Document Text Contents
Page 1
AN990
Analog Sensor Conditioning Circuits – An Overview
INTRODUCTION
Target Audience
This application note is intended for hardware design
engineers that need to condition the output of common
analog sensors.
Goals
• Review sensor applications (e.g., temperature)
• Review sensor types (e.g., voltage output)
• Show various conditioning circuits
• Give technical references
Description
Analog sensors produce a change in an electrical
property to indicate a change in its environment. This
change in electrical property needs to be conditioned
by an analog circuit before conversion to digital.
Further processing occurs in the digital domain but is
not addressed in this application note.
The applications mentioned are:
• Electrical
• Magnetic
• Temperature
• Humidity
• Force, Weight, Torque and Pressure
• Motion and Vibration
• Flow
• Fluid Level and Volume
• Light and Infrared (IR)
• Chemistry
For each type of electrical property, commonly used
conditioning circuits are shown. Each circuit has an
accompanying list of advantages and disadvantages,
and a list of sensor types appropriate for that circuit.
The electrical properties covered are:
• Voltage
• Current
• Resistance
• Capacitance
• Charge
In addition, circuit and firmware concerns common to
many embedded designs are briefly mentioned:
• Input Protection
• Sensor Failure Detection
• Filtering
• Analog-to-Digital (A-to-D) Conversion
• Correction of Results
References to documents that treat these subjects in
more depth have been included in the “References”
section.
SENSOR APPLICATIONS
This section reviews a few analog sensor applications.
For each application, a list of common sensor types is
given for convenience. A good resource for many of
these applications is OMEGA® Engineering’s
handbooks [1, 2].
There are many more analog sensors than the ones
discussed in this application note. For example:
• Time/frequency counters [14]
• Distance ranging sensor [25]
• Current sensing transformer [6]
Emphasis is placed on the electrical behavior of the
various sensors. It is necessary to know this
information when selecting an appropriate sensor
conditioning circuit.
Electrical
These applications measure the state at some point in
an electrical circuit. They include monitoring the
condition of a crucial electrical circuit or power source.
TABLE 1: ELECTRICAL APPLICATIONS
Author: Kumen Blake
Microchip Technology Inc.
Sensor Electrical Parameter
Voltage Voltage
Current Current
Charge Charge
© 2005 Microchip Technology Inc. DS00990A-page 1
Page 16
DS00990A-page 16 ! 2005 Microchip Technology Inc.
AMERICAS
Corporate Office
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200
Fax: 480-792-7277
Technical Support:
http://support.microchip.com
Web Address:
www.microchip.com
Atlanta
Alpharetta, GA
Tel: 770-640-0034
Fax: 770-640-0307
Boston
Westborough, MA
Tel: 774-760-0087
Fax: 774-760-0088
Chicago
Itasca, IL
Tel: 630-285-0071
Fax: 630-285-0075
Dallas
Addison, TX
Tel: 972-818-7423
Fax: 972-818-2924
Detroit
Farmington Hills, MI
Tel: 248-538-2250
Fax: 248-538-2260
Kokomo
Kokomo, IN
Tel: 765-864-8360
Fax: 765-864-8387
Los Angeles
Mission Viejo, CA
Tel: 949-462-9523
Fax: 949-462-9608
San Jose
Mountain View, CA
Tel: 650-215-1444
Fax: 650-961-0286
Toronto
Mississauga, Ontario,
Canada
Tel: 905-673-0699
Fax: 905-673-6509
ASIA/PACIFIC
Australia - Sydney
Tel: 61-2-9868-6733
Fax: 61-2-9868-6755
China - Beijing
Tel: 86-10-8528-2100
Fax: 86-10-8528-2104
China - Chengdu
Tel: 86-28-8676-6200
Fax: 86-28-8676-6599
China - Fuzhou
Tel: 86-591-8750-3506
Fax: 86-591-8750-3521
China - Hong Kong SAR
Tel: 852-2401-1200
Fax: 852-2401-3431
China - Shanghai
Tel: 86-21-5407-5533
Fax: 86-21-5407-5066
China - Shenyang
Tel: 86-24-2334-2829
Fax: 86-24-2334-2393
China - Shenzhen
Tel: 86-755-8203-2660
Fax: 86-755-8203-1760
China - Shunde
Tel: 86-757-2839-5507
Fax: 86-757-2839-5571
China - Qingdao
Tel: 86-532-502-7355
Fax: 86-532-502-7205
ASIA/PACIFIC
India - Bangalore
Tel: 91-80-2229-0061
Fax: 91-80-2229-0062
India - New Delhi
Tel: 91-11-5160-8631
Fax: 91-11-5160-8632
Japan - Kanagawa
Tel: 81-45-471- 6166
Fax: 81-45-471-6122
Korea - Seoul
Tel: 82-2-554-7200
Fax: 82-2-558-5932 or
82-2-558-5934
Malaysia - Penang
Tel:011-604-646-8870
Fax:011-604-646-5086
Philippines - Manila
Tel: 011-632-634-9065
Fax: 011-632-634-9069
Singapore
Tel: 65-6334-8870
Fax: 65-6334-8850
Taiwan - Kaohsiung
Tel: 886-7-536-4818
Fax: 886-7-536-4803
Taiwan - Taipei
Tel: 886-2-2500-6610
Fax: 886-2-2508-0102
Taiwan - Hsinchu
Tel: 886-3-572-9526
Fax: 886-3-572-6459
EUROPE
Austria - Weis
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark - Ballerup
Tel: 45-4450-2828
Fax: 45-4485-2829
France - Massy
Tel: 33-1-69-53-63-20
Fax: 33-1-69-30-90-79
Germany - Ismaning
Tel: 49-89-627-144-0
Fax: 49-89-627-144-44
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
England - Berkshire
Tel: 44-118-921-5869
Fax: 44-118-921-5820
WORLDWIDE SALES AND SERVICE
04/20/05
AN990
Analog Sensor Conditioning Circuits – An Overview
INTRODUCTION
Target Audience
This application note is intended for hardware design
engineers that need to condition the output of common
analog sensors.
Goals
• Review sensor applications (e.g., temperature)
• Review sensor types (e.g., voltage output)
• Show various conditioning circuits
• Give technical references
Description
Analog sensors produce a change in an electrical
property to indicate a change in its environment. This
change in electrical property needs to be conditioned
by an analog circuit before conversion to digital.
Further processing occurs in the digital domain but is
not addressed in this application note.
The applications mentioned are:
• Electrical
• Magnetic
• Temperature
• Humidity
• Force, Weight, Torque and Pressure
• Motion and Vibration
• Flow
• Fluid Level and Volume
• Light and Infrared (IR)
• Chemistry
For each type of electrical property, commonly used
conditioning circuits are shown. Each circuit has an
accompanying list of advantages and disadvantages,
and a list of sensor types appropriate for that circuit.
The electrical properties covered are:
• Voltage
• Current
• Resistance
• Capacitance
• Charge
In addition, circuit and firmware concerns common to
many embedded designs are briefly mentioned:
• Input Protection
• Sensor Failure Detection
• Filtering
• Analog-to-Digital (A-to-D) Conversion
• Correction of Results
References to documents that treat these subjects in
more depth have been included in the “References”
section.
SENSOR APPLICATIONS
This section reviews a few analog sensor applications.
For each application, a list of common sensor types is
given for convenience. A good resource for many of
these applications is OMEGA® Engineering’s
handbooks [1, 2].
There are many more analog sensors than the ones
discussed in this application note. For example:
• Time/frequency counters [14]
• Distance ranging sensor [25]
• Current sensing transformer [6]
Emphasis is placed on the electrical behavior of the
various sensors. It is necessary to know this
information when selecting an appropriate sensor
conditioning circuit.
Electrical
These applications measure the state at some point in
an electrical circuit. They include monitoring the
condition of a crucial electrical circuit or power source.
TABLE 1: ELECTRICAL APPLICATIONS
Author: Kumen Blake
Microchip Technology Inc.
Sensor Electrical Parameter
Voltage Voltage
Current Current
Charge Charge
© 2005 Microchip Technology Inc. DS00990A-page 1
Page 16
DS00990A-page 16 ! 2005 Microchip Technology Inc.
AMERICAS
Corporate Office
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200
Fax: 480-792-7277
Technical Support:
http://support.microchip.com
Web Address:
www.microchip.com
Atlanta
Alpharetta, GA
Tel: 770-640-0034
Fax: 770-640-0307
Boston
Westborough, MA
Tel: 774-760-0087
Fax: 774-760-0088
Chicago
Itasca, IL
Tel: 630-285-0071
Fax: 630-285-0075
Dallas
Addison, TX
Tel: 972-818-7423
Fax: 972-818-2924
Detroit
Farmington Hills, MI
Tel: 248-538-2250
Fax: 248-538-2260
Kokomo
Kokomo, IN
Tel: 765-864-8360
Fax: 765-864-8387
Los Angeles
Mission Viejo, CA
Tel: 949-462-9523
Fax: 949-462-9608
San Jose
Mountain View, CA
Tel: 650-215-1444
Fax: 650-961-0286
Toronto
Mississauga, Ontario,
Canada
Tel: 905-673-0699
Fax: 905-673-6509
ASIA/PACIFIC
Australia - Sydney
Tel: 61-2-9868-6733
Fax: 61-2-9868-6755
China - Beijing
Tel: 86-10-8528-2100
Fax: 86-10-8528-2104
China - Chengdu
Tel: 86-28-8676-6200
Fax: 86-28-8676-6599
China - Fuzhou
Tel: 86-591-8750-3506
Fax: 86-591-8750-3521
China - Hong Kong SAR
Tel: 852-2401-1200
Fax: 852-2401-3431
China - Shanghai
Tel: 86-21-5407-5533
Fax: 86-21-5407-5066
China - Shenyang
Tel: 86-24-2334-2829
Fax: 86-24-2334-2393
China - Shenzhen
Tel: 86-755-8203-2660
Fax: 86-755-8203-1760
China - Shunde
Tel: 86-757-2839-5507
Fax: 86-757-2839-5571
China - Qingdao
Tel: 86-532-502-7355
Fax: 86-532-502-7205
ASIA/PACIFIC
India - Bangalore
Tel: 91-80-2229-0061
Fax: 91-80-2229-0062
India - New Delhi
Tel: 91-11-5160-8631
Fax: 91-11-5160-8632
Japan - Kanagawa
Tel: 81-45-471- 6166
Fax: 81-45-471-6122
Korea - Seoul
Tel: 82-2-554-7200
Fax: 82-2-558-5932 or
82-2-558-5934
Malaysia - Penang
Tel:011-604-646-8870
Fax:011-604-646-5086
Philippines - Manila
Tel: 011-632-634-9065
Fax: 011-632-634-9069
Singapore
Tel: 65-6334-8870
Fax: 65-6334-8850
Taiwan - Kaohsiung
Tel: 886-7-536-4818
Fax: 886-7-536-4803
Taiwan - Taipei
Tel: 886-2-2500-6610
Fax: 886-2-2508-0102
Taiwan - Hsinchu
Tel: 886-3-572-9526
Fax: 886-3-572-6459
EUROPE
Austria - Weis
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark - Ballerup
Tel: 45-4450-2828
Fax: 45-4485-2829
France - Massy
Tel: 33-1-69-53-63-20
Fax: 33-1-69-30-90-79
Germany - Ismaning
Tel: 49-89-627-144-0
Fax: 49-89-627-144-44
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
England - Berkshire
Tel: 44-118-921-5869
Fax: 44-118-921-5820
WORLDWIDE SALES AND SERVICE
04/20/05
