8: Film Viewing Conditions Flashcards
On a radiograph, to detect a 2% change in thickness, the density must change by at least what?
2%
What type of material may be used to mask or remove excessive light (edges, glare, etc)
An opaque material
For optimal viewing, lighting around the viewing surface should be limited to around what?
20 lux or 2 ft. candles
A viewer should be capable of transmitting how much visible light through film for proper interpretation?
20 lux (2 ft. candles)
Densities ranging from 3.0 to 4.0
Our ability to detect changes depends on what 3 factors?
- Degree of contrast between light & dark areas
- Distance & angle from eyes to film surface
- Overall brightness transmitted through
“Point size” is a fixed unit size which is…
1/72 of an inch
What are the 2 things that visual size is affected by?
Size constancy and perspective
What would be considered optimal viewing?
Viewing radiograph on a plane perpendicular to film and from 25-650 cm (approx. 10-24”) away.
What will be affected if the radiograph is viewed from any angle besides perpendicular?
Interpretation/visual size
What does noise describe?
Difference in photon interactions or photon spacial distribution across 2 separate areas of film (but smaller size)
What interferes with complete visibility of fine detail?
Noise
Describe the signal to noise ratio:
Ratio of number of photons that reach and interact with film for a given exposure
In general, discontinuities are related to what?
When they occurred
When do inherent discontinuities occur?
As liquid turns to a solid state
Ex. Castings
Processing discontinuities are divided into 2 categories, what are they?
- Primary: rolling, forging, etc.
2. Secondary: heat treating, machining, grinding, etc.
What are in service discontinuities a direct result of?
Continued or over use
Ex. Fatigue, over-stress cracks, wear, etc.
What do hot tears resemble on a radiograph?
Marble
A crack formed in the casting process is referred to as what?
A hot tear
What does shrinkage porosity present itself like on a radiograph of a weld?
Lacy/honey comb
What are the 3 main types of inclusions on welds?
Slag, oxide and tungsten
Where does incomplete penetration form?
Middle of the weld
What welding discontinuity occurs at the toe of weld, paralleling weld toe and immediately adjacent to it?
Undercut
How does lack of fusion and incomplete fusion occur?
In groove/fillet welds and usually oriented parallel to weld direction
When do hot and cold cracks form?
Cold cracks form after solidification and hot cracks form during
