Chapter 10Input and Output DevicesHuman Performance Engineering Robert W. Bailey, Ph.D.Third Edition
Traditional Human Factors or Ergonomics??
Displays and ControlsSometimes 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)
Visual DisplaysRequirements are developed by combining characteristics of Human Information Processing with information gathered during task analysis.
Common Visual Displays- ???
Task-related considerations- ???
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.
Other Major Considerations:Type of display
2.Information content and format
Electronic DisplaysCathode Ray Tube Most PopularAdvantages: 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.
Flat- Panel- CRT Some are as thin as 5 cm.
LightEmitting Diode (LED) Calculators, wristwatches
Comparison of display technologies in textbook.
Information CodingColor 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.
Information CodingBrightness and rate of flash are only moderately useful when coding information- better to vary only 2 properties : Color and on/off status.
Dont use color to indicate conditions contrary to what they typically represent.
Table 12-3 Recommended Colors for Alarm and Status WordsWord1. active2. alarm3. clear4. critical5. disable6. emergency7. enable8. failure9. major10. minor11. normal12. off13. on14. on-line15. power16. run17. standby18. stop
Table 12-3 Recommended Colors for Alarm and Status WordsWordColor
1. activegreen2. alarmred3. clearwhite4. criticalred5. disablered6. emergencyred7. enablegreen8. failurered9. majorred 10. minoryellow 11. normalgreen 12. offblack 13. ongreen 14. on-linegreen 15. powerred 16. rungreen 17. standbyyellow18. stopred(adapted from Warren, 1980)
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).
Avoid color mismatches such asGreen 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.
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.
Size CodingSmall Square vs. Large Square
Dot CodingOne dot population of 3,000Two dots- population of 6,000
Geometric Shaped CodingCircles, Triangles- Road Maps
Redundant CodingPosition, Color, Labels
Figure 12-4 Traffic light showing redundancy.GoStop
Limit Coded InformationThree Mile Island over 100 alarms, most of them visual, went off with no way of discerning the unimportant ones from the important ones.
If both information and warning lights are used on a panel, warning lights should be a different color or three to five times brighter than the information lights.
Warning lights should be well within the users range of vision.Three Mile Island- Some of the key visual displays were located on the back of the control panel.
Factors Involved in Selecting a Coding Technique:The kind of information. A lot of information Alphanumeric, on/off a lightThe amount of information to be displayed. Color not practical for many items.The space requirements for the code.Ease and accuracy of understanding.Interaction of displays at any given time.
Code CompatibilityGood correspondence between the data to be coded and how they are coded.
Ex. Exact quantitative data-> NumbersEx. Qualitative data-> Color
Code DiscriminabilityPermits the observer to distinguish one coded value from another. This requires recognition of the word, character, or symbol used for coding.
Physical Characteristics of DisplaysImportant scale characteristicsScale range The numerical difference between the highest and lowest value on a scale.Numbered- Interval value- The numerical difference between adjacent numbers on a scale.Graduation- Interval value- The numerical difference represented by adjacent graduation marks.
Figure 12-5 Important Scale Characteristics
Scale SelectionDesigner should decide on the appropriate scale range and should estimate the reading precision required.
Figure 12-7 Sample Tachometer Dials
All displays should indicate values in an immediately usable form so that users need not perform a mental conversion.
Scale DesignThere must be enough separation between scale indexes to make reading easy.
No Scale InterpolationQuantitative scales should be designed for reading to the nearest graduation mark.Graduation mark for each unitLess space available may be too crowded for accurate and rapid readingA scale that requires interpolation- could increase reading errors
Figure 12-10 Sample Quantitative Scales.
Scale LayoutNumbers 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.
Figure 12-11 Examples of Scale Layouts (adapted from Van Cott and Kinkade, 1972)
Zone MarkingIndicate various operating conditions on many indicators such as operating range (upper, lower) or danger limits, caution, etc. The zone marking might be colored coded.
Figure 12-12 Examples of Zone Markings (adapted from Van Cott and Kinkade, 1972)
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 users job requires considerable movement
Common use of Auditory Displays- Alarms and WarningsConsiderable 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.
ControlsEnable 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.
Controls Serve Four Kinds of Functions: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
Quantitative Settings- Individual settings of a control device that vary along some continuous quantitative dimension. Ex. Volume adjustment on a radio
Continuous Control- Constant control of equipment Ex. Steering an automobile.
Consider Four Areas When Selecting A Control:Function of the control- Purpose, importance, critical, minor adjustment, what does it affectTask requirements- Degree of precision, how fast must the setting be made, emergency controlUser information requirements- Can the user find it, how quickly must user work with it.Work Layout- Where should it be located, availability of space, importance
Consider Foot Controls:
When the application of moderate-to- large forces is necessary.
When the hands are overburdened.
The five most common methods for coding controls are labeling, color, shape, size, and location.
The Choice of Coding Method Depends on the Following Factors:Total demands on the userExtent and methods of coding already in useIllumination of the users workplaceSpeed and accuracy with which controls must be identifiedSpace available for the location of controlsNumber of controls to be coded
The simplest way to indicate a control is to label it.
General Recommendations for LabelingLocate labels systematically in relation to controlsDesign labels to tell what is being controlledMake labels briefOnly employ unusual technical terms when absolutely necessaryDo not use abstract symbolsUse a letter and number style that is easily readableLocate labels so they can be easily seen
Color CodingMost effective when a specific meaning can be attached to the color
Shape, Size, and LocationOther ways to code controls
Especially useful when controls must be identified without the use of vision.
General Principles for ControlsCritical 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.
Arrangement of Controls and DisplaysUser expectation Make decisions that are consistent with what the user expects.
GroupingWhen using a large number of controls and displays grouping should aid in determining:
Which control affects which display
Which control affects which equipment component
Which equipment component is described by each display
Population StereotypesControl-movement habit patterns that are consistent from person to person without special training or instructions; responses that individuals make most often.
Four General Direction-of- Movement RulesThe preferred direction of movement for most hand controls is horizontal, rather than vertical.
All the equipment that the same person uses should have the same controls-display motion relationship.
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.
Four General Direction-of- Movement Rules4. The direction of movement of a control should be considered in relation to:The location of the user relative to the control,The position of the display relative to the control, andThe change resulting from the control movement.
PlacementControls 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.
The workplace design processDetermining GoalsImproving performance
Help ensure the health and safety of the user
Identifying Constraints- Budget, space
User Profile- Age, enthusiastic, skeptical
Activity Analysis What do users do all day
Selecting Furniture- Ergonomically designed
Workplace Layout- Consider personal preferences
Evaluating the environment- Light, noise, temperature
Workplace Testing- Productivity and satisfaction