2: The Ultrasonic System Flashcards

1
Q

What is a block diagram?

A

An entire circuit stage/section is represented by geometric figures and the path is shown with lines/arrows.

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2
Q

What material coats the CRT screen?

A

A phosphorus compound.

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3
Q

What kind of particles bombard the oscilloscope to create an image?

A

Electrons

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4
Q

In a pulse-echo instrument, which circuit produce the base line?

A

Sweep circuit

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5
Q

In a pulse-echo instrument, which circuit generates a burst of energy that is applied to the sending transducer?

A

Pulser/pulse generator

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6
Q

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?

A

Sweep circuit (draws the sweep/time base line)

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7
Q

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?

A

Sweep delay

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8
Q

In a pulse-echo instrument, which control expands or compresses the display on the CRT?

A

Sweep range

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9
Q

In a pulse-echo instrument, which control may be used to shorten the pulse duration?

A

Pulse length or dampening

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10
Q

In a pulse-echo instrument, which control may be used to vary how often the pulses are being applied to transducer?

A

Pulse repetition rate/frequency

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11
Q

What are 3 ways to improve front surface resolution?

A

Using a broad bandwidth (damped) transducer, decrease pulse length, use a dual transducer or use a delay shoe.

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12
Q

What is meant by piezoelectricity?

A

Characteristic of certain crystals to generate electrical charges when subjected to mechanical vibrations and reverse.

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13
Q

In a transducer, what is the purpose of a crystal?

A

It vibrates and produces the mechanical wave that will be transmitted in the material.

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14
Q

How is the thickness of the crystal related to the frequency of the transducer?

A

Thinner the crystal = higher the frequency produced.

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15
Q

In a transducer, what is the purpose of the electrodes?

A

Provide means for applying a voltage gradient across the crystal.

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16
Q

Name a material that would make a good transmitter of mechanical energy.

A

Any of the ceramics such as Lead Zirconate Titanate and Barium Titanate.

17
Q

Name a material that would make a good receiver of mechanical energy.

A

Lithium sulphate

18
Q

List some advantages of quartz and when used as a piezoelectric crystal.

A

Can operate at high temps, mechanical/electrical stability, insolubility and resistance to aging.

19
Q

In a transducer, what are the 2 main functions of the backing member?

A
  1. Places load on crystal and damps the ringing.

2. The damping material rapidly attenuates energy in backward direction.

20
Q

What is meant by the mechanical “Q” of a transducer?

A

The amount of time it rings after the applied electrical pulse is removed.

21
Q

If the “Q” is reduced, how would that affect the bandwidth of the transducer and its front-surface resolution ability?

A

Reduction of Q will produce increase in bandwidth and better front-surface resolution.

22
Q

What functions can a frontal member on a transducer perform?

A

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
23
Q

What is a delay shoe used for?

A

To improve front-surface resolution and facilitate thickness measurements of thin sections.

24
Q

What is a paintbrush transducer used for?

A

Fast scanning of large surfaces

25
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.
26
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.
27
How is cross-talk prevented in a double transducer?
A sound barrier
28
What is the usual reason for using a cylindrical lens?
Mostly for contour correction to improve sound transmission.
29
What is the most important purpose for using calibration blocks and reference standards?
Reproducibility of results.
30
What are the 3 general purposes for using calibration blocks and reference standards?
1. Calibration of time base 2. Setting the sensitivity level 3. Verification that equipment is performing as required
31
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”
32
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
33
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