1 temperature measurement. 2 how to measure temperature temperature can be measured by detecting...
TRANSCRIPT
![Page 1: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/1.jpg)
1
Temperature Measurement
![Page 2: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/2.jpg)
2
How to measure temperature
Temperature can be measured by detecting changes in various temperature-dependent properties
Volume liquid-in-glass thermometerPressure gas thermometerDisplacement bimetallic stripVoltage ThermocoupleResistance RTD & thermistorRadiation spectrum Infra Red detectors
![Page 3: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/3.jpg)
3
Source: Mechanical Engineering magazine, March 2010
![Page 4: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/4.jpg)
4
Thermoelectric effect: when any two different metals are connected together, an emf that is a function of the temperature is generated at the junction between the metals:
Thermocouple
21 2
nne a T a T a T
For certain pairs of materials, 1e a T
(a) Thermocouple; (b) equivalent circuit
Hot junction
Reference junction
http://www.thermoworks.com/products/logger/images/digisense_dualogr_lg.jpg
![Page 5: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/5.jpg)
5
Characteristics of thermocouples
Thermocouple tables Sensitivity
![Page 6: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/6.jpg)
6
• Varying resistance devices• Rely on the fact that the
resistance of a metal varies with temperature
• Also known as resistance thermometers or thermistors depending on material used (metal or semiconductor)
• Variation can be non-linear, resulting in inconvenient measurement
• Platinum exhibits most linear behavior
• Platinum is also chemically inert
Resistance Temperature Detectors (RTDs)
![Page 7: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/7.jpg)
7
• Two common designs:• Coil wound on mandrel• Film deposited on substrate
• Wheatstone bridge: used to measure resistance change for an RTD
• Excitation voltage has to be chosen carefully: while a high voltage is desirable for high sensitivity, this causes self-heating
Resistance thermometers orResistance Temperature Devices (RTDs)
http://www.extech.com/instrument/products/400_450/407907.html
![Page 8: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/8.jpg)
8
Mechanical temperature sensing devices
• Liquid-in-glass thermometer• Bimetallic thermometer
• Commonly used as a thermostat (on-off switch in control applications)
• When displacement is measured, it acts as a thermometer
• Tip displacement: against a calibrated scale, or electrical output such as LVDT
• Pressure thermometer Liquid-in-glass thermometer
Bimetallic thermometer
Pressure thermometer
![Page 9: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/9.jpg)
9
Pressure measurement
![Page 10: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/10.jpg)
10
Diaphragm & bellows
• Pressure causes displacement of diaphragm (thin sheet), which can be measured by a displacement transducer
• Can be used with an LVDT or strain gauge
Bellows
Diaphragm
![Page 11: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/11.jpg)
11
Application: sound measurement
1020log0.0002p
PS
• Sound is measured as sound pressure level:• Microphone: diaphragm-type pressure sensor
• Converts sound pressure into displacement• Displacement is commonly measured using
a piezoelectric-type transducer
![Page 12: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/12.jpg)
12
Bourdon tube
• Pressure causes Bourdon tube to unwind• displacement transducer• Can also be used with an LVDT or strain
gauge
![Page 13: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/13.jpg)
13
Manometer
• Can be used to measure gauge pressure: p gh• Can also measure differential pressure: 1 2p p gh • Type of liquid
• Water is cheap & convenient• Water evaporates & is difficult to see
through• Not to be used if reacts with fluid
• Well-type: need only to measure liquid level in one tube
• Inclined-type: better sensitivity
![Page 14: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/14.jpg)
14
Force measurement
![Page 15: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/15.jpg)
15
AF Strain Sensing:
APF Pressure Sensing:
amF Acceleration Sensing:
xkF Elastic Sensing: Beams, rings
Strain gauges
Piezoelectric elements
Force sensing
![Page 16: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/16.jpg)
16
Load cell• Force produces measurable displacement• Design objectives:
• Achieve linear input/output relation• Make the instrument less sensitive to
forces not applied along sensing axis
Use of strain gauges in a torque cellHydraulic load cell
Based on strain gauge measurement
![Page 17: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/17.jpg)
17
Flow measurement
![Page 18: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/18.jpg)
18
Conveyor-based methods
• To measure flow of solids or particles• Mass is measured with a load cell
M = mass of materialL = length of conveyorv = velocityQ = mass flow rate
MvQ
L
![Page 19: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/19.jpg)
19
Pipe flow• Flow measurement :
• Local properties (velocity, pressure, temperature, density, viscosity)• Integrated properties (mass flow rate, volumetric flow rate)• Global properties (visualization of entire flow)
• If the velocity profile is known, it is enough to measure one velocity (centerline) to determine the total flow rate
• Otherwise, cross-section must be mapped by a grid of velocity data
Laminar Flow Turbulent Flow
![Page 20: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/20.jpg)
20
Principles of flow measurement
1 1 2 2v A v A
1 22 P PQ const
2 21 1 2 2
1 22 2
P v P vz z
g g g g
1v
2v
z1
z2
Bernoulli’s equation:
Conservation of mass:
For a horizontal pipe:2 2
1 2 1 2
2
P P v v
Pressure difference is a measure of flow rate
Q = volume flow rate
![Page 21: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/21.jpg)
21
Orifice Plate
D d
![Page 22: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/22.jpg)
22
Types of flowmeters
Orificesflow m eter
Venturi Tubeflow m eter
Flow Tubeflow m eter
Flow Nozzlesflow m eter
Pilot Tubesflow m eter
Others
PressureTypes
Turbineflow m eter
RecipocateingPiston flow m eter
Oval-Gearflow m eter
Others
M echanicalTypes
Hot-w ireflow m eter
Resistive-bridgeflow m eter
Others
Therm alTypes
Vortexflow m eter
Electrom agneticflow m eter
UltrasonicFlow m eter
Others
O therTypes
Flow m eters
![Page 23: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/23.jpg)
23
Differential pressure meters• Rely on the insertion of some device info a fluid-carrying pipe to obstruct the
flow, thus creating a pressure difference• Obstruction-type meters or flow-restriction meters• Common devices: orifice plate, Venturi tube, flow nozzle• Pressure difference usually measured with a differential pressure transducer• Advantage: no moving parts; robust, reliable & easy to maintain• Disadvantage: permanent loss of pressure
![Page 24: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/24.jpg)
24
Pitot static tube• Negligible obstruction of flow• Measures flow at a single point• Measures average flow velocity
02 sp pv
![Page 25: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/25.jpg)
25
Turbine flowmeter• Speed of rotation of turbine is proportional to flow rate
![Page 26: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/26.jpg)
26
Electromagnetic flowmeter• Used for electrically conductive fluids• Non-invasive device (no obstruction to fluid flow)• No pressure loss
![Page 27: 1 Temperature Measurement. 2 How to measure temperature Temperature can be measured by detecting changes in various temperature-dependent properties](https://reader036.vdocuments.mx/reader036/viewer/2022062808/56649dbd5503460f94aafe2f/html5/thumbnails/27.jpg)
27
Hot wire anemometer
• Consists of an electrically heated fine wire which is immersed in the flow.
• As the fluid velocity increases, the rate of heat flow from the heated wire to the flow stream increases.
• Thus a cooling effect on the wire occurs, causing its electrical resistance to change.
• In a constant current anemometer, the fluid velocity is determined from measurement of the change in resistance.