Earth's Magnetic Field
Helmholtz Coil(s)
Magnetic Shielding
Magnetic Stars In Outer Space
Superconducting Magnets
Sensor Types
Magnetoresistive (MR)
Giant Magnetoresistive (GMR) & Spin Valve
Coil Antenna
Hall Effect
Magnetic Precission
Silicon Integrated Circuit
Medical Applications
Nuclear Magnetic Resonance (NMR)
Magnetic Reasonance Imaging (MRI)
Magnetoencephalograph (MEG) & MCG
UXO UneXploded Ordnance Detection
MICR (Check) Processing
Magnetic Ink in U.S. Paper Money
Credit and other cards with a Magnetic Stripe
Anti-Shoplifting Garmet Tags
Geophone Based Intrusion - Seperate Web Page
Earth's Gravity

Light      Photometers
IR        Detectors
Laser      Distance Measuring
Cloud     Turbidity




Building Wall Stud


Gyroscopic   North Finding Module

Human movement

Explosive Detection




Rotary Angle

Hobo Data Logger


Web Links


There are a number of technologies that are used to sense magnetic fields.  I have also included some places where magnetic fields are used like in MRI, NMR, particle accelerators that use super conducting magnets.

1 Oersted = 79.58 Ampere-Turns/Meter
1 nano tesla = 10 micro Oe = 1 Gamma
1 Tesla = 10,000 Gauss
Papers about Magnetism -
Journal of Magnetism and Magnetic Materials - For over 100 years, Elsevier Science has been dedicated to facilitating the exchange of information.
The Magnetic Measurements Handbook -

Earth's Magnetic Field

The National Geophysical Data Center lists a number of models and is the key US web site for the Earth's magnetic field.  The World Magnetic Model   is updated every five years by the DoD.  This model will give you all three components of the Earth's magnetic filed if you know the date,  Longitude, Latitude and Elevation.  They also have a good links page.  The WMM95 model is built into the current versions of the Motorola VP Oncore GPS receivers.  A magnetic compass and this GPS receiver could be used to give true bearings, not just magnetic bearings.  Now add a long range laser range finder and you can locate anything within range in absolute coordinates  . . .  just what the military needs for targeting.
Nominal value of Earth's field = 0.5 Oe = 0.5 Gauss = 39.79 A-T/m = 5E-5 t = 50 ut = 50,000 nt.
Experiment Relating to the Vertical Component of the Earth's Field -

The International Association of Geomagnetism and Aeronomy -
USGS - geomagtism page - Magnetic Observatories - National Geomagnetic Information Center  - models - links -
WWV - Official Announcements - includes geomagnetic field activity activity
Hermanus Magnetic Observatory - CSIR - Geomagnetic Field Models and Maps -
International Geomagnetic Reference Field (1995) -
British Geological Survey - Geomagnetism - Instrumentation -
Bartington Instruments Ltd - Magnetic Instrumentation Products - Mag-01H Declinometer/Inclinometer - comprises a single axis fluxgate magnetometer, with the magnetometer sensor mounted on a non-magnetic optical theodolite
Australian INTERMAGNET Observatory Information -
Schonstedt Instrument Company - Lab Magnetometers - Surveying, Unexploded Ordnance Detection, Construction, Police, Utility (Water and Electrical), and Undersea pipe and cable location.
Dunham & Morrow - surveying marker locator designed by the same people that designed the Schonstedt GA-32/52 series.
Institute for Defense Analyses - Sensors, Surveillance & Target Acquisition - Magnetic Sensors (MEMS)DARPA MEMS -
Leica DMC - Digital Magnetic Compass - combined compass and 2-axis tilt sensor
MicroStrain - 3DM  - Orthogonal arrays of magnetometers and accelerometers are used to compute the pitch, roll and yaw angles over a wide angular range. Dev Kit $695
Geomagnetic Field Synthesis Program (Version 3.0) Input Form - on line determination of all 3 components of field
Swedish Institute of Space Physics (IRF) - Real Time plot - Today's and Earlier Space Weather -
Home Built Magnetometer for Solar Studies - magnet suspended on "E" guitar string - AAVSO Solar Division -
The Great Magnet, the Earth by  Daniel Stern of the NASA-  Commemorating the 400th anniversary of "De Magnete" by William Gilbert


The direction of the horizontal component of the Earth's magnetic field can be determined by a compass.  These range from the "Cracker Jack" type to very high quality models.

Note that the Earth's magnetic field can be thought of as having three components (Calif. values shown):

  • down in the direction of gravity  = 44,862 nt
  • to true North (not magnetic North) = 22,460 nt
  • and an East-West component at right angles to true North = 6,479 nt
The East - West component causes what is called declination, or the compass points to "magnetic north".
The true North component is in the horizontal plane, but
The down component is much stronger than the North component!  If the compass is not level then it will have a large error because it is starting to read the down component of the Earth's field.  This is why all conventional compass' need to be held in a level position.

Chris M. Goulet's Frequently Asked Questions - Magnetic Declination
Suunto - MC-1 G Global - unique needle balanced for worldwide use.Although there are 12 US patents held by Suunto, I don't see the global.   Vector wrist top computer (thermometer, altimeter, barometer, compass, watch - I have one of these) - Although I have not experienced it, there are reports that all batteries have ferrous metal and typically are magnetized and might cause trouble with the compass.  The instructions say to re-calibrate the compass every time the battery is changed.  The person making the complaint may have been in a strong magnetic field that changed the batteries magnetic field.
Recta - at Perret Optical - at MapSport - at TugawarPhotos -
Silva - Products -
Brunton - Pocket Transit = Army M2 comes calibrated in either degrees or mils (1 mil is 1 meter lateral @ 1,000 meters range)
Celestaire, Inc -Marine and Air Navigation Instruments - Compasses -
Stocker & Yale, Inc. - manufacturer of  Lensatic Compass  -
Cammenga - Current  Lensatic Compass manufacturer
Point Research Corporation - PointMan - drift-free dead reckoning navigation system - Engineering Evaluation Kit is $2,495 (2/13/99) US5583776 -
There are 3 magnetometers and 3 accelerometers on orthogonal axes, plus a barometric altimeter. The accelerometer triad senses the gravity vector to tilt compensate the compass, and is also used for stride detection.  Distance is measured by counting the user's steps (whose length is calibrated by GPS or other method) rather than by double integrating the accelerometer data. GPS and DR data are combined in an on board Kalman filter.
Jack Runyon
Microstrain, Inc. - Orientation sensor 3 magnetometers & 3 accelerometers
Photos: Surveyor's - M2 - Lensatic - German - Army Marching -
How Stuff Works - How a Compass Works -

Helmholtz Coil(s)

A Holholtz coil consists of two coils aligned on a common axis.  Their fields add in such a way that there is a region at the geometric center where the magnetic field has constant magnitude and angle.  The magnitude of the magnetic field is linearly proportional to the applied current through the two coils.

This is a good way to test magnetic sensors.

A single Helmholtz coil could be positioned so that it's axis was in line with the Earth's local magnetic field and then the DC drive current adjusted to cancel the Earth's field.  An alternate procedure is to use 3 Helmholtz coils in an X-Y Z configuration.

Wood, plastic, fiberglass are suitable for either DC ar AC driven Helmholtz coils.  For Earth's field work where only DC will be used aluminum, brass, and copper can also be used because there will be no AC eddy current problems.
UC Press - Hermann von Helmholtz & the Foundations of Nineteenth-Century Science -
Magnet-Physik - Moment measuring coils - for measuring permanent magnetics
Biot-Savart law - web plotting
Walker Scientific - Helmholtz coil - Gaussmeters - Fluxmeters - magnetometers -
Rapid Magnet Evaluation -
Magnetic Applied Devices -
3m diameter Helmholtz Coil at the National Physical Laboratory -
Billingsley Magnetics - 1 meter, 2.2 meter - coils
US5126666: Method and apparatus for substantially eliminating magnetic field interference to a magnetometer caused by DC current carrying conductors
Lake Shore Cryotronics - and magnetic field instruments

Magnetic Shielding


The electron beam in a Cathode Ray Tube (CRT) used in computer monitors and TV sets is bent by the magnetic field of the Earth.  In some applications where precision beam positioning is important the CRT has a Mu-metal shield.  There are numerious permeabilities offered some alloys are called Netic and Co-Netic.
MµShield materials -
AD-Vance Magnetics -
Magnetic Shield Corporation  - FAQ -Netic and Co-Netic - Helmholtz Coil Assemblies  -Zero Gauss Chambers
Sunbo - Korea raw materials & shield cases for magnetic recoreing heads
Riken - Magnetic Materials Laboratory - Japan


If a magnetic sensor is used in a feedback loop to control the current in a Helmholtz coil and bring the sensed field to Zero those devies in the sweet spot  volume of the coil will not see any magnetic field.


National Geophysical Data Center - related servers -
Scripps Paleomagnetic Laboratory - analyze the magnetic properties of rocks - Equipment & Facilities - links -
Geomagnetism and Paleomagnetism Section - of the American Geophysical Union -
Gisco -geophysical instrument source - Paleomagnetics index - Magnetometers -
Coast Ranges of Oregon and Washington - Magnetics in the exploration of the ground -


Theodern  fluxgate works by using a torroid with windings both going through the hole and others going outside the hole.

Fluxgate sensors were called "Flux Valves" prior to WW2.  At that time the indicator was a 400 cps Syslen and the Flux Valve was constructed on a "spider" that had 3 legs each 120 degrees apart.  The coils were wound on bobbins and slipped onto the legs.  An outer ring was then attached to the central core and this ring had three gaps.  The whole assembly was mounted on a pendulum and part of the calibration was to be sure that the center of mass of the Flux Valve was centered so that it would hang plumb.  See my Fluxgate Patents page for more on them.  The MC-1 uses this "Y" type core.

Pacific Rim (Japan) A-Plus

A-Plus Photo  They make fluxgate magnetometer unique in that they use a sandwich of printed circuit boards instead of winding wire around a core.  There are 3 seperate coils, one with turns  through the center of the toriod, one ourside for X and another outside for Y.   The turns are done with traces and plated through holes.  They may be a big player in the automotive compass market. Their fax in Japan is 03-5281-2064 & tel 03-5281-2067
Paper on very similar idea -
Applied Physics Systems - Fluxgate Magnetometers, DC SQUID Magnetometers
ASC Scientific - Magnetometers -
Barington @ ASC Scientific -
Billingsley Magnetics - Swales Aerospace - Atitude Control Magnetometers -
Don Lancaster's article muse104 - another muse 103 -
EMDS - (301) 840-5710
Fat Quarters Software - They sell units made in England by Speake & Co Limited.  They have an internal oscillator and an output whose frequency varies with magnetic field.  Also carried are some ASIC (microcontrollers) to do common functions.  A number of app notes are also available, now as HTML documents.
KVH Industries - C100 - They have a commercial monocular that has an optical readout of the magnetic bearing of the item sighted.  Typically used by mariners.  USD0325041: Multifunction monocular  US5020902: Rangefinder with heads-up display
Magnetic Research, Inc. - book with detailed circuit diagrams and fluxgate sensors
MC-1 Aircraft fluxgate compass field calibration kit -
Watson Industries - combinations of heading sensors, accelerometers, angular rate gyros, and angle references as well as a line of magnatometers.

Magneto-Inductive (MI)

Magnetoresistive (MR)

This is a technology that makes use of semiconductor type processes.  The resistance of an element changes due to magnetic field strength.  It is now being used in the read heads of computer disk drives.  Note in this application the output signal does NOT depend on the speed of the disk like it does with inductive heads.  Giant MR disk heads are starting to be used for disk drives, but GMR technology is not as good as MR for Earth field sensing.  The science of magnetic materials is a practical application of quantum mechanics.  This makes the study of these materials a Phd project.  The magnetic properties relate to both the electron orbiting and the spin of the electron it's self.  Electrons can spin in the "up" direction or the "down" direction.

The offerings form Honneywell and Philips Semiconductor appear to be about the same in capability.
Honeywell- Has extensive app notes on many aspects of these including the "setting" and "re-setting" circuits. Honeywell
Philips Semiconductor - Has very little information on their magnetic field sensorsKMZ51 units.  DigiKey p/n 9082CA-ND (9000 series Fig 2) is an 8-pin SOIC to 8-pin SIP surfboard for the KMZ51 package. Scanner Image - 9082 w/KMZ51 -
Leica has a 3 axis unit that is very accurate because it includes an inclinometer. They do not say which technology is used in the top web page, maybe further reading will reveal the technology.
Pegasus - InSb Magnetoresistors -
San Diego Magnetics - MR, GMR sensors for tape and a new type of magnetic card

US5260653  Thin film very high sensitivity magnetoresistive magnetometer having temperature compensation and simple domain stability
US5119025 High-sensitivity magnetorresistive magnetometer having laminated flux collectors defining an open-loop flux-conducting path
Searching for ( (magnetoresistive) <in> AB) and ( (Eastman Kodak) <in> PA) at - yeilds 24 patents that may now be assigned to SDM

Giant Magnetoresistive (GMR) & Spin Valve

These are technologies being looked into for the next generation computer hard disk drives.
GMR Physics -
NonVolatatile Electronics Inc. - makes a number of magnetic sensor based products

Coil Antenna

The May '96 issue of Scientific American Amateur Scientist article "Detecting low-frequency electromagnetic waves" on page 98. This is a follow up to the Fraser-Smith (Stanford) detection of low frequency waves prior to the Loma Prieta Quake.
Stanford University -Space, Telecommunications, and Radioscience Laboratory - ULF/ELF Magnetic Noise -ULF Group -
A. C. Fraser-Smith: Research Interests - ULF Earthquake Measurment Sites in Calif. -
Electromagnetic Field Measurements - U.C. Berkerley
The Earth-ionosphere cavity resonances - Stanford STAR
ElectroMagnetic Instruments, Inc. - Magnetotelluric (MT) Earth impedance measurements

Hall Effect

These are not sensitive enough for Earth's field applications.  There is a cleaver product (model 1490)  that uses Hall Effect sensors combined with a rotating magnet (compass) for coarse direction indication made by Dinsmore Instruments. 1814-T Remell St. Flint, MI 48503 4482 USA Tel: 810-744-1330 Fax: 810-744-1790  There are a couple of new sensors Model 1525 and 1655 (uses Allegro 3507) that may use a moving magnet (like in a compass) and a couple of analog Hall sensors to allow getting a bearing reading. This will require reading 2 analog signals and computing a vector.   I have one on order and will have more information when I have had a chance to test it.
US5157841: Portable electronic compass
US4402142: Electronic compass for automotive vehicles 1983 compass needle & 4 Hall sensors
US4250626: Electronic compass - Lazar; Harold - Feb. 17, 1981 / Aug. 20, 1979

Not by Dinsmore an interesting combined sphercial LED tilt and compass sensor  based on 3 flux gates.
US5526022: Sourceless orientation sensor - 1993

Allegro MicroSystems Inc. - Integrated Circuits - AN 27702A for strong mag fields apps, not Earth's field
Analog Devices - AD22151G - This is a Hall Effect unit with built in temperature compensation, it is for strong magnetic fields like from a nearby permanent magnet, not for Earth's field application.
Honneywell - Hall Effect sensors -
Cherry - HE503000 -
Micronas - Hall Sensors - HAL800 - HAL400@ Digikey -
F W Bell - Hall catalog.pdf - has theory section
Allergo -
American Electronic Components (AEC) - analog rotary position -
Panasonic -digital @Digikey -
Cosmo Electric Corporation - H301A1digital @Jameco sensor  ftp site -
Melexis - MLX90215 Precision programmable linear Hall effect sensor
Advanced Hall Sensors (AHS) - using III-V compounds to achieve very good specifications - no data sheets yet
Lake Shore Cryotronics - Magnetic Measurement Instrumentation & Temperature Sensors and Instrumentation

 Magnetic Precission

This is a high end (read expensive) technique used to measure the total magnetic field.  To get total field with any of the sensors that only read a single axis, three sensor outputs need to be combined. This is tough to do since all three need to be very closely matched and be perfectly orthogonal.

Quantum Magnetometry Laboratory - Processor Overhauser Sensor POS-1 - The Quantum Magnetometry Laboratory (QMLab) was established in 1981 by the USSR Government attached to the Ural State Technical University (USTU), for a purpose of the development of sensors on the base of magnetic resonance for geology and defense.
Geometrics - Proton Magnetometer - The technology depends on detecting the flip in the outer electron of Cesium caused by the Earth's field. - G-823A Airborne Magnetometer Sensor -
Scintrex's Airborne Systems & Surveys - CS-2 Cesium Magnetometer -
Naval Technology - Magnetometers - Marine Magnetometers -
ASC Scientific - Magnetometers -
Quantro - underwater Proton magnetometer - $2,750+
J. W. Fishers Proton 4 Mag - $9,495
Dan's Homegrown Proton Precession Magnetometer -
Proton Precession Gradiometer by Jim Koehler - 1 1MB file * spreadsheet - these are very sensitive metal detectors
The Proton Magnetometer Mailing List  - is a gathering place for persons interested in homebuilding proton mags
Phil's Magnetometer & Prospecting Pages -How to build a low cost Differential Proton Precession Magnetometer. CD-ROM

SQUID - Superconducting QUantum Interference Device

Reed College - Definition
Jena Superconductive Electronics Foundry - Department of Cryolectronics - LTS SQUID group -
Columbia Univ. - EE E4302: Magnetic Sensors and Instruments for Medical Imaging -
IMFM - Dep of Physics - RF SQUID & DC SQUID explained -
University of Illinois - Materials Research Laboratory - Magnetic Characterization Facility -
ASC Scientific - Magnetic & Paleomagnetic Instrumentation -
Helsinki University Central Hospital - BioMag Laboratory - Transcranial Magnetic Stimulation (TMS) is the converse of MEG: The brain is stimulated through the skull with magnetic fields.
F.I.T. Messtechnik GmbH - HS20 SQUID Chip -
Applied Physics SystemsModel 581 DC SQUID -
Images from IBM Scanning SQUID Microscope Group - Scanning SQUID Microscope & the Half-Integer Flux Quantum Effect -
Institute of Applied Physics Justus-Liebig-University Giessen- Inspection of Aircraft Parts with High Remanent Magnetization by Eddy Current SQUID NDE -
Stanford -Einstein - SatelliteTest of the Equivalence Principle - Superconducting Quantum Interference Devices
Johns Hopkins University - Dep of Physics - Condensed Matter Physics -
Peking U - Xiaoxing Xi - High Temperature Superconducting Electronics -
Principles and Applications of SQUIDS - ISBN 981-02-0911-8 US$116 / £80
NRL - Code 6177 Surface Nanoscience and Sensor Technology - Force Amplified Biological Sensor (FABS) -

Silicon Integrated Circuit

Integrated Resonant Magnetic Field Sensor - a current carrying coil formed in Silicon mechanically vibrates and it's motion is effected by the Earth's magnetic field.  The effect is sensed by means of capactive sensors.
US5731703: Micromechanical d'arsonval magnetometer

Magnetic Stars In Outer Space

On 27 Aug. '98 high energy gamma rays from outer space passed through our solar system.  These came from a Magnetar.  This had effects of HF radio propagation.
Press release.  This is very interesting since it came from outside our Solar system.

Nuclear Magnetic Resonance (NMR)

Stanford - Stanford Magnetic Resonance Laboratory (NMR) -
Varian - NMR page - Varian NMR Users on the Web -
The WWW NMR Spectrometer is a 7 Tesla system designed for real-time acquistion of NMR signals using a Web browser - on line NMR

Magnetic Reasonance Imaging (MRI)

Introduction to MRI - explains how it works and a lot more
Magnetic Resonance Imaging FAQs - for people about to get an MRI scan
MRI Corner - The Basics of MRI -
Magnetic Resonance Imaging on WWW  - good set of links and they are organized
News Groups: sci.physics.electromag & sci.technologies.mag-reasonance -

Magnetoencephalograph (MEG)

Yokogawa & KIT - MEG measures activities of brain by employing a non-contact, non-invasive method to detect weak magnetic signals generated in the brain.  208 SQUID sensors are in this system.
Neuromagnetism at BioMag -
Shimadzu - SBI-100 -
Siemens - Schematic presentation of the SQUID system -
Tokyo Denki University - Applied Superconductivity Research Lab -

Cardiomagnetism (MCG)

Cardiomagnetism at BioMag -
Cryogenic Electronic Systems Corporation - makes MCG equipment

Superconducting Magnets - mostly used for particle accelerators

Tutorial on Superconducting Accelerator Magnets -
AMI - Superconducting Magnet Systems -
National High Magnetic FIeld Labratory - User Projects - Magnet Technology -
Indiana University - Picture Gallery -
Fermi National Accelerator Laboratory -


A long time ago I had a wire recorder.  Like a tape recorder except the medium was a spool of fine wire.  When it broke, the wire could easily get tangled.  We now have tape, floppy disk and hard disk recording devices.  The early devices used sensors that were just a coil of wire on a magnetic core with a gap next to the magnetic media.  Now the high tech devices like the hard drive in your computer are using MR and GMR read heads.

Santa Clara University -The Institute for Information Storage Technology - Inventor Poulsen and History of Analog Magnetic Recording - Links -
IEEE Magnetics Society -
International Disk Drive Equipment Materials Association - IDEMAJ -
Magnetism and Magnetic Recording Devices - on line book based on tape recorder, but good general information
Magnetic Recording Books  -
Alison Chaiken's Magnetic Recording Web Sites - Excellent extensive, sorted list of all kinds of magnetic recording & other magnetic web sites
NCITS Announces the Public Comment Period for ISO/IEC 13923:1996 - 3.81 mm tape cartridge
National Storage Industry Consortium (NSIC) -
Data Storage - magazine has links: Companies, Advertizers, Organizations

UXO UneXploded Ordnance

The world has an extremely large number of land mines that continue to maim and kill people after the military force that installed them leaves the area.
Unexploded Ordnance Detection Using Imaging Giant Magnetoresistive (GMR) Sensor Arrays - by Alison Chaiken
See my Demining page for more information

MICR (Magnetic Ink Character Recognition) Check Processing

The numbers at the bottom of your checks are read by a magnetic reader, not an optical character reader.  There are 16 characters 10 numbers and 6 special characters.  The early systems used a single gap read head following a write head to magnetize the characters.  The magnitude of the read waveform vs. time was used to recognize the characters at about 1,000 documents per minute.  The character pitch is 1/8".  Some newer higher speed machines use multiple gaps and actually form an image of the character providing a lower false recognition rate at a higher system price.

X9 - U.S. MICR standards and others - requires $250/yr fee to access documents
American National Standards Institute (ANSI online) -search on MICR -> Banking, Information and Imaging Standards from a User's Perspective - has a history and lists a lot of standards -
Canadian Payments Association - Standards And Specifications For MICR-Encoded Documents - the actul "Standard 006"
World Magnetics - makes the sensor to read the check numbers
Plug-in MICR module for Hewlett-Packard LaserJet printers for Corporate Check Printing Systems - software and special magnetic toner
Tips For Detecting Counterfeit Checks -
Stanford Research Institute - in 1960's developed ERMA & MICR technology

Magnetic Ink in U.S. Paper Money - NOT - well OK there is something here

The magnetic stripe idea is a myth, in the new paper money.  I received an email for the Treasury and the stripe is a plastic, it glows in UV light and it's position in the bill indicates the denomination.
Coin Currency & Document Systems Inc. - Currency Processing Equipment - MD-3 Magnetic Ink Detector - I don't know what this is
4/25/99 - I have been told that the ink used to print US currency has magnetic properties and a magnetic sensor is used in some bill changers. The Nov 2001 issue of Sensors has an article about reading the magnetic signature of a new $20 bill.

Credit and other cards with a Magnetic Stripe

ANSI on line - standards for magnetic cards - search magnetic cards for a large number of hits
Anatomy of The M.I.T. Card - M.I.T. engineering students analyzing their school ID card
Dorado Systems - Magnetic Stripe Encoders & Readers
Standards for Smartcards -

Anti-Shoplifting Garmet Tags - Electronic Alarm Systems (EAS)

Although some of these systems depend on magnetic materials others use RF loops and/or loops with diodes.
Electronic Shoplifting Deterrent Systems - Magnetic tag notes - Knogo -
US3747086: Deactivatable Ferromagnetic Marker for Detection of Objects Having Marker Secured Thereto and Method and System of Using Same - this patent is called out by 47 other patents so it is a good place to start
US5288980: Library check out/check in system  - references 40 patents going back to 1939
US3990065: Theft detection system - magnetic method
US4642640: Signal receptor-reradiator and surveillance tag using the same - mixer type
US4139844: Surveillance method and system with electromagnetic carrier and plural range limiting signals - mixer type
US4429302: Electronic security system with noise rejection - sweeping through a reasonance and counting the pulses out put frequency - Checkpoint?
US5349332: EAS system with frequency hopping - calls out 10 prior art patents including the two above
US5821859: Concealed magnetic ID code and antitheft tag

MRAM Magnetic Random Access Memory

Conventional DRAM chips use the electric field on an electron to store a binary state.  These need to be refreshed frequently or they loose their data.  By using the spin on the electron to store data magnetically a nonvolatile memory can be made that promises to be faster than DRAMS.  I think the first patent was by Honeywell US4455626: Thin film memory with magnetoresistive read-out
Filed March 21, 1983 for a military version.  Then Nonvolatile Electronics, Inc started development of commercial versions.  They have a good online white paper.  HP, IBM, Motorola and others have dozens of patents in the area.  This technology uses standard CMOS chips with the magnetic element sitting over a single CMOS FET.  It has the potential to replace FLASH chips and hard disk drives.
A computer that used MRAM would be like the early computers that had magnetic core memory.  You would have protection from power outages and have "instant on" operation.  Whatever program you were running when you powered down would come up running when you power on. The military is very interested in this technology and Honeywell is offering products.  In Dec 2000 NVE stopped sub licensing this technology in exchange for a million dollars.


See the U.C. Berkley on line tutorial  Types of Accelerometers  for some information.
Tutorial on Inertial Navigation Systems - with sensor errors in an appendix, 84.46 minute Schuler oscillation derivation

Force Balance

Jewell - Inertial Sensors, Accelerometers , Inclinometers -
Systron Donner 4310 series - web page with patent links (maybe the same as Jewel)


These have a beam with many fingers that are interleaved with other fingers that are at ground.  The capacitance between the fingers on the beam and the grounded fingers is measured.  In this was acceleration can be measured.
Analog Devices - Made for automotive air bag, New ADXL150 & ADXL250 lower noise versions of the popular older ones.  They have a large number of app notes on their web site covering all kinds of practical areas of concern like temperature dependency in DC coupled systems.

ADXL202 - Low-G, 2- axis - Crossbow Evel Kits - has PWM output for direct microcontroller interface.  Note that this is the first acceleration sensor designed for static gravity work.  The other sensore have been aimed at the automotive air bag crash detection market.

Rocket Altimeter Project (RAP) - PIC micontroller based with ADXL190

Brooke's ADXL202 web page

KMI - sisemic sensor - used to shut down equipment when strong motion quake detected
Button-free Tilt and Gesture Input for Itsy - new imput method for PDA
Adding a tilt sensor to the PalmPilot - PalmPilot Programs and Hardware Hacks -
SmartQuill - Handwriting recognition is achieved through accelerometers that monitor hand movements
Microsoft Corporation's Hardware Division for its new SideWinder® Freestyle Pro game controller

US5621157: Method and circuitry for calibrating a micromachined sensor
US5540095: Monolithic accelerometer
US5465604: Method for adjusting sensitivity of a sensor
US5345824: Monolithic accelerometer

Applied MEMS - 3 axis accelerometer withlow noise.  double integration for 60 seconds gives less than 0.1 inch movement on a fixed sensor.
Motorola - Like the Analog Devices model it is a micromachined Silicon sensor aimed primarily at automotive air bag applications.
     US05814727 09/29/1998 Semiconductor accelerometer having reduced sensor plate flexure
     US05590241 12/31/1996 Speech processing system and method for enhancing a speech signal in a noisy environment
     US05545912 08/13/1996 Electronic device enclosure including a conductive cap and substrate
     US05487305 01/30/1996 Three axes accelerometer
     US0531383505/24/1994 Integrated monolithic gyroscopes/accelerometers with logic circuits
     US05249465 10/05/1993 Accelerometer utilizing an annular mass
     US05044201 09/03/1991 Double-integrating silicon acceleration sensing device
     US04677913 07/07/1987 Safe and arming device
     US04378510 03/29/1983 Miniaturized accelerometer with piezoelectric FET
     US05818093 10/06/1998 Semiconductor device having a movable gate
     US05400644 03/28/1995 Knock detection system
Silicon Designs, Inc. - Combines the micromachined chip with conditioning electronics.
           US4736629: Micro-miniature accelerometer
Kistler Instrument Corporation - Piezoelectric, Piezoresistive and Variable Capacitance Based Sensors
US05347841 09/20/1994 Self-testing transducer curcuit
US04771637 09/20/1988 Accelerometer
Draper Labs -
US5507911: Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency
US5817942: Capacitive in-plane accelerometer
Entran - Accelerometers - small & Automotive including racing and R&D
Kerfott -
US5656778: Micromachined acceleration and coriolis sensor
US4945765: Silicon micromachined accelerometer
Crossbow - Silicon Accelerometer based products & Analog Devices eval kits
Breed Electronics - Lakeland, FL
(Sumitomo Precision Products) Silicon Sensing Systems Japan Ltd - Capacitive Type 3-axis Accelerometer C3AP - Links -
Integrated MEMS Inertial Measurement Unit - accelration & gyro sensors on a chip
Manufacturing Low-Cost MEMS Inertial Sensors - Draper Laboratory
Flexible Manufacturing of Dissolved-Wafer Silicon Capacitive Sensors (CAPS) - Integrated Sensing Systems, Inc.
VTI Hamlin - SCA600 -

Silicon Piezoresistive Accelerometer

Fujikura Ltd. - FACS Accelerometers -Single Chip 2­ and 3­ axis signal conditioned, 1 and 2g
Oceana Sensor Technologies - Low cost, Piezoelectric Accelerometers - Eval Kits -
Morgan Matroc -  PZT piezoelectric ceramics manufactured for specific application
Mitsubishi Electric Corporation - Semiconductor Acceleration Sensor - Because of their ability to detect accelerations of static characteristics, low-acceleration sensors can be applied to Inclination meter, Vibration detection, game-playing equipment, etc. High-acceleration sensors have a high frequency response and can be applied to airbag systems based on analysis of shock waveforms and other signal waveforms.
Summit Instruments - ? Technology
Measurement Specialties Incorporated (MSI) - piezo thin films, analog test printed circuit board - with schematic
EG&G (now called PerkinElmer, Inc) -Data Sheets -3031, 3038, 3022, 3028.    3140- 2G, 3145-2G 0.5 - 5.0 V out.   3255- 50, 500 G, 3265 - 5G - 3052 & 3058 -2G have internal temp comp capability good for quality DC apps
GS Sensors Inc. -FA1131 -  Ephrata, PA


Electromagnetic & Capactive
Laser Vibrometers


Variable capactance
Servo (Force Balance)
US5808198: RF balanced capacitive vibration sensor system


A device to determine how far a person (horse?) has gone.   Used in modern dead reckoning systems.
US5724265: System and method for measuring movement of objects - this patent references many others
US4991126: Electronic-automatic orientation device for walkers and the blind - distance & direction


Remec - Humphrey - thermal accelerometer (click on New Products)
The IC is carried by Fat Quarters.  This is a patented low bandwidth acceleration sensor that depends on the inertia of heat. They have an app note on making an Earthquake sensor based on this unit.
Memsic - Dual axis, analog 7 digital outputs, absolute or  ratiometric - a # of Evaluation Boards - June 01 Sensors mag article - Comparison of Accelerometer Technologies by Memsic Inc.

Earth's Gravity

Links to Gravity Groups that have FG5 absolute gravimeters (and Web Sites)
The Earth's gravity has been very thoroughly mapped in areas where rockets are launched.
A cleaver way to measure gravity is to drop, in a vacuum, a retro-reflector whose position is being measured by a laser in real time.  See the Micro-g Solutions web page for information on this method.  Note that the acceleration due to the Earth's gravity is NOT 1.0 every where.  You should not use 1.0 as a value for calibration of accelerometers unless you have measured the acceleration at your test location first. A-10 Outdoor Absolute Gravimeter -
Intelligent Detection Systems - Scintrex CG-3 - Seagrav -
LaCoste & Romberg - Dr. LaCoste - a pioneer in the development of these instruments - has a large line of meters - Portable Earth Tide -
Scintrex -
Carson Services Inc./Aerogravity Division - US5661649: Airborne gravity and magnetic field surveying method
NSF Absolute Gravity Facility - uses the FG5
24 April 2001 LaCoste & Romberg, Scintrex, and Micro-g Solutions Merge
Possible new theory of everything by David Allan (Mr. TIME) can be tested by measuring gravity


Redwood City Public Seismic Network - Home construction information & links
USGS Earthquake page - automated reports
Don Lancaster's info -
Geometrics - R and RX Series Seismographs - SmartSeisTM Exploration Seismograph  -
News Groups:  sci.geo.earthquakes & seismic.general -
Seismo-Watch Earthquake Reports -
Kinemetrics - Products - App Notes - Links -
Pinpoint Earthquake News - Interesting links to a lot of diverse areas
UC Berkeley Seismological Laboratory - Hayward Fault - Seismometers- Make your own seismogram! -
Simple seismograph -
Welcome to the Caltech/USGS SeismoCam -
University of Wisconsin - Milwaukee's Seismic Station -
How to Build an Inexpensive Seismometer -


Two popular outputs from pressure sensors measuring the atmosphere are the barometric (like in barometer) pressure and displaying the answer in units of altitude.  These same sensors come in various pressure ranges and are also used for measuring, for example, the pressure in a pipe or other pressure sensing application.

I know of a security system where they had copper tube that looked exactly like bare #10 ground wire like used in electrical systems.  It was run in the electrical conduits and ended up in some fixture in a room that was being protected.  At the other end in the security center there was a very sensitive pressure sensor.  If anyone opened a door or window or cut a hole in a wall in the protected room they could sense the pressure change and it set off the alarm.
 Exploratorium  - Sound Spectrum Chart -

Simulator, Barometric Presssure, SM-384/URM-125, Sperry Utah Company, Division of Sperry Rand Corp., Order No. 682-PM-58, U.S.

This is an instrument (9" high, 4.75" wide and 14" long) that contains a manual pump, valves and a calibrated barometric altimeter.  The range is - 2,000 to + 18,000 feet.  It does not have a provision to set the local pressure, i.e. it is an absolute reading altimeter.  Available from Herback & Rademan as TM98GGE3132.
Name Plate,    Front Panel,   Diagram -


Advanced Custom Sensors Inc.-
DH Instruments, Inc - pressure & flow calibration
Entran - Sub-Miniature Silicon Chip Diaphragm - Silicon bridge
Exar -Click on Silicon Microstructures
FISO Technologies Inc. - Fiber optic 0.55mm OD x 0.5 mm size -50 to 300 mmHg
Fuji - pressure sensitive film changes color to record max pressure
Honneywell - High end - Pressure and Force Sensors - industrial
Integrated Micromachines Inc. - Silicon Low Pressure Sensors -
Integrated Sensing Systems Inc. - ISSYS - Pressure Sensing -
Intersema - absolute pressure - 1 meter resolution altimeter
Kavlico - various technologies available 1/2" h2o to 20,000 psi
Lucas - NovaSensor - Better linearity than Motorola - Many Versions of the NPC-1210 are available from 1800 962 7364 x6118.
Melexis - tried to use change in ring oscilation frequency as measure of pressure in their MLX90211 Altimeter pressure sensor - not recomended for new designs
Mitsubishi - piezoelectric-resistance Pressure Sensors -
Motorola - Extensive app notes: Click on Sensors then Pressure Sensors
Pressure Systems - quartz very high accuracy sensors
SensoNor - SP10 tire  Patent US5591679: Sealed cavity arrangement method - method for making sealed cavities on silicon wafer surfaces, they also make accelerometers for crash sensing
Sensortechnics - high pressure piezoresistive with fittings
Setra - packaged with fittings, long term stability
Servoflo - Fujijura pressure & Oxygen sensors -
Siemens - 100 pressure sensors in a mat to go under passenger seats in vehicles.  Can recognie baby seat and size of occupant.
Standard MEMS, Inc. - Silicon On Sapphire Pressure Transducers - virtually hysteresis-free sensing
TI has acquired Integrated Sensor Solutions - Industrial & automotive pressure sensors - steel & brass housings
Visteon - Automotive Products - MAP sensor.pdf -
For a low cost sensor the MAP (Manifold Absolute Pressure) sensor form a late model GM car should provide a rugged temperature compensated unit for almost nothing from a wreacking yard, although I have not tried it.  If you do let me know.


Altimeters - Pretel - Thommen - Avocet - Peet - complete products rather than just a sensor
Altimeters - Thommen Pocket - Suunto/Pretel ALTIplus - AIR, Inc. -
Aviation Safety Reporting System - International Altimetry -
Revue ThommenAirspeed Altimeter - at Abnet - at Gioielleria Fabbrini -
Avocet - Vertech - Barometer - Altimeter - very accurate
US Patents:
US5058427: Accumulating altimeter with ascent/descent accumulation thresholds
US5295085: Pressure measurement device with selective pressure threshold crossings accumulator
US4694694: Solid state accumulating altimeter
Ciclosport - HAC4 - bicycle data system with 1 meter altutide resolution (katalog-catalog)
Peet Bros. - Pocket Altimeters - Book: "The Sportsman's Altimeter/Barometer"
US4969358: Electronic altimeter/barometer
US5001929: Electronic altimeter
Casio - Timepieces - Altimeter-Barometer - Forester ATC1200-1V - G-Shock Alti-Meter Watch - Twinsensor Alti-Thermo - Pathfinder -
Dalvey - Barometer Altimeter - conventional aironoid type
Suunto USA - Vector Altimeter compass watch -
Swift Instruments -Weather478 Altimeter / Barometer -
Geneq (many types of sensor)- Barometric Pressure Sensor II - Micro Series Surveying Altimeters - Air Inc. Models -
Using an Aircraft Altimeter as a Barometer  -
Back Yard Nuclear Weapons - The Mechanism of The Bomb - altimeter used in fuse
John Coker's Rocketry - Altimeter Comparison with web links - Aerotech hybrid rocket motor


Sound in the .02 to 10 Hz range.
Air Seismology -
InfraSonic Introduction - InfraSonic Links by VK2ZTO
Infrasonics Program - Univ of Alaska
Parapsychology - A Sound Theory? - may explain some haunted buildings
Elephant Infrasound  -
Geotech Instruments, LLC - Latest Projects - Korea Seismic-Acoustic array.pdf -
Honeywell - Data Instruments Products - DCAL401DN
Listening to the Heartbeat of the World -
Infrasound Monitoring with a Microbarograph -
Infrasound monitoring of the Comprehensive Test Ban Treaty -
MKS Instruments - Type 223B Baratron Differential Capacitance Manometer -
Nuclear Explosion Monitoring Research & Engineering Program - Infrasound Monitoring Research - United States Infrasound Prototype -
NOAA - Infrasonics Program - weather and natural phenomenon related
Sonic Weapon of Vladimir Gavreau -

Light =40 nm to 1,000,000 nm

VUV (Vacuum UV) 40 to 300 nm
UV is 320 to 400 nm
Visable 400 to 750 nm in wavelength
Near IR 750 to 3,000 nm  not body heat, viewer requires light source M18 binoculars
Mid IR 3,000 to 30,000 nm
Far IR 30,000 to 1,000,000 nm
The atmosphere has a window that passes visable light, IR around 10,000 nm and radio in the 5 cm (6 GHz) to 10 meter (30 MHz) range,
all other wavelenghts are blocked by the atmoshpere.
Exploratorium - Electromagnetic Spectrum Chart - a verry well done chart
Hamamatsu app notes: Optical Detector Selection: A Delicate Balancing Act - Silicon Photodiodes Principle of Operation -


EIT, Inc. - radiometers for UVA (320nm-390nm), UVB (280-320nm) , UVC  (250-260nm), and UVV (395-445nm) mainly for UV cure process characterization
International Light, Inc. - 250-1100 nm spectroradiometer
NSF - Polar UV Monitoring Network - SUV-100 high resolution, scanning spectroradiometer - ozone work
Multi-channel Solar Ultraviolet Radiometer - for ozone work
Optix - UVA&UVB Radiometer 300 ÷ 370 nm
OL-754: UV/VIS/NIR Spectroradiometer 200 to 1600 nm
Wedgewood Technology - AF44 UV Sensor -
Uvitec - uses filter over Si detector
Grunder - Schottky-type UV-photodiodes 230 - 370 nm in TO-18 & -39 transistor packages with no visible sensivity
Apogee - hand held UV meters 250 - 400 nm
Spectrex - SharpEye UV Detectors - flame detection 185 - 260 nm  1 sq.ft. gasoline fire at 50ft
Solar Light - UV light sources, solar simulators, and radiometers. sunscreen product development and SPF certification worldwide.


T.I. - Eval Module - TSL-230 Series Light to frequency converters with very wide dynamic range
TAOS - has taken over the TI line of optical sensors - TSL230 Evaluation Module for $100
Gigahertz-Optik GmbH - both sources and measuring instruments

Lateral Photo Diodes

 X-Y output of light spot position.  This is NOT a 4 quadrant detector but rather a very unique way to locate a spot of light very precisely.
UDT Sensors Inc. -
EG&G - Photodiodes -
Steinbichler - COMET 100 Digitizing Sensor - US5289264: Method and apparatus for ascertaining the absolute coordinates of an object
GOM - The Mobile Optical 3D-Coordinate Measuring Machine -

Avalanche Photo Diodes

Advanced Photonix, Inc. - 581 series

Silicon CCD

The quantum efficiency of Silicon for capturing light is way better than the human eye or photographic film.  This is why the astronomers are using CCD arrays for viewing objects in the night sky.
Mitsubishi - artificial retina - CCD array & image processon in one package 32x32 or 128x128 pixels - aimed at low cost applications like games and surveillance, hand gesture recognition, etc.  but may have many other uses.

GameBoy has a camera add on that uses the aritficial retina

Search for "game boy camera"
Inside Game Boy Camera - the start of some reverse engineering
GameBoy Developers -
AVR + GameBoy(tm) Camera = Fun -
M64282FP Artificial Retina Technicial Information -


Tektronix -
Sencore - CP288 - Auto "ColorPro II" Color Analyzer -
International Light -



Servo - IR detectors. - Thermistor [2,000 - 20,000 nm]( traditional bolometers both hand made & semiconductor type) & Pyroelectric [2,000 - 15,000 nm](Lithium Tantalate &  P(VDF-TrFE))  hi-end stuff.  This is long wavelength IR.
Photonics IR Detector manufacturers list -
EG&G - IR Detector page listing many chemistries and their wavelength range -
Opto Diode Corp. - IR emitters & detectors
I.S.I. Group, Inc. - VideoTherm® 2000 : 8 - 14 micron uncooled  focal plane array camera
Fermionics - HgCdTe Infrared Photodetectors - room temp to 2.8 um, thermoelectric cooled to 6 um, LN to 16 um
Hamamatsu - IR detectors - response curves for different types -
Litton's Infrared Product Group - IR line and area arrays -
Linear Laboratories - Non contact IR temperature measurement

Vishay Telefunken - automotive winshield Rain Detector TSRF900 -
CMC - Cincinnati Electronics Corporation - IR detectors - IR Imagers -
Thermometrics - MEMS & CMOS IC in same package thermopile sensor (measure temperature of objects)-
    filters: standard 6 - 13 um for tire temp, ear thermoters, human body detection
             F1          8 - 14 um for occupancy detectors 7 intrusion alarms
             F2          2 -   5 um for flame detectors
             F3          1 - 10 um flame detectors & high temp thermometry
Judson - 800 to 26,000 nm & 4 quadrent position sensors

IR temperature

Melexis - ML 90601 IR thermometer module -50 to +1,000 C +/- 0.1 C, analog, SPI or PWM outputs
Mikron -
Raytek -

IR Cameras

Indigo Systems -


The Oxenhope automated observatory has it's own Weather Station that includes a cloud sensor.  These are for use at night.  A Peltier junction is sandwiched between two plates.  On a clear night the sky is colder than the Earth and a voltage is generated.  When it's cloudy the output is lower.
Cloud Sensor revised (12/06/97) - description of the above sensor -Herbach and Rademan - Part Number TM92HVC2178 -
The Hanna City Robotic Observatory - Description of the cloud sensor electronics & circuit diagram -
Qualimetrics - 8329-A/B Laser Ceilometer -
Vaisala  - CT25K Laser Ceilometer -
PMS/CSIRO Hot Wire Liquid Water Probe -
ARCS Data Management Facility - Tropical Western Pacific Instrumentation - SKYRAD Upward Pointing IRT - Infrared Thermometer -
Synergy of Active Instruments in the Earth Radiation Mission - collection of papers
YES - YES is currently developing an automated cloud observation sensor based on a solid state, digital charge-coupled device (CCD) camera.
Penn State Dept of Meteorology - Measurement Systems and Field Sites -
Scinetific American - Detecting "Hot" Clouds -
Astronomical Society of Australia -Introduction - Thermopile Cloud Detector - Sensitivity to Cloud - Conclusions - References - 8 to 14 micrometers
Advanced Visible and Near-Infrared Radiometer (AVNIR) - satellite
My Cloud detector using the H&R TM92HVC2178
The idea of using the Sun's shadow will only work during the day time.


This would be the sensor to use in a swimming pool to determine the optimum time to clean the filter.
Honeywell -

IrDA (InfarRed Data Access?)

This is a protocol for transferring data by means of IR.  It is used in many lap and table top computers and is available as an add on product for any computer.
Aiglent (HP) - HSDL-1100-017

CCD - my web page about astronomical CCD sensors

Intelligent Vision

There are some light based sensors that have intellengence added.
Agilent - optical mouse sensor
Corrsys-Datron - "pupil splitting" technology HS-CE 3-Axis Measurements


Distance Measuring

By using various techniques the distance to an object can be measured with light.  Two big applications for this are military targeting systems and land surveyor "total stations" and "Distance Measuring Equipment (DME)".  The surveying models typically work with retro-reflectors.  A more consumer oriented application is the BushnellYardage Pro range finder(FAQ) for golfers that reads out in yards or meters.  Leica makes a line of OEM range finders with millimeter read out, binocularsthat have RS-232 output and a built in comapss. Leica makes the Disto,  a hand held unit for the construction industry that is also carried by Edmond Scientific  It has mm resolution.  $895 to $1700 with web ordering.  Some of the Disto models have RS-232 interfaces and there is free Leica computer software and third party software for mapping.

Riegl has a number of laser distance measuring instruments as well as a 3-D image scanner.
Swarovski Optik - Laser Range Finder RF-1 - to 1,000 meters @ +/- 1 meter
Acuity Research - 0.1" to 2000'
Measurement Devices Ltd. (MDL) - LaserAce® 300 range finder & others - WIN CE PDA
Laser Technology - maybe makes the Yardage Pro for Bushnell? - WIN CE PDA
Laser Atlanta - Advantage - 5 to 2,000 feet accuracy +/- 1/2 ft., 0 to 359.9 deg compass & MiNiLASER - 0.6 to 100 ft
Cyra - 3D field measurements to 50m with 6mm accuracy

Leica Range Measuring Instruments: (the tilt is limited to +/- 45 deg, so no good for astronomy)
Model Range Compass Tilt Data Price
Geovid 7x42BDA  Binoculars 1 km Yes No No
Geovid 7x42BD  Binoculars 1 km No No No
Vector GIS  Binoculars 1 km Yes Yes Yes
Vector 1500  Binoculars 2+ km Yes Yes Yes
Vector IV  Binoculars 4+ km Yes Yes Yes
MRF2000 monocular 3.8 km No No Yes
SG12 Digital Compass na Yes ? Yes
Disto Basic 100 m No No No US$ 895
Disto Memo 100 m No No Yes US$ 1095
Disto Pro 100 m No No Yes US$ 1695
Power Disto >140 m No No ?
Data Disto GSI use with T460D >100 m No No Yes
Data Disto RS232 >100 m No No Yes
NIVEL20 Dual axis inclination sensor na No Yes Yes



Thermistors have a well known resistance -vs.- temperature characteristic.  It is called the Steinhart-Hart equation.
that is experssed as
1/T= A + B*Ln(R) + C*(Ln(R))^3
or a simplified form that's less acurate

T= 1/(Ln(R) -A)) - C

In the above equations, T is in deg K and R is in Ohms.

The following equation appears on the Agilent web site, T = 1 / (A + W * (B+C * W*W)) - 273.15
where T is in deg C, A, B and C are the thermistor coeficients, W= Ln(R) and R is the measured resistance (Ohms) of the thermistor.  For the Agilent 34308 (and probably most other) 5k Ohm at 25 deg C thermistors the coefficients are: A = 1.28463e-3 B = 0.23625e-3 C = 9.2697e-8

Note that although the Steinhart-Hart equation is of the third order with respect to R, it is linear with respect to the coefficients, thus you can fit temperature vs. resistance data for a given thermistor easily.  This can be done by using three points on the R vs T curve, but is better done by using a statistical fit on a much larger number of points.

You can buy thermistors  specified so that upon interchanging sensors you will have 0.1 deg. C accuracy.  This is much better than the semiconductor IC type or a thermocouple.

Yellow Springs Instruments - Thermistors
Radio Shack Precision 10 K Ohm Thermistor 271-110 - on the back of the blister pack is a table of R vs T (103AT)
Agilent 34308 5 k - 40653B 10 k - Practical Temperature Measurements (AN 290  5965-7822E.pdf ) 32 pages, highly recomended for all types of temperature sensors. Includesthe Steinhart-Hart equations.

Self heating is mentioned as a problem with thermistors, but it is also the basis of fluid flow measurements using thermistors.
If the thermisor is biased so that there is some self heating and a fluid is moving past it, the fluid will carry away heat in proportion to the speed of the fluid.  For normal applications you need to be careful to bias the thermistor so that is does not self heat.

Silicon Semiconductors

These are analog integrated circuits that have an output that is a linear function of temperature.  They are not as accurate as thermistors but are easier to use.
Dallas Semiconductor - Thermal Management
Analog Devices - Temperature Sensors
National Semiconductor - Analog Temperature Sensors
Honeywell -
Airpax - temp sensors -
On Semiconductor (formerly part of Motorola) - LM75DM - 2-wire serial w/trip point


The Resistance Temperature Detector is a metal element whose restence changes linearly with temperature.  They typically are wired using a 3 or 4 wire Kelvin connection so that the resistance in the wires to the device are not part of the measurement.
Burns Engineering - ITS-90 & DIN 43760 and IEC 751 software downloads
Minco - small RTD

Fiber Optic

Nortec - non metalic sensor using light reflected from a semiconductive crystal.
FISO Technologies, inc. -


There are a number of ways to measure the humidity.  The popular Honneywell and Philips units use a capacitor whose value changes with humidity.  Dew point can be measured very precisely using light bouncing off of a mirror and looking for the dew.

Automata, Inc. - AQUA-TEL-TDR Soil Mositure probe uses Time Domain Reflectometry
Buck Research Instruments - humidity instrumentation
Delphi Auto -under hood capactive humidity sensor
General Eastern - sensors,  including mirror type & generators
Honneywell - HyCal - Humidity & Moisture - the latter recommended by Vernier Software

Micorconversion Technologies Co. - SAW based dew point
Michell Instruments - cooled mirror and other technologies
Ohmic Instruments Co. - Humidity Sensors - resistive eval kits
OKI Semiconductor MSCM64162 - This microcontroler is designed for temperature and humidity detection.  It is used in the Radio Shack 63-1015/Oregon Scientific Weather Station Temperature & Humidity sensor.    It runs on 1.5 volts and in this application the returned digital data stream is very feeble and will not directly trigger TTL level circuits.  This may be the cause of the 30 foot wire limit. It's LCD drive capability is NOT used in the WX-200 application but I suspect that it is used for stand alone temp & humidity displays that are battery powered.
Panametrics - Sensors
Philips - Distrubitor Listing 691-90001 - Factory .pdf documents -
Rotronic - HygroClip Humidity & Temperature
Sensirion - Sensmitter AH31 Digital RH & temp with SPI digital output
Yankee Environmental Systems (YES) - Total Sky Imager (TSI-440A) - Ultraviolet Instrumentation - Humidity -


Maxim + PIC - The source code is there, but I didn't see any mention of what sensor is used.
The Fredericks Company - Liquid based
AOSI - Polymer based, non glass rugged shatter proof tilt sensors survive during crash testing, systems, Inclinometers and Compasses
Spectron - Tilt & Inclination - Liquid based
LEICA NIVEL20 with compact opto-electronic sensor unit - light reflected from liquid surface as used in theodolites
US4827624 05/09/1989 Electronic level - Zircon International, Inc., Campbell, CA
Columbia Research Laboratories, Inc. - Force Balance Inclinometers -
UST Research Inc. (Wagner Lipnharski)- Ball in Cage -
Applied Geomechanics Inc. -  tiltmeter and clinometer technology
Kavlico Corporation - TS904 Tilt Sensor - for rugged applications
Nanotron, Inc. - electrolitic liquid based smaller than 1 inch up to +/- 70 deg

Building Wall Stud

US5619128: Stud sensor with over-stud miscalibration via circuit which stores an initial calibration density, compares that to a current test density and outputs result via indicator - Zircon International, Inc., Campbell, CA  capactive based
US5352974: Stud sensor with digital averager and dual sensitivity Zircon International, Inc., Campbell, CA  capactive based


Polaroid - ranging transductor etc. not only from cameras but built for other applications like cars
Mobile Robotics - Ultrasonic Positioning - based on the measurement of ultrasonic pseudorandom noise and its cross-correlation
Cheap Ultrasonics: Software - PIC microcontroller based
Fascinating Electronics, Inc. - Ultrasonic Radar - ploar plot
Massa Products - Underwater TR-208A/SQS-23, TR-237, TR-238, and the TR-330/SQS-56 & Air - Articles -
Airmar - Ultrasonic Air -
Honeywell -


Classical spinning mass

These are classicial spinning mass type gyros like are sold as toys except with more mass and electrical motor powered.
Arcmax - model helicopter - ?technology
Harold Crabtree, An Elementary Treatment of the theory of Spinning Tops and Gyroscopic Motion. This is the definitive work on tops and gyroscopes. It even discusses the mysterious rattlebacks we will see in the demo on tops.
Charles Stark Draper developed gyroscope systems that stabilized and balanced gunsights and bombsights and which were later expanded to an inertial guidance system for launching long-range missiles at supersonic jet targets. Patent No. 2,752,790
Charles Stark Draper Laboratory, Cambridge, Mass., was awarded a $35,310,026 contract for product improvement/producibility and evaluation studies on the urrent Trident II (D5) Pendulous Integrating Gyroscopic Accelerometers (PIGA's).  Work will be performed in Cambridge, Mass., and is expected to be ompleted by December 1999.  The Navy's Strategic Systems Program, Washington, D.C., is the contracting activity.
Elmer Ambrose Sperry invented gyroscope-guided automatic pilots for ships and airplanes that have also been applied to spacecraft. Patent No. 1,242,065
Litton Marine Systems (formerly Sperry Gyroscope) - Sperry Marine - Gyrocompass
Watson Industries - combinations of heading sensors, accelerometers, angular rate gyros, and angle references as well as a line of magnatometers.

Fiber Optic

KVH Industries - Fiber Optic Gyro - US5768462: Grooved optical fiber for use with an electrode and a method for making same ; US5739944: Support system for resonating element of phase modulator - 20 deg/hour = 1/3 deg per minute
US5610815: Integrated vehicle positioning and navigation system, apparatus and method
US4634282: Multimode fiber optic rotation sensor
US4135822: Laser gyroscope
US5365338: Wavelength sensor for fiber optic gyroscope - Secretary of the Navy

Crossbow - FOG


ATA Sensors, Albuquerque, NM  ARS-20 with no moving parts.
The Magneto hydrodynamic effect depends on the combination of a conducting liquid, a magnetic field and a force.  It was featured in the movie "Red October" as the propulsion system for a submarine.

Vibrating Tuning Forks & Wheels , Piezo

BEI Systron Donner - vibrating Quartz tuning forks
                                Aug '99 Sensors V 16 # 8 Cover Photo & Article on Coriolis-Based Micromachined Quartz Angular Rate Sensor
British Aerospace (Systems & Equipment), Inc. -sensorsVibrating Structure Gyroscope -Charlie Hopper -
CFX Technologies - gyros, accelerometers, Inclinometers, Ultra Low Noise Seismic Force Balance Accelerometers
Delphi Automotive Systems - MEMS angular rate sensor

MEMS Clearinghouse - Micromachined Gyroscope - Two-Dimensional Micromachined Gyroscope-
Gyration, Inc. - Gyration has designed a low-cost, micro-consumer gyroscope sensor for automotive applications; computer cursor management; and camcorder stabilization products

US5825350: Electronic pointing apparatus and method
US5698784 : Vibratory rate gyroscope and methods of assembly and operation
US5594169 :Optically sensed wire gyroscope apparatus and system, and methods for manufacture and cursor control
US5440326 : Gyroscopic pointer
US5138154 : Shaft angle encoder with rotating off-axis interference pattern
USD0378751: Graphic display controller
Airtronics - SG10 Piezo Gyro System for models
Bosch - Acceleration combined with Coriolis Yaw for automative handling applications
Draper Labs -
US5481914  Electronics for Coriolis Force and Other Sensors -
US5505084: Micromechanical tuning fork angular rate sensor - >100 other patents This patent for Silicon (prior art was quartz)
US5496436: Comb drive micromechanical tuning fork gyro fabrication method - >110 referenced patents
US5515724: Micromechanical gyroscopic transducer with improved drive and sense capabilities
US5535902: Gimballed vibrating wheel gyroscope
US5555765: Gimballed vibrating wheel gyroscope
US5650568: Gimballed vibrating wheel gyroscope having strain relief features
US5251483: Piezoelectric sensor element intended for a gyro
Temic - DRZ-75X - automotive application?
Inertial Science, Inc.- RRS75 Resonator Rate Sensor -
(Sumitomo Precision Products) Silicon Sensing Systems Japan Ltd - Vibrating Structure Gyroscope SGN1-100 - Links-
Fujitsu - GyroSensors -
Micro Piezo Gyro - on the Acroname robitics page
Murata -  ENC-03J GYROSTAR -
Irvine Sensors Corporation - MicroSensors, Inc. - Micro Ring Gyro - 1 deg/min
Silicon Sensing Systems - MEMS rate sensors and gyroscopes
Home Made Piezo gyro by Scott Stephens (see the PIC archive)

North Finding Module

In addition there is a "North Finding Module" that can determine North very accurately.  The military is interested for targeting and surveyors use them inside caves where they work well while a magnetic compass can have large errors if there is ferrous metal in the ground nearby (which may be unknown).  These work by measuring the Earth's rotation (15 deg/hr) in 2 planes 90 deg appart and use an accurate plumb measuring device like an accelerometer.

AN/PAQ-3 Modular Universal Laser Equipment (MULE) - Target locator and guide for laser-guided projectiles - FAS - DDN - BH -
Azimuth Technologies Ltd. - NORS62 - not gyro but astronomic & GPS based
Defense North Finding Products -
Federation of American Scientists- SE.09.02.A North Finding Module -
KVH Industries - North Finding Gyro -
Smiths Industries Aerospace -
US4694728: Fiber optic guided missile aimer - NFM North Finding Module; Sperry Gyroscope; May 1977. - Gyros, Platforms, Accelerometers; Kearfott Systems Division, General Precon Systems, Inc. 7th Ed. Nov. 1967, (pp. 26-28).
Wild T16 Theodolite with GAKII Gyro - by Jim Arnold P.E.


Bicycle 9.35 Gyroscopic Forces -
Peleng 1240 GyroStabilized Binoculars -
Gyroscopic stabalized cameras -
Gyroscopic Stabilizers - for model helicopters - Airtronics - Futaba - Hitec/RCD
20 mm Auto Shotgun TL A Military Specs - stablized gun
Ship Gyroscopic stabilization -
Gyroscopic Beverage Holder -
ES 300 Naval Weapons Systems - Chapter 5 Automatic Tracking Systems -

Gyroscopic Links

Exploritorium - Gyroscope - a number of topics are covered, good to leard about them
BMI Surplus - Gyroscope Test Equipment -
Gyroscopic Ball - for golf training
Air Force Institute of Technology - MECH 712 - Nonlinear Oscillations -
Wright-Patterson AFB - Gyroscopic Controls on Sperry "Messenger -
World Scientific - Stability Of Gyroscopic Systems - book in chaos series
Comptons Encyclopedia - Gyroscope -

HEV Flywheel Safety- gyroscopic effects of the flywheel can cause a vehicle to roll over during a turn
Pendulum to Gyroscope - 1852 Gyroscope Jean Bernard Léon Foucault
TB 11-6625-247-35 Gyro Magnetic Compass AN/ASM-61 Test Set @ETM

Human movement

Simon Fraser University - School of Kinesiology - Human movement tracking technology: resources -British Columbia Association of Kinesiologists (BCAK) -
AN/GSQ-160 - seperate web page

Explosive Detection

-Smiths -
Also see my UneXploded Ordinance (UXO) page


Figaro - Semiconductor Gas Sensors Combustible, Toxic, Organic Solvents, CFCs (HCFCs and HFCs), Indoor Pollutants, Cooking Vapors, Oxygen, Humidity
Chemical Sensors -
Electrovac - Amperometric Oxygen Sensor -
Hong Tak Electronic Co.,Ltd. - Oxygen Sensors
City Tech - electrochemical and catalytic bead gas sensors


Sensory Inc. - $50 eval kit - 15 words, user trained


Cyrano - wroking with Agilent (was part of HP)  to investigate the commercial viability of their electronic nose technology
HP (now Agilent, BC) and Cyrano Sciences, Inc. Sign Research Agreement -
Agilent 4440A chemical odor sensor -
Electronic Sensor Technology - zNose™

Rotary Angle

Netzer Percison - FAQ - 360 deg absolute to 10 arc seconds after calibration, Sin Cos output

Hobo Data Logger

Onset Computer Corporation - HOBO® 4-Channel External Logger - Radio Shack can order as RSU12045522 - My HOBO web page


Fujitsu Microelectronics America - Biometric fingerprint - metal contacts forming capacitors at 500 dpi + software to recognize duplicate prints.  Two types, one is a static 1.5 cm square the other, MBF300 is a 1.28 x 0.2 cm strip that the finger is swept over.  Designed for use on things like cell phones, PDAs, laptops, access systems, etc.  How hard would it be to make a latex copy and would it fool the sensor?

Web Links

Motorola Sensors - Inirtial, pressure & smoke
Sentech - Sensor distributor
Texas Instruments -Calculator Based Laboratory (CBL) - has many low cost sensors used for education.
The interface between the calculator, although RS-232 based, has a T.I. proprietary format so that this very handy data logger can not be used with a lap top or anything other than a T.I. calculator.  The CBL is also sold by EduCALC.
Veriner Software - many sensors for the CBL & general use aimed at education
Sensors Magazine - As the title says they are devoted to Sensors.  There is also an annual trade show. There are sensors for almost anything that can be sensed.  I have only included the ones that I find interesting.  The Dec. 98 issue has a overview article on magnetic sensors.  Dec 2001 "List Servers" article by Brooke Clarke
In theFeb. '99 Issue Jack Johnson proposes the following end use based definitions:
Transducer - is an I/O device that transformes energy in one form to energy in the same or another form for the purpose of transmitting energy or power.
Sensor -        is an I/O device that transformes energy in one form to energy in the same or another form for the purpose of transmitting (e.g. displaying, indicating, generating) information (e.g. data, status).
Instrumentation & Control Systems - Industrial oriented but also has a lot of sensor information
Instrumentation of amateur rockets -
International  Frequency  Sensor  Association  (IFSA) - products and papers
Remote Measurement Systems - Sensor theory & Products -
Photonics Spectra - a magazine with lots of good information and a Directory + Dictionary + buyer's guide +
EG&G - Optoelectronics Product Guide -
Hamamatsu Photonics - USA page -
MIT Lincoln Laboratory's Programs with the DARPA Sensor Technology Office -
Temic (Dalimer - Chrysler) Automotive Sensors -
Sensors and Actuators A: Physical -is an ELSEVIER pub
Handy Board Robotics Links - a Motorola mocrocontroller based generic PC board for robotics applications
LEGO - Mindstorms - touch & light sensors - TECHNIC CyberMaster - includes 2 way wireless communications to/from PC.
Onset Computer Corporation - HOBO® 4-Channel External Logger - Also can be ordered from Radio Shack as RSU 12045522
Honeywell Sensors - main index to all kinds
PC Interfaces by Tomi Engdahl
Linear Technology - LTC2400 24 bit ADC on a chip
NASA - Instrument and Sensing Technology - Spin-off Sensor Technology -
JPL - Chapter 12. Typical Science Instruments -
Sensor Technology at the Lawrence Livermore National Laboratory -
Allen Bradley (Rockwell) Sensors - Presence Sensing
Sensors and Transducers - by Bruce Carter
Cornell Autonomous Helicopter Project - using Earth's Magnetic field & other sensors
Russell Bik Design - electric field sensor, 12' range to detect people in a room
Remote Measurement Systems - Remote Measurement Systems -
Tekscan - tactile sensors
Quantum Research Group - Charge Transfer sensors - many interesting applications for this patented technology -E97S Eval Board
Brooke's Home Page
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