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What I learned in week 11?, Patthiya Srimahaprom 61010789 - Coggle Diagram
What I learned in week 11?
Pressure measurement
Electrical pressure elements
Piezoresistive (strain gauge) sensors
Electrical resistance of any conductor is proportional to the ratio of length over cross-sectional
Pressure forces the diaphragm to deform causes the strain gauge to change resistance
A resistance that changes value with applied pressure
Differential capacitance sensors
The sensing element is a taut metal diaphragm
Comprising 3 plates for a complementary pair of capacitors
Difference of pressure across the cell causes the diaphragm to flex in the direction of least pressure
Resonant element sensors
DPharp
Sensor signal is easily digitized
Frequency becomes an indication of tension
Force-balance pressure transmitters
Differential pressure is sensed by a liquid-filled diaphragm capsule which transmits force to a force bar
Distinct advantage is the constraining of sensing element motion
Force-balance mechanisms tend to add noise to the output signal
Differential pressure transmitters
Senses the difference in pressure between two ports and outputs a signal representing that pressure in relation to a calibrated range
Difference of pressure between the two ports causes
the diaphragm to flex from its normal resting (center) position
Used to measure pressure differences, positive (gauge) pressures, negative (vacuum) pressures, and even absolute pressures
Level measurement
Level gauges (sight glasses)
Liquid level measurement as manometers are to pressure measurement
Non-magnetic metal tubes are used to solve the weakening problem of glass-tube level gauges
Float
Simplest form of solid or liquid level measurement
The float must be less density than the substance of interest
Controlled by computer uses a spring-reel to constantly tension the cable holding the float
Hydrostatics
Bubbler systems
The purge gas is used to measure hydrostatic pressure in the liquid container.
Compensated leg systems
Need to connect a second impulse line from the low port of the transmitter to the top of the vessel
Tank expert systems
Use the computer device electronically subtract the two pressures to subtract gas pressure inside an enclosed vessel
Displacement
Detect liquid level by measuring the weight of a displacer immersed in the liquid
Echo
Use waves to measure the level of liquid.
Ultrasonic level measurement
Using reflected sound waves
Heavy dust or high temperatures are not well-suited
Measure the height of solid materials
Liquids with a heavy layer of foam floating on top are more difficult
Radar level measurement
Using the radio waves
Guided radar, or time domain refractometry (TDR)
Instead of the radar transmitter broadcasting the signal via the air, a cable or rod guides the radar signal
Condensation has no effect on TDR
Operates on a lower frequency than the other radar technologies
Noncontact
Rely on antennas to direct microwave energy into the vessel, and to receive the echo (return) energy
Pulse-generated free-space radar and frequency-modulated continuous-wave (FMCW) radar (Noncontact)
Free-space radar: for liquid and solid level measurement applications
Non-contact radar devices suffer much more signal loss than guided-wave radar devices
Consider before selecting free-space radar
Condensation on the antenna
Foam on the liquid surface
Weight
Directly measuring the weight of the vessel
Measure both liquid and solid materials
Weight-based measurements are often employed where the true mass of a quantity must be ascertained
Sensing element for detecting vessel weight
Load cell
Patthiya Srimahaprom 61010789