Seismometer

© Brooke Clarke 2007 -2009


Hilger Watts
                    Seismometer


PSR-1
                    Geophone
Quake Alarm

Hilger & Watts  Seismometer
Geophone Quake Alarm EarthQuake Alert
Background
Vibration Sensors
Hilger & Watts
Cal Tech
Geophone
Quake Alarm
EarthQuake Alert
Atomic Bomb Test Ban
Earthquake Early Warning
Quake-Catcher Network
    Earthquakes
Patents
Related
Links

Background

Seismometers & geophones are some of the sensor types that I find interesting.  The applications are varied. 

Earthquakes

Classically seismometers have been used to record the ground shaking as the result of earthquakes.  By measuring the time from the "P" wave to the slower waves the radial distance between the sensor and epicenter can be calculated.  The magnitude and duration of the slow waves gives an indication of the energy.  This is the application that first got me interested.

Oil Exploration

Geophones are used to look for reflections caused by changes in density of sub surface layers after a surface explosion or a tamper initially shakes the ground.  These are typically used in large arrays.

Intrusion Detection

Outdoor intrusion detectors use geophones as well as other methods to detect ground vibrations caused by moving men and machines.  Knowing about the use of seismometers for recording earthquakes and  then seeing this application reinforced my interest.

Machine Balancing & monitoring

Some industrial motors are connected to a system that can be balanced so sensing the out of balance helps make the initial adjustments.

In an industrial environment when a machine is breaking down or is about to, it starts to shake and detecting the vibration allows shutting the motor off before there's a catastrophic problem.

Detecting Nuclear Blasts

As part of the Non Nuclear Proliferation treaty a need arose to detect nuclear blasts and differentiate them from other types of blasts.  Seismometers are able to do that by the wave form shape.

Note that the technology used for seismometers is very similar to that used for pendulums and gravity meters.

Vibration Sensors

There are a number of technologies used for vibration sensing.  One of these is very similar if not identical to the geophone.  The difference may be in the frequency range that's being monitored.  Vibration sensors typically are concerned with audio frequencies and into the ultrasonic whereas geophones and seismometers are looking at infrasound frequencies.

Hilger & Watts

Label SG450, 157222, Made in England.
The Teledyne Geotech S13 Seismometer looks very similar and they show up on eBay now and then.


Variable Oscillation Period Seismometer (see patent below) that can be used vertically or horizontally.  Permanent magnet and coil of wire.
Hilger
                    Watts seismometer Opened Hilger Watts
                    Seismometer Close Up Open
Hilger
                    Watts Bottom wiring
Hilger Watts
                    Seismometer
Hilger Watts Seismometer Open
Hilger Watts Seismometer Close Up
Bottom showing 2 of 3 possible windings
Top

Mechanical

Diameter 6.625", height to top of handle under 15" (varies with leveling feet) 27.5 pounds.
patent 3199072 page 1



 



Voltage Generator6 is a floating permenant magnet with a fixed coil (20) in the gap.  Three bottom spokes 8 and two top spokes 10 locate the magnet so that it's free to move up and down (as shown in the patent drawing, but there's a way to use it on it's side).




Spring Lifting System

The arms (14) are firmly attached to the magnet by a central rod.   Four triangular leaf springs (19) their base ends clamped to arms (14) and their pointed ends are linked (18)  to the pointed ends of the top springs (19).  There's a plate anchored to the frame (shown just above 26a) which holds brackets at the base of two of the top springs (19).  One of these is shown in the upper left of the drawing.  There are two Allan head screws that clamp the spring to the bracket (the upper left screw and another behind it not shown).  There are two pivot screws whose ends sit on the plate (above 26a) shown as the single screw to the right of the bracket.  The central screw goes through a clearance hole in the bracket and into a tapped hole in the plate.  These two screws have horizontal holes in the head so they can be adjusted from the side. 






Spring Lifting System - Not shown in patent drawing

Hilger Watts
              Seismometer Floating plate not shown in patent 3199072The other two top springs (19) are held by an identical pair of brackets, but instead of being connected to the plate (above 26a) they are connected to a plate that's been cut out of the first plate.  An an are bolted to the top of the plate (above 26a) and cantilevered out over the cut out section of plate.  In it's outer end there's a tapped hole.  The screw in that hole can be turned to cause the floating plate to move and this changes the tension of the spring system.  The screw can be accessed by removing the large headed screw that holds the cover over the clamping screw (22).  The highest dial setting that I can get to work in the vertical position is "18" and here the spring lifting system adjustment screw is backed out so that it's cantilevered is almost touching the floating plate.

Setting Period

If the dial associated with the period adjustment (knob at top left) is set to full CCW it stops at about 23.  But it's impossible using the spring lifting system screw to center the magnet (6) in it's range of travel.  This might require using a pin to adjust the other two screws or some other adjustment, or maybe it can't be done.  The resistor that caused critical damping when the dial was at 15 is much too weak when the dial is at 18 and the period is some number of seconds.  It takes a number of cycles of ringing until the mass stops.

If  you have any documentation on how to use this Hilger & Watts seismometer please let me know.

Electrical

The three coil termination pairs have letters scratched in the phenolic.  Although there are positions for 6 output wires, on this unit only 4 are used.   The patent mentions that the damping needs to be adjusted for the selected period.   This unit has two separate coils, C-D (1k5 Ohms) and E-F (7k6 Ohms).  There is a brown jumper between D and E thus presenting the full coil between C and F (White and Yellow).  Connector pins B & F go to a pair of  wires terminated with a 6k7 Ohm resistor that I choose for best damping. 

Coil
Position
Wire
Color
Connector
A
na
na
B
na
na
C
White
B
D
Blue
broken
E
Black
A
F
Yellow
F
Chassis
Red
broken
The connector is marked in the center of the insulating block 148-CP  and has 6 male pins.  Threads for mating shell are 0.864" O.D.  mating insert OD less than 0.691" O.D. with a single grove for keying.

Period

The dial calibrated from 0 to 25 which should change the period instead seems to move the mass up or down and when at 15 the rod in the height viewing dome is level with the center fiducial mark.  Moving this dial to either extreme bottoms the mass.

The label on the outside "1NS" implies this was used in the horizontal position.  But when placed horizontally the mass locks up.  So it's really not working correctly.  There is probably something that needs to be done to get proper operation when vertical, which is the position I'd like to use.

These look similar to the sensors used in the GR-8 Sound Ranging Set.

Patents by Willmore:

3199072 Variable Oscillation Period Seismometer, Patrick L. Willmore, August 3, 1965, 367/185
3292145 Willmore Long Period Vertical Seismograph, Patrick L. Willmore
2909759 Sensitive Vertical Displacement Seismometer, George W. Cook, Oct 20 1959, 367/186 ; 327/518
2933715 Seismic Device, Beuermann (Firma Seismos, DE), Apr 19 1960, 367/184 ; 310/15; 310/27; 73/654 -
3297982 Horizontal seismometer
2939079 Method of Calibration an Electromagnetic Seismograph, Patrick L. Willmore

Cal Tech

Cal Tech
          Horizontal Seismometer patent 3685011

3685011 Seismometer, Francis E. Lehner (Cal Tech), Aug 15 1972, 367/182 ; 73/654 - ciol in magnet type with calibration pulse input, maybe 5 second period (adjustable).
Calls:
3194060 Seismic Displacement Transducer, L.T. Greenwood (NASA), Jul 13 1965, 73/654 ; 367/179; 73/382R -
2074043 Seismograph, Louis Statbam (Std Oil), Mar 16, 1937, 367/182 ; 310/15; 73/654 - cylindrical package, down hole? permanent horseshoe magnets
2873103 Seismological Instruments, R.F. Hautly, Feb 10 1959, 73/653 ; 73/514.14; 73/650 - torsional damped limited frequency response reflecting mirror
Calls:
1869828 Devices for Measuring and Recording Vibrations in Three Directions
2268526 galvanometer
2487793 Object Controlling Electric Motor System, (Sperry Gyro) - used as part of aircraft auto pilot
2542018 Compass, Ferrill (Sperry Corp), Jr. et al, Feb 10 1951, 33/360 ; 33/362; 33/363Q; 73/504.14 - vibratory compass
2552722 Electromagnetic Accelerometer, John G. King, May 15 1951, 73/514.12 ; 324/127; 33/DIG.5; 336/135; 336/30; 336/67; 336/92; 336/94; 340/870.35; 73/514.31- magnet if bob of pendulum
2616681 Angular Velocity Responsive Apparatus, C.T. Morrow (Sperry Corp), Nov 4 1952, - ref 2513340
2842752 Geophones, W.M. Jones (British Petrolum), Jly 8 1958, 367/182 ; 267/160; 336/100; 336/136
2852769 Time Interval Multiplier, R.L. Plouffe (Navy), Sep 16 1958, 342/186 ; 327/134; 327/172; 327/174; 368/115

3704764 Air deliverable seismic system,  Harold B Henderson, Texas Instruments Inc, Dec 5, 1972, - saw patent number of a different seismometer on eBay.
.

Geophone

This geophone is from the PSR-1 Seismic Intrusion Detector set.

12.7 oz.

Quake Alarm

The Quake Alarm is just a simple brass rod pendulum whose lower end is in a triangular opening in a brass block.  The brass block can be moved in and out by means of the adjusting screw on the front thus changing the gap between the rod and block, i.e. the sensitivity.  BUT, this is not a P wave detector but rather a horizontal motion detector, not what I was looking for.
This one is made by jds Products andis their model QA-2000.

At a prior house I had a similar looking unit that was a true P wave (Wiki) detector to give earlier warning of a quake.

EarthQuake Alert

This is a P-wave (Wiki) detector that sounds a warning prior to the arrival of the S (shear) wave that has the high energy.  The p-wave is an up-down motion that arrives before the S-wave, where the time difference depends on the distanct to the epi center.  Not much warning if the quake is local, but a couple of minutes for someone in San Francisco during the 1989 Loma Prieta quake (Wiki).

Atomic Bomb Test Ban

By using a high dynamic range and wide bandwidth ( 10 seconds to 10 Hz) seismograph the difference between an earthquake and an explosion can be detected.  The Vela Uniform project (Wiki) investigated how to do this. Keywords: Long Range Seismic Measurements

Patents

1784415 Electrical Recording Seismograph, H. Benioff (Carnegie), Dec 9 1930, 340/870.16 ; 310/15; 340/870.31; 340/870.44; 346/107.1; 346/65; 367/179; 367/182; 73/654
Called By: 
2933715 Seismic Device,Beuermann, Apr 1960,
Calls:
2269453 Device for Detecting Displacements, E.L. Gayhart, Jan 1942
2348225 Magnetic Seismometer, O.S. Petty, May 1944 - oil prospecting geophone
2576775 Seismometer System, F.D. Case (Diamond Inst), Nov 1951, - long period earthquake detection in small size
2683867 <See below>
2756406 Vibration Detector, G.S. Schurman (Calif. Research Inst), July 1956, - Frequency Response vs. Geophone mass - oil prospecting
2788512 Low Frequenc Seismometer, W.J. Reichert (Shell), April 9 1957,
2707776 Magnetron Type Seismometer, Cruzan (Phillips Petro), May 1955 -
2683867 Parachuted Radio Seismic Transducer, J.O. Vann (not assigned), July 13 1954, - for measuring polar ice
3225328 Transportable Seismograph, F Lecroart,

2111643 Seismometer, H. Salvatore (Western Geophysical Co), Mar 22 1938, - combine permenant magnets and coils - prospecting
Called by:
2418953 Transducing System, R.W. Raitt
2519916 Inertial Electromagnetic Throat Microphone, D.W. Martin (RCA),
2470244 ELECTRICAL REPRODUCING STYLUS - for machine shop duplicating
2562983 Frequency Adjustable Seismic Wave Detector, D.H. Clewell, Aug 7 1951, - oil prospecting
2643367 MAGNETOSTRICTION SEISMOMETER, (Phillips Petroleum Co)
2663088 Pendulum and Acceleration Compensation System, R.T. Cloud (N. Am Geo)
2540796 VIBRATION TRANSLATOR, A.N Stanton
2671202 VIBRATION PICKUP, M.O. Petroff (Stewart-Warner), Mar 2 1954 - wheel balancing
2595067 INERTIA TYPE VIBRATORY PICKUP, J.A. Flint (Jeffrey Mfg), Apr 1952
2659065 SEISMOMETER, R.L. Cordell (Stanolind Oil)
3066526 UNBALANCE DETECTION APPARATUS, H.R. Tear (Stewart-Warner),- wheel balancing
3480808 POWER GENERATOR, F. Rieth (Packard-Bell) - probably for TV remote
4740775 Automobile burglar alarm, R. Price,
4584569 Motion sensitive security system, M.J. Lopez,
5323133 Method and apparatus for making electrical connection with a movable member, - loudspeaker

The above patents were found by looking for patents that are called by or call the Hilger & Watts patent.

2359245 Electrical displacement vibrometer, Gulf Research Development Co, Sep 26, 1944, 73/654, 367/178, 73/DIG.400, 340/870.16, 338/2, 381/162, 338/5, 338/43, 310/25
------------------ Korean Conflict-----------
2533249 Seismic Detector, December 12, 1950, 310/25 ; 367/183; 73/496
2636160 Vertical Component Low Frequency Geophone, April 21, 1953, 318/680
----------------- Korean Conflict end -----------
2696592 Vib Pickup, December 7, 1954, 336/30 ; 335/285; 336/100; 336/136; 336/90; 73/654
2745085 Seismic Detector, May 8, 1956, 367/185 ; 310/14
2748370 Seismometer, May 29, 1956, 367/187 ; 174/77R; 267/160
2751573 App Chg Reas Freq, June 19, 1956, 367/183 ; 310/25
coil current changes reas freq and can be done on whole string.
2753544 Seismic Detector, July 3, 1956, 367/182 ; 267/159; 310/25; 73/654
2754435 Voltage Generating Vibratory Pickup Devices, T. Ongaro, International R&D, July 10, 1956, 310/27 ; 367/183; 73/661
Machine Balancing or Monitoring
2756406 Vibration Detector, G.A. Schurman, California Research, July 24, 1956, 367/184 ; 310/15
oil exploration
2764019 Vib Meas Dev, September 25, 1956, 73/654 ; 310/27; 73/661
rectify AC output and drive a meter, no batteries machine monitor
2788510 Seismic Prospecting Apparatus, April 9, 1957, 367/86 ; 174/70S; 367/176
2788511 Frequency Seismometer, E.H. Marshall, Texas Inst, April 9, 1957, 367/187 ; 267/161, - oil exploration
2788512 Frequency Seismometer, April 9, 1957, 367/14
2788513 Cable, E.T. Howes, United Geophysical Corp, April 9, 1957, 367/180 ; 174/102SC; 174/106R; 174/27; 174/71R; 310/338; 310/357; 367/154
2842752 Geophones, July 8, 1958, 367/182 ; 267/160; 336/100; 336/136
2923367 M App for Seismic sur, February 2, 1960, 367/34 ; 367/48; 367/58
2933715 Geophones, April 19, 1960, 367/184 ; 310/15; 310/27; 73/654
2939079 METHOD OF CALIBRATING AN ELECTROMAGNETIC, May 31, 1960, 324/537 ; 324/202; 367/13
---------------- Vietnam Era ---------------
2980042 Method for Planting Seismic Detectors, B. McCollum, April 18, 1961, 405/177 ; 111/199; 111/89; 343/719; 405/175; 405/183 - oil exploration
3020767 Linear Accelerometer, W.P. Kistler, KistlerInst Corp., February 13, 1962, 73/497 ; 267/160
feedback provices linear, sensitive operation
3057209 Seismic Vibration Pickup Means, K.F. Frank, Micro Balancing Inc., October 9, 1962, 73/654 ; 336/40
dynamic balancing machine
3067404 Vibration Detector, A.B. Hilderbrandt, Jersey Prod Res, December 4, 1962, 367/182 ; 310/15; 310/27; 73/652
oil exploration
3199072 Variable Oscillation Period Seismometer, August 3, 1965, 367/185
Hilger & Watts earthquake type
3202847 Tunable Vibration Pickup Device, L.H. Erickson, August 24, 1965, 310/14 ; 310/15; 367/184; 73/654
alarm or balancing equipment, reasonant type
3212057 Long Period Seismometer, F.E. Romberg, Texas Inst, October 12, 1965, 367/184
portable horizontal period much longer than equivalent pendulum, not as sensitive to tilt (tolerates 0.5 deg).
aimed at nuclear detection
3241375 Transducer, R.M. Canzoneri, Consolidated Electrodynamics Corp., August 24, 1965, 310/14 ; 310/15; 367/184; 73/654 - strain gauge type, instrumentation, tolerates hi G
3451040 Spring Suspension for Low Frequency Geophone, W.P. Johnson III, Mark Products,  June 17, 1969, 367/183
oil exploration
3545286 Holder which is Displaceable Along one Axis, L.A. Stenstrom, Philips, December 8, 1970, 248/604 ; 267/154; 267/160; 73/514.24; 73/654
3577184 Low Distortion Seismometer, W.O. McNeel, Geo Space Corp., May 4, 1971, 525/342 ; 525/332.9; 525/333.1; 525/333.2; 525/359.1; 525/359.3; 525/359.5; 525/359.6; 525/361; 526/240
oil exploration
3582874 Electrodynamic Seismic Receiver, N.E. Fedoseenko, June 1, 1971, 206/6.1 ; 206/366
oil exploration
3582875 Geophone Device, S.H. Van Wambeck, June 1, 1971, 206/433 ; 229/120.23; 229/120.27
oil exploration
3609674 Seismometer, S. Hansen, Hughes Aircraft Co., September 28, 1971, 65/135.7 ; 373/27; 65/136.4; 65/324; 65/327; 65/347; 65/356 - bubble movement is sensed and a PID feedback loop provides wide bandwidth
---------------- Vietnam Era ends---------------
4043175 Automatic method and apparatus for digitally indicating response characteristics of geophones of a geophysical data acquisition system 4259563 Method for dynamically tuning a seismic transducer
4323994 Geophone Spring, J.M. Coogler, Geosource, April 6, 1982, 367/183 ; 267/158; 267/161; 367/187
4458344 Tapered Geophone SpringJ.M. Coogler, Geosource, July 3, 1984, 367/183 ; 267/161; 367/187
4623991 Delta Shaped Geophone Spring, F.A. Vitringa, Geosource, November 18, 1986, 367/183 ; 267/161; 367/187
5113375 Method and apparatus for testing geophones
5134593 Geophone Spring, R.M. Logan, Western Atlas Intl Inc., July 28, 1992, 367/187 ; 267/141.3; 367/183
6658362 Method and apparatus for testing components
6816434 Seismic detection

Warning Alarm Patents

Class 340/ COMMUNICATIONS: ELECTRICAL
500 CONDITION RESPONSIVE INDICATING SYSTEM
540 Subclass 540 indent level is 1 Specific condition
686.1 Subclass 686.1 indent level is 2 Position responsive
690 Subclass 690 indent level is 3 Geophysical (e.g., fault slip)

4689997 Motion detector suitable for detecting earthquakes and the like, September 1987, 73/652 ; 181/122; 340/580; 340/690; 367/182; 73/654
5633463 Earthquake detector, May 1997, 73/654 ; 181/122; 200/61.45R; 340/690; 367/182 - all mechanical
5837951 Inertia switching device, acceleration responsive device and method of  Making Acceleration Responsive Device, November 1998, 200/61.45R - ball in cage switch
6121888 Earthquake detector, September 2000, 340/690 ; 340/540; 340/686.1 - long spring sensor/switch
Calls:
2689341 SAFETY DEVICE FOR INDICATING SHIFTING September 1954 340/690 ; 200/51.11; 200/61.45R
4262289 Seismic tremor sensor alarm April 1981 340/690 ; 200/61.51; 74/89.14; 74/89.1
4297690 Earthquake alarm system October 1981 340/690 ; 200/61.49; 200/61.51; 340/669; 340/689
4359722 Earthquake detection system with pendulum switch November 1982 340/540 ; 307/117
4484186 Earthquake indicator November 1984 340/689 ; 116/303; 200/61.52; 33/391; 33/402; 340/690; 73/652
4689997 Motion detector suitable for detecting earthquakes and the like September 1987 73/652 ; 181/122; 340/580; 340/690; 367/182; 73/65
4801793 Orientation indicating device (camera portrait or landscape)
January 1989 396/50 ; 396/287
4945347 Motion and orientation responsive device for seismic, intrusion, and tilt July 1990 340/689 ; 200/61.45R; 340/690     like Quake Alarm
4978948 Combined earthquake sensor and night light December 1990 340/690 ; 340/321; 362/253; 362/806
5418523 Earthquake motion detector alarm May 1995 340/690 ; 200/61.45R; 200/61.51; 340/66
5596183 Seismically activated appliance switch January 1997 200/61.45R ; 200/61.48; 200/61.51; 307/117; 340/690
5633463 Earthquake detector, May 1997 73/654 ; 181/122; 200/61.45R; 340/690; 367/182
5644300 Seismoscopic detector July 1997 340/690 ; 340/540; 340/691.5; 340/693.5
5867099  ----- bad patent no.------
February 1999
5929767 Earthquake detector and alarm July 1999 340/690 ; 200/61.45R; 340/601; 340/689

6459379 Earthquake-alarm device, October 2002, 340/601 ; 200/61.52; 200/DIG.20; 340/689; 340/690; 340/691.1; 340/693.5; 702/15; 73/649 - like Quake Alarm
7006000 Earthquake detecting and warning device, February 28, 2006, 340/690 ; 200/61.52; 73/579; 73/594; 73/649; 73/658 - inverted bowl

Earthquake Early Warning

USGS April 2012 talk - by using a network of sensors the warning time can be maybe twice what you can get from an on site P-wave detector.

Earthquake Hazards Program

California Integrated Seismic Network - Earthquake Early Warning -

Quake-Catcher Network

They also has an Android app that uses the 3-axis g sensor combined with the magnet compass when the phone is sitting unused on the charger to report quakes.
This is better than the USB hardware which should be oriented to magnetic North.


Quake-Catcher USB
                    Network Seismometer

In the padded envelope you get:
* The seismometer,
* a couple of mounting wood screws
* a USB-A male to USB-B male cable
* one page of instructions.



On order is a pair of USB to CAT-5 LAN
adapters which should allow making a USB
extension cable over CAT-5 cable.


Also on order is a 100 foot CAT-5 LAN cable.

For $50 you can have  your own USB seismometer connected to the internet.
The sensor contains a 3-axis MEMS accelerometer and a USB interface.
http://www.youtube.com/user/QuakeCatcherNetwork

Sensor

ONavi B 16 bit.
The QCNLive display of the 3 sensor outputs does auto scale, so there should be some benefit from mounting the sensor away from the house.

USB-CAT5 adapters & 100" CAT5 cable

This does not work.  Why? Ans: handshake timing limits cable length.  But, an active USB extension cable does work and these could be cascaded.

Questions:
1. can the USB cable be extended say 100 feet to allow sensor location far from the house?
2. does the software contain a circular memory so that the data can be uploaded at a later time if there's a network problem in real time?
3. Is there any intelligence in the sensor, i.e. a micro controller?
4. Is there provision for adding different sensors, like those on this page? Yes & No.  There's a list of supported sensors, but they are all USB based.  There's not provision for a 2-wire input type sensor like the Hilger-Watts.

Software

There are three programs that need to be downloaded and installed (Instructions)

  • Boinc (Berkeley Open Infrastructure for Network Computing)- allows your computer to talk to the server over your internet connection.
    Add QCN to “My Projects”:
Select “Add Project” (Lower Right).
Select “Next”.
Under “Project URL” type the following: qcn.stanford.edu/sensor
USB driver for the specific sensor you have
QCNLive - program running on your computer
File\Local Settings - Lat, Lon, Ele, etc.

Windows Firewall needs to have Boinc added as an exception.

Earthquakes

Earthquake 25 Sep 2012 8:15 am Ukiah

The electronic equipment was swaying North-South and it almost fell over.
Very strong shaking.
USGS web page.  M4.5

Earthquake
              25 Sep 2012 8:15 am Ukiah


Related

Outdoor Intrusion Detectors and Related Equipment (most seismic, magnetic and/or Doppler)
GEO_ID - TRC-3, PEWS, USQ-42, Turd
GSQ154 - All GSQ-154
GSQ160 - Frequency Disconnect -GSQ-160, USQ-46, TS-2963, PP-6446 - TCw - cylindrical module pinouts.
GSS26 - AN/GSS-26 minimal info
Intrusion Alarm Patents
USQ_Rx - Igloo White, USQ-42, USQ-46 details,
PSR-1 - Seismic intrusion detector with audio output
Modular Outdoor Intrusion Sensors (REMBASS?)
Sonobuoy Based Outdoor Intrusion Sensors & Sonobuoies - CRT-1B Sonobuoy (hydrophone depends on Magnetostriction) - Roswell Connection

Sensors

Links

Brooke's: PRC68, Alphanumeric Index of web pages, ContactSensors,  Page
-  page created 22 July 2007.