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Instrumentation And Measurement > Instrument Characteristics > Flashcards

Instrument Characteristics Flashcards

1
Q

What is instrumentation?

A

the use of an instrument to indicate, record and control a measurement.

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2
Q

what are the steps that need to be considered before you make a measurement

A

i) the type of instrument that needs to be used, the instruments characteristics such as accuracy
ii) method and procedures of measurement
iii) characteristics of the input
iv)characteristics of the output
v)quality of measurement in terms of time and cost
vi)safety measure

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2
Q

why do we need measurement?

A

in order to control something

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3
Q

what are the steps after control

A

monitoring and improvement

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4
Q

input and output must be

A

measurable and quantifical

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5
Q
A
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6
Q

what is input?

A

-instructions
-a signal that causes a reaction

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7
Q

what is output?

A

the reaction or expected outcome that occurs once the input signal is applied.

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8
Q

name 3 alternatives to input and output

A

input can be also
-expected
-ideal
-calculated
-desired output
-calibrated
-desired output

output
- actual
-measured

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9
Q

explain in brief what an open loop is and give an example

A

in an open loop
input is processed and an output is given. for example a fan. a user can input a speed for the fan and thus the fan blade increased in speed. over time the fan blade can collect dust and thus the speed can decrease gradually over time.
-In an open loop there is no error detection or error correction
-this makes them low cost and easy to make/design.

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10
Q

Example in brief what a closed loop is and give an example

A

-closed loops get input and it is processed to give an output.unlike an open loop there is error dectection. if an error is detected the loop goes back to the start (input) this loop back is called a negative feedback loop
there is also sometimes a summing junction in between the input and process this adds to the error to give the correct output
e.g an ac you can input 16 C if the output is 15 C then the feedback loop takes place and the summing junction would add +1 C
- has lower level error compensation.

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11
Q

what is over compensation?

A

this is when the error compensators over corrects the ouput value and goes over the desired value causeing another error

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12
Q

what is a summing junction

A

a summing junction is a transductor that converts analog signals to electrical signals.
note: these signals are needed for the processer to understand as it does not understand analog eg motion but only electrial signals.

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13
Q

what is a unit?

A

a quantity used as a standard of measurement

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14
Q

why do measurement need units

A

so that you can define and explain a quality of measure

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15
Q

what are standard unis

A

these are internationally agreed units and they are needed to achieve universality and uniformity

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16
Q

what are the 7 SI base unis

A

-unit of length in (meter)
-unit of mass in (kilograms)
- units of thermodynamic temperatures (kelvins)
-unit of amount of substance (moles)
-unit of (luminous) intensity(candela)
-unit of electric current (ampere)
-unit of time second

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17
Q

what are the four measurement standards

A

-international
-primary
-secondary
-working

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18
Q

state what is an international standard is

A
  • these are international agreements of certain units of measurement.

they are to the closest possible accuracy attained by the science and technology of measurement and used for comparison with primary standards.

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19
Q

What are Primary standards and give examples

A

These are the units standard used on a national level.
e.g the SIRIM in malaysia and national bureau of standard in washington DC
the are mainly used for calibration and verification of secondary standards.
- think about how they use miles in dc and km here in malaysia

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20
Q

explain secondary standard

A

these are unit standards used by industrial laboratories within a country. each lab is responsible for its own secondary standard. but this standard has to be checked, verified and calibrated by the primary standard of that country. once calibrated the labs are issued a certificate and have there standards check periodically.

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21
Q

Working standard

A

​the working standard is used to check and calibrate the instruments used in low level laboratories e.g schools and univeristies or
to make comparison measurement in industrial application ​

  • Example: the standard resistor, capacitors, inductor which usually found in an electronics laboratory are classified as working standards
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22
Q

what is accuracy

A

accuracy is the closeness of measured values to the true value.

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23
Q

how do u measure percentage error

A

error% = (true value - measured value )/ true value * 100

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24
Q

percentage accuracy

A

accuracy = 100% - |error%|

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25
Q

absolute error

A

true value - measured value

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26
Q

relative accuracy

A

1 - true value - measured value / true value

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27
Q

what is precision

A

precision is the measure of the stability and reliabity of an instrument and its ability to reproduce the same measurement over and over again from the same input signal. aka its reproducablity and repeatablity

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28
Q

lack of accuracy result from what?

A

systematic error

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29
Q

lack of precision results from what?

A

random error

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30
Q

what is repeatablity

A

a child of precision. it is the closeness of output readings to each other over a short period of time and under the same conditions

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31
Q

what kind of conditions need to be the same in order to assure repeatability

A
  • measurement conditions
  • same instrument and observer
    -same location
  • same conditions of use
    -same time period in between measurements

​

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32
Q

what is range

A

measured maximum - measured minimum

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33
Q

resolution%

A

= minimum change/ range * 100

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34
Q

thershold

A

the minimum input required to get a resolution

35
Q

what is repeatability?

A

this is the closeness of output readings to each other when the same input signal is repeated under the same conditions.

36
Q

reproduciblity

A

this is the consitent measurement produced from the same physical quality when the conditions have changed. for example with a long time in-between readings

37
Q

name one other way reproducibility can be tested for an instrument

A

dismantling the instrument and reassembling it.

38
Q

what is resolution?

A

this is the smallest increment of input signal change needed to reproduce a detectable change in output

39
Q

how to measure range

A

measured range = Xmax - Xmin

40
Q

how to measure resolution %

A

change in X / measured range * 100

41
Q

sensitivity?

A

this is the absolute ratio of change of the output signal to that of the input signal

42
Q

sensitivity equation

A

change in output/ change in input

43
Q

non linearity equation

A

= deviation/full scale deviation * 100

44
Q

non linearity with oscillation of a fixed amplitude

A

= maximum deviation (+-) full scale deviation

45
Q

what is non linearity with oscillation of a fixed amplitude

A

this is when the actual output of the instrument oscillates with a fixed amplitude about the best fit line

46
Q

what happens when there is non linearity with oscillation of varying amplitude

A
  • this is when the actual output of the instrument oscillates around the best-fit straight line, but its amplitude varies with input value.
  • The slopes of the lines connecting positive and negative are determined and the highest deviation from the best-fit line is used to express the percent nonlinearity with respect to the input value.​

​

47
Q

what are static characteristics

A

these are characteristics of an instrument that is constant or changes very slowly with time.

48
Q

list the desirable static characteristics

A
  • accuracy
  • precision
    -reproducibility
    -repeatability
  • resolution
    -sensitivity
49
Q

list down undesirable static characteristics

A
  • dead zone
  • drift
  • static error
50
Q

list the types of deadzone

A

-creep
- threshold
-hysteresis

51
Q

what is deadzone

A

anything below the threshold and resolution is considered deadzone. this amount of input signal can not cause a detectable change in output.

52
Q

non linearity

A

the errors happen inbetween the minimum and maximum. they are non linear and do not follow the fixed line.

53
Q

drift

A

the drift from the null reading that occurs in the instrument when the measured is maintained at a steady for a long period of time

54
Q

what are the kinds of drift

A

span drift
zero and combined

55
Q

what is zero drift

A

the error remains the same through out the reading

56
Q

what is span drift

A

the error increase over time from 0 error to max error

57
Q

what is combined drift

A

this is a combination of span and zero error the drift

58
Q

hysteresis

A

if an input measured quantity to the instrument is steadily increased from a negative value then steadily decreased the two curves produced do not follow the same path this is hysteresis

59
Q

what causes hysteresis

A

is the parameters being measured expand in some way eg temp and pressure

or the meter type being a pmmc a permanent magnet moving coil

60
Q

what is creep

A

on a graph of output vs time there is a steady increase at some point when the output hits maximum it forms a step curve before zeroing. the

61
Q

creep recovery

A

the sudden drop from max to min

62
Q

where is creep present

A

in instruments that deal with expansion

63
Q

gross error

A

human error due to:
parallax error: error when reading the instrument
systematic error: using a worn instrument
instrument error: using a faulty or not correctly calibrated instrument

64
Q

environmental error

A

due to external conditions such as humidity temperature

65
Q

random error

A

error that remains even after gross and systematic error have been reduced

66
Q

limiting error

A

provided by the manufactures the instrument is accurate to a certain percentage of the full scale reading

67
Q

what are the types of input order systems

A

zero order system
first order system
second order system

68
Q

what is zero order system

A

this is a system where there is no time delay between when input is feed and output is given. it is instantaneous. but it is rare due to it being to fast and simple.

69
Q

characteristics of a first order system

A

there is a gradual increase to the final value

70
Q

what can we use to check the speed of the response in terms of first order

A

rise time, time constant, settling time

71
Q

what is rise time

A

this is the time taken for the response to get from 10% to 90% of the final value

72
Q

time constant

A

this is the time taken for the response to reach 63% of the final value

73
Q

settling time

A

this is the time taken for the response to reach an stay within (-/+5%) of the final value.

74
Q

does error in first order go beyond the final?

A

no

75
Q

what is the similarity between 1st and 2nd order

A

there is time delay between when u feed your input and receive an output response

76
Q

what is peak time

A

the time taken for the response to reach its highest value

77
Q

overshoot formula

A

cmax(peak time)- final value/ final value

78
Q

types of 2nd order due to damping

A

underdamped
overdamped
undamped
critically damped

79
Q

underdamped characteristics

A

has overshoot
oscillations
the settling time takes long
damping ratio is greater then 0 but less than 1

80
Q

critically damped characteristics

A

looks like first order
no oscillations
no overshoot
damping ration = 1

81
Q

over damped

A

takes time to reach final value
damping ratio is greater than 1
has a possibility of error

82
Q

undamped

A

does not get to zero
oscillations increase
damping ratio is 0

83
Q

damping ration formula

A

-ln(%os/100)
/
sqauroot of
pi^2 + ln^2 (%OS/100)

84
Q
A

Instrumentation And Measurement (2 decks)

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