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a POSITION AND MOTION SENSORS I Linear Position: Linear Variable - - PowerPoint PPT Presentation
a POSITION AND MOTION SENSORS I Linear Position: Linear Variable - - PowerPoint PPT Presentation
PRACTICAL DESIGN TECHNIQUES FOR SENSOR SIGNAL CONDITIONING 1 Introduction 2 Bridge Circuits 3 Amplifiers for Signal Conditioning 4 Strain, Force, Pressure, and Flow Measurements 5 High Impedance Sensors I 6 Position and Motion Sensors 7
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6.2 LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT)
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AC SOURCE VOUT = VA – VB + _ VOUT POSITION + _ VOUT POSITION + _ VA VB 1.75" THREADED CORE SCHAEVITZ E100
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6.3 SCHAEVITZ E100 LVDT SPECIFICATIONS
I Nominal Linear Range: ±0.1 inches (± 2.54mm) I Input Voltage: 3V RMS I Operating Frequency: 50Hz to 10kHz (2.5kHz nominal) I Linearity: 0.5% Fullscale I Sensitivity: 2.4mV Output / 0.001in / Volt Excitation I Primary Impedance: 660Ω Ω I Secondary Impedance: 960Ω Ω
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6.4 IMPROVED LVDT OUTPUT SIGNAL PROCESSING
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AC SOURCE + ABSOLUTE VALUE ABSOLUTE VALUE FILTER FILTER + _ VOUT _ POSITION + _ VOUT + _ LVDT
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6.5 PRECISION ABSOLUTE VALUE CIRCUIT (FULL-WAVE RECTIFIER)
V / I + + _ _
×
± 1 COMPARATOR gm STAGE MULTIPLIER INPUT OUTPUT
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6.6 AD598 LVDT SIGNAL CONDITIONER (SIMPLIFIED)
AMP
~
+ _ A – B A + B ABS VALUE FILTER ABS VALUE FILTER FILTER AMP VA VB VOUT
AD598
EXCITATION 5-WIRE LVDT OSCILLATOR
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6.7
A B
AD698 LVDT SIGNAL CONDITIONER (SIMPLIFIED)
AMP
~
+ _ FILTER AMP VB VOUT
AD698
EXCITATION 4-WIRE LVDT OSCILLATOR A B VA REFERENCE A, B = ABSOLUTE VALUE + FILTER
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6.8 HALF-BRIDGE LVDT CONFIGURATION
A B AMP
~
+ _ FILTER AMP VOUT
AD698
EXCITATION HALF BRIDGE LVDT OSCILLATOR A B REFERENCE A, B = ABSOLUTE VALUE + FILTER
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6.9 HALL EFFECT SENSORS
I I T B VH CONDUCTOR OR SEMICONDUCTOR I = CURRENT B = MAGNETIC FIELD T = THICKNESS VH = HALL VOLTAGE
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6.10 HALL EFFECT SENSOR USED AS A ROTATION SENSOR
HALL CELL
B I
+ _
VH VTHRESHOLD COMPARATOR WITH HYSTERESIS GAIN MAGNETS ROTATION VOUT
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6.11 AD22151 LINEAR OUTPUT MAGNETIC FIELD SENSOR
_ + CHOPPER AMP VCC / 2 R1 R2 R3 OUTPUT AMP VCC = +5V VCC / 2 TEMP REF + _ VOUT = 1 + R3 R2 0.4mV Gauss NONLINEARITY = 0.1% FS
AD22151
VOUT
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6.12 INCREMENTAL AND ABSOLUTE OPTICAL ENCODERS
LIGHT SOURCES SENSORS CONDITIONING ELECTRONICS SHAFT DISC LIGHT SOURCES SENSORS CONDITIONING ELECTRONICS DISC 5 BITS SHAFT
INCREMENTAL ABSOLUTE
5 BITS
θ θ θ θ
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6.13 SYNCHROS AND RESOLVERS
R1 R2 S1 S2 S3 R1 R2 S1 S2 S3 S4 S1 TO S3 = V sin ω
ωt sin θ
θ S3 TO S2 = V sin ω
ωt sin (θ
θ + 120°) S2 TO S1 = V sin ω
ωt sin (θ
θ + 240°) S1 TO S3 = V sin ω
ωt sin θ
θ S4 TO S2 = V sin ω
ωt sin (θ
θ + 90°) = V sin ω
ωt cos θ
θ ROTOR ROTOR STATOR STATOR ROTOR STATOR
SYNCHRO RESOLVER
V sin ω
ωt
V sin ω
ωt
θ θ
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6.14 RESOLVER-TO-DIGITAL CONVERTER (RTD)
COSINE MULTIPLIER SINE MULTIPLIER DETECTOR INTEGRATOR UP / DOWN COUNTER VCO V sin ω
ωt sin
θ θ V sin ω
ωt cos θ
θ V sin ω
ωt sin θ
θ cos ϕ
ϕ
V sin ω
ωt cos θ
θ sin ϕ
ϕ
_ + V sin ω
ωt [sin (θ
θ – ϕ
ϕ )]
ERROR V sin ω
ωt
ROTOR REFERENCE STATOR INPUTS LATCHES K sin (θ θ – ϕ
ϕ ) ϕ ϕ ϕ ϕ = DIGITAL ANGLE ϕ ϕ
VELOCITY WHEN ERROR = 0, ϕ
ϕ = θ
θ ± 1 LSB
ϕ ϕ
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6.15 PERFORMANCE CHARACTERISTICS FOR AD2S90 RESOLVER-TO-DIGITAL CONVERTER
I 12-Bit Resolution (1 LSB = 0.08° = 5.3 arc min) I Inputs: 2V RMS ± 10%, 3kHz to 20kHz I Angular Accuracy: 10.6 arc min ± 1 LSB I Maximum Tracking Rate: 375 revolutions per second I Maximum VCO Clock Rate: 1.536MHz I Settling Time: N 1° Step: 7ms N 179° Step: 20ms I Differential Inputs I Serial Output Interface I ± 5V Supplies, 50mW Power Dissipation I 20 Pin PLCC
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6.16 LINEAR INDUCTOSYN
SCALE V sin ω
ωt
V sin ω
ωt sin 2 π
π X
S V sin ω
ωt cos 2 π
π X
S SCALE TRACES SINE COSINE SLIDER TRACES TWO WINDINGS SHIFTED BY 1/4 PERIOD (90°) EXPANDED S SLIDER X
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6.17 AC INDUCTION MOTOR CONTROL APPLICATION
VECTOR TRANSFORM PROCESSOR PWM POWER STAGE (INVERTER) AC MOTOR RESOLVER RESOLVER TO DIGITAL CONVERTER ADCs DSP HOST COMPUTER POSITION, VELOCITY MOTOR CURRENTS
ADMC300, ADMC330, or ADMC331
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6.18 ACCELEROMETER APPLICATIONS
I Tilt or Inclination N Car Alarms N Patient Monitors I Inertial Forces N Laptop Computer Disc Drive Protection N Airbag Crash Sensors N Car Navigation systems N Elevator Controls I Shock or Vibration N Machine Monitoring N Control of Shaker Tables I ADI Accelerometer Fullscale g-Range: ± 2g to ± 100g I ADI Accelerometer Frequency Range: DC to 1kHz
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6.19 ADXL-FAMILY MICROMACHINED ACCELEROMETERS (TOP VIEW OF IC)
FIXED OUTER PLATES CS1 CS1 < CS2 = CS2 DENOTES ANCHOR BEAM TETHER CS1 CS2 CENTER PLATE
AT REST APPLIED ACCELERATION
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6.20 ADXL-FAMILY ACCELEROMETERS INTERNAL SIGNAL CONDITIONING
OSCILLATOR
A1
SYNCHRONOUS DEMODULATOR
BEAM PLATE PLATE
CS1 CS2 SYNC 0° 180° A2 VOUT CS2 > CS1 APPLIED ACCELERATION
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6.21 USING AN ACCELEROMETER TO MEASURE TILT
X 0° +90°
θ θ
1g Acceleration X –90° –1g 0° +1g +90° Acceleration = 1g × sin θ
θ θ θ
0g –90°
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6.22 ADXL202 ±2g DUAL AXIS ACCELEROMETER
OSCILLATOR DEMOD DEMOD DUTY CYCLE MODULATOR X Y SENSOR SENSOR 32kΩ Ω 32kΩ Ω
+3.0V TO +5.25V VDD VDD CX CY XFILT YFILT SELF TEST RSET T2 XOUT YOUT
µC
T1 T2 A(g) = 8 (T1 /T2 – 0.5) 0g = 50% DUTY CYCLE T2 = RSET/125MΩ Ω
ADXL202
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