2: The Ultrasonic System

Question 1

What is a block diagram?

Answer 1

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

Question 2

What material coats the CRT screen?

Answer 2

A phosphorus compound.

Question 3

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

Answer 3

Electrons

Question 4

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

Answer 4

Sweep circuit

Question 5

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

Answer 5

Pulser/pulse generator

Question 6

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?

Answer 6

Sweep circuit (draws the sweep/time base line)

Question 7

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?

Answer 7

Sweep delay

Question 8

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

Answer 8

Sweep range

Question 9

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

Answer 9

Pulse length or dampening

Question 10

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

Answer 10

Pulse repetition rate/frequency

Question 11

What are 3 ways to improve front surface resolution?

Answer 11

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

Question 12

What is meant by piezoelectricity?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

Thinner the crystal = higher the frequency produced.

Question 15

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

Answer 15

Provide means for applying a voltage gradient across the crystal.

Question 16

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

Answer 16

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

Question 17

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

Answer 17

Lithium sulphate

Question 18

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

Answer 18

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

Question 19

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

Answer 19

1. Places load on crystal and damps the ringing.

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What functions can a frontal member on a transducer perform?

Answer 22

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

Question 23

What is a delay shoe used for?

Answer 23

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

Question 24

What is a paintbrush transducer used for?

Answer 24

Fast scanning of large surfaces

Question 25

What is the most important character of if a paintbrush transducer?

Answer 25

Intensity of beam varies very little over entire length of transducer to unsure uniform sensitivity.

Question 26

Advantages of using a double transducer over a single element transducer?

Answer 26

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.

Question 27

How is cross-talk prevented in a double transducer?

Answer 27

A sound barrier

Question 28

What is the usual reason for using a cylindrical lens?

Answer 28

Mostly for contour correction to improve sound transmission.

Question 29

What is the most important purpose for using calibration blocks and reference standards?

Answer 29

Reproducibility of results.

Question 30

What are the 3 general purposes for using calibration blocks and reference standards?

Answer 30

1. Calibration of time base
2. Setting the sensitivity level
3. Verification that equipment is performing as required

Question 31

What do all the blocks in the Alcoa AREA Amplitude set have in common?

Answer 31

All 8 blocks are the same height (3 3/4”) with a constant front-surface to FBH distance of 3”

Question 32

What is different between each block in the Alcoa AREA Amplitude set?

Answer 32

Diameter of FBH is different - ranging from 1/64th of an inch to 8/64th of an inch

Question 33

What is different between each of the blocks in the Alcoa Distance Amplitude set?

Answer 33

Each of the 19 blocks have a different height = different distance from front surface to FBH