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What I learned after mid-term week 2, 61011195 Anutida Thongchawee -…
What I learned after mid-term week 2
Temperature measurement
Electrical techniques
Resistance temperature detector (RTDs)
Typrs
Wire wound
Film
Amount of resistance
3-wire ETDs
4-wire ETDs
2-wire ETDs
Principle
The electrical resistance of metal conductors increase with increasing temperature
Advantage&Disadvantage
Better accuracy than thermocouple
Lower temperature limits
More expansive
Termistor/Semi-conductor sensor
Disadvantages
Fragile
Upper temperature limit lower than RTDs
Temperature span must be narrow
Advantages
Small size
Fast response
Can detect small temperature changes
Thermocouples (TCs)
Laws
Independent of temperatures of wires connecting the junctions
Not change when a new conductor is introduced
Depends only on temperature of the junctions
Intermediate metals
Intermediate temperatures
Types
Base-metal (Types E, J, K, N, T)
Precious-metal (Types S, R, B)
Principle
Measuring voltage
Seeback effect
Components
Metal sheath
Thermowell
Plug/Connector/Accessories
Signal conditioning component/Readout
Extension/Compensation wire
Thermocouple wire
Optical&Radiation techniques
Thermal imaging
Provide graphic color display of objects according to their temperature
Non-contact sensor
Pyrometer
For very high temperature
Principle
Convert thermal radiation emitted by the object to electrical voltage
Non-contact sensor
Thermal expansion techniques
Liquid-in-glass thermometer
Types
Partial immersion
Total immersion
Principle
As the temperature rises, the fluid expands along the capillary tube
Bimetallic thermometer
Configuration
Connection at bottom of indicator dial
Connection at back of indicator dial
Bonding 2 straight metal strips
Principle
The coefficient of expansion is not the same for all metals
Metals expand with increasing temperature
Chemical techniques
Principle
The color of metal salt changes as a function of temperature
Examples
Crayon
Lecquer
Flow measurement
Pressure-based flowmeter
Types
V-cone
Segmental wedge
Flow nozzle
Pipe elbows
Orifice plate
Tap locations
Radius taps
Corner taps
Vena contracta taps
Pipe taps
Flange taps
Pitot tube
Venturi tube
Annubar flow element
Target flow sensor
Principle
Using Bernoulli's + Continuity's equations for calculation
The difference of pressure generated by accelerating/deaccelerating fluid
61011195 Anutida Thongchawee