Sensors help to capture what is going on in the real world. This deck explains how real-world information, such as pressure, temperature, speed is converted into a useful electronics format that can be analyzed, manipulated, stored or sent to another device.
1. The World Leader in High Performance Signal Processing Solutions
FUNDAMENTALS OF DESIGN
Class 1
Introduction
Presented by David Kress
2. The Goal
Capture what is going on in the real world
Convert into a useful electronic format
Analyze, Manipulate, Store, and Send
Return to the real world
4. Analog to Electronic signal processing
Sensor Amp Converter Digital Processor
(INPUT)
Actuator Amp Converter
(OUTPUT)
5. The Sensor
Analog, but Analog
Sensor
NOT (INPUT) AND
Amp Converter Digital Processor
electronic electronic
Actuator Amp Converter
(OUTPUT)
6. Popular sensors
Sensor Type Output
Thermocouple Voltage
Photodiode Current
Strain Gauge Resistance
Microphone Capacitance
Touch Button Charge Output
Antenna Inductance
7. Thermocouple
Very low level (µV/ºC)
Non-linear
Difficult to handle
Wires need insulation
Susceptible to noise
Fragile
8. Sensor Signal Conditioning
Sensor Amp
Analog, Analog,
electronic, electronic,
but “dirty” and “clean”
•Amplify the signal to a noise-resistant level
•Lower the source impedance
•Linearize (sometimes but not always)
•Filter
•Protect
9. Types of Temperature Sensors
THERMOCOUPLE RTD THERMISTOR SEMICONDUCTOR
Widest Range: Range: Range: Range:
–184ºC to +2300ºC –200ºC to +850ºC 0ºC to +100ºC –55ºC to +150ºC
High Accuracy and Fair Linearity Poor Linearity Linearity: 1ºC
Repeatability Accuracy: 1ºC
Needs Cold Junction Requires Requires Requires Excitation
Compensation Excitation Excitation
Low-Voltage Output Low Cost High Sensitivity 10mV/K, 20mV/K,
or 1µA/K Typical
Output
10. Common Thermocouples
TYPICAL NOMINAL ANSI
JUNCTION MATERIALS USEFUL SENSITIVITY DESIGNATION
RANGE (ºC) (µV/ºC)
Platinum (6%)/ Rhodium- 38 to 1800 7.7 B
Platinum (30%)/Rhodium
Tungsten (5%)/Rhenium - 0 to 2300 16 C
Tungsten (26%)/Rhenium
Chromel - Constantan 0 to 982 76 E
Iron - Constantan 0 to 760 55 J
Chromel - Alumel –184 to 1260 39 K
Platinum (13%)/Rhodium- 0 to 1593 11.7 R
Platinum
Platinum (10%)/Rhodium- 0 to 1538 10.4 S
Platinum
Copper-Constantan –184 to 400 45 T
11. Thermocouple Output Voltages
for Type J, K and S Thermocouples
THERMOCOUPLE OUTPUT VOLTAGE (mV) 60
50
TYPE K
40 TYPE J
30
20
TYPE S
10
0
-10
-250 0 250 500 750 1000 1250 1500 1750
TEMPERATURE (°C)
12. Thermocouple Seebeck Coefficient vs.
Temperature
70
60 TYPE J
SEEBECK COEFFICIENT - µV/ °C
50
TYPE K
40
30
20
TYPE S
10
0
-250 0 250 500 750 1000 1250 1500 1750
TEMPERATURE (°C)
13. Thermocouple Basics
A. THERMOELECTRIC VOLTAGE C. THERMOCOUPLE MEASUREMENT
Metal A Metal A
V1 – V2
Metal A
V1 T1 Thermoelectric V1 T1 T2 V2
EMF
Metal B Metal B
B. THERMOCOUPLE D. THERMOCOUPLE MEASUREMENT
Copper Copper
Metal A R Metal A V
Metal A Metal A
I T3 T4
V1 T1 T2 V2 V1 T1 T2 V2
Metal B Metal B
R = Total Circuit Resistance
I = (V1 – V2) / R V = V1 – V2, If T3 = T4
14. Using a Temperature Sensor for Cold-
Junction Compensations
V(OUT) TEMPERATURE
V(COMP) COMPENSATION
CIRCUIT
COPPER COPPER
METAL A SAME METAL A
TEMP TEMP
SENSOR
T1 V(T1) V(T2) T2
METAL B
V(COMP) = f(T2)
ISOTHERMAL BLOCK
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
15. AD594/AD595 Monolithic Thermocouple
Amplifier with Cold-Junction Compensation
+5V
0.1µF BROKEN
4.7k THERMOCOUPLE VOUT
ALARM 10mV/°C
OVERLOAD
TYPE J: AD594 DETECT
TYPE K: AD595
THERMOCOUPLE AD594/AD595 +A
– – –TC
ICE
G + G POINT
+ + COMP
+TC
16. Basic Relationships For Semiconductor
Temperature Sensors
IC IC
N TRANSISTORS
ONE TRANSISTOR
VBE VN
kT IC kT IC
VBE ln VN ln
q IS q N IS
kT
VBE VBE VN ln(N)
q
INDEPENDENT OF IC, IS
17. Classic Bandgap Temperature Sensor
+VIN
R R "BROKAW CELL"
+ VBANDGAP = 1.205V
I2 @ I1
Q2 Q1
NA A
VN VBE
kT
VBE VBE VN ln(N) R2 (Q1)
q
R1 kT
VPTAT = 2 ln(N)
R2 q
R1
18. Analog Temperature Sensors
Product Accuracy Max Accuracy Operating Supply Max Interface Package
(Max) Range Temp Range Current
Range
± 0.5°C 25°C -55°C to TO-52,2-ld FP,
AD590 4 to 30V 298uA Current Out
± 1.0°C -25°C to 105°C 150°C SOIC, Die
± 0.5°C 25°C -25°C to 298uA
AD592 4 to 30V Current Out TO-92
± 1.0°C -55°C to 150°C 105°C
0°C to 85°C -55°C to TO-92, SOT23,
TMP35 ± 2.0°C 2.7 to 5.5V 50uA Voltage Out
-25°C to 100°C 150°C SOIC
TO-92, SOT23,
-40°C to 125°C -55°C to 50uA
TMP36 ± 3.0°C 2.7V to 5.5V Voltage Out SOIC
150°C
± 2.0°C -50°C to 150°C -50°C to
AD22100 4 to 6.5V 650uA Voltage Out TO-92, SOIC, Die
150°C
± 2.5°C 0°C to 100°C 0°C to 100°C
AD22103 2.7 to 3.6V 600uA Voltage Out TO-92, SOIC
19. Digital Temperature Sensors
Comprehensive Portfolio of Accuracy Options
Product Accuracy (Max) Max Accuracy Interface Package
Range
± 0.2°C -10°C to 85°C
ADT7420/7320 I2C/SPI LFCSP
± 0.25°C -20°C to 105°C
ADT7410/7310 ± 0.5°C -40°C to 105°C I2C/SPI SOIC
± 1°C (B grade) 0°C to 85°C
ADT75 I2C MSOP, SOIC
± 2°C (A grade) -25°C to 100°C
± 1°C 0°C to 70°C
ADT7301 SPI SOT23, MSOP
± 1°C 0°C to 70°C
TMP05/6 PWM SC70, SOT23
± 1.5°C -40°C to 70°C
AD7414/5 I2C SOT23,MSOP
ADT7302 ± 2°C 0°C to 70°C SPI SOT23,MSOP
± 4°C
TMP03/4 -20°C to 100°C PWM TO-92,SOIC,TSSOP
21
20. Position and Motion Sensors
Linear Position: Linear Variable Differential Transformers
(LVDT)
Hall Effect Sensors
Proximity Detectors
Linear Output (Magnetic Field Strength)
Rotational Position:
Optical Rotational Encoders
Synchros and Resolvers
Inductosyns (Linear and Rotational Position)
Motor Control Applications
Acceleration and Tilt: Accelerometers
Gyroscopes
21. +
THREADED
CORE VA
~ VOUT = VA – VB
AC
SOURCE VB
1.75"
_
VOUT VOUT
SCHAEVITZ
_ POSITION + _ POSITION +
E100
LVDT – Linear Variable Differential
Transformer
22. AD698
EXCITATION AMP ~ REFERENCE
OSCILLATOR
B
VB
+
A VOUT
FILTER AMP
B
A
VA
A, B = ABSOLUTE VALUE + FILTER
_
4-WIRE LVDT
AD698 LVDT Signal Conditioner
23. Hall Effect Sensors
T CONDUCTOR
OR
SEMICONDUCTOR
I I
VH
I = CURRENT
B
B = MAGNETIC FIELD
T = THICKNESS
VH = HALL VOLTAGE
24. AD22151 Linear Output Magnetic
Field Sensor V / 2 V = +5V CC
CC VCC / 2
R2
+
R1 TEMP
REF _ R3
_
AD22151 VOUT
+
OUTPUT
AMP
CHOPPER
AMP
VOUT = 1 + R3 0.4mV Gauss NONLINEARITY = 0.1% FS
R2
25. Accelerometer Applications
Tilt or Inclination
Car Alarms
Patient Monitors
Cell phones
Video games
Inertial Forces
Laptop Computer Disc Drive Protection
Airbag Crash Sensors
Car Navigation systems
Elevator Controls
Shock or Vibration
Machine Monitoring
Control of Shaker Tables
ADI Accelerometer Fullscale g-Range: ± 2g to ± 100g
ADI Accelerometer Frequency Range: DC to 10kHz
35. Preamplifier DC Offset Errors
1000M R2
IB
~ _
OFFSET
VOS RTO
R1
IB
+
R3 DC NOISE GAIN = 1 + R2
R1
IB DOUBLES EVERY 10 C TEMPERATURE RISE
R1 = 1000M @ 25 C (DIODE SHUNT RESISTANCE)
R1 HALVES EVERY 10 C TEMPERATURE RISE
R3 CANCELLATION RESISTOR NOT EFFECTIVE
36. Sensor Resistances Used In Bridge
Circuits Span A Wide Dynamic Range
Strain Gages 120, 350, 3500
Weigh-Scale Load Cells 350 - 3500
Pressure Sensors 350 - 3500
Relative Humidity 100k - 10M
Resistance Temperature Devices (RTDs) 100 , 1000
Thermistors 100 - 10M
37. Wheatstone Bridge Produces An Output Null
When The Ratios Of Sidearm Resistances Match
VB
THE WHEATSTONE BRIDGE:
R4 R3
R1 R2
VO VB
R1 + R4 R2 + R3
VO AT BALANCE,
R1 R2
VO = 0 if
R4 R3
R1 R2
38. Output Voltage Sensitivity And Linearity Of Constant Current Drive
Bridge Configurations Differs According To The Number Of Active
Elements
IB IB IB IB
R R R+R R R RR R+R RR
VO VO VO VO
R R+R R R+R R R+R RR R+R
R
VO: IBR R
IB
R
IB
R IB R
4 R + 2 2
4
Linearity
0.25%/% 0 0 0
Error:
(A) Single-Element (B) Two-Element (C) Two-Element (D) All-Element
Varying Varying (1) Varying (2) Varying
39. A Generally Preferred Method Of Bridge Amplification Employs
An Instrumentation Amplifier For Stable Gain And High CMR
VB
OPTIONAL RATIOMETRIC OUTPUT
VREF = VB
+VS
R R
R
VB
VOUT = R GAIN
4 R +
RG 2
IN AMP
REF VOUT
+
R
R+R -VS*
* SEE TEXT REGARDING
SINGLE-SUPPLY OPERATION
40. Upcoming webcasts
Converter Simulation: Beyond the Eval Board
January 19th at 3:00 p.m. (ET)
RF Detectors
February 16th at Noon (ET)
Challenges in Embedded Design for real-time systems
March 16th at Noon (ET)
www.analog.com/webcast
41. 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
www.analog.com/webcast
Notas do Editor
As you probably know, our first challenge is that light, sound, weight, speed, temperature, even smell are analog, or continuous wave forms. That’s okay for us analog human beings, but a lousy format for electronic devices.It gets worse, because those real world analog signals aren’t electronic, either.That means we have two challenges: One is to capture the physical attributes and signals from the real world – these analog signals, and Two, convert them to electronic signals that we can manipulate…
How we do that is what we’ll be covering in this 12-part course. In the coming months we’ll go through each stage of the basic signal chain, from amplifiers to data converters – those components that convert the analog electronic signal into a digital stream – then to the heart of many modern circuits, the digital processor. We’ll also cover what is needed to power today’s circuits, how to make them portable, and how to lay them out .So let’s go back to the beginning of the circuit and address the first task of turning that analog, non electrical signal into an analog electrical one. How do we do that?
By employing sensors. Sensors are devices that respond to changes in these analog, non-electronic signals – temperature, speed, weight, pressure, and so on and turn them into electronic analog signals. Those signals can be in many different forms.
As you can see, for the measurement of different kinds of analog real-world signals, different sensors provide different outputs. In all cases, we have achieved goal number one – capturing that signal so we can move it down the signal chain.
Let’s look at one example of a sensor. The Thermocouple is a device made of dissimilar metals welded at one end, which generate a voltage that increases with temperature. The output, as we just saw, is a varying voltage. Like any electronic device and like any sensor, it has its benefits and its problems, most important to our goal is that the output of this device is very low level – which means the signal can be below the ambient noise level of the circuit – which in turn means we cannot discriminate it from the noise.
Which means we need to take that low-level, fragile signal and perform Sensor Signal Conditioning. In this critical step we will:Amplify the signal to a noise-resistant levelLower the source impedanceLinearize (sometimes but not always)FilterProtectionThe result is a signal clean enough to be sent to the converter for digitizing. Without this critical stage data conversion would be inaccurate, rendering the entire circuit useless. It’s that important.
A series of thermocouple amplifiers is available from Analog Devices so you can find the right accuracy and operating temperature range for your needs. These products use very little power, less than 1mW, and are in a small MSOP package. Two of the important things to look at when using a thermocouple amplifier are the initial accuracy and the temperature range where the amplifier is accurate. This is the temperature of the board that the amplifier is on, not the temperature of the thermocouple itself.
Before Dave takes any questions, I want to remind you that every month Analog Devices presents a webcast on a current Hot Topic in designing with Semiconductors. A week from today at 3pm, on January 19th, we’ll present a webcast on software simulation for data converters. Next month we’ll be presenting a webcast on the use of RF Detectors and in March on Embedded Design. Registration will be available shortly for both at www.analog.com slash webcast, where you can also access our library of archived webcasts that you can view anytime, on demand.