Visual Inspection and Basics - Module 2 - Part 3

Question 1

Pre-attentive stage the brain…

Answer 1

focuses on the entire field of vision, not spending a lot of time or energy

Question 2

When we are actively searching for discontinuities and defect indications that we use our…

When we are trying to identify the nature of the indication and evaluate its severity, we use…

Answer 2

…central vision (the area defined by the macula)

…the most sensitive area of our central vision (defined by the fovea).

Question 3

When selecting a scanning rate and pattern, consider the following:

Answer 3

• How large is the indication we are looking for?
The smaller the indication is expected to be, the slower the scan rate and the tighter the space between scans.

• How much contrast will the indication present? Lower contrast will require slower scans.
• How much information is in the central vision area that is not pertinent to the inspection, or how “busy “is the area to be inspected?

Examples of busy visual environments include weld caps, rough surfaces, the presence of wiring, markings and scratches etc. It takes time to identify and classify each thing in our field of vision and we need to slow our scan to allow time for that to happen.

Question 4

With inspection, think of a scan as…

Answer 4

…a grid or matrix…not necessarily a smooth continuous motion. More accurately, a series of repeated movements and hesitations.

Question 5

Perception

Answer 5

the physical and psychological act of detecting and defining indications

Question 6

As our brain processes the data from the field of vision, it breaks it into components such as…

Answer 6

…patterns, colours and shapes.

Question 7

Patterns are viewed as…

_____ lines get prioritized before _______ and ________ lines.

Answer 7

…a unit.

angled…horizontal and vertical

Question 8

______ are prioritized over pattern and colour

Answer 8

angles

Question 9

priorities change when removing the element of…

Answer 9

pattern

Question 10

Patterns, colours, angle changes and their priorities

Answer 10

• Our brain processes data in patterns and single element images differently.
• Changes in patterns are easily recognizable, even more when there are angle changes
that correspond with a change in the pattern.
• Coloured changes stand out well, but not as much as some other image elements like pattern changes or shapes.
• In non-pattern images, our brains prioritize closed shapes, especially circles.

Question 11

the _______ of an indication is easier and more reliably detected than the ________ of an indication.

Answer 11

presence, absence

It can be argued that persistence of vision plays a role in this phenomenon.

Question 12

Weber’s Law

Answer 12

states that when differences exist in the field of vision the bigger the elements are, the bigger the differences need to be in order to detect them.

Question 13

3 Main factors affecting inspections:

Answer 13

• Climate
• Conditions in surrounding areas
• Human factors

Question 14

Aids to Inspection

3 broad categories

Answer 14

• Lighting
• Remote viewing
• Magnification

Question 15

If light levels are too low…

If light levels are too high…

Answer 15

…sufficient contrast is not achieved

…light levels create discomfort and create glare that can reduce contrast. In extreme cases, this can cause eye damage

Question 16

Light around the inspection area that is not added for the purpose of inspection.

Issues

Answer 16

Ambient light

Backlighting

Question 17

flashlights, work lights or lights brought in specifically for an inspection.

Answer 17

Supplemental light

Have the advantage of being directed at specific items making the hesitations in the scan pattern easier to adhere to; the angle can also be adjusted to enhance contrast of fine defects.

Question 18

Angle of viewing and angle of light…

distance of eye

Answer 18

a viewing angle not less than 30 degrees measured from the inspection surface

the eye must be closer than 25 inches, but not so close that the eye cannot focus correctly

Question 19

The predominant reason for angling the light source…

Answer 19

…is to improve the contrast of surface irregularities by introducing shadows.

Question 20

Remote Visual Inspection

also called

most common tool

Answer 20

also called indirect viewing

The mirror is probably the simplest and most common tool used for indirect viewing. Inspection mirrors come in different sizes and shapes. They are commonly mounted to a shaft with a pivot.