as rosetta stone (animazione) con logo rev.1 ufficiale
TRANSCRIPT
Overview through Article by James.W.Houf, Harmon Distance,
NAS410 Rev.2 and 3
UnderstandingNear Vision Eye Tests
by M.F.Bianchi & M.Capriolo Bytest SVM & ASVM in Nadcap NDT Task Group
1
Rosetta StoneThe Rosetta Stone is an Ancient Egyptian artifact which was instrumental in advancing modern understanding of Egyptian hieroglyphic writing. The stone is a Ptolemaic era stele with carved text made up of three translations of a single passage: two in Egyptian language scripts (hieroglyphic and Demotic) and one in classical Greek. It was created in 196 BC, discovered by the French in 1799 at Rosetta and contributed greatly to the deciphering of the principles of hieroglyph writing in 1822 by the British scientist Thomas Young and the French scholar Jean-Francois Champollion. Comparative translation of the stone assisted in understanding many previously undecipherable examples of hieroglyphic writing. The text on the stone is a decree from Ptolemy V, describing the repeal of various taxes and instructions to erect statues in temples.
from: en.wikipedia.org/wiki/Rosetta_Stone
For Egyptian hieroglyphic writing :
2
as Rosetta Stone for us !
by James W.Houf, Senior Manager, Technical Services Department, ASNT, Columbus, OH 43228. (800) 222-2768, [email protected]
For Visual Acuity Test finally:
Thank you, Mr. Houf !
3
Jaeger
Times New Roman
SNELLEN
TIMES NEWROMAN
JAGER
What means “20/20” and “20/30” ?
5’ = (1/12)°
6/6 = 20/20
9/9 = 20/20
6/9 = 20/30
5’ = (1/12)°
4
from
J.W.Houf
article
5 minutes
(20/30 )
Character size for 20/20 according to Snellen technique
C = 2 D x tg(2.5’) = 0.00145 x D
5
• D is distance from eye lens to reading chart.
• C is the size of character to be read.
( ) )'5.2(2/'52/
tgtgD
C ==
)'5.2(2/ tgDC ⋅=
)'5.2(2 tgDC ⋅⋅=
60’:1°=2.5’:X, and X=2.5/60= 1/24 – the tangent is 0.000725
Some important highlights
6
from
J.W.Houf
article
Jaeger versus Snellen (and Times Roman)
Each viewing distance requires specific character sizeThat means that SNT-TC-1A requires J2 at 20”, J1 at 15” and a character whose size is 12xJ1size/15 at 12”.In standard Jaeger chart we will see that this is equivalent to 20/20 Snellen that is more severe than 20/25 according to NAS410 Rev.3.
mm
Jaeger versus Snellen20/20 if chart is held
at this distance:
7
from
J.W.Houf
article
5’ = (1/12)°
NAS410 Rev.2 according to Snellen technique
12”/15” = 20/2515” viewing distance J 1
12”
Jaeger #1 (D15”)
0.58 mm
0.56 mm
12” x 2.54 = 30.48 cm 30 cm
8
Actual measurement from
5’ = (1/12)°
NAS410 Rev.3 according to Snellen technique
16”/20” = 20/2516”
16” x 2.54 = 40.64 cm 41 cm < 42 cmEffect of this wrong conversion is not very severe but•NAS410 Rev.3•AC7114•pr4179:2008should be emended.
Jaeger #2 (D20”)
0.71 mm
0.76 mm
9
20” viewing distance J 2
Actual measurement from
mm
So this is the effect of change in NAS410 !
12”/15” = 20/25 Snellen
16”/20” = 20/25 Snellen
Jaeger #2 (D20”)
0.71 mm
0.76 mm
Jaeger #1 (D15”)
0.58 mm
0.56 mm
Note: where 15” is applied (16-1”) 20/27 Snellen is permitted
10
6.5’ = 0.108°
16”12”
But do you know Harmon Distance ?
HD
HD
11
Do all near point activity at HARMON distance of slightly further. This is the distance from the centre of the middle knuckle to the centre of the elbow measured on the outside of the arm. Working at the Harmon distance reduces near point visual stress.There is a lot of Web sites
speaking about “Harmon Distance”; your optometrist knows it and, generally, is surprised for mandatory viewing distance !The square above comes from “Visual Hygiene” on www.optometryatcooroy.com.au/about_visual_hygiene.html
Har
mo
n D
ista
nce
can
be
app
lied
NAS410 Rev.2: “Jaeger No. 1 or equivalent, not less than 3O cm / 12 inches”
SNT-TC-1A: “…. The applicant is capable of reading a minimum of Jaeger Number 2…at a distance designated on the chart but not less than 12 inches (30.5 cm) on a standard Jaeger test chart”
Harmon Distance (HD) versus Inspector Heigth
12
y = 39 cm (HD) y = 43 cm (HD) y 47 cm (HD)x = 152 cm x = 164 cm x = 182 cm x 200 cmy = 36 cm (HD)
y = 0,2325x + 0,7456
30
35
40
45
50
55
130 140 150 160 170 180 190 200 210 220 230
y = Harmon Distance (cm)
x = Inspector Heigth (cm)
Area of NAS410 Rev.3requirement LONG
ARM
SHORTARM STD
ARM
Except for anomalous arm length....
…….NAS410 Rev.3 seems to favour inspectors whose heigth range from 161 cm to 183 cm !
Why?
What means “or equivalent as determined bythe Responsible Level 3” as established by NAS410 Rev.3 ?
Question: Is Equivalence established in last column correct where Visual Acuity is tested using “Times new roman As Printed And Measured” Chart supplied in the following slide ?14
TAPAM Chart=
Times new romanAs Printed And
Measured Chart
15
=J1
<J2
ISO9712 at D 12”
20/25 at D=8” 20/25 at D=10”
Important Remark: Chart can be printed as file word using as resolution as possible by a standard printer (e.g. 1200 dpi by home printer HP PSC1500 as shown in following pictures) and measured by lens x7 at least to determine actual C.
20/25 at D=12”
20/25 at D=13” 20/24 at D=16” 20/24 at D=18” 20/26 at D=20”>J3
EN473 at D 12”
SNT-TC-1A at D=20”
What’s the reason to inspect at low distance ?(Example)
16
Indication to be detected (0.2 mm or less !) without any minimum size to be disregarded
For Snellen 20/20 D = C / 0.00145 = 1/0.00145= 690 - C For Snellen 20/25 D = C x 690 x( 20 / 25) = 552 For porosity above Snellen 20/25 is obtained at 552 x0.2 = 110 mm = 4.34 inches ! (distance at which the 5’ are subtended for the found indication)
Obviously this is a typical situation where magnification lens shall be used but for preliminary detection of a large amount of production continuous use of lens cannot be practice. Can the responsible level 3 in this actual condition consider “effective”vision acuity performed ?
Criticaldensity range
1.8
3.7
Steel with high amount of tungsten
Mild steel
EBW
X ray
TAPAM Chart is just one of possible charts that can be proposed using any other kind of
optotipe or glifo
5 X
X
X
X
X
X
The most important thing is define feature principles as spatial resolution as possible by Snellen “E” where arms and spaces is equal-sized(as double-wire IQI for DR and CR !).
17
E Snellen Character where x is equal to 1 minute of arc
Conclusion
NAS 410 Rev.3 Visual Acuity Requirement should establish:
1. Which character size should be readable at 16±1”
2. Equivalence of character 0.7366 mm in size with Jaeger #2 at 20” as shown, for example, by Western Optical® reading card sold by ASNT, that means that J2 in this card can be used as target for Visual Acuity Test at 16”.
3. The range for “equivalency to be determined by Responsible Level 3” that should decide variations from standard requirement based on 20/25 (Snellen) as J3 at 20” or J1 at 12” or character 0.41 mm in size at 9” or any other condition considered as reliable for specific kind of inspection taking into account Harmon distance also where possible.
18
