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Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

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Page 1: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Chapter 10Input and Output Devices

Human Performance Engineering

Robert W. Bailey, Ph.D.

Third Edition

Page 2: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Traditional Human Factors or Ergonomics

??

Page 3: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Displays and Controls

Sometimes the distinction is blurred.

Ex. Light switch is a control.

It also functions as a display – the position of the switch conveys information.

Example of misreading displays and misusing controls:

Disaster September 1, 1983. (P255)

Page 4: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Visual Displays

Requirements are developed by combining characteristics of

Human Information Processing with information gathered during task analysis.

Common Visual Displays- ???

Task-related considerations- ???

Page 5: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Designer must decide which sense to use.

Favor visual presentation if:The auditory sense of the user is overburdened.The message is complex and/or long.The message deals with a specific location on a

panel.The message must be referred to later.The user works primarily in one location.The receiving location is so noisy that some

auditory messages may be missed or misheard.

Page 6: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Other Major Considerations:

1. Type of display

2. Information content and format

3. Physical characteristics

Page 7: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Electronic Displays

Cathode Ray Tube – Most Popular

Advantages: High writing speed, high resolution, full color capabilities, full range of gray scales, storage capability, large range of screen sizes.

Disadvantages: Bulkiness of the equipment, curvature of the screen, high voltage required, relatively delicate equipment (vacuum tubes), limitations of maximum screen size.

Page 8: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Flat- Panel- CRT – Some are as thin as 5 cm.

Light–Emitting Diode (LED) – Calculators, wristwatches

Comparison of display technologies in textbook.

Page 9: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Information Coding

Color Coding

Colored lights are generally used in situations that change and where the environment is not fixed.

Lights can also flash on and off as an attention-getting device.

Page 10: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Information Coding

Brightness and rate of flash are only moderately useful when coding information- better to vary only 2 properties : Color and on/off status.

Don’t use color to indicate conditions contrary to what they typically represent.

Page 11: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Table 12-3 Recommended Colors for Alarm and Status Words

Word• 1. active• 2. alarm• 3. clear• 4. critical• 5. disable• 6. emergency• 7. enable• 8. failure• 9. major• 10. minor• 11. normal• 12. off• 13. on• 14. on-line• 15. power• 16. run• 17. standby• 18. stop

Page 12: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Table 12-3 Recommended Colors for Alarm and Status Words

Word Color

1. active green2. alarm red3. clear white4. critical red5. disable red6. emergency red7. enable green8. failure red9. major red

10. minor yellow 11. normal green 12. off black 13. on green 14. on-line green 15. power red 16. run green 17. standby yellow

18. stop red(adapted from Warren, 1980)

Page 13: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

A study of color-coding of displays in nuclear power plant control rooms found that red denoted “on” or “flow” and green denoted “off” or “no-flow” (1978).

Page 14: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Avoid color mismatches such as

“Green” in purple letters

• Tends to slow down identification of its color.

• Slows down reading.

• May impede the performance of concurrent activities.

• Can contribute to misidentification of word or message.

Page 15: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Some people are color blind or color weak.

The color associations in different cultures may be different.China: Red= “On”, Blue= “Off”, White= “Cold”

Do not use colors as the only means for coding.

Page 16: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Size Coding

Small Square vs. Large Square

Dot Coding

One dot – population of 3,000

Two dots- population of 6,000

Page 17: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Geometric Shaped Coding

Circles, Triangles- Road Maps

Redundant Coding

Position, Color, Labels

Page 18: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-4 Traffic light showing redundancy.

Go

Stop

Page 19: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Limit Coded Information

Three Mile Island – over 100 alarms, most of them visual, went off with no way of discerning the unimportant ones from the important ones.

Page 20: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Factors Involved in Selecting a Coding Technique:

1. The kind of information. A lot of information – Alphanumeric, on/off – a light

2. The amount of information to be displayed. Color not practical for many items.

3. The space requirements for the code.4. Ease and accuracy of understanding.5. Interaction of displays at any given time.

Page 21: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Code Compatibility

Good correspondence between the data to be coded and how they are coded.

Ex. Exact quantitative data-> Numbers

Ex. Qualitative data-> Color

Page 22: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Code Discriminability

Permits the observer to distinguish one coded value from another. This requires recognition of the word, character, or symbol used for coding.

Page 23: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Physical Characteristics of Displays

Important scale characteristics1. Scale range – The numerical difference

between the highest and lowest value on a scale.

2. Numbered- Interval value- The numerical difference between adjacent numbers on a scale.

3. Graduation- Interval value- The numerical difference represented by adjacent graduation marks.

Page 24: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-5 Important Scale Characteristics

Page 25: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Scale Selection

Designer should decide on the

appropriate scale range and should

estimate the reading precision required.

Page 26: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-7 Sample Tachometer Dials

Page 27: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

All displays should indicate values in an immediately usable form so that users need not perform a mental conversion.

Page 28: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Scale Design

There must be enough separation between scale indexes to make reading easy.

Page 29: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-10 Sample Quantitative Scales.

Page 30: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Scale Layout

Numbers should ******* in a clockwise direction on circular and curved scales,

from bottom to top on vertical straight scales,

and from left to right on horizontal straight scales.

Page 31: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-11 Examples of Scale Layouts (adapted from Van Cott and Kinkade, 1972)

Page 32: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Zone Marking

Indicate various operating conditions on many indicators such as operating range (upper, lower) or danger limits, caution, etc. The zone marking might be colored coded.

Page 33: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Figure 12-12 Examples of Zone Markings (adapted from Van Cott and Kinkade, 1972)

Page 34: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Auditory Displays – Preferred When:

• The message is relatively short

• Response time to the message is important

• The vision of the user is already overburdened

• The receiving locations is not suitable for the reception of visual information

• The user’s job requires considerable movement

Page 35: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Common use of Auditory Displays- Alarms and Warnings

• Considerable distance-> Loud, but low frequency, readily distinguishable.

• Should cease only after the user responds appropriately to the cause of the alarm.

The sound made by any piece of equipment is to some extent an auditory display. For example, the sounds made by a disk drive when reading or writing a disk.

Page 36: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Controls

Enable a user to make a change in the system and often are used with displays. Ex.: Keyboards, mice, steering wheels, knobs, levers, push buttons, etc.

Page 37: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Controls Serve Four Kinds of Functions:1. Activation- An on and off switch, or some other binary

action. Ex. Pressing keys on keyboard.

2. Discrete Setting – A control set to a position representing any of three or more discrete system responses. Ex. Automobile gear positions

3. Quantitative Settings- Individual settings of a control device that vary along some continuous quantitative dimension. Ex. Volume adjustment on a radio

4. Continuous Control- Constant control of equipment Ex. Steering an automobile.

Page 38: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Consider Foot Controls:

• When the application of moderate-to-

large forces is necessary.

• When the hands are overburdened.

Page 39: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

General Principles for Controls• Critical and frequently used controls should be located

within easy reach.• The force, speed, accuracy, and range of body

movement required to operate a control should never exceed the capability limits of the least capable user.

• The total number of controls should be kept to a minimum.

• Control movements should be as simple, easy, and as natural as possible.

• Control actions should result in a positive indication to the user.

• Control surfaces should be designed to prevent slipping.• Controls should be designed and located to prevent the

probability of accidental operation.

Page 40: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Arrangement of Controls and Displays

User expectation – Make decisions that are consistent with what the user expects.

Page 41: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Population Stereotypes

Control-movement habit patterns that are consistent from person to person without special training or instructions; responses that individuals make most often.

Page 42: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Four General Direction-of- Movement Rules

1. The preferred direction of movement for most hand controls is horizontal, rather than vertical.

2. All the equipment that the same person uses should have the same controls-display motion relationship.

3. Control-Movement relationships are particularly important in vehicle movement. A movement of control to the right should result in a movement to the right, right turn.

Page 43: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Four General Direction-of- Movement Rules

4. The direction of movement of a control should be considered in relation to:

a. The location of the user relative to the control,

b. The position of the display relative to the control, and

c. The change resulting from the control movement.

Page 44: Chapter 10 Input and Output Devices Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

Placement

Controls should be arranged so that a user can see or use them from a normal working position, without excessive shifting of the head or body.