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FUNDAMENTALS OF DESIGNClass 1
Introduction
Presented by David Kress
The Goal
Capture what is going on in the real worldConvert into a useful electronic formatAnalyze, Manipulate, Store, and SendReturn to the real world
The real world is NOT digital
Analog to Electronic signal processing
Sensor(INPUT)
Digital ProcessorAmp Converter
Actuator(OUTPUT)
Amp Converter
The Sensor
Sensor(INPUT)
Digital ProcessorAmp Converter
Actuator(OUTPUT)
Amp Converter
Analog, but NOT
electronic
AnalogAND
electronic
Popular sensors
Sensor Type Output
Thermocouple Voltage
Photodiode Current
Strain Gauge Resistance
Microphone Capacitance
Touch Button Charge Output
Antenna Inductance
Thermocouple
Very low level (µV/ºC)Non-linearDifficult to handleWires need insulationSusceptible to noiseFragile
Sensor Signal Conditioning
Sensor Amp
Analog, electronic, but “dirty”
Analog,electronic,
and “clean”
• Amplify the signal to a noise-resistant level
• Lower the source impedance
• Linearize (sometimes but not always)
• Filter
• Protect
Types of Temperature Sensors
THERMOCOUPLE RTD THERMISTOR SEMICONDUCTOR
Widest Range:
–184ºC to +2300ºC
Range:
–200ºC to +850ºC
Range:
0ºC to +100ºC
Range:
–55ºC to +150ºC
High Accuracy and
Repeatability
Fair Linearity Poor Linearity Linearity: 1ºC
Accuracy: 1ºC
Needs Cold Junction
Compensation
Requires
Excitation
Requires
Excitation
Requires Excitation
Low-Voltage Output Low Cost High Sensitivity 10mV/K, 20mV/K,
or 1µA/K TypicalOutput
Common Thermocouples
JUNCTION MATERIALS
TYPICAL
USEFUL
RANGE (ºC)
NOMINAL
SENSITIVITY
(µV/ºC)
ANSI
DESIGNATION
Platinum (6%)/ Rhodium-
Platinum (30%)/Rhodium
38 to 1800 7.7 B
Tungsten (5%)/Rhenium -
Tungsten (26%)/Rhenium
0 to 2300 16 C
Chromel - Constantan 0 to 982 76 E
Iron - Constantan 0 to 760 55 J
Chromel - Alumel –184 to 1260 39 K
Platinum (13%)/Rhodium-
Platinum
0 to 1593 11.7 R
Platinum (10%)/Rhodium-
Platinum
0 to 1538 10.4 S
Copper-Constantan –184 to 400 45 T
Thermocouple Output Voltages for Type J, K and S Thermocouples
-250 0 250 500 750 1000 1250 1500 1750-10
0
10
20
30
40
50
60T
HE
RM
OC
OU
PL
E O
UT
PU
T V
OL
TA
GE
(m
V)
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
-250 0 250 500 750 1000 1250 1500 1750-10
0
10
20
30
40
50
60T
HE
RM
OC
OU
PL
E O
UT
PU
T V
OL
TA
GE
(m
V)
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
Thermocouple Seebeck Coefficient vs. Temperature
-250 0 250 500 750 1000 1250 1500 17500
10
20
30
40
50
60
70S
EE
BE
CK
CO
EF
FIC
IEN
T -
µV
/ °C
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
-250 0 250 500 750 1000 1250 1500 17500
10
20
30
40
50
60
70S
EE
BE
CK
CO
EF
FIC
IEN
T -
µV
/ °C
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
Thermocouple Basics
T1
Metal A
Metal B
ThermoelectricEMF
RMetal A Metal A
R = Total Circuit ResistanceI = (V1 – V2) / R
V1 T1 V2T2
V1 – V2
Metal B
Metal A Metal A
V1
V1
T1
T1
T2
T2
V2
V2
VMetal AMetal A
Copper Copper
Metal BMetal B
T3 T4
V = V1 – V2, If T3 = T4
A. THERMOELECTRIC VOLTAGE
B. THERMOCOUPLE
C. THERMOCOUPLE MEASUREMENT
D. THERMOCOUPLE MEASUREMENT
I
V1 T1
Metal A
Metal B
ThermoelectricEMF
RMetal A Metal A
R = Total Circuit ResistanceI = (V1 – V2) / R
V1 T1 V2T2
V1 – V2
Metal B
Metal A Metal A
V1
V1
T1
T1
T2
T2
V2
V2
VMetal AMetal A
Copper Copper
Metal BMetal B
T3 T4
V = V1 – V2, If T3 = T4
A. THERMOELECTRIC VOLTAGE
B. THERMOCOUPLE
C. THERMOCOUPLE MEASUREMENT
D. THERMOCOUPLE MEASUREMENT
I
V1
Using a Temperature Sensor for Cold-Junction Compensations
TEMPERATURECOMPENSATION
CIRCUIT
TEMPSENSOR
T2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAMETEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
TEMPERATURECOMPENSATION
CIRCUIT
TEMPSENSOR
T2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAMETEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
AD594/AD595 Monolithic Thermocouple Amplifier with Cold-Junction Compensation
ICEPOINTCOMP
+
OVERLOADDETECT
VOUT10mV/°C
+5V
BROKENTHERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594TYPE K: AD595
0.1µF
ICEPOINTCOMP
+
OVERLOADDETECT
VOUT10mV/°C
+5V
BROKENTHERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594TYPE K: AD595
0.1µF
Basic Relationships For Semiconductor Temperature Sensors
IC IC
VBE VN
VBE VBE VNkTq
N ln( )
VBEkTq
ICIS
ln VN
kTq
ICN IS
ln
INDEPENDENT OF IC, IS
ONE TRANSISTORN TRANSISTORS
Classic Bandgap Temperature Sensor
"BROKAW CELL"R R
+I2 @ I1
Q2NA
Q1
A
R2
R1
VN VBE
(Q1)
VBANDGAP = 1.205V
+VIN
VPTAT = 2R1R2
kTq ln(N)
VBE VBE VNkTq
N ln( )
Analog Temperature Sensors
Product Accuracy (Max) Max Accuracy Range
Operating Temp Range
Supply Range
Max Current
Interface Package
AD590 ± 0.5°C± 1.0°C
25°C-25°C to 105°C
-55°C to 150°C 4 to 30V 298uA Current Out TO-52,2-ld FP,
SOIC, Die
AD592 ± 0.5°C± 1.0°C
25°C-55°C to 150°C
-25°C to 105°C 4 to 30V 298uA Current Out TO-92
TMP35 ± 2.0°C 0°C to 85°C-25°C to 100°C
-55°C to 150°C 2.7 to 5.5V 50uA Voltage Out TO-92, SOT23,
SOIC
TMP36 ± 3.0°C -40°C to 125°C -55°C to 150°C 2.7V to 5.5V 50uA Voltage Out
TO-92, SOT23, SOIC
AD22100 ± 2.0°C -50°C to 150°C -50°C to 150°C 4 to 6.5V 650uA Voltage Out TO-92, SOIC, Die
AD22103 ± 2.5°C 0°C to 100°C 0°C to 100°C 2.7 to 3.6V 600uA Voltage Out TO-92, SOIC
Digital Temperature SensorsComprehensive Portfolio of Accuracy Options
21
Product Accuracy (Max) Max Accuracy Range
Interface Package
ADT7420/7320 ± 0.2°C± 0.25°C
-10°C to 85°C-20°C to 105°C I2C/SPI LFCSP
ADT7410/7310 ± 0.5°C -40°C to 105°C I2C/SPI SOIC
ADT75 ± 1°C (B grade)± 2°C (A grade)
0°C to 85°C-25°C to 100°C I2C MSOP, SOIC
ADT7301 ± 1°C 0°C to 70°C SPI SOT23, MSOP
TMP05/6 ± 1°C 0°C to 70°C PWM SC70, SOT23
AD7414/5 ± 1.5°C -40°C to 70°C I2C SOT23,MSOP
ADT7302 ± 2°C 0°C to 70°C SPI SOT23,MSOP
TMP03/4 ± 4°C -20°C to 100°C PWM TO-92,SOIC,TSSOP
Position and Motion Sensors
Linear Position: Linear Variable Differential Transformers (LVDT)
Hall Effect SensorsProximity Detectors Linear Output (Magnetic Field Strength)
Rotational Position:Optical Rotational EncodersSynchros and ResolversInductosyns (Linear and Rotational Position)Motor Control Applications
Acceleration and Tilt: AccelerometersGyroscopes
LVDT – Linear Variable Differential Transformer
~AC
SOURCE
VOUT = VA – VB
+
_
VOUT
POSITION +_
VOUT
POSITION +_
VA
VB
1.75"
THREADEDCORE
SCHAEVITZE100
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
Hall Effect Sensors
I I
T
B
VH
CONDUCTOROR
SEMICONDUCTOR
I = CURRENT
B = MAGNETIC FIELD
T = THICKNESS
VH = HALL VOLTAGE
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
Accelerometer Applications Tilt or Inclination
Car AlarmsPatient MonitorsCell phonesVideo games
Inertial ForcesLaptop Computer Disc Drive ProtectionAirbag Crash SensorsCar Navigation systemsElevator Controls
Shock or VibrationMachine MonitoringControl of Shaker Tables
ADI Accelerometer Fullscale g-Range: ± 2g to ± 100g ADI Accelerometer Frequency Range: DC to 10kHz
ADXL-family Micro-machined Accelerometers
FIXEDOUTERPLATES
CS1 CS1< CS2= CS2
DENOTES ANCHOR
BEAM
TETHER
CS1 CS2
CENTERPLATE
AT REST APPLIED ACCELERATION
Using an Accelerometer to Measure Tilt
X
0°
+90°
1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin
0g
–90°
X
0°
+90°
1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin
0g
–90°
Gyro Axes of Rotational Sensitivity
Coriolis acceleration example.
Displacement due to the Coriolis Effect
Photograph of mechanical sensor.
High Impedance Sensors
Photodiodes
Piezoelectric Sensors AccelerometersHydrophones
Humidity Monitors
pH Monitors
Chemical Sensors
Smoke Detectors
Charge Coupled Devices and
Contact Image Sensors for Imaging
Photodiode Equivalent Circuit
PHOTOCURRENT
IDEALDIODE
INCIDENTLIGHT
RSH(T)
100kW -100GW
CJ
NOTE: RSH HALVES EVERY 10°C TEMPERATURE RISE
Current-to-voltage Converter (Simplified)
ISC = 30pA
(0.001 fc)
+
_
R = 1000MW
VOUT = 30mV
Sensitivity: 1mV / pA
Preamplifier DC Offset Errors
~
VOS
IB
IB
R1
R21000MW
+
_
IB DOUBLES EVERY 10°C TEMPERATURE RISE
R1 = 1000MW @ 25°C (DIODE SHUNT RESISTANCE)
R1 HALVES EVERY 10°C TEMPERATURE RISE
DC NOISE GAIN = 1 + R2R1
OFFSETRTO
R3
R3 CANCELLATION RESISTOR NOT EFFECTIVE
Sensor Resistances Used In Bridge Circuits Span A Wide Dynamic Range
Strain Gages 120W, 350W,
3500W
Weigh-Scale Load Cells 350W - 3500W
Pressure Sensors 350W - 3500W
Relative Humidity 100kW - 10MW
Resistance Temperature Devices (RTDs) 100W , 1000W
Thermistors 100W - 10MW
Wheatstone Bridge Produces An Output Null When The Ratios Of Sidearm Resistances Match
T H E W H EA T ST O N E B R ID G E:
V O
R 4
R 1
R 3
R 2
VB
R3R2
R2
R4R1
R1VV BO
A T B A LA N C E,
V O R 3
R 2R 4R 1
if0=
Output Voltage Sensitivity And Linearity Of Constant Current Drive Bridge Configurations Differs According To The Number Of Active Elements
R R
R R+R
R+R
R+R R+R R+R
R R R+R R RR R
R R R
VOVO VO
VO
IB IB IB IB
VO:
LinearityError: 0.25%/% 0 0 0
IBR4
RR4R +
IB2
R IB RIB2
R
(A) Single-ElementVarying
(B) Two-ElementVarying (1)
(C) Two-ElementVarying (2)
(D) All-ElementVarying
R
R R
R
+
IN AMP
REF VOUT
RG
+VS
-VS*R+R
* SEE TEXT REGARDINGSINGLE-SUPPLY OPERATION
OPTIONAL RATIOMETRIC OUTPUTVB
VREF = VB
VB4
RR2R +
VOUT = GAIN
A Generally Preferred Method Of Bridge Amplification Employs An Instrumentation Amplifier For Stable Gain And High CMR
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Fundamentals Webcasts 2011
January Introduction and Fundamentals of Sensors February The Op Amp March Beyond the Op Amp April Converters, Part 1, Understanding Sampled Data Systems May Converters, Part 2, Digital-to-Analog Converters June Converters, Part 3, Analog-to-Digital Converters July Powering your circuit August RF: Making your circuit mobile September Fundamentals of DSP/Embedded System design October Challenges in Industrial Design November Tips and Tricks for laying out your PC board December Final Exam, Ask Analog Devices
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