Mind map

Measurement Principles

Rhianna Bromwich English

Map content

Sensors and measurement
- Sensitivity -- measure of the chnage in output of a sensor for a unit change in input
  - Can be obtained from the gradient of a graph of output as a function of input
- Accuracy -- a measure of how close the measured value is to the true value
- Repeatability -- a measure of the similarity of output values when the same input is applied repetitively
- Resolution -- the smallest change in output that will produce a detectable change in the output of a sensor at a particular point in its active range
- Potential -- the ability of a charge to do the work of moving another charge by attraction or repulsion
- Potential difference -- the work which must be done against electrical forces to move a unit of charge from one point to another
- Current -- rate of movement of electrical charge
- V = IR
- Series circuit rules:
  - Rtotal = R1+R2 +...+Rn
  - Vtotal = V1+V2+...+Vn
  - V1 = I*R1 etc.
  - Current at all parts of the circuit is the same
- Parallel circuit rules:
  - Vtotal = V1 = V2 = Vn
  - Itotal = I1+I2+...+In
  - I1 = V1/R1
  - 1/Rtotal = 1/R1+1/R2+...+1/Rn
  - Voltage drop across each branch will be the same
- Sensor use in sport tech:
  - 1. Temperature measurement
    - Conduction -- transfer of heat within a substance or between substances through interaction
    - Convection -- heat transfer within fluid by the movement of heated molecules from one place to another
    - Radiation -- heat transfer in form of electromagnetic waves (usually infrared)
  - 2. Strain gauges
  - 3. Piezoelectric sensors
    - Piezoelectric material (quartz) generates electric potential when subjected to a force
  - 4. Pressure distribution
- Measuring temperature:
  - 1. Thermocouples
  - 2. Resistance thermometers
  - 3. Thermistor
  - 4. Radiation pyrometer
  - 5. Thermogrsphic camers
- Error in strain gauge measurement:
  - 1. Bonding faults
  - 2. Hysteresis
  - 3. Cross-sensitivity
  - 4. Moisture
  - 5. Temperature
Metrology
- SI base units:
  - Length (metre)
  - Mass (kg)
  - Time (seconds)
  - Current (ampere)
  - Temperature (kelvin)
  - Mole
  - Candela
- Accuracy -- a qualitive term that describes how close the measurements are to their actual value
- Precision -- the degree to which repeated measurements under the same conditions show the same reuslts
- Atomic clocks -- most accurate time and frequency standards known
- Human reaction time = 0.2s
- Line standards -- length measurmed between the centres of two engraved lines e.g. metre
- End standards -- length measured between ends e.g. gauge blocks
- Roundess -- amount of deviation of a circular feature from a geometrically exact circle
- Measuring roundess:
  - 1. Diameter method
  - 2. Vee-block method
  - 3. Radius method
- Roundess evaluation methods:
  - 1. Maximum inscribed circle (MIC)
  - 2. Minimum circumscribed circle (MCC)
  - 3. Minimum zone circle (MZ)
  - 4. Least sqaure circle (LSC)
- Fatigue life -- repeated reversal of stress causes fatigue
- Bearings -- a perfect surface with no irregularities would not be a good bearing
- Rate of wear is dependent on the surface area of the matieral contact
- Types of surface texture:
  - 1. Roughness
    - Closely seperaterd irregularities arising from the inherent action of the cutting process
  - 2. Waviness
    - The irregularities caused by machine vibration an deflections under cutting force
  - 3. Errors of form
    - The departure from the geometrical shape
- Error -- difference between an induvidual reuslt and the true value of the measured value
- Systematic error -- can be controlled and eliminated
- Random error -- caused by unknown and unpredictable changes in the experiment
- Deformation causes:
  - 1. Due to the force exerted to the test piece by the measurement instrument
  - 2. The method of support used for the test item
  - 3. The method of support of the measurement istrument
- Airy point -- two point support and make the end faces parallel
- Bessel point -- two point support and minimise the change in overall length
- Sine error -- magnification of angular error over distance
- Absolute error -- range of measurements in which true valye of measurement lies
Human Performance
- Inertia parameters:
  - 1. Mass
  - 2. Length
  - 3. CoM location
  - 4. Moment of inertia
- CoM -- position where the entire mass of a body considered to be concentrated
- Moment of inertia (MOI) -- distribution of mass about the axis of rotation
- Model assumptions:
  - 1. Rigid segments
  - 2. Simple pin/hinge joints
  - 3. Uniform segment density
  - 4. Standard segment mass/MOI values
- Measuring segmental inertia parameters:
  - 1. Direct Measurement
  - E.g. tape measure
  - 2. Regression Equations
  - 3. Mathematical Modelling
  - Body modelled as 11 geometric shapes
- Body composition -- measurement of percentage of fat, bone and muscle in the human body
- Measuring body composition:
  - 1. Somatotypes
  - 2. BMI
  - 3. Bioelectrical impedance
  - 4. Skinfold measurements
  - 5. Bod Pod
  - 6. Dual energy X-ray absorptiometry (DXA)
  - Scoring of 3 body types
  - lean body tissue is more conductive than fat
  - Handheld caliper used to measure thickeness of fat stores
  - measures air displaced by subject in sealed chamber
  - measurement of absorption of X-ray beam
- Power -- the ability of a muscle to produce maximal force over a short period of time
  - power = work/change in time = force x velocity
- Endurance -- the ability of a muscle to exert force over an extended period of time
- Power measurement = jump height
- Jump height measurement methods:
  - 1. Vertec vertical challenger/wall scale
  - 2. Jump mat
  - 3. Force plates
  - jump to move as many lin markers with hand
  - Measures time of flight
  - measures resultant force and where it's applied
  - Jump height: Impulse momentum method
    - change in momentum equals impulse applied to it
- Issues with 1 rep mac (1-RM) strength testing:
  - 1. Highly specialised skill
  - 2. Time consuming due to warm up
  - 3. Injury risk
- Alternative to 1-RM:
  - Measure the reps to failure
  - sub maximal load and use
  - regression equation to predict 1-RM
- Isovelocity dynamometers (IVD)
  - measures joint torque at a single joint
  - E.g. knee extension
  - IVD measures torque exerted by the subjet on the crank arm
- ROM = range of movement
- IVD measurement considerations:
  - 1. Consistency of effort
  - 2. Only net joint torque
  - 3. Single joint only
- Isovelocity image:
- Cross Bridge Cycle
- 1. Free myosin binds to actin filament to form the cross bridge
  - 2. The cross bridge generates force (rate limiting step of contraction)
    - 3. The actin-myosin birdge rapidly dissociates
      - 4. Free myosin head moves into position to attach to actin
- Ultrasound allows in vivo images of muscle fibres to be obtained -- fibre length and angle can be measured by digitalising the images
- Fibre types:
  - Type 1: Slow oxidative fibres
  - Type 2A: Fast oxidative fibres (aerobic)
  - Type 2B: Fast glycolytic fibres (anaerobic)
  - Fast twitch fibres can generate force quicker than slow twitch
- Motor Unit = motor neurone + all the muscle fibres it innervates
- Measuring neuromuscular function:
  - 1. Control signal from brain
  - 2. Motor unit firings
  - 3. MU electrical signal - MU force output
  - 4. Muscle electrical signal - muscle force output
- EMG = Electromyography
  - EMG electrodes record the action potentials to give window into neuromuscular system
  - Types of EMG electrodes:
    - 1. Surface electrodes
      - Non-invasive, whole muscle
    - 2. Indwelling electrodes
      - Invasive, best for deep muscles
- EMG signals are very small
  - Amplifier needed
  - Variable gain = output signal/input signal
- Aerobic exercise -- exercise that involves oxygen consumption by the body
- Running economy -- energy demand for a given velocity of submaximal running
- Fundamentals of aerobic exercise:
  - 1. Heart rate increases
  - 2. Oxgyen intake increases
  - 3. Lactic acid increases
  - 4. Ventilation increases
  - 5. Carbon dioxide output increases
- Anaerobic threshold -- exercise intensity at which alctic acid starts to accumalate
- VO2 max -- maximum capacity of an induvidual's body to transport and utilise oxygen during incremental exercise
  - mlmin-1kg-1
- Measuring physiological responses to exercise (lab)
  - 1. Precision ergometer e.g. treadmill
  - 2. Respiratory flow metre
  - 3. Gas exchange
  - 4. Heart rate/ECG monitoring
  - 5. Blood sampling
- Measuring physiological responses to exercise (field)
  - 1. Shutter test e.g. bleep
  - 2. Rating of percieved exertion
  - 3. Heart rate monitors
  - 4. Portable analysers