2: The Ultrasonic System Flashcards
What is a block diagram?
An entire circuit stage/section is represented by geometric figures and the path is shown with lines/arrows.
What material coats the CRT screen?
A phosphorus compound.
What kind of particles bombard the oscilloscope to create an image?
Electrons
In a pulse-echo instrument, which circuit produce the base line?
Sweep circuit
In a pulse-echo instrument, which circuit generates a burst of energy that is applied to the sending transducer?
Pulser/pulse generator
In a pulse-echo instrument, which circuit causes a stream of electrons in the CRT to travel back and forth between the HORIZONTAL deflection plates?
Sweep circuit (draws the sweep/time base line)
In a pulse-echo instrument, which control allows one to move the viewing screen along the depth of the test part without changing the distance between pips?
Sweep delay
In a pulse-echo instrument, which control expands or compresses the display on the CRT?
Sweep range
In a pulse-echo instrument, which control may be used to shorten the pulse duration?
Pulse length or dampening
In a pulse-echo instrument, which control may be used to vary how often the pulses are being applied to transducer?
Pulse repetition rate/frequency
What are 3 ways to improve front surface resolution?
Using a broad bandwidth (damped) transducer, decrease pulse length, use a dual transducer or use a delay shoe.
What is meant by piezoelectricity?
Characteristic of certain crystals to generate electrical charges when subjected to mechanical vibrations and reverse.
In a transducer, what is the purpose of a crystal?
It vibrates and produces the mechanical wave that will be transmitted in the material.
How is the thickness of the crystal related to the frequency of the transducer?
Thinner the crystal = higher the frequency produced.
In a transducer, what is the purpose of the electrodes?
Provide means for applying a voltage gradient across the crystal.
Name a material that would make a good transmitter of mechanical energy.
Any of the ceramics such as Lead Zirconate Titanate and Barium Titanate.
Name a material that would make a good receiver of mechanical energy.
Lithium sulphate
List some advantages of quartz and when used as a piezoelectric crystal.
Can operate at high temps, mechanical/electrical stability, insolubility and resistance to aging.
In a transducer, what are the 2 main functions of the backing member?
- Places load on crystal and damps the ringing.
2. The damping material rapidly attenuates energy in backward direction.
What is meant by the mechanical “Q” of a transducer?
The amount of time it rings after the applied electrical pulse is removed.
If the “Q” is reduced, how would that affect the bandwidth of the transducer and its front-surface resolution ability?
Reduction of Q will produce increase in bandwidth and better front-surface resolution.
What functions can a frontal member on a transducer perform?
Different shapes to serve different purposes:
- used as a wear plate/protects crystal (in contact testing)
- improve front-surface resolution/thickness measurements for thin material (as a delay column)
- used as a wedge to produce shear waves
- contoured to improve sound transmission
What is a delay shoe used for?
To improve front-surface resolution and facilitate thickness measurements of thin sections.
What is a paintbrush transducer used for?
Fast scanning of large surfaces
What is the most important character of if a paintbrush transducer?
Intensity of beam varies very little over entire length of transducer to unsure uniform sensitivity.
Advantages of using a double transducer over a single element transducer?
Duals are usually preferred in thickness measurements of thin sections (when near-surface resolution is important) and inspection can be improved by using 2 different crystals.
How is cross-talk prevented in a double transducer?
A sound barrier
What is the usual reason for using a cylindrical lens?
Mostly for contour correction to improve sound transmission.
What is the most important purpose for using calibration blocks and reference standards?
Reproducibility of results.
What are the 3 general purposes for using calibration blocks and reference standards?
- Calibration of time base
- Setting the sensitivity level
- Verification that equipment is performing as required
What do all the blocks in the Alcoa AREA Amplitude set have in common?
All 8 blocks are the same height (3 3/4”) with a constant front-surface to FBH distance of 3”
What is different between each block in the Alcoa AREA Amplitude set?
Diameter of FBH is different - ranging from 1/64th of an inch to 8/64th of an inch
What is different between each of the blocks in the Alcoa Distance Amplitude set?
Each of the 19 blocks have a different height = different distance from front surface to FBH
