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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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