ML20198B090

Issue a to DD-CRT-1, Design Directive for CRT Selection

ML20198B090
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/06/1983
From:	PUBLIC SERVICE CO. OF COLORADO
To:
Shared Package
ML20198B035	List: ML20198B030 ML20198B069 ML20198B073 ML20198B090 ML20198B123 ML20198B132 ML20198B141 ML20198B146 ML20198B152
References
DD-CRT-1, NUDOCS 8511060291
Download: ML20198B090 (5)

Text

, PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION DD-CRT-1

• ISSUE A Page 1 of 5 DESIGN DIRECTIVE FOR CATHODE RAY TUBE SELECTION PRE , Y: REVIEWED BY: APPROVED BY:

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FOREWORD: Cathode Ray Tubes (CRTs) providing interface between the computer output and operating personnel shall be selected for maximum readability. While software generation, CRT location and room lighting conditions are important considerations in determining readability, the factors given in this Design Ofrective shall be applied in the FSV Control Room.

Where given factors are contingent upon software, location, and room lighting conditions, the associated Design Directives are to be evaluated in conjunction with this directive prior to selecting or specifying CRTs.

SELECTION CONSIDERATIONS I. SCREEN LUMINANCE - The following screen background considerations for ambient light environments are preferred; however, where conformity to existing installations is a consideration, only the contrast ration must be met.

A. For low to medium ambient illumination environments (typically 5 to 20 footcandles), utilize light characters on a dark background, with a screen luminance of 23 foot lambert (ft-L) minimum and 45 ft-L preferred.

Contract between light characters and a dark screen background shall be 15:1 minimum and 20:1 preferred, in 20 ft-L of ambient light.

B. For medium to high ambient illumination environm1nts (typically 20 and above footcandles), utilize dark characters on a light background, with a screen background luminance of 23 foot-Lamberts (ft-L) minimum and 46 ft-L preferred.

Contrast between dark characters and a light screen background shall be 1:15 ft-L minimum and 1:20 preferred, in 20 ft-L cf ambient light.

8511060291 851029 PDR ADOCK 05000267 F PDR

PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION

' DD-CRT-1 ISSUE A Page 2 of 5 II. GEOMETRIC DISTORTION -

The cumulative effects of all geometric distortion shall not displace any point within the viewable area of the screen from its correct position by more than 5% of picture height.

III. RESOLUTION -

Discrimination of fine detail is a function of the number of scan lines or addressable points

(" resolution elements") per unit length.

O

.) A. CRTs for displaying simple aplha-numeric text shall have a minimum of 20 resolution elements per inch.

8. CRTs for displaying complex symbols and graphic detail shall have a minimum of 100 resolution elements per inch.

C. Complex symbols which must be distinguished from other complex shapes shall have a minimum of 10 resolution elements for the longest dimension of the

. symbol.

h D. Alpha-numeric characters shall have a minimum of 10 resolution elements per character height.

IV. REGENERATION RATE - The regeneration rate for a particular CRT display shall be above the critical frequency at s fusion so that the occurrence of disturbing flicker is not perceptible.

V. SYMBOLS AND CHARACTERS The dimensional factors of data displayed on a CRT take on greator significance because of the movement of operators from cne benchboard position to another in a control room or other operating area. Distance from the operator to the screen is, therefore, variable, and must be taken into account during CRT selection. As an operator's distance from the CRT increases, the perceived dimensicns of CRT characters, symbols, spacing, etc. decreases proportionately because of a reduction of the " visual angle" (see figure 1). This is the vertical angle subtented at the eye by a viewed object, symbol, or character, utually expressed in minutes of arc. For visual angles less than 600 minutes, this relationship is shown by:

(57.3) (60) L a=

0 FORM 372 22 3643

PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION g, ,

ISSUE A Page 3 of 5 where "L" is measured perpendicular to the line of sight.

Under optimum conditions (illumination, contrast, etc.)

the human eye can identify characters of the alphabet at visual angles of 5 minutes of arc (defining 20:20 vision).

Since presentations on CRT displays in an operational environment do not approach the optimum conditions of vision testing, this lower level must be increased.

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% VISUAL ANGLE (4 LENGTH (L) b'p ~

f-I (DISTANCE (D) l FIGURE 1 Visual angle as a function of

. distance and character size.

A. SYMBOL SIZE -

When a displayed symbol of complex shape is to be distinguished from another symbol shape that is also complex, the visual angle of the symbol shall subtend not less than 20 minutes of arc at the required viewing distance.

B. ALPHA-NUMERIC CHARACTER SIZE

1. The height of alpha-numberic characters shall have a visual angle of not less than 12 minutes of arc at the required viewing distance.

2. Alpha-numberic characters should be uppercase letters. .

C. CHARACTER WIDTH-TO-HEIGHT RATIO -

The width-to-height ration for alpha-numerics shall be between 3:5 and 1:1.

D. LINE (or dot) WIDTH-TO-CHARACTER-HEIGHT RATIO - line (or dot) width-to-character-height ratio shall be between 1:5 and 1:10.

E. GRAPHICS -

A graphic line will appear continuous if the separation between addressable points, or resolution elements, is less than one minute of arc.

To provide the illusion of continuity, graphic lines shall contain a minimum of 50 resolution elements per inch.

PorM 372 22 3643

PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION DD-GT-1 ISSUE A Page 4 of 5 F. CHARACTER AND SYMBOL SEPARATION

1. Horizontal separation between characters or symbols shall be between 10*.' and 65% of character or symbol height.

2. Separation shall be not less than 25% of character or symbol height when any of the following degraded conditions exists:

When character or symbol width is less than 85% of height; When character or symbol luminance is less than 12 ft-L; When luminance contrast is less than 88%;

When CRT screen location is greater than 35' to the left or right of the operator's straight-ahead line of sight; When the visual angle subtended by symbol height is less than 15 minutes of arc; When the visual angle subtended by character height is less than 12 minutes of arc.

G. CHARACTER SYTLE (FONT)

1. Simple character fonts shall be used, with no serifs, variable stroke widths, slanting, etc.

2. When dot-matrix characters are used, a 5x7 dot matrix is considered a minimum with a 7x9 matrix preferred.

3. Character styles such as Lincoln / Mitre or Leroy shall be used.

VI. CRT DISPLAY CONTROLS A. Luminance (brightness), and contrast controls shall be visible and accessible from the operator's position. (control location behind hinged panels is acceptable, provided the panel when open, does not restrict operator access or vision.)

POMM 372 22 3643

l PUBLIC SERVICE COMPANY 'OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION gg_gg7,7 ISSUE A Page 5 of 5 1

8. A deguassing control shall be visible and accessible from the operator's position, if manually actuated daguassing is required as a part of routine operation.

C. Operator controls shall conform to the following guidelines:

1. The minimum distance between the outermost gripping surface of any rotary control and any other control or panel structure shall be one (1) inch.

2. The minimum distance between the outermost circumferential edge of any pushbutton and other control or panel structure shall be one-half (1/2) inch.

3. Rotary knob length shall be a minimum of five-eighths (5/8) inch in length.

4. Rotary knob mean diameter shall be minimum of one-half (1/2) inch.

ASSOCIATED DIRECTIVES 00-00 Requirements and Guidance for Preparing Design Directives DD-CRL Cathode Ray Tube Location DD-SLS Screen Layout and Structuring SOURCE MATERIALS AND REFERENCES NUREG-0700 Human Factors in Engineering, McCormick, 1976 FORM J72 22 364