Safety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 2: Displays

This European Standard gives guidance on the selection, design and location of displays to avoid potential ergonomic hazards associated with their use. It specifies ergonomics requirements and covers visual, audible and tactile displays.
It applies to displays used in machinery (e.g. devices and installations, control panels, operating and monitoring consoles) for occupational and private use. Specific ergonomics requirements for visual display terminals (VDTs) used for office tasks are given in the standard EN ISO 9241.

Sicherheit von Maschinen - Ergonomische Anforderungen an die Gestaltung von Anzeigen und Stellteilen - Teil 2: Anzeigen

Diese Europäische Norm enthält Empfehlungen über die Auswahl, Gestaltung und Anordnung von Anzeigen, um mögliche ergonomische Gefährdungen, die mit ihrem Gebrauch in Verbindung stehen, zu vermeiden. Es werden ergonomische Anforderungen angegeben und optische, akustische und taktil wahrnehmbare Anzeigen behandelt.
Die vorliegende Norm gilt für Anzeigeeinrichtungen an Maschinen (z. B. Geräten und Anlagen, Instrumententafeln, Steuer- und Überwachungskonsolen) für gewerbliche und private Zwecke. Besondere ergonomische Anforderungen an Bildschirmgeräte für die Büroarbeit sind in der Norm Reihe EN ISO 9241 angegeben.

Sécurité des machines - Spécifications ergonomiques pour la conception des dispositifs de signalisation et des organes de service - Partie 2: Dispositifs de signalisation

La présente norme européenne donne des recommandations sur la sélection, la conception et l'emplacement des
moyens de présentation d'information, de manière à éviter les risques ergonomiques potentiels liés à leur emploi.
Elle spécifie des spécifications ergonomiques et inclut les dispositifs de signalisation visuelle, auditive et tactile.
Elle s'applique aux dispositifs de signalisation utilisés sur les appareils (par exemple machines et installations,
panneaux de commande, consoles d'exploitation et de surveillance) destinés à l'usage professionnel et privé.
Des exigences ergonomiques spécifiques pour les terminaux à écran de visualisation utilisés pour les travaux de
bureau sont données dans la norme EN ISO 9241.

Varnost strojev - Ergonomske zahteve za načrtovanje prikazovalnikov in krmilnih stikal - 2. del: Prikazovalniki

General Information

Status
Published
Publication Date
28-Oct-2008
Current Stage
9093 - Decision to confirm - Review Enquiry

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SLOVENSKI STANDARD
SIST EN 894-2:2000+A1:2009
01-januar-2009
9DUQRVWVWURMHY(UJRQRPVNH]DKWHYH]DQDþUWRYDQMHSULND]RYDOQLNRYLQNUPLOQLK
VWLNDOGHO3ULND]RYDOQLNL

Safety of machinery - Ergonomics requirements for the design of displays and control

actuators - Part 2: Displays
Sicherheit von Maschinen - Ergonomische Anforderungen an die Gestaltung von
Anzeigen und Stellteilen - Teil 2: Anzeigen

Sécurité des machines - Spécifications ergonomiques pour la conception des dispositifs

de signalisation et des organes de service - Partie 2: Dispositifs de signalisation

Ta slovenski standard je istoveten z: EN 894-2:1997+A1:2008
ICS:
13.110 Varnost strojev Safety of machinery
13.180 Ergonomija Ergonomics
SIST EN 894-2:2000+A1:2009 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 894-2:2000+A1:2009
---------------------- Page: 2 ----------------------
SIST EN 894-2:2000+A1:2009
EUROPEAN STANDARD
EN 894-2:1997+A1
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2008
ICS 13.110; 13.180
English Version
Safety of machinery - Ergonomics requirements for the design of
displays and control actuators - Part 2: Displays

Sécurité des machines - Spécifications ergonomiques pour Sicherheit von Maschinen - Ergonomische Anforderungen

la conception des dispositifs de signalisation et des an die Gestaltung von Anzeigen und Stellteilen - Teil 2:

organes de service - Partie 2: Dispositifs de signalisation Anzeigen

This European Standard was approved by CEN on 3 January 1997 and includes Amendment 1 approved by CEN on 14 August 2008.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the CEN Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the

official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
C O M I T É E U R O P É E N D E N O R M A LI S A T I O N
EUR OP ÄIS C HES KOM ITEE FÜR NOR M UN G
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 894-2:1997+A1:2008: E

worldwide for CEN national Members.
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
Contents Page

Foreword..............................................................................................................................................................3

Introduction .........................................................................................................................................................4

1 Scope......................................................................................................................................................4

2 Normative references............................................................................................................................4

3 Definitions..............................................................................................................................................4

4 Visual displays.......................................................................................................................................5

4.1 Requirements for detection of visual displays...................................................................................6

4.1.1 Positioning the display .........................................................................................................................6

4.1.2 Functional relationships between the display and the operator ......................................................7

4.1.3 Environmental factors...........................................................................................................................7

4.1.4 Other conditions to observe for facilitating signal detection ...........................................................8

4.2 Requirements for identification of visual displays ............................................................................8

4.2.1 Symbols used for displays ...................................................................................................................8

4.2.2 Digital displays.....................................................................................................................................10

4.2.3 Analogue displays...............................................................................................................................10

4.2.4 Choice of scales for analogue displays ............................................................................................11

4.2.5 Choice of displays in relation to different types of tasks................................................................14

4.2.6 Grouping displays...............................................................................................................................15

4.3 Requirements for interpretation of visual displays..........................................................................16

5 Auditory displays.................................................................................................................................16

5.1 Requirements for detection of auditory displays.............................................................................17

5.2 Requirements for identification of auditory displays ......................................................................17

5.3 Requirements for interpretation of auditory displays......................................................................17

6 Tactile displays....................................................................................................................................18

6.1 Requirements for detection of tactile displays.................................................................................18

6.2 Requirements for identification of tactile displays ..........................................................................18

6.3 Requirements for interpretation of tactile displays .........................................................................18

Annex A (informative) Shape of digits ............................................................................................................20

Annex ZA (informative) !!!!Relationship between this European Standard and the Essential

Requirements of EU Directive 98/37/EC, amended by 98/79/EC"""" ...............................................21

Annex ZB (informative) !!!!Relationship between this European Standard and the Essential

Requirements of EU Directive 2006/42/EC""...................................................................................22

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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
Foreword

This document (EN 894-2:1997+A1:2008) has been prepared by Technical Committee CEN/TC 122

“Ergonomics”, the secretariat of which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by April 2009, and conflicting national standards shall be withdrawn at the

latest by December 2009.
This document includes Amendment 1, approved by CEN on 2008-08-14.
This document supersedes EN 894-2:1997.

The start and finish of text introduced or altered by amendment is indicated in the text by tags ! "

This European Standard has been prepared under a mandate given to CEN by the European Commission

and the European Free Trade Association, and supports essential requirements of EU Directive(s).

!For relationship with EU Directive(s), see informative Annexes ZA and ZB, which are integral parts of this

document."

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and United Kingdom.
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
Introduction

This standard has been prepared to be a harmonised standard in the sense of the Machinery Directive and

associated EFTA regulations.
1 Scope

This European Standard gives guidance on the selection, design and location of displays to avoid potential

ergonomic hazards associated with their use. It specifies ergonomics requirements and covers visual, audible

and tactile displays.

It applies to displays used in machinery (e.g. devices and installations, control panels, operating and

monitoring consoles) for occupational and private use. Specific ergonomics requirements for visual display

terminals (VDTs) used for office tasks are given in the standard EN ISO 9241.
2 Normative references

This European standard incorporates by dated or undated reference, provisions from other publications.

These normative references are cited at the appropriate places in the text and the publications are listed

hereafter. For dated references subsequent amendments to, or revisions of, any of these publications apply to

this European standard only when incorporated in it by amendment or revision. For undated references the

latest edition of the publication referred to applies.

EN 292-1, Safety of machinery - Basic concepts, general principles for design - Part 1: Basic terminology,

methodology.

EN 292-2, Safety of machinery - Basic concepts, general principles for design - Part 2: Technical principles

and specifications.

EN 457, Safety of machinery – Auditory danger signals – General requirements, design and testing (ISO

7731).

EN 614-1, Safety of machinery – Ergonomics design principles – Part 1: Terminology and general principles.

EN ISO 9241, Ergonomics requirements for office work with visual display terminals (VDTs).

EN 61310-1, Safety of machinery – Indication, marking and actuation – Part 1: Requirements for visual,

auditory and tactile signals (IEC 1310-1).

EN 61310-2, Safety of machinery – Indication, marking and actuation – Part 2: Requirements for marking (IEC

1310-2).
3 Definitions
For the purposes of this European Standard, the following definitions apply:
3.1
operator

the person or persons given the task of installing, operating, adjusting, maintaining, cleaning, repairing or

transporting machinery [EN 292-1]
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
3.2
work task

an activity or activities required to achieve an intended outcome of the work system [EN 614-1]

3.3
work equipment

machinery, tools, vehicles, devices, furniture, installations and other components used in the work system [EN

614-1]
3.4
signal

stimulus related to the status, or change in status, of work equipment which has a potential effect on the

senses of an operator. This European Standard describes signals which may be detected by the eyes (from

visual displays), the ears (from auditory displays), or from the skin (tactile displays)

3.5
display

device for presenting information that can change with the aim of making things visible, audible or

discriminable by touch (tactile)
3.6
digital display
display in which the information is shown in numerical code
3.7
alphanumeric display

display in which the information is shown as a combination of digits and letters.

3.8
analogue display

display in which the status information is shown as a function of length, angle or other dimension. In the case

of visual displays, the information may be shown as a function of pointer deflection, length of a bar graph, or

similar visual quantity. In the case of auditory displays, information may be transmitted as a function of pitch or

loudness. In the case of tactile displays, the information may be transmitted as a function of the display's

vibration (frequency or amplitude), or of the display's displacement.
3.9
symbols

letters, digits, pictorial representations, or combinations of these, used for labelling a display's graduations, or

as a means of identifying the display itself.
3.10
perception

psychophysiological process occurring in the central nervous system, the product of which is knowledge about

the environment. Perception is a dynamic process and is not determined merely by the parameters of the

signals which initiated it. As a consequence, it is possible that the information obtained may be incomplete,

uncertain, or incorrect.

Knowledge may be based on one or more of the following levels of perception: detection, identification, and

interpretation. Detection is the perceptual process by which the operator becomes aware of the mere

presence of a signal. Identification is the perceptual process by which the detected signal is distinguished from

other signals. Interpretation is the combination of perceptual and cognitive processes by which the contents

and significance of the identified signal are recognised.
4 Visual displays

Visual displays can be used to transmit large quantities of information to the operator, in a variety of ways.

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EN 894-2:1997+A1:2008 (E)
4.1 Requirements for detection of visual displays
4.1.1 Positioning the display

The physiological and functional requirements of the operator and the unobstructed lines of sight available

during task performance determine the positioning of the visual display relative to the operator. The size of the

operator's visual field is limited, which in turn limits the number of displays which can be attended to at any

one time.

Two different types of visual task are distinguished: detection tasks and monitoring tasks. Detection tasks are

those where the operator has to be alerted by the system, monitoring tasks are those in which the operator

actively seeks information.

Three zones of decreasing efficiency for visual signal detection are identified for both detection and monitoring

tasks as "Recommended", "Acceptable" and "Not suitable" (see Table 1). The centre-lines of the

"Recommended" and "Acceptable" zones lie in the median plane and correspond with the line of sight, as

shown in figures 1 and 2. In the detection task the line of sight depends on the main centre of attention. For

monitoring tasks displays may be positioned around a line of sight that is at an angle below the horizontal

which is known to be more comfortable for the operator.

The angles presented in these figures are general ergonomic recommendations; it is assumed that the

operator has normal vision, and is able to maintain a relaxed and stable (preferably seated) position, close to

the displays.
Table 1 — Levels of suitability
Level of suitability Significance
A: Recommended This zone shall be used wherever possible
B: Acceptable This zone may be used if the recommended zone
cannot be used
C: Not suitable This zone should not be chosen
Vertical field of vision for detection Horizontal field of vision for detection
Legend: S: Line of sight, direction is imposed by external task requirements
Figure 1 — Detection tasks
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)

Vertical field of vision for monitoring Horizontal field of vision for monitoring

Legend: S : Normal line of sight, 15° to 30° below the horizontal
Figure 2 — Monitoring tasks

Visual displays shall not be positioned outside the "Recommended" and "Acceptable" zones unless

appropriate aids have been provided by the designer. For example additional auditory displays, or other

devices which do not require large changes in the operator's posture. The "Not suitable" zone should only be

used for displays which are not critical for safe operation.

Where the operator's ability to discriminate colour is important for the correct use of displays, the limits of the

"Acceptable" zone must be reduced, because the size of the central visual field (which is sensitive to colour) is

smaller than the field of which is sensitive to white light.
4.1.2 Functional relationships between the display and the operator

In general, these relationships are of two types. The first is where the operator seeks out and observes the

display. The second is where the operator's attention is demanded by the display itself (e.g. flashing warning

or acoustic alarm); or the operator is alerted by one or more types of display (e.g. a combination of visual and

auditory displays); or the operator is alerted by the status of the system to check the display.

For either of these two functional relationships, the most frequently used and/or the most important display

shall have the highest priority for location in the immediate area of the operator's natural line of sight (Zone A).

Lower priority displays may be located towards the periphery of vision (Zone B or even Zone C if necessary).

Conditions which maximise the effectiveness with which alerting or warning displays gain attention shall be

achieved by design. Since the human visual system is sensitive to change in the visual environment, the

designer could choose, for example, a flashing characteristic to alert the operator, as the changing nature of a

flashing display will be readily detected. Note that the flashing characteristic should be coupled with low

luminance to avoid the creation of afterimages in the operator's eyes. Alternatively, it may be useful to couple

an auditory display with a continuous, low luminous intensity visual display.
4.1.3 Environmental factors

The most important environmental factors are illumination and vibration. Special care should be taken to

design displays that compensate for their possible adverse effects.

At workplaces with passive (non light emitting) displays there should be an illumination intensity of at least 200

lx. Where this is not possible, compensatory measures must be taken, e.g. enlargement of the displayed

information, provision of local lighting or active illumination (light-emitting displays). Shadows with high

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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)

contrast or reflections disturb perception and shall be avoided. Thus, room lights which may produce

reflections on displays shall be installed at illumination angles taking account of the typical viewing directions.

Compensatory measures are to incline the displays and/or install non-reflective display surfaces. Light

sources that allow the differentiation of coloured display elements from their background shall be chosen.

Reading performance can be influenced by continuous or peak vibration of the displays, the operator or both.

Low frequency (1 Hz to 3 Hz) vertical vibration of digital displays leads to large reading errors directly

proportional to acceleration at accelerations above 5 m/s .

Reading errors increase with frequencies from 3 Hz to 20 Hz. When operators and displays are

synchronously subjected to vertical vibrations, reading performance is affected least at frequencies below 3

Hz, but will decrease significantly with higher frequencies.

At frequencies between 3 Hz and 20 Hz vertical acceleration greater than 5 m/s decreases reading

performance, and there is a linear dependency between these two parameters. Multiple single axis sinusoidal

vibration can cause a deteriorating reading performance because of interference effects. Dual axis vibration

can result in one rotary movement. Reading errors and reading time will then increase with the vibration

frequency.
Compensatory measures are:
a) A high luminance of the display to improve contrasts beyond the usual level;

b) A stroke width in the direction of the vibration between 5% and 7% of the height of the displayed

characters;

c) A display vibration frequency matching the vibration frequency of the operator.

4.1.4 Other conditions to observe for facilitating signal detection

The operator's line of sight shall be uninterrupted for all ergonomically acceptable working positions, and for

all anthropometric characteristics of the user population.

For good identification, representation in black and white is preferred. However, coding displays with colour

can help detection where symbol density is high, or where the operator must search for specified information.

Surrounding related displays with a single colour can also help to reinforce the link between the displays. See

also EN 61310-1 and EN 61310-2.
4.2 Requirements for identification of visual displays

The image quality of the display shall be high under all normal and emergency observation conditions:

contrast shall be as high as practicable, and confusability between displays (or components of displays) shall

be minimised by using different shapes, colours, labels or any other suitable means for distinguishing one

display from another.

The contrast between symbols, letters, numbers, pointers, lines and their immediate backgrounds and

surroundings shall be sufficient to provide levels of legibility and discriminability which are compatible with the

perceptual speed and accuracy demanded by the task. In the case of light-emitting (active) displays the

contrast ratio (ratio of foreground to background luminance) shall be at least 3:1 to comply with this

requirement; a ratio of 6:1 is recommended. The covers of light-emitting displays shall not reflect other light

sources to any large extent (i.e. the contrast ratio between the reflected light and the surroundings shall be as

low as possible), otherwise the display may appear to be on when it is not or be difficult to read.

4.2.1 Symbols used for displays

For letters and numerals simple and preferably familiar forms are recommended. It is essential to avoid

confusability between characters (e.g. B with 8, 6 with 5; see Annex A). Thus, seven-segment numerals (LED

or LCD) are only acceptable if their use is restricted to representing digits. Depending on the prevailing

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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)

perceptual conditions, 5 x 7 and 7 x 9 dot-matrix characters may be acceptable but larger sizes of matrix shall

be preferred. Where pictorial symbols are used, they shall be simple in form, and easily identified and

interpreted by the population using the display.

Figure 3 defines the important dimensions which relate to character size and proportion. Note that viewing

distance (d) is only one of a number of important factors which will determine appropriate character

dimensions. The level of illuminance, the contrast between characters and background, and the overall

legibility of the characters will all affect these dimensions.
Legend
d: Distance from eye to character
α: Angle of vision of character in arc minutes
h: Height of character
w: Width of character
s: Stroke width of character
Figure 3 — Definition of the dimensions

The recommended character heights (h) are produced when α lies in the range of 18 to 22 arc minutes,

though where α is in the range of 15 to 18 arc minutes, character heights would be acceptable, character

heights produced when α is less than 15 arc minutes are not suitable. Recommended character heights can

be approximately calculated by:

 The recommended range for character width (w) is between 60 % and 80 % of character height. Only

where the display surface is curved, or the viewing angle is oblique should a range between 80 % and

100 % of character height be used. Character width of less than 50 % of character height is not suitable.

 Suitable ranges for stroke width of characters (s in fig 3) are given in Table 2. It is recommended that

appropriate spacing between letters (20 % to 50 % of character width) and between words (1 to 1,5

character widths) is provided.
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
Table 2 — Suitability of different stroke widths of characters
Type of display
Stroke width of character as a percentage of character Suitability level
height
1) 2)
Positive representation Negative representation
Active display from 17 to 20 from 8 to 12 recommended
from 14 to < 17 from 6 to < 8 acceptable
> 12 to 14
from 12 to < 14 from 5 to < 6 conditionally acceptable
> 14 to 15
Passive display from 16 to 17 from 12 to 14 recommended
from 12 to < 16 from 8 to < 12 acceptable
> 14 to 16
from 10 to < 12 conditionally acceptable
> 17 to 20 > 16 to 18
Positive representation: dark characters on a light background
Negative representation: light characters on a dark background
Under particularly favourable viewing conditions
4.2.2 Digital displays

The design of the numerals, and their contrast with the background shall adhere to the recommendations

above. If the digital display is mechanical (the numerals are printed on the rims of rotating wheels), it is

recommended that the numerals shall be fully visible in the display window, and shall not be partially obscured

as the display wheels rotate (e.g. by snap action).

Since digital displays require little space, large digits are practicable, and shall be preferred. Where many

digits must be displayed, reading errors can be minimised by grouping digits into small blocks. Blocks

containing three or two digits shall be preferred, unless interpretation of the display is facilitated by having

more digits per block.
4.2.3 Analogue displays

The index (e.g. pointer, liquid level) shall be visible at all times, even when the index has moved off the scale

itself. The use of displays with a moving index and a fixed scale is recommended. Figure 4 illustrates

appropriate directions of index movement for indicating decreasing and increasing quantities.

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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)
Legend:
a) Increase
b) Decrease
Figure 4 — Appropriate directions of movement for pointers

The scale zero shall be located so that increases are denoted by either left-to-right, clockwise or upward

movement of the pointer, and so that decreases are denoted by right-to-left, anticlockwise or downward

movement of the pointer.
4.2.4 Choice of scales for analogue displays

To achieve good perception and to reduce reading errors, scale dimension, graduation, labelling and pointer

design shall be considered.

The different dimensions of a scale shall be designed according to reading distance and environmental

illumination. Table 2 gives recommendations for scale dimensions under different illumination conditions at a

typical reading distance of 700 mm. For other distances a formula is given below:

x=d⋅tan
Legend:
x: Dimension A to G in Table 3
d: Distance from scale to eye (mm)
α: Angle of vision (arc minutes)

NOTE For ease of calculation x is approximately equal to d⋅ , if L is replaced by the appropriate dimension A

700
to G from Table 3 where the reading distance is 700 mm.
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SIST EN 894-2:2000+A1:2009
EN 894-2:1997+A1:2008 (E)

Table 3 — Graduation mark dimensions for high/normal and low illumination levels for 700 mm

reading distance

Notation from Explanation of High/normal illumination level Low illumination level < 100 lx

figure 5a notation
arc minutes mm arc minutes mm
A Width of major 1,5 0,3 4,5 0,9
graduation
mark
B Width of 1,5 0,3 3,5 0,7
intermediate
graduation
mark
C Width of minor 1,5 0,3 3 0,3
graduation
mark
D Height of major 24 4,9 24 4,9
graduation
mark
E Height of 18 3,7 18 3,7
intermediate
graduation
mark
F Height of minor 12 2,4 12 2,4
graduation
mark
G Minimum
distance
between
adjacent
graduation
marks:
 No divisions
or 2
4 0,8 6 1,2
divisions
 5 divisions
12 2,4 12 2,4

Graduation of scales, as an important way to improve the identification of scale values, shall correspond to the

precision of measurement required, and shall be compatible with the accuracy of the transducer. There shall

not be more than three levels of graduation (major, intermediate and minor). There shall not be more than four

intermediate marks (i.e. five divisions) between two major marks, and there shall not be more than four minor

marks (i.e. five divisions) between two intermediate marks. The measurement interval values between two

minor graduation marks may be 1, 2, 5, or a decimal multiple thereof. Identifiability is not the same for all scale

...

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