Transcript An Evolvable and Reconfigurable System-on

Instrumentation
Dr. Xiaofeng Wu
Instrumentation (AMME2700)
1
Piezoelectric Sensors
 A piezoelectric material produces an
electric charge when it is subjected to
a force or pressure.
qs a
*
q
Instrumentation (AMME2700)
Voltage Follower Circuit for
Piezoelectric Sensors
C  Ct  Cc  Cs
1
1 1
 
Ceq C Cb
S q*
vo
vo 
 a
RCeq C *
Sq
s
vo ( s )
H (s) 
 C
a( s) s  1
RCeq
Instrumentation (AMME2700)
Sv 
S q*
C
3
Displacement, Velocity and
Acceleration Measurement in Inertial
Space
my  C ( y  x )  k ( y  x)  F (t )
Instrumentation (AMME2700)
Dynamic Response of the Seismic
Model
z
1
H (s)  
R ms 2  cs  k
R(t )  F (t )  mx
1
jt
z
R
e
0
2
 m  cj  k
R0

e j (t  )
(k  m 2 ) 2  (c ) 2

R0
k (1  r 2 ) 2  (2rd ) 2
  tan
1
e j (t  )
d  C /(2 km)
r   / n
C
1 2rd
 tan
2
k  m
1 r 2
Instrumentation (AMME2700)
Seismic Acceleration Transducers:
Linear Seismic Accelerometer
z
m
k (1  r )  (2rd )
2 2
2
x  
z
1

2
n
(1  r )  (2rd )
2 2
m
1
x   2 x
k
n
Instrumentation (AMME2700)
2
x
Accelerometer Design
Instrumentation (AMME2700)
Piezoelectric Accelerometer
Characteristics
Instrumentation (AMME2700)
Example 1
An accelerometer with a charge sensitivity of 100pC/g ±1pC/g (95%) and a capacitance
of 200pF ± 2pF (95%) is connected to a voltage follower with an input connector
capacitance of 20pF (in parallel with the cable capacitance), a 10,000pF blocking
capacitor and a 100MΩ resistance. A 3m long cable with a capacitance of 280pF
connects the accelerometer and the voltage follower. Determine:
1.
The schematic of the instrument;
2.
The instrument’s sensitivity in mv/g;
Instrumentation (AMME2700)
9
Temperature Measurement
Instrumentation (AMME2700)
Expansion Methods for Measuring
Temperature
l  l0T
1. Liquid-in-Glass Thermometer
1) An operator is needed, so the
thermometer cannot be used in a closedloop control systems.
2)The time required to reach the
equilibrium temperature is excessive
2. Bimetallic Thermometer
The bimetallic sensor is used in
temperature control systems, and is the
primary element in most dial
thermometers and many thermostats.
Instrumentation (AMME2700)
Resistance Thermometers
 Resistance temperature detector
(RTD)
 Materials like platinum, nickel and so on
 Stable and provide a reproducible
response to temperature over long
periods of time
 Thermistors
 Fabricated from semiconducting
materials
 Very high accuracy
Instrumentation (AMME2700)
Resistance Temperature Detector
 A RTD consists of a wire coil sensor, a
sheath, a linearizing circuit, a
Wheatstone bridge, and a voltage
display instrument.
Instrumentation (AMME2700)
Resistance Temperature Detector
R  R0 (1   1 (T  T0 )   2 (T  T0 )2     n (T  T0 )n )
γ1, ··· γn are temperature coefficients of
resistivity
R0 is the resistance of the sensor at a
reference temperature T0.
R
  1 (T  T0 )
R0
R
  1 (T  T0 )   2 (T  T0 ) 2
R0
Instrumentation (AMME2700)
Sensor Circuit
vo  0  RRTD
R1R3

R2
Instrumentation (AMME2700)
Example 2

An RTD forms one arm of an equal-arm Wheatstone bridge. The fixed
resistances, R2 and R3 are equal to 25Ω±0.01 Ω (95%). The RTD has a resistance
of 25Ω at a temperature of 0oC and is used to measure a temperature that is
steady in time. Suppose the coefficient of resistance for this RTD is 0.004oC-1. A
temperature measurement is made by placing the RTD in the measuring
environment and balancing the bridge by adjusting R1. The value of R1 required
to balance the bridge is 37.36Ω. Determine the temperature of the RTD and its
uncertainty.
Instrumentation (AMME2700)