ECE 796896 Human Factor Engineering

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ECE 796/896Human Factor Engineering

• Chapters 16,17,18,19
• Light,climate,noise,motion

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Illumination

• 380-780 nm spectrum
• Eyes are most sensitive to about 550nm
• 2 sources luminescent incandescent bodies
• Natural color - color of an object under white
  light.
• An objects color - dominant wavelength,
  luminance, and saturation

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Measurement of Light

• Photometry - is the measurement of light.
• Unit is Candela (cd) 1 cd 12.57 lm
• 100W bulb 1740 lm
• 1lm/sq.ft. 1 (fc) foot candle
• Lluminance(lx) (cd)/D2
• Dist. In meters D

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Cont.

• Reflectance luminance(fl)/illuminance(fc)

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Tab16.1
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Lamps and Luminaires

• Luminaire is a device that consists of lamps and
  components for distributing the light.
• Lamp is an artificial light source.

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Lamps

• Two types, Incandescent filament lamp and
  gas-discharge lamp.
• Gas discharge have three types - high-intensity
  discharge (HID), mercury, metal halide, high
  pressure sodium, low pressure sodium and
  fluorescent lamps.
• Fluorescent lamps produce ultraviolet that excite
  a phosphor coating.

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Cont.

• Lamp Color CRI (color rendering index)
• As CRI increases color judgment errors decrease.
• Energy Considerations lamp efficacy amount of
  light produced per unit of power consumed.
• Fluorescent vs. incandescent lasts 20 times
  longer, uses 41 less energy, and give 30 more
  light.

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Tab16.2
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Effect of Lighting on Performance

• Both field and laboratory studies.
• Visually difficult tasks are effected more by
  lighting levels than visually easy tasks.
• Speed improvement noted by over 50 with lighting
  level changes.

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Luminance - Glare

• Glare is caused by brightness in the field of
  view that is greater than the luminance to which
  the eye is adapted, so as to cause discomfort and
  annoyance.
• Direct or reflected glare
• Reflected - spread,specular, diffuse,compound.

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Glare - Cont.

• Discomfort, disability and blinding.
• Discomfort A measure Borderline between comfort
  and discomfort (BCD)
• The higher the BCD the less glaring was the
  source or less sensitive was the person.
• DGR Discomfort Glare Rating- can be converted
  to VCP (visual comfort prob)

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Disability glare

• Glare the directly effects visibility and visual
  performance is Disability glare.

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Reducing Glare

• Reduce direct glare from luminaires.
• Select with low DGR, reduce the luminance of
  sources, position far from line-of-sight,
  increase luminance around glare source
• Reduce direct glare from windows
• Set above floors, overhang above window outside
• Reduce reflected glare
• Keep luminance level low as possible for
  luminaries, small light sources, diffuse light,
  use surfaces that diffuse light

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Computer terminals

• 1. Frosting or etching of front surface to reduce
  specular reflections.
• 2. Quarter wave thin-film coatings
• 3. Neutral-density filters
• 4. Circular polarizers
• 5. Micromesh filters

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Chapter 17

• Climate

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Heat Exchange

• Avenues of Heat Exchange
• 1. Conduction Heat transfer by direct contact.
• 2. Convection Transfer of heat by currents of
  air.
• 3. Radiation Transmission of heat between
  objects by electromagnetic radiation.
• 4. Evaporation perspiration converted to vapor.

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Heat Exchange Equation

• DS (M-W) - R - C - E
• Where
• DS change in body heat content.
• M metabolism, W work performed, R radiative
  heat exchange, C Convective, and E evaporative
  heat loss
• If the body is in equilibrium -gt DS0

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Fig 17.1
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Environmental Factors Influencing Heat Exchange

• Air temperature, air flow, humidity, temperature
  of the surroundings.
• Effects of clothing Insulation provided by air
  trapped inside the weavings of the fabric.
• CLO measure of insulation necessary to maintain
  comfort - 70F and 50. 1 CLO can effect a 16
  degree temp change. Eskimo 12.

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Measurement of Thermal conditions

• Dry-bulb temperature, relatively humidity,
  hydrometer, wet-bulb temperature, mean radiant
  temperature, and air velocity.

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Cont.

• Effective Temperature (et - et) two indices,
  combinations of temperature, humidity, air
  movement that has equal sensation of warmth. ET
  has a more complex equation shown on the
  following graph.

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17.2
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Other Factors

• Oxford Index WD.85WB.15DB
• WB wet bulb, DB Dry bulb
• Wet-Bulb Globe Temperature
• WBGT .7NWB .3GT
• Botsball BB WBGT - 3 degrees

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The effect of Heat on Work

• As external temperature increases, heart rate
  increases to increase blood flow to the skin to
  cool.
• This can also cause a shortage of blood to
  muscles and essentially cause a longer amount of
  time to recovery from work.
• Sweat is necessary when convection and radiation
  does not cool a person.

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Heat Illness

• 1. Heat rash prickly heat
• 2. Heat Cramps salt loss
• 3. Heat Exhaustion dehydration
• 4. Heat Stroke sweat production loss
• Fitness,aging,gender,body fat, alcohol

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Cognitive and Perceptual Motor Performance

• As temperature - WBGT increases the performance
  decreases steadily.

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17.11
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17.12
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Reducing Heat Stress

• Easiest way to reduce heat stress is cool the
  environment and lower the humidity.
• Reducing the energy needed for a task is another
  way of lowering heat stress.

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Cold Stress

• Most workers that work outside in cool weather
  can dress properly. Most people who have work
  related cold weather usually have problems when
  vehicles break down or they are somehow stranded
  in the weather without protection.

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Index of cold Stress - wind chill

• Wind chill Index or its derivative, equivalent
  wind chill index temperature.
• Index not used , the modified temp used.

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Tab17.3
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Cold Performance

• Manual Performance is related to skin
  temperature.
• Tactile Sensitivity adversely effected by cold.

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Chapter 18

• Noise

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Sound Level Meter Scales

• Meters have scales A,B,C,D
• Psychophysical Indicies
• Physical properties
• Psychological properties
• Phon decibel level of the 1000 hz tone
• Ex 60db sound at 1000Hz 60 phons

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Noise and Loss of Hearing

• Deafness Nerve and Conduction.
• Nerve deafness is a deterioration of the hairs in
  the organ of Corti.
• Conduction some blockage of the transmission of
  sound to the inner ear.

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Measuring Hearing

• 500,1000,2000,3000,4000,6000,8000hz
• Presbycusis hearing loss due to aging.
• Sociocusis hearing due to non-normal cause.

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Occupational Hearing Loss

• Temporary loss from continuous noise
• 2 min after the exposure, temporary shift
  (TTS)
• . Permanent loss from continuous noise
• (PTS) permanent threshold shift

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Effects of Noise on Performance

• General Conclusions
• With the exception of tasks requiring the use of
  short-term-memory it takes noise in excess of
  95db.
• Performance of routine tasks show no effect of
  noise.
• If a person has to react to a signal at a
  definite time, performance will be good even at
  high noise.

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Cont.

• Visual acuity are not effected by noise.
• Motor performance is rarely effected.
• Simple reaction time is unimpaired.
• Noise tends to have the most effect on continuous
  tasks without rest.

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Noise Exposure Limits

• OSHA has established noise guidelines
• TWA 8h time weighted average sound level.
• Noise dose level of 50 percent ( TWA85dba) as
  the ACTION level.

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Tab 18.3
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Tab 18.4
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Noise Control

• Control at the Source
• Selecting quieter equipment, damping out noise
• Control along the Path
• High frequency noise can be controlled through
  barriers
• Control at the ReceiverHearing protection devices

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Chapter 19

• Motion

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Motion Senses

• Exteroceptors - eyes, ears
• Proprioceptors a class of these are Kinesthetic
  receptors.
• Semi-circular canalsIn each ear that form a
  rough 3D coordinate system.
• Utricle and Saccule Utricle(V), Saccule(H),
  triggers nerve impulses via hair cells.

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Motion - Vibration

• Visual data will override other motion/position
  senses.
• Vibration Attenuation/Amplification and
  Resonance.
• Human resonance 3-5hz (neck,back,shoulder),
  20-30(head-shoulders),60-90 eyes.

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Health Effects of Vibration

• Long term effects
• Pain in chest and abdomen (4-10hz)
• Backaches, (8-12hz)
• Headaches,eyestrain (10-20hz)
• Visual performance (10-25hz)
• Whole body

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19.6
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Limits of Body Exposure

• ISO 2631 (1978,1982a,1982b) Fatigue decreased
  proficiency at tasks.
• Standard has criticisms the details

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Acceleration

• Acceleration can cause vision distortion and
  blackout.
• Measured in Gs ( times the force of gravity)
• 2G - increase in wt. (Z)
• 3-4 Impossible to raise oneself, hard to raise
  legs and arms.
• 5-6, tunnel vision, after 5 secs loss of
  consciousness, convulsions if continued.

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Cont.

• Forward acceleration
• 2-3 abdominal pressure
• 3-6 tightness in chest, hard to breath,blurring
  of vision
• 6-9 increased chest pain, body parts cant be
  lifted
• 9-12 fatigue, loss of peripheral vision
• 12-15 loss of vision, speaking difficult

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19.13
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Motion Sickness

• Connected to most forms of travel.
• People who are motion sick with one form of
  transportation are most likely susceptible to all
  others except space sickness.
• Symptoms Headaches, nausea.
• Cause Sensory rearrangement theory, incongruity
  among the spatial senses.

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Cont.

• For it to be considered motion sickness the
  vestibular (semicircular canals, etc) must be
  implicated and that implies acceleration.
• 2 classes of sensory rearrangement
• Visual-inertia and canal-otolith
• Both these do two things to cause the sickness .
• 1. Both systems simultaneously signal
  contradictory information.
• 2. One system signals the absence of an expected
  signal.

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Cont.

• Simulator Sickness
• Non-moving simulators (driving , flying), exhibit
  motion sickness like symptoms in users.
• Appears to be connected to wide-field-of-view,
  realistic out-of-window scenes and visual and
  simulator-system delays.
• Incongruity between visual and vestibular senses,
  or what is experienced by the sense vs. what is
  expected-by-the senses.