Characteristics of Measurement Systems

Question 1

Acquiring a measurement:

Answer 1

o Sense
o Acquire
o Analyse
o Express

Question 2

8 Properties of sensors:

Answer 2

o Sensitivity
o Resolution
o Repeatability
o Reproducibility
o Dynamic Range
o Non-linearity
o Hysteresis
o Response Time

Question 3

o Repeatability

Answer 3

§ A measure of the closeness in agreement between successive
measurements (usually quantified by the standard deviation of the
measurements)

Question 4

o Reproducibility

Answer 4

§ Repeatability assessed by a different user under different operating
conditions

Question 5

o Dynamic Range

Answer 5

§ Ratio of a measurement range to resolution

5%)

Question 6

o Non-linearity

Answer 6

§ Maximum deviation from linearity of input:output relationship

Question 7

o Hysteresis

Answer 7

§ Condition when input:output relationship changes depending on
direction or range of the input variable

Question 8

o Response Time

Answer 8

§ Time taken for the output of a sensor to reach within a certain range
of a new steady state (usually within

Question 9

o Sensitivity

Answer 9

§ Ratio of output signal to input quantity

Question 10

o Resolution

Answer 10

§ Minimum change in input quantity resolvable at the output

Question 11

o Peak to Peak

Answer 11

§ Difference between max and min

Question 12

o DC component

Answer 12

§ Mean of the signal

Question 13

o Root-mean-square amplitude

Answer 13

§ Square root of the mean of the squared signal

Question 14

o Relationship between AC, DC and RMS

Answer 14

§ AC Component
• The RMS of a signal that has had the DC component removed
is called the “AC” component of the signal, and is equivalent
to the standard deviation of the signal
§ The DC and AC components contribute to the total RMS of the signal

Question 15

Power

Answer 15

o Total power
§ Time average of the square of the signal
x,power = x(t) ^2
§ Unit of power is (unit of x)2

Question 16

o Thermal Noise

Answer 16

§ Caused by random thermal agitation in conductors
V= sqrt(m4kRT. f
§ Power spectrum: Uniformly distributed (“white”)

Question 17

o 1/f Noise

Answer 17

§ Many origins, including fluctuating conductivity due to imperfect
contact between two materials
§ Power spectrum: 1/f

Question 18

Shot Noise

Answer 18

§ Caused by statistical fluctuations in the movement of charge
§ Power spectrum: uniform

Question 19

o Popcorn Noise

Answer 19

§ Caused by manufacturing defects, usually a metallic impurity, in the
junction of semiconductor device
§ Power density: 1/f^n, where n is usually 2

Question 20

• Interference
  and
  o Methods of controlling:

Answer 20

o Interference is a kind of noise caused by events outside the measurement
system.
§ Shielding
§ Grounding
§ Balancing
§ Filtering

Question 21

Addition of Noise

Answer 21

v total ^2 =v1 ^2 + v2 ^2 + 2 gamma v1.v2

§ Where gamma is correlation coefficient; and = 0 if noise is uncorrelated

Question 22

Accuracy

Answer 22

o Refers to the closeness of the result of a measurement to the “true value”
of the measurand.
o A qualitative concept and should not be used in a quantitative sense.

Question 23

o Uncertainty

Answer 23

§ A parameter that characterizes the dispersion of the values that
could be reasonable associated with the measurand
§ Often quantified by the standard error in the mean:
u= omega/ root(n)
omega =stdv

Question 24

Uncertainty in sensor measurements:

Answer 24

ux= sqrt( (u,y/y)^2 + u,s/s)^2) *X )