Lecture Sensors and analytical devices: Sensors characteristics include all of the following: Sensors characteristics (Static characteristics, dynamic characteristics), some basic measurement methods, measurement systems.
AMBIENT/
Chủ đề:
Nội dung Text: Lecture Sensors and analytical devices: Sensors characteristics - Nguyễn Công Phương
- Nguyễn Công Phương
Sensors and Analytical Devices
Sensors Characteristics
- Contents
A. Introduction
B. Sensors Characteristics
I. Static Characteristics
II. Dynamic Characteristics
C. Some Basic Measurement Methods
D. Measurement Systems
sites.google.com/site/ncpdhbkhn 2
- Static Characteristics
1. Accuracy
2. Precision
3. Repeatability
4. Reproducibility
5. Stability
6. Error
7. Noise
8. Drift
9. Resolution
10. Minimum detectable signal
11. Calibration curve
12. Sensitivity
13. Linearity
14. Selectivity
15. Hysteresis
16. Measurement range
17. Response & recovery time
sites.google.com/site/ncpdhbkhn 3
- Accuracy
• Accuracy: the correctness of a sensing system’s output
in comparison to the actual value of a measurand.
• To assess the accuracy:
– The system is benchmarked against a standard measurand,
or
– The output is compared with a measurement system with a
superior accuracy
More accurate
Less accurate
http://hubshooting.com/hub-products/600px-
25_meter_precision_and_50_meter_pistol_target-svg/
sites.google.com/site/ncpdhbkhn 4
- Precision
• Precision: the capacity of a sensing system to give
the same reading when repetively measuring the
same measurand under the same condition.
• It is a statistical parameter & can be assessed by
the standard deviation (variance) of a set of
readings of the system for similar inputs
Low precision High precision High precision
Low accuracy Low accuracy High accuracy
sites.google.com/site/ncpdhbkhn 5
- Repeatability
• When all operating & environmental
conditions remain constant, repeatability is the
sensing system’s ability to produce the same
response for successive measurements.
• It is closely related to precision.
Temperature
The actual
temperature
10:00 10:02 20:00 20:02 Time
10:01 20:01
sites.google.com/site/ncpdhbkhn 6
- Reproducibility
• The sensing system’s ability to produce the
same responses after measurement conditions
have been altered.
sites.google.com/site/ncpdhbkhn 7
- Stability
• The sensing system’s ability to produce the
same output value when measuring the same
measurand over a period of time.
sites.google.com/site/ncpdhbkhn 8
- Static Characteristics
1. Accuracy
2. Precision
3. Repeatability
4. Reproducibility
5. Stability
6. Error
7. Noise
8. Drift
9. Resolution
10. Minimum detectable signal
11. Calibration curve
12. Sensitivity
13. Linearity
14. Selectivity
15. Hysteresis
16. Measurement range
17. Response & recovery time
sites.google.com/site/ncpdhbkhn 9
- Error
• Error is the difference between the actual
value of the measurand and the value produced
by the sensing system.
• It can be systematic or random.
Absolute error Output True value
Output True value
Relative error
True value
sites.google.com/site/ncpdhbkhn 10
- Noise
• Noise: the unwanted fluctuations in the output signal of the
sensing system, when the measurand is not changing.
• Electronic noise: thermal energy causes charge carriers to
move in random motion, which results in random variations
of current and/or voltage.
• Shot noise: the random fluctuations, which are caused by
the carriers’ random arrival time, produce shot noise.
• Generation – recombination noise: it is produced from the
generation & recombination of electrons & holes in
semiconductors
• Pink noise (or 1/f noise): in this type of noise the
components of the frequency spectrum of the interesting
signals are inversely proportional to the frequency.
sites.google.com/site/ncpdhbkhn 11
- Drift
• It is observed when a gradual change in the
sensing system’s output is seen, while the
measurand actually remains constant.
• It is the undesired change that is unrelated to
the measurand.
Temperature
The actual
temperature
Time
sites.google.com/site/ncpdhbkhn 12
- Resolution
• Resolution (sometimes discrimination): the
minimal change of the measurand that can
produce a detectable increment in the output
signal.
• It is strongly limited by any noise in the signal.
sites.google.com/site/ncpdhbkhn 13
- Minimum Detectable Signal
• Minimum Detectable Signal (MDS) is the
minimum signal increment that can be
observed, when all interfering factors are taken
into account.
• When the increment is assessed from zero, the
value is generally referred to as threshold or
detection limit.
• If the interferences are large relative to the
input, it will be difficult to extract a clear
signal & small MDS can not be obtained.
sites.google.com/site/ncpdhbkhn 14
- Static Characteristics
1. Accuracy
2. Precision
3. Repeatability
4. Reproducibility
5. Stability
6. Error
7. Noise
8. Drift
9. Resolution
10. Minimum detectable signal
11. Calibration curve
12. Sensitivity
13. Linearity
14. Selectivity
15. Hysteresis
16. Measurement range
17. Response & recovery time
sites.google.com/site/ncpdhbkhn 15
- Calibration Curve
• Calibration curve: the relationship between the
measured variable x & the signal variable
generated by the system y.
• A sensing system has to be calibrated against a
known measurand to assure that the sensing
results in correct outputs.
y
sites.google.com/site/ncpdhbkhn
x 16
- Sensitivity
• Sensitivity: the ratio of the incremental change
in the sensor’s output (Δy) to the incremental
change of the measurand in input (Δx).
• An ideal sensor has a large & preferably
constant sensitivity in its operating range.
y y
x
sites.google.com/site/ncpdhbkhn
x 17
- Linearity
• Linearity: the closeness of the calibration
curve to a specified line.
• The degree of resemblance to a straight line
describes how linear a system is.
sites.google.com/site/ncpdhbkhn 18
- Selectivity
• Selectivity: the sensing system’s ability to
measure a target measurand in the presence of
other interferences.
sites.google.com/site/ncpdhbkhn 19
- Hysteresis
• Hysteresis: the difference between output
readings for the same measurand, depending
on the trajectory followed by the sensor.
• It may cause false & inaccurate readings.
y
sites.google.com/site/ncpdhbkhn
x 20
Thêm vào BST
Báo xấu
Download
Vui lòng tải xuống để xem tài liệu đầy đủ
