Semester test 1 content

• What is Hambley's paradox?

  For statically indeterminate structures, adding more elements may increase the force in some elements
• What is the main difference between an arduino and a raspberrry pie?

  An arduino is a microcontroller while an r is raspberry pi is a microprocessor.
• Name the 7 base units

  Meter, kilogram, second, ampere, kelvin, mole and candela
• Write down the letter units of the 7 base units 


  m, kg, s, A, K, mol, cd
• What were the first units of length based on?

  Human body parts
• What is the definition of a cubit?

  The length of the arm from the elbow to the tip of the middle finger
• What is the definition of the span?

  The distance between the tip of the thumb and the little finger when the fingers are extended
• What was the definition of the inch?

  A 12th of a foot
• What is the 1790's definition of a meter?

  One ten-millionth of the distance along Earth's meridian from pole to the equator passing through Paris
• What did Delambre and Mechain use to measure the distance along the meridian from Dunkirk to Barcelona?

  They used triangulation
• What is the 1960 definition of the meter?

  1 650 763.73 wavelengths of LASER light emitted by the krypton-86 atom in a vacuum.
• What is the 1983 definition of the meter?

  The distance which light travels in vacuum in (1/c) seconds where c = speed of light = 3*10^8 m/s
• What is the definition of the second?

  The duration of 9 192 631 770 periods of radiation of the caesium 133 atom
• What is the 2018 definition of the kilogram?

  The international prototype kilogram made of a platinum-iridium alloy and is stored in a vault at the International Bureau of weights and measures in Paris.
• What device is used to measure the kilogram?

  The kibble balance
• What are the two phases that the Kibble balance has?

  A static and a dynamic phase
• What is the heirachy of the measurement standards?


  The international bureau of weights and measures in Paris, SABS, CSIR, local calibration laboratories
• What is accuracy?


  The difference between the true value and the measured value. (Note: it can only be determined by calibration against a known standard)
• What is precision?


  Precision is repeatability. High precision does not necessarily mean high accuracy
• Is it possible to have high accuracy without high precision?

  No. High accuracy is impossible without high precision
• What is resolution?


  Resolution is the smallest change in value that the instrument can detect or display. (i.e., the smallest discernable increment).
• What is the resolution on an analogue instrument?

  infinite
• What is sensitivity?


  It is the ratio between output and input.
• Define linearity 


  The gap between an input vs output curve and a straight line

  
• What are the advantages of high linearity?

  It means a simplistic relationship between input and output. Linearity is independent of zero position***
• Define hysteresis 


  The difference (gap) between the load and unload curve
• Draw a graph showing an example of hysteresis

  b

  
• Where are the 3 places where we can expect hysteresis in instruments?

  In instruments with gears, linkages and where friction occurs between components
• What are 3 kinds of noise that can cause random measurement variations in instruments and an example of each noise?

  Electrical noise (computers, power lines and florescent lights); mechanical noise (such as vibration), and thermal noise (daily or seasonal changes in temperature)
• Define error


  The difference between the true value and the measured value
• READ THROUGH THE CAUSES AND REMEDIES OF MEASUREMENT ERROR!!!
• What are the two classes of fiber optic instruments used?

  Discrete strain and temperature measurement vs distributed strain and temperature measurement
• What are the 3 scatterings that we can get in optical fibers and what do they measure?

  Rayleigh scattering (Fiber condition), Brillouin (strain) and Raman (temperature)
• How do we get information on the optical fiber from the waves?

  With Rayleigh and Raman waves, we can get information about the fiber condition and the temperature by the amplitude changes. With Brillouin waves we can use the phase shift to determine the strain in the fiber
• What kind of instrument are surveying instrument?

  Optical instruments
• What is surveying?


  The act of determining relative positions of points above, on or beneath the surface of the earth
• What are the 3 different kinds of map projections we can get and what are the two most popular projections?

  Planar, conical and cylindrical. Planar and cylindrical are the two most popular
• What are the three coordinates and the symbols that we need to find a place on a map?

  Longitude (phi) , latitude (lambda) and height
• Explain the angles needed to find the position of a place on a map:

  Lambda increases as we move left from the greenwhich meridian
• What are some reasons we prefer a digital sensor to an analog one?

  A digital sensor can be easily read by a computer. The information can also be remotely monitored and stored more efficiently