Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Precision, Measurement and Control > Measurement > Flashcards

Measurement Flashcards

1
Q

what is the general structure of a measurement system?

6 elements

A

input (true value )

sensing element

signal conditioning element

signal processing element

data presentation element

output (measured value)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the sensing element of a measurement system do? And what are 2 examples?

A

In contact with he physical process (being measured) and gives an output.

  1. Strain gauges
  2. Thermocouple
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the signal conditioning element of a measurement system do? And what are 2 examples?

A

Takes the output of the sensing element and converts it into a form more suitable for processing - usually dc voltage or current.

  1. Bridge circuit
  2. Amplifier
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are 4 things the signal processing element of a measurement system do?

A

Further amplification of signal

linearisation

error compensation

data conversion (analogue to digital)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the 2 fundamental characteristics of a measurement system?

A

Static characteristic (system response to a constant or slowly changing input)

Dynamic characteristic (system response to a sudden or periodic change in input)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Name 9 characteristics considered ‘static’

A

Range

Resolution

Accuracy

Precision

Repeatability

Linearity

Sensitivity

Hysteresis

Thermal drift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is resolution?

what limits resolution?

A

the smallest mount of input signal change that an instrument or sensor can detect.

nosie
The least significant bit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How to you calculate resolution with ref. to the leats significant bit.

12-bit A/D converter has input range of 10 V

A

Resolution given by:

1/2^bits x input range =

1/2^(12) x 10 (V) =

2.44 e-3 (V)

if input range is +/- :

1/2^(bits-1) x input range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Static characteristics:

Linearity, explain.

A

Relationship between output and input is expressed in a straight line equation.

y = Kx + a

K = sensitivity =
output range / input range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Static characteristics

Hysteresis, explain.

A

For a given input x, the output y may be different depending on whether the input is increasing or decreasing. Hysteresis is the difference.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

static characteristics

Thermal drift, explain.

A

zero drift, when x=0 but y not equal to 0…. the reading has drifted due to temp change

sensitivity drift: the sensitivity of an instrument varies with the ambient temp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what do dynamic characteristics of a measurment system describe ????

A

behaviour between the time when the input changes and the time when the output attains a steady value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are the two typical output responses for dynamic characterstics

A

STEP RESPONSE

FREQ. RESPONSE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

most measurements can be classified into two types…. of systems

A

first order systems

second order systems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how to identify whether a system is first order?

A

if there is no mechanical movement
a movement of mass
detection part there is a sensor or an instrument

E.g temperature sensors, and RC circuit, RL circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Characteristic of signlas

3 things)(brief exp

A

Deterministic signals - values at any time can be exactly predicted by mathematical models.

Random signals - not predictable treated as noise - but can be estimated statistically

Real.Measured signals - combination of the above two

17
Q

Variance intergral ?

equation

A

σ^2 =
1/T integral( y(t) - ymean )^2 dt

(between To and 0)

18
Q

Any signal can be expressed by Fourier series - what domain is it in?

A

frequency breddah

19
Q

Internal noise sources (2)

A

Thermal or Johnson noise

- random temp-induced motion of electrons and other charge carries

20
Q

Noise sources

A
  • shot noise
    caused by random charge fluctuations across a junction in diodes and transistors

-1/f flicker noise
1/f spectrum

21
Q

external noise sources (2)

A

-interference
electromagnetic interference from power source, motors
radio and TV

-vibration

22
Q

ways to reduce external noise

A

electromagnetic shielding to reduce inductive coupling by twisted pairs to reduce the loop area, as the magnitude of the induced voltage is proportional to the loop area

electrostatic screening and shielding to reduce captive coupling by proper grounding

23
Q

ways to reduce internal noise

A

irreducible in general

can be bypassed through physical decoupling mechanisms

24
Q

Four types of filters

A

low pass
band pass
high pass
band stop

25
Q

Filters can be implanted in two forms ..

A

analogue

digital

26
Q

Analogue first order lop pass

2 kinds? examples of each

A

Passive

  • RC circuit
  • RL circuit

Active
- RC + op-amp

27
Q

digital filters :

and ideal filter should have :
2

A
  • high attenuation rate, ideally straight vertical line

- very small phase shift, ideally zero

28
Q

what is meant by attenuation ?

A

reduction of the amplitude of a signal

29
Q

digital filters:

the higher the order, the sharper the ….?

A

DROP EDGE

30
Q

what are signal conditioning circuits used for ? (4)

A

Amplify weak signals
filter out noise
convert voltage to current or current to voltage
implement special functions (linearisation , log an antilog, integration, differential etc)

31
Q

over what frequency will the first order frequency response no longer give a good response

A

1/tau

32
Q

how do you get steady state sensitivity for a second order transfer function

A

make substitutions to get transfer function into standard form (and the factor is the your sensitivity) KG(s)

33
Q

Laplace to complex domain by….

A

s = jw

34
Q

At low frequencies w/wn what is the value of the magnitude of the transfer function G(jw) for second and first order systems
(can be seen in tables)

A

1

35
Q

how do you calculate the displacement from a step input to a second order response?

A

y(t) = K x fo(t)

the resulting change in displacement =
steady-state sensitivity × unit step response

36
Q

what is bandwidth

A

it is the range of signals for which the magnitude of the transfer function (GAIN) is greater than 1 / root(2) …. or 0.707

37
Q

Three components of two port network measurement system

A

sensing source

amplifier

load as indicator/ display unit

Precision, Measurement and Control (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions