memory. Pulse-Echo Instrumentation

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9 8 8 7 7 8 9 8 8 8 7 9 8 8 8 8 8 8 8 8 8 8 8 8 SMOOTHING Pulse-Echo Instrumentation

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The DSC is not necessary for image display but is needed for the following post-processing functions. • Video Invert •Display Invert • Display Subdivision • Zoom Magnification Pulse-Echo Instrumentation

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Zoom Magnification • Read Zoom • Write Zoom Pulse-Echo Instrumentation

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Resolution at the DSC 1. Find Matrix size 2. Determine FOV width/length 3. Calculate pixels/cm 4. Find linear distance/pixel resolution Pulse-Echo Instrumentation

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Data Reformatting Data Post- Processing Data Collection Formatting ADC Data Pre- Processing Display RAM Echo Signal Positional Data Pulse-Echo Instrumentation

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1.ROM 2.PROM 3.RAM Pulse-Echo Instrumentation

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65. In Figure 3 transducer A is being used to establish: A. Verification of wedge angle B. Sensitivity calibration C. Resolution D. An index point

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66. In Figure 3 transducer C is being used to check: A. Distance calibration B. Resolution C. Sensitivity calibration D. Verification of wedge angle 67. In Figure 3 transducer D is being used to check: A. Sensitivity calibration B. Distance calibration C. Resolution D. Verification of wedge angle

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68. When the incident angle is chosen to be between the first and second critical angles the ultrasonic wave generated within the part will be: A. Longitudinal B. Shear C. Surface D. Lamb

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69. In Figure 4 transducer B is being used to check: A. The verification of wedge angle B. Resolution C. Sensitivity calibration D. Distance calibration

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Q: In a UT test system where signal amplitudes are displayed on a CRT an advantage of a frequency-independent attenuator over a continuously variable gain control is that: A. the pulse shape distortion is less B. the signal amplitude measured using the attenuator is independent of frequency C. the dynamic range of the system is decreased D. the effect of amplification threshold is avoided Q: An amplifier in which received echo pulses must exceed a certain threshold voltage before they can be indicated might be used to: A. suppress amplifier noise unimportant scatter echoes or small flaw echoes which are of no consequence B. provide a screen display with nearly ideal vertical linearity characteristics C. compensate for the unavoidable effects of material attenuation loss D. provide distance amplitude correction automatically

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Q: The output voltage from a saturated amplifier is: A 180 degrees out of phase from the input voltage B lower than the input voltage C nonlinear with respect to the input voltage D below saturation Q: The transmitted pulse at the output of the pulser usually has a voltage of 100 to 1000V whereas the voltages of the echo at the input of the amplifier are on the order of: A 10 Volts B 50 Volts C .001 to 1 Volts D 1 to 5 Volts

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Q: The intended purpose of the adjustable calibrated attenuator of a UT instrument is to: A control transducer dampening B increase the dynamic range of the instrument C broaden the frequency range D attenuate the voltage applied to the transducer