Lecture Sensors and analytical devices: Mass, force, and torque measurement presents the following content: Mass (Weight) measurement, force measurement, torque measurement. Inviting you refer.
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Nội dung Text: Lecture Sensors and analytical devices: Mass, force, and torque measurement - Nguyễn Công Phương
- Nguyễn Công Phương
Sensors and Analytical Devices
Some Basic Measurement Methods,
Mass, Force, and Torque Measurement
- Contents
A. Introduction
B. Sensors Characteristics
C. Some Basic Measurement Methods
D. Measurement Systems
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- Some Basic Measurement Methods
I. Sensor Technologies
II. Temperature Measurement
III. Pressure Measurement
IV.Flow Measurement
V. Level Measurement
VI.Mass, Force, and Torque Measurement
VII.Translational Motion, Vibration, and Shock
Measurement
VIII.Rotational Motion Transducers
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- Mass, Force, and Torque
Measurement
1. Introduction
2. Mass (Weight) Measurement
3. Force Measurement
4. Torque Measurement
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- Introduction
• Mass, force, & torque are closely related
quantities.
• Mass: the quantity of matter that a body
contains.
• Force:
F = ma
• Weight:
P = mg
• Torque: can be regarded as a rotational force.
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- Mass (Weight) Measurement
• The mass of a body is always quantified in terms
of a measurement of the weight of the body.
• Weight: the downward force exerted by the body
when it is subject to gravity.
• Three methods used to measure this force:
– Load cell: measure the downward force exerted by a
mass subject to gravity.
– Spring balance: also measure the downward force
exerted by a mass subject to gravity.
– Mass balance: compare the gravitational force on the
mass being measured with the gravitational force on a
standard mass.
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- Mass, Force, and Torque
Measurement
1. Introduction
2. Mass (Weight) Measurement
a) Electronic Load Cell (Electronic Balance)
b) Pneumatic & Hydraulic Load Cells
c) Mass Balance (Weighing) Instruments
d) Spring Balance
3. Force Measurement
4. Torque Measurement
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- Electronic Load Cell (1)
• A.k.a. electronic balance.
• Now the preferred type of load cell in
most application.
• Within an electronic load cell:
– The gravitational force on the body being
measured is applied to an elastic element.
– This element deflects according to the http://www.bme.uconn.edu/sendes/
magnitude of the body mass Fall04/Team2/FInal%20report.htm
– Mass measurement is then translated into
a displacement measurement task.
http://www.hbm.com/en/menu/tips-
tricks/load-measurement/how-does-a-
bending-beam-load-cell-work/
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- Electronic Load Cell (2)
http://www.houseofloadcell.com/
http://www.hbm.com/en/menu/tips-
tricks/load-measurement/how-does-a-
bending-beam-load-cell-work/
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- Electronic Load Cell (3)
http://www.hbm.com/en/menu/tips-
tricks/load-measurement/how-does-a-
bending-beam-load-cell-work/
• The elastic element design is to:
– Obtain a linear output relationship between the applied force & the
measured deflection, and
– To make the instrument insensitive to forces that are not applied
directly along the sensing axis.
• Load cells:
– Compression type: the measured mass is placed on top of a platform
resting on the load cell, which compresses the cell.
– Tension type: the mass is hung from the load cell, putting the cell into
tension.
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- Electronic Load Cell (4)
• Various types of displacement transducers are used to
measure the deflection of the elastic elements: strain gauge
& piezoelectric device.
• The strain gauge:
– Used most commonly
– Inaccuracy: less than ±0.05%
– Range:
• Small masses: 0.1 – 5 kg
• Other: 10 – 3000 tonne.
• The piezoelectric device:
– Range: 0 – 1000 tonne.
– Physically small
– Can measure dynamically changing forces only.
– Inaccuracy: ±1%.
– Inexpensive.
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- Electronic Load Cell (5)
• Advantages:
– Relatively low cost
– Wide measurement range
– Tolerance of dusty & corrosive environments
– Tolerance of shock loading
– Easy installation.
• Disadvantage: permanent deformation that an
elastic element undergoes after it has been
under load for a period of time.
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- Mass, Force, and Torque
Measurement
1. Introduction
2. Mass (Weight) Measurement
a) Electronic Load Cell (Electronic Balance)
b) Pneumatic & Hydraulic Load Cells
c) Mass Balance (Weighing) Instruments
d) Spring Balance
3. Force Measurement
4. Torque Measurement
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- Pneumatic Load Cell
• Translate mass measurement
into a pressure measurement.
• Less common than the
electronic load cell.
• The output pressure measured
in the cell is approximately
proportional to the magnitude
of the gravitational force on
the applied mass.
PRESSURE
• Requires a flow of air at its METER
input of around 0.25 m3/h at a
pressure of 4 ar. http://www.buildingcontrolworkbench.com/
• Range: BCWInfo/GrayBook/Gpneubsc.htm
– Small masses: 25 kg
– Other: 25 tonne
• Inaccuracy: ±0.5%.
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- Hydraulic Load Cell
• Translate mass measurement
into a pressure measurement.
• Less common than the
electronic load cell.
• Hydraulic fluid (e.g., oil)
contained within an enclosed
chamber.
• Designed for measuring much
larger masses than pneumatic http://www.npl.co.uk/science-+-technology/mass,-
cell. force,-pressure/force/hydraulic-load-cell
• Range: 500 tonne – 50,000
tonn.
• Inacurracy: ±0.05%.
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- Mass, Force, and Torque
Measurement
1. Introduction
2. Mass (Weight) Measurement
a) Electronic Load Cell (Electronic Balance)
b) Pneumatic & Hydraulic Load Cells
c) Mass Balance (Weighing) Instruments
i. Beam Balance (Equal Arm Balance)
ii. Weigh Beam
iii. Pendulum Scale
iv. Electromagnetic Balance
d) Spring Balance
3. Force Measurement
4. Torque Measurement
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- Beam Balance
• Standard masses are added to a pan on one side of a pivoted beam
until the magnitude of the gravity force on them balances the
magnitude of the gravitational force on the unknown mass acting at
the other pan.
• This equilibrium position is indicated by a pointer that moves
against a calibrated scale.
• Range: less than 0.01 gram.
• Inaccuracy: ±0.002%.
• Disadvantages:
– Lack of ruggedness: continous
use & shock loading will lead
to deterioration in accuracy &
resolution.
– A relatively long time to make
each measurement http://visual.merriam-webster.com/science/measuring-
devices/measure-weight/robervals-balance.php
• Used as a calibration standard &
not used in day-to-day
production environments.
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- Weigh Beam
http://emmaandmelissa.blo
gspot.com/2013/01/unit-2-
3-project.html
• Similar principles to the beam balance, but much
more rugged.
• Range: up to 50 tonne.
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- Mass, Force, and Torque
Measurement
1. Introduction
2. Mass (Weight) Measurement
a) Electronic Load Cell (Electronic Balance)
b) Pneumatic & Hydraulic Load Cells
c) Mass Balance (Weighing) Instruments
i. Beam Balance (Equal Arm Balance)
ii. Weigh Beam
iii. Pendulum Scale
iv. Electromagnetic Balance
d) Spring Balance
3. Force Measurement
4. Torque Measurement
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- Pendulum Scale
http://www.wedo.de/index.php?id=10778&lang=3
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