Embed Size (px)
Citation preview
Introduction to Modeling
Define the terms System Surroundings Input/output Transducer
Distinguish between sensors and actuators For a given transducer, identify the
appropriate inputs and outputs For a given transducer, find find/calculate
span, full scale output, sensitivity, accuracy, and resolution
Distinguish between static and dynamic response characteristics of transducers
For a given transducer, find find/calculate
response time, overshoot, gain, and phaseshift, and
Explain the concept of resonance
Some definitions
System:Region of space set aside for analysis
Boundary:Defines a system such that everything within it is the system
Surroundings:Everything outside the system
Interactions between the system and surroundings:• Inputs from surroundings to the system• Outputs from system to the
surroundings.
boundary
system
surroundings“Stuff” can be a physical quantity (p. ej., masa, energía) or something more abstract (p. ej, information, a signal, or a reading)
Levels of modeling
An automotive airbag system
A block diagram
Levels of modeling
Levels of modeling
Levels of modeling
This is the “MEMS” you would buy.
Levels of modeling
This is the “MEMS” you would buy.
MEMSsensor
This is the “MEMS” we usually model.
Levels of modeling
MEMSsensor
This is the “MEMS” we usually model.
• How many inputs/outputs are
there?
• What are the inputs?
• What are the outputs?
• What is the relationship between
the inputs and the outputs?
• What do we need to know about
what is inside the “black box” in
order to find those relationships?
Transducers
Most MEMS are transducers.
Sensors
• Input is some physical quantity whose value we wish to know (p. ej., temperatura)
• Output is some other physical quantity (p. ej., voltage) whose value correlates to the measurand
Sensors measure something
Actuators
• Input is usually a voltage or some other electrical signal
• Output is physical motion of some kind
Actuators move something
Sensor or actuator?
Thermometer
Input
Output
Thermocouple
Input
Output
Sensor or actuator?
Bimetallic micro-valve
Input
Output
(http://www.konicaminolta.com)
Ink jet print head
Input
Output
Sensor or actuator?
Digital micromirror device
Input
Output
Capacitive accelerometer
Input
Output
Sensor or actuator?
Comb drive
Input
Output
“Micro-reactor” microfluidic device
Input
Output
Loading
The act of measuring alters the thing we’re trying to measure
loading
Power input to transducers
Many sensors require a voltage supply as a second input to provide power for signal conditioning—circuits that help convert the output signal to a form useful for the application
Sensors and actuators require different amounts of input power. Sensors are low input-power devices; actuators are high-input-power
devices
Power input Converted into the actuation outputControl input Tells the system what to do
Transducer characteristics
Static response characteristics
Span (or full scale input)Range of input values over which a transducer produces output values with acceptable accuracy
UnitsSame as input. (p. ej., Pa for a pressure sensor)
Full-scale output (FSO)Range of output values corresponding tothe span.
UnitsSame as output (p. ej., V for a pressure sensor)
For an actuator? μm
Transducer characteristics
Static response characteristics
Sensitivity Constant of proportionality between output and input for a linear transducer.
Slope of the best-fit line.
UnitsOutput units/input units.
Accuracy How close the transducer output is to
• (sensor) true value of the measurand, or
• (actuator) the desired output effect.
Accuracy is determined by a calibration procedure
Transducer characteristics
Static response characteristics
Resolution
• (sensor) smallest detectable change in the measurand
Unitsunits of the measurand
• (actuator)smallest change in output that can effected by changing the input
Unitsunits of the output effect(e.g., μm for displacement)
Te toca a ti
For the PX26-001DV model differential pressure transducer:
1. What is the measurand?2. What is the span?3. What is the full-scale output?4. Determine the system sensitivity. 5. Can this transducer be used to measure ΔP, for P1 = 25 psi and P2 = 24.5 psi?
Explain your answer.
Dynamic versus static response
MEMSTransducer
Steady input Steady output
Time varying input
Time varying output
Static response
Dynamic response
Step input Sinusoidal input
Time
Time
Response to step input
MEMSTransducer
Response time
Time required for output to reach new steady state value
Overshoot
Amount the initial response exceeds the desired value
TimeTime
or
Response to sinusoidal input
MEMSTransducer
Time Time
y(t)
Amplitude ratio (or gain)
Ratio of the output amplitude to the input amplitude• Usually reported in decibels (dB)• dB = 20log(gain).
Can change as a function of the input frequency
Can be magnified at some frequencies and attenuated (reduced) at others.
Frequency
Amplitude
Phase
Same as frequency
larger, smaller, or the same
In or out phase
Response to sinusoidal input
Resonance
Large magnification at certain frequencies and not others
Phase shift
• Amount of by which an output sine wave is “misaligned” with the input
• Usually reported as phase angle φ = ωt
resonance frequencies
in phase out of phase
Response to sinusoidal input
(not tim
e)
Sh
ow
s b
oth
gain
an
d p
hase
Bode plot
Volunatarios para temas
1. Resistive sensing Piezoresistive sensing Magnetoresistive sensing Thermo-resistive sensing ______________________
2. Capacitive sensing Piezoelectric sensing ______________________
3. Resonant sensing Variable-frequency resonator Variable-amplitude resonator ______________________
4. Thermoelectric sensing Thermo-electric cooling ______________________
5. Magnetic sensing
Reluctance sensing Inductive sensing ______________________
6. Capacitive actuation Piezoelectric actuation ______________________
7. Thermo-mechanical actuation Bimetallic actuation Thermopneumatic actuation Shape memory alloy actuation Hot arm actuation ______________________
8. Magnetic actuation Magnetostrictive actuation ______________________
