practical design techniques for sensor signal … · sensor signal conditioning 1 introduction 2...
TRANSCRIPT
a 6.0
PRACTICAL DESIGN TECHNIQUES FORSENSOR SIGNAL CONDITIONING
1 Introduction
2 Bridge Circuits
3 Amplifiers for Signal Conditioning
4 Strain, Force, Pressure, and Flow Measurements
5 High Impedance Sensors
n 6 Position and Motion Sensors
7 Temperature Sensors
8 ADCs for Signal Conditioning
9 Smart Sensors
10 Hardware Design Techniques
a 6.1
POSITION AND MOTION SENSORS
n Linear Position: Linear Variable Differential Transformers (LVDT)
n Hall Effect Sensors
u Proximity Detectors
u Linear Output (Magnetic Field Strength)
n Rotational Position:
u Rotary Variable Differential Transformers (RVDT)
u Optical Rotational Encoders
u Synchros and Resolvers
u Inductosyns (Linear and Rotational Position)
u Motor Control Applications
n Acceleration and Tilt: Accelerometers
a 6.2
LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)
~AC
SOURCE
VOUT = VA – VB
+
_
VOUT
POSITION +_
VOUT
POSITION +_
VA
VB
1.75"
THREADEDCORE
SCHAEVITZE100
a 6.3
SCHAEVITZ E100 LVDT SPECIFICATIONS
n Nominal Linear Range: ±0.1 inches (± 2.54mm)
n Input Voltage: 3V RMS
n Operating Frequency: 50Hz to 10kHz (2.5kHz nominal)
n Linearity: 0.5% Fullscale
n Sensitivity: 2.4mV Output / 0.001in / Volt Excitation
n Primary Impedance: 660ΩΩ
n Secondary Impedance: 960ΩΩ
a 6.4
IMPROVED LVDT OUTPUT SIGNAL PROCESSING
~AC
SOURCE
+ ABSOLUTEVALUE
ABSOLUTEVALUE
FILTER
FILTER
+
_
VOUT
_
POSITION +_
VOUT+
_
LVDT
a 6.5
PRECISION ABSOLUTE VALUE CIRCUIT(FULL-WAVE RECTIFIER)
V / I
+
+
_
_
×
± 1
COMPARATOR
gm STAGE
MULTIPLIER
INPUT
OUTPUT
a 6.6
AD598 LVDT SIGNAL CONDITIONER (SIMPLIFIED)
AMP ~
+
_
A – BA + B
ABSVALUE
FILTER
ABSVALUE
FILTER
FILTER AMP
VA
VB
VOUT
AD598EXCITATION
5-WIRE LVDT
OSCILLATOR
a 6.7
AB
AD698 LVDT SIGNAL CONDITIONER (SIMPLIFIED)
AMP ~
+
_
FILTER AMP
VB
VOUT
AD698
EXCITATION
4-WIRE LVDT
OSCILLATORA
B
VA
REFERENCE
A, B = ABSOLUTE VALUE + FILTER
a 6.8
HALF-BRIDGE LVDT CONFIGURATION
AB
AMP ~
+
_
FILTER AMPVOUT
AD698
EXCITATION
HALF BRIDGE LVDT
OSCILLATORA
B
REFERENCE
A, B = ABSOLUTE VALUE + FILTER
a 6.9
HALL EFFECT SENSORS
I I
T
B
VH
CONDUCTOROR
SEMICONDUCTOR
I = CURRENT
B = MAGNETIC FIELD
T = THICKNESS
VH = HALL VOLTAGE
a 6.10
HALL EFFECT SENSOR USED AS A ROTATION SENSOR
HALLCELLB
I
+
_
VH
VTHRESHOLD
COMPARATORWITH
HYSTERESISGAIN
MAGNETS
ROTATION
VOUT
a 6.11
AD22151 LINEAR OUTPUT MAGNETIC FIELD SENSOR
_
+
CHOPPERAMP
VCC / 2
R1
R2
R3
OUTPUTAMP
VCC = +5V
VCC / 2
TEMPREF
+
_
VOUT = 1 + R3R2
0.4mV Gauss NONLINEARITY = 0.1% FS
AD22151 VOUT
a 6.12
INCREMENTAL AND ABSOLUTE OPTICAL ENCODERS
LIGHTSOURCES
SENSORS
CONDITIONINGELECTRONICS
SHAFT
DISC
LIGHTSOURCES
SENSORS
CONDITIONINGELECTRONICS
DISC
5 BITS
SHAFT
INCREMENTAL
ABSOLUTE
5 BITS
θθ θθ
a 6.13
SYNCHROS AND RESOLVERS
R1
R2
S1 S2
S3
R1
R2
S1
S2
S3
S4
S1 TO S3 = V sin ωωt sin θθS3 TO S2 = V sin ωωt sin (θ θ + 120°)S2 TO S1 = V sin ωωt sin (θ θ + 240°)
S1 TO S3 = V sin ωωt sin θθS4 TO S2 = V sin ωωt sin (θ θ + 90°) = V sin ωωt cos θθ
ROTOR
ROTOR
STATOR
STATOR
ROTOR
STATOR
SYNCHRO
RESOLVER
V sin ωωt
V sin ωωt
θθ
a 6.14
RESOLVER-TO-DIGITAL CONVERTER (RTD)
COSINEMULTIPLIER
SINEMULTIPLIER
DETECTOR
INTEGRATOR
UP / DOWNCOUNTER
VCO
V sin ωωt sinθθ
V sin ωωt cos θθ
V sin ωωt sin θ θ cos ϕϕ
V sin ωωt cos θ θ sin ϕϕ
_
+
V sin ωωt [sin (θ θ – ϕ ϕ )]
ERROR
V sin ωωt ROTOR REFERENCE
STATORINPUTS
LATCHES
K sin (θ θ – ϕ ϕ )
ϕϕ
ϕϕ = DIGITAL ANGLE
ϕϕ
VELOCITY
WHEN ERROR = 0, ϕϕ = θθ ± 1 LSB
ϕϕ
a 6.15
PERFORMANCE CHARACTERISTICS FORAD2S90 RESOLVER-TO-DIGITAL CONVERTER
n 12-Bit Resolution (1 LSB = 0.08° = 5.3 arc min)
n Inputs: 2V RMS ± 10%, 3kHz to 20kHz
n Angular Accuracy: 10.6 arc min ± 1 LSB
n Maximum Tracking Rate: 375 revolutions per second
n Maximum VCO Clock Rate: 1.536MHz
n Settling Time:
u 1° Step: 7ms
u 179° Step: 20ms
n Differential Inputs
n Serial Output Interface
n ± 5V Supplies, 50mW Power Dissipation
n 20 Pin PLCC
a 6.16
LINEAR INDUCTOSYN
SCALE
V sin ωωt
V sin ωωt sin 2 π π XS
V sin ωωt cos 2 π π XS
SCALETRACES
SINE COSINE
SLIDERTRACES
TWO WINDINGS SHIFTED BY 1/4 PERIOD (90°)
EXPANDED
S
SLIDER
X
a 6.17
AC INDUCTION MOTOR CONTROL APPLICATION
VECTORTRANSFORMPROCESSOR
PWMPOWERSTAGE
(INVERTER)
ACMOTOR
RESOLVERRESOLVER TO
DIGITALCONVERTER
ADCsDSP
HOSTCOMPUTER
POSITION, VELOCITY
MOTOR CURRENTS
ADMC300, ADMC330, or ADMC331
a 6.18
ACCELEROMETER APPLICATIONS
n Tilt or Inclination
u Car Alarms
u Patient Monitors
n Inertial Forces
u Laptop Computer Disc Drive Protection
u Airbag Crash Sensors
u Car Navigation systems
u Elevator Controls
n Shock or Vibration
u Machine Monitoring
u Control of Shaker Tables
n ADI Accelerometer Fullscale g-Range: ± 2g to ± 100g
n ADI Accelerometer Frequency Range: DC to 1kHz
a 6.19
ADXL-FAMILY MICROMACHINED ACCELEROMETERS(TOP VIEW OF IC)
FIXEDOUTERPLATES
CS1 CS1< CS2= CS2
DENOTES ANCHOR
BEAM
TETHER
CS1 CS2
CENTERPLATE
AT REST APPLIED ACCELERATION
a 6.20
ADXL-FAMILY ACCELEROMETERSINTERNAL SIGNAL CONDITIONING
OSCILLATOR A1SYNCHRONOUSDEMODULATOR
BEAM
PLATE
PLATE
CS1
CS2
SYNC
0°
180°A2
VOUT
CS2 > CS1
AP
PL
IED
AC
CE
LE
RA
TIO
N
a 6.21
USING AN ACCELEROMETER TO MEASURE TILT
X
0°
+90°
θθ1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin θθ
θθ0g
–90°
a 6.22
ADXL202 ±2g DUAL AXIS ACCELEROMETER
OSCILLATOR
DEMOD
DEMOD
DUTYCYCLE
MODULATOR
X
Y
SENSOR
SENSOR
32kΩΩ
32kΩΩ
+3.0V TO +5.25V
VDD VDDCX
CY
XFILT
YFILT
SELF TEST
RSET
T2
XOUT
YOUT
µC
T1
T2A(g) = 8 (T1 /T2 – 0.5)0g = 50% DUTY CYCLET2 = RSET/125MΩΩ
ADXL202
a 6.23
ADXL FAMILY OF ACCELEROMETERS
ADXL202
ADXL05
ADXL210
ADXL150
ADXL250
ADXL190
g RANGE
±2g
±5g
±10g
±50g
±50g
±100g
NOISEDENSITY
0.5mg/√√Hz
0.5mg/√√Hz
0.5mg/√√Hz
1mg/√√Hz
1mg/√√Hz
4mg/√√Hz
SINGLE/DUAL AXIS
Dual
Single
Dual
Single
Dual
Single
VOLTAGE/DUTY CYCLE
OUTPUT
Duty Cycle
Voltage
Duty Cycle
Voltage
Voltage
Voltage