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 Temperature Sensors 8 ADCs for Signal Conditioning 9 Smart Sensors 10 Hardware Design Techniques 6.0 a

POSITION AND MOTION SENSORS I Linear Position: Linear Variable Differential Transformers (LVDT) I Hall Effect Sensors N Proximity Detectors N Linear Output (Magnetic Field Strength) I Rotational Position: N Rotary Variable Differential Transformers (RVDT) N Optical Rotational Encoders N Synchros and Resolvers N Inductosyns (Linear and Rotational Position) N Motor Control Applications I Acceleration and Tilt: Accelerometers 6.1 a

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT) + THREADED CORE V A V OUT = V A – V B ~ AC SOURCE V B 1.75" _ V OUT V OUT SCHAEVITZ _ _ POSITION E100 POSITION + + 6.2 a

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: 660 Ω Ω I Secondary Impedance: 960 Ω Ω 6.3 a

IMPROVED LVDT OUTPUT SIGNAL PROCESSING ABSOLUTE + FILTER VALUE V OUT + ~ _ AC SOURCE ABSOLUTE FILTER _ VALUE LVDT V OUT + _ + POSITION _ 6.4 a

PRECISION ABSOLUTE VALUE CIRCUIT (FULL-WAVE RECTIFIER) gm STAGE + MULTIPLIER INPUT V / I × OUTPUT _ + ± 1 _ COMPARATOR 6.5 a

AD598 LVDT SIGNAL CONDITIONER (SIMPLIFIED) AD598 AMP ~ EXCITATION OSCILLATOR V A ABS + FILTER VALUE V OUT A – B FILTER AMP A + B ABS FILTER _ VALUE V B 5-WIRE LVDT 6.6 a

AD698 LVDT SIGNAL CONDITIONER (SIMPLIFIED) AD698 REFERENCE EXCITATION AMP ~ OSCILLATOR B V B + V OUT A FILTER AMP B A V A A, B = ABSOLUTE VALUE + FILTER _ 4-WIRE LVDT 6.7 a

HALF-BRIDGE LVDT CONFIGURATION AD698 REFERENCE EXCITATION AMP ~ OSCILLATOR + B V OUT A FILTER AMP B A _ A, B = ABSOLUTE VALUE + FILTER HALF BRIDGE LVDT 6.8 a

HALL EFFECT SENSORS T CONDUCTOR OR SEMICONDUCTOR I I V H I = CURRENT B B = MAGNETIC FIELD T = THICKNESS V H = HALL VOLTAGE 6.9 a

HALL EFFECT SENSOR USED AS A ROTATION SENSOR ROTATION I COMPARATOR GAIN WITH HYSTERESIS V H HALL B + CELL _ V OUT V THRESHOLD MAGNETS 6.10 a

AD22151 LINEAR OUTPUT MAGNETIC FIELD SENSOR V CC = +5V V CC / 2 V CC / 2 R2 + R1 TEMP REF _ R3 _ V OUT AD22151 + OUTPUT AMP CHOPPER AMP V OUT = 1 + R3 0.4mV Gauss NONLINEARITY = 0.1% FS R2 6.11 a

INCREMENTAL AND ABSOLUTE OPTICAL ENCODERS INCREMENTAL θ θ θ θ ABSOLUTE LIGHT LIGHT SOURCES SOURCES DISC DISC SHAFT SHAFT SENSORS SENSORS CONDITIONING CONDITIONING ELECTRONICS ELECTRONICS 5 BITS 5 BITS 6.12 a

SYNCHROS AND RESOLVERS S1 S2 STATOR SYNCHRO ROTOR ROTOR R1 S1 TO S3 = V sin ω ω t sin θ θ θ θ S3 TO S2 = V sin ω ω t sin ( θ θ + 120°) V sin ω ω t S2 TO S1 = V sin ω ω t sin ( θ θ + 240°) R2 S3 RESOLVER ROTOR S4 R1 S1 TO S3 = V sin ω ω t sin θ θ V sin ω ω t S4 TO S2 = V sin ω ω t sin ( θ STATOR θ + 90°) STATOR = V sin ω ω t cos θ θ S2 R2 S3 S1 6.13 a

RESOLVER-TO-DIGITAL CONVERTER (RTD) V sin ω ω t ROTOR REFERENCE V sin ω ω t [sin ( θ θ – ϕ ϕ )] V sin ω ω t sin V sin ω ω t sin θ θ cos ϕ ϕ COSINE θ θ MULTIPLIER _ STATOR ϕ ϕ DETECTOR INPUTS + SINE θ – ϕ ϕ ) K sin ( θ MULTIPLIER V sin ω ω t cos θ V sin ω ω t cos θ θ sin ϕ ϕ ERROR θ ϕ ϕ INTEGRATOR UP / DOWN VCO COUNTER VELOCITY ϕ = DIGITAL ANGLE ϕ LATCHES WHEN ERROR = 0, ϕ ϕ ϕ ϕ = θ θ ± 1 LSB 6.14 a

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 6.15 a

LINEAR INDUCTOSYN ω t sin 2 π π X ω t cos 2 π π X V sin ω V sin ω S S V sin ω ω t SLIDER EXPANDED SCALE S X SCALE TRACES SLIDER TRACES SINE COSINE TWO WINDINGS SHIFTED BY 1/4 PERIOD (90°) 6.16 a

AC INDUCTION MOTOR CONTROL APPLICATION ADMC300, ADMC330, or ADMC331 VECTOR POWER AC TRANSFORM PWM STAGE MOTOR PROCESSOR (INVERTER) MOTOR CURRENTS DSP ADCs RESOLVER TO DIGITAL RESOLVER POSITION, VELOCITY CONVERTER HOST COMPUTER 6.17 a

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 6.18 a

ADXL-FAMILY MICROMACHINED ACCELEROMETERS (TOP VIEW OF IC) APPLIED ACCELERATION AT REST CS1 CS2 CENTER PLATE TETHER BEAM CS1 CS1 = CS2 < CS2 FIXED OUTER PLATES DENOTES ANCHOR 6.19 a

ADXL-FAMILY ACCELEROMETERS INTERNAL SIGNAL CONDITIONING SYNC APPLIED ACCELERATION CS2 > CS1 0 ° PLATE CS1 SYNCHRONOUS A1 BEAM OSCILLATOR DEMODULATOR CS2 PLATE 180 ° A2 V OUT 6.20 a

USING AN ACCELEROMETER TO MEASURE TILT +90° X 1g X θ θ Acceleration 0° –90° +1g Acceleration = 1g × sin θ θ θ θ 0g +90° 0° –90° –1g 6.21 a

ADXL202 ±2g DUAL AXIS ACCELEROMETER +3.0V TO +5.25V C X V DD V DD SELF TEST X FILT XOUT X DEMOD SENSOR 32k Ω Ω DUTY ADXL202 OSCILLATOR CYCLE µC MODULATOR 32k Ω Ω YOUT Y DEMOD SENSOR Y FILT T2 C Y R SET T2 A(g) = 8 (T1 /T2 – 0.5) 0g = 50% DUTY CYCLE T1 T2 = R SET /125M Ω Ω 6.22 a

ADXL FAMILY OF ACCELEROMETERS g RANGE NOISE SINGLE/ VOLTAGE/ DENSITY DUAL AXIS DUTY CYCLE OUTPUT 0.5mg/ √ √ Hz ADXL202 ±2g Dual Duty Cycle 0.5mg/ √ √ Hz ADXL05 ±5g Single Voltage 0.5mg/ √ √ Hz ADXL210 ±10g Dual Duty Cycle 1mg/ √ √ Hz ADXL150 ±50g Single Voltage 1mg/ √ √ Hz ADXL250 ±50g Dual Voltage 4mg/ √ √ Hz ADXL190 ±100g Single Voltage 6.23 a