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a STRAIN GAGE BASED MEASUREMENTS I Strain: Strain Gage, - - PowerPoint PPT Presentation
a STRAIN GAGE BASED MEASUREMENTS I Strain: Strain Gage, - - PowerPoint PPT Presentation
PRACTICAL DESIGN TECHNIQUES FOR SENSOR SIGNAL CONDITIONING 1 Introduction 2 Bridge Circuits 3 Amplifiers for Signal Conditioning I 4 Strain, Force, Pressure, and Flow Measurements 5 High Impedance Sensors 6 Position and Motion Sensors 7
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4.2 UNBONDED WIRE STRAIN GAGE
STRAIN SENSING WIRE AREA = A LENGTH = L RESISTIVITY =ρ ρ RESISTANCE = R FORCE FORCE R = ρ ρ L A ∆ ∆R R ∆ ∆L L = GF • GF = GAGE FACTOR 2 TO 4.5 FOR METALS >150 FOR SEMICONDUCTORS ∆ ∆L L = MICROSTRAINS ( µε
µε )
1 µε
µε = 1×10–6 cm / cm = 1 ppm
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4.3 BONDED WIRE STRAIN GAGE
I I SMALL SURFACE AREA I I LOW LEAKAGE I I HIGH ISOLATION FORCE FORCE
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4.4 METAL FOIL STRAIN GAGE
I I PHOTO ETCHING TECHNIQUE I I LARGE AREA I I STABLE OVER TEMPERATURE I I THIN CROSS SECTION I I GOOD HEAT DISSIPATION FORCE FORCE
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4.5 COMPARISON BETWEEN METAL AND SEMICONDUCTOR STRAIN GAGES
PARAMETER Measurement Range Gage Factor Resistance, Ω Ω Resistance Tolerance Size, mm METAL STRAIN GAGE 0.1 to 40,000 µε µε 2.0 to 4.5 120, 350, 600, …, 5000 0.1% to 0.2% 0.4 to 150 Standard: 3 to 6 SEMICONDUCTOR STRAIN GAGE 0.001 to 3000 µε µε 50 to 200 1000 to 5000 1% to 2% 1 to 5
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4.6 STRAIN GAGE BEAM FORCE SENSOR
R1 R2 R3 R4 FORCE
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R1 R2 R4 R3 VB
+ _
RIGID BEAM
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4.7 6-LEAD LOAD CELL
+VB +SENSE –VB +VOUT –SENSE –VOUT FORCE
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4.8 PRESSURE SENSORS
PRESSURE SOURCE PRESSURE SENSOR (DIAPHRAGM) STRAIN GAGE SIGNAL CONDITIONING ELECTRONICS MECHANICAL OUTPUT
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4.9 PITOT TUBE USED TO MEASURE FLOW RATE
DIFFERENTIAL PRESSURE TRANSDUCER STRAIN GAGES CONDITIONING ELECTRONICS FLOW PITOT TUBE MECHANICAL OUTPUT P1 P2
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4.10 MEASURING FLOW RATE USING THE VENTURI EFFECT
DIFFERENTIAL PRESSURE TRANSDUCER STRAIN GAGES CONDITIONING ELECTRONICS MECHANICAL OUTPUT RESTRICTION FLOW P1 P2
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4.11 BENDING VANE WITH STRAIN GAGE USED TO MEASURE FLOW RATE
FLOW BENDING VANE WITH STRAIN GAGE CONDITIONING ELECTRONICS "R"
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4.12 PRECISION STRAIN GAGE SENSOR AMPLIFIER
OP177 AD620 AD589 STRAIN SENSOR: Columbia Research Labs 2682 Range: –3500µε
ε to +5000µε ε
Output: 10.25mV/1000µε ε +15V +1.235V 499Ω Ω 100Ω Ω 100Ω Ω 1.7kΩ Ω 8.2kΩ Ω 2N2907A 30.1kΩ Ω 124Ω Ω 27.4kΩ Ω +15V +15V –15V –15V 0.1µF +15V 10mA +1.235V 7 1 8 6 5 4 2 3 2 3 7 4 6 + – + – VOUT –3.500V = –3500µε
ε
+5.000V = +5000µε
ε
1kΩ Ω 1kΩ Ω 1kΩ Ω 1kΩ Ω
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4.13 PRECISION LOAD CELL AMPLIFIER
350Ω Ω 350Ω Ω 350Ω Ω 350Ω Ω AD620 AD588 2 1 3 9 4 6 8 10 13 12 11 16 –15V +15V +15V 1kΩ Ω +10.000V 2N2219A 6 7 3 2 4 +15V –15V – – + –15V +15 2 3 4 5 6 8 1 7 475Ω Ω 100Ω Ω VOUT 0 TO +10.000V FS + +10.000V 350Ω Ω LOAD CELL 100mV FS OP177
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4.14 SINGLE SUPPLY LOAD CELL AMPLIFIER
350Ω Ω 350Ω Ω 350Ω Ω 350Ω Ω 1/2 OP213 1/2 OP213 REF195 +5.000V +VS 2 4 6 10kΩ Ω 1kΩ Ω 28.7Ω Ω 196Ω Ω 1kΩ Ω 10kΩ Ω – – + + G = 100 VOUT 1µF 2 8 3 4 1 7 6 5 (VREF)
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4.15 LOAD CELL APPLICATION USING THE AD7730 ADC
+5V AVDD GND + AIN – AIN + VREF – VREF RLEAD RLEAD 6-LEAD LOAD CELL
AD7730 ADC 24 BITS
+SENSE – SENSE
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+FORCE – FORCE DVDD +5V/+3V
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