Vibration sensor

A vibration sensor (10) that more effectively distinguishes between various causes of vibrations is disclosed. The vibration sensor includes a housing (18), a plurality of spaced contacts (22-34) positioned above the floor (44) of the housing, a central electrode (36) positioned within the housing, and an electrically-conductive ball (38) configured for movement within the housing. The contacts are interconnected by a plurality of electrically-conductive elements (50-62) such as resistors and are configured for connecting to a first terminal (12) of an alarm system (16). The central electrode is spaced from the contacts and is configured for connecting to a second terminal (14) of the alarm system. The ball is configured for simultaneously contacting at least one of the contacts and the central electrode so that it provides an electrical path between the first and second terminals to allow the transfer of an electrical signal therebetween. When the sensor is vibrated, the ball moves within the chamber over the spaced contacts so that it touches different ones of the contacts while remaining in contact with the central electrode. This changes the electrical characteristics of the signal passing through the first and second terminals. The alarm system monitors these changes in the signal to determine characteristics of the sensor. These characteristics are then analyzed to determine the magnitude, duration and/or other characteristic of the vibration to distinguish between various causes of the vibration.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to vibration or shock sensors. More 
particularly, the invention relates to a vibration sensor that more 
effectively measures certain characteristics of vibrations and shocks to 
determine the cause thereof. 
2. Description of the Prior Art 
Vibration or shock sensors are commonly used in alarm systems to activate 
an alarm whenever the devices to which they are attached are touched, 
moved, or otherwise vibrated. For example, vibration sensors are commonly 
placed in windows of buildings to sense glass breakage and in car alarm 
systems to detect vehicle tampering. Additionally, the UL now requires 
high security safe and vault alarm systems to include vibration sensors. 
Prior art vibrations sensors typically utilize ball or reed-type switches 
that open or close a contact when they are vibrated or moved. 
Unfortunately, these types of sensors often cause false alarms because 
they cannot distinguish between vibrations that occur due to normal causes 
and those that occur due to attempted unauthorized entry. For example, 
when placed in windows or doors, prior art sensors will often trigger an 
alarm when someone merely knocks on the window or door or when the window 
or door is vibrated due to thunder or wind as well as when someone 
attempts to illicitly gain entry through the window of door. This is 
because prior art vibration sensors only sense vibrations by detecting the 
opening and/or closing of a contact, which will occur regardless of the 
magnitude and/or duration of the vibrations. 
There is therefore a need for an improved vibration sensor that more 
effectively distinguishes between various causes of vibrations. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention solves the above-described problems and provides a 
distinct advance in the art of vibration sensors. More particularly, the 
invention provides a ball-type vibration sensor that more effectively 
distinguishes between various causes of vibrations. 
The vibration sensor of the present invention achieves the foregoing by 
sensing not only the opening and/or closing of a contact by a ball in a 
ball switch, but also other characteristics such as the position, velocity 
and trajectory of the ball and the time that it takes the ball to return 
to its equilibrium position. This enables the sensor to determine the 
magnitude, duration and/or other characteristic of vibrations to 
distinguish between various causes of the vibrations, thus reducing false 
alarms and increasing the effectiveness and utility of the sensor. 
One embodiment of the vibration sensor broadly includes a housing, a 
plurality of spaced contacts positioned above the floor of the housing, a 
central electrode positioned within the housing, and an 
electrically-conductive ball configured for movement within the housing. 
The contacts are interconnected by a plurality of electrically-conductive 
elements such as resistors and are configured for connecting to a first 
terminal of an alarm system. The central electrode is spaced from the 
contacts and is configured for connecting to a second terminal of the 
alarm system. The ball is configured for simultaneously contacting the 
central electrode and at least one of the contacts so that it provides an 
electrical path therebetween for the transmission of an electrical signal. 
The ball is biased to an equilibrium position in the housing whenever the 
device to which the sensor is attached is not being vibrated. When the 
senor is vibrated, the ball moves over the spaced contacts and about the 
central electrode so that it touches different ones of the contacts while 
remaining in contact with the central electrode. As the ball moves, the 
electrical characteristics of the signal passing through the first and 
second terminals changes. The changes in the signal are affected by 
characteristics of the ball movement such as the position, velocity, and 
trajectory of the ball as well as the time that it takes the ball to 
return to its equilibrium position. These signal changes are analyzed by 
the alarm system or other controller to determine the magnitude, duration 
and/or other characteristic of the vibration to distinguish between 
various causes of the vibrations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawing figures, and particularly FIGS. 1-4, a vibration 
sensor 10 constructed in accordance with a preferred embodiment of the 
invention is illustrated. The sensor is configured for coupling with a 
pair of first and second terminals 12,14 of an alarm system 16 and broadly 
includes a housing 18, a plurality of spaced contacts 
20,22,24,26,28,30,32,34 positioned above the floor of the housing, a 
central electrode 36 positioned within the housing, an 
electrically-conductive ball 38 configured for movement within the 
housing, and a magnet 40 or other mechanism for biasing the ball to an 
equilibrium position within the housing. 
In more detail, the housing 18 is generally cup-shaped and includes a 
cylindrical sidewall 42 and a floor 44 defining a hollow interior chamber 
46 therebetween. As illustrated in FIG. 2, the floor is preferably 
downwardly sloped toward the center of the housing, but may also be flat 
as illustrated in FIG. 5. The housing may be formed of metal, plastic or 
any other suitable material but is preferably non-magnetic. 
The contacts 20-34 are preferably elongated strips of conductive material 
that are printed on a circular circuit board 48 that rests on top of the 
housing floor 44. The contacts extend radially out from the center of the 
circuit board and are angularly spaced in a spoke configuration and are 
raised above the upper surface of the circuit board. Adjacent contacts are 
spaced sufficiently close to ensure that the ball 38 is always touching at 
least one of the contacts as it moves across the floor of the housing as 
best illustrated in FIG. 3. 
As schematically illustrated in FIG. 4, the contacts 20-34 are 
interconnected by a plurality of electrically-conductive elements 
50,52,54,56,58,60,62 such as resistors so that they form a single, 
series-connected electrical path. The resistors preferably all have the 
same resistive value of approximately 20-30 ohms. The end contact 34 is 
configured for connecting to the first terminal 12 of the alarm system 16. 
This may be accomplished by electrically connecting the contact to the 
housing 18 and in turn connecting the housing to the alarm system as 
illustrated in FIG. 1 or by connecting the contact directly to the alarm 
system with a wire or other conductor. 
The central electrode 36 is preferably an elongated pin or rod formed of 
electrically conductive metal. The electrode is positioned vertically 
within the housing 18 near the center of the chamber 46. The lower edge of 
the electrode is spaced from the upper surface of the circuit board 48 and 
the contacts 20-34 and the upper edge extends out the open-end of the 
housing so that it can be readily connected to the second terminal 14 of 
the alarm system. The electrode is supported in the housing and above the 
circuit board by a ring-shaped insulator 64 that is held in the open-end 
of the housing by an annular eyelet 66 or washer. 
The ball 38 is preferably formed of electrically conductive ferromagnetic 
material and is sized so that it freely moves along the upper surface of 
the circuit board 48 and about the central electrode 36. The ball is 
configured for simultaneously contacting at least one of the contacts 
20-34 and the central electrode so that it provides an electrical path 
between the first and second terminals 12,14 to allow the transfer of an 
electrical signal therebetween. 
The magnet 40 is preferably positioned below the housing floor 44 and is 
oriented so that it biases the ball 38 to an equilibrium position. For 
example, the magnet may be oriented to bias the ball to the position 
indicated by the letter "A" in FIG. 4. The magnet also attracts the ball 
downward and toward the center of the housing so that the ball firmly 
contacts both the center electrode 36 and the contacts 20-34 to improve 
the conductivity therebetween. The magnet may be eliminated by sloping the 
floor in such a manner so that the ball is biased by gravity to its 
equilibrium position. The exact equilibrium position of the ball is not 
important; however, it is important that the ball always return to this 
position whenever the device to which the sensor is attached is not being 
vibrated. 
Although not required, the ball 38 may be formed of permanent magnetic 
materials to increase the magnetic attraction between the ball and the 
magnet 40. This improves the contact rating of the ball and permits the 
use of a smaller biasing magnet 40. 
As illustrated in FIG. 1, the alarm system 16 preferably includes a 
controller 68 and an alarm device 70 such as a bell or horn. The 
controller is operable for transmitting an electrical signal through the 
first and second terminals 12,14 and for analyzing the characteristics of 
the signal such as the signal's voltage and/or current level. 
In use, the sensor 10 is placed in a window, door, or any other object that 
is to be monitored for vibrations or shocks. The sensor is then 
electrically connected to the alarm system 16 by connecting the end 
contact 34 to the first terminal 12 and the central electrode 36 to the 
second terminal 14 in a conventional manner. Because the electrically 
conductive ball 38 is always in contact with at least one of the contacts 
and the central electrode, the contacts, central electrode, ball, and 
first and second terminals form a closed circuit that is connected to the 
alarm system. 
The controller 68 transmits an electrical signal through the circuit and 
monitors vibrations and shocks that move the ball 38 in the housing 18 by 
monitoring the electrical characteristics of the signal. When the sensor 
10 is in its normal state, i.e., not being vibrated or moved, the ball is 
in its equilibrium position indicated by the letter "A" in FIG. 4. While 
the ball is in this position, the signal must pass through the resistors 
54,56,58,60,62, so that the circuit has a total resistance of 100 ohms if 
each of the resistors has a value of 20 ohms. 
If the sensor 10 is vibrated sufficiently to overcome the bias of the 
magnet 40 or the sloped floor 44, the ball 38 moves from its equilibrium 
position across the floor about the central electrode 36. As the ball 
moves, it passes over the spaced contacts 20-34 so that it touches 
different ones of the contacts while remaining in contact with the central 
electrode. This changes the total resistance of the circuit and therefore 
changes the electrical characteristics of the signal passing through the 
first and second terminals 12,14. For example, if the ball is moved from 
position "A" to position "B" in FIG. 4, the signal passes only through the 
single resistor 62, so the circuit resistance drops from 100 ohms to 20 
ohms. 
The changes in the signal are determined by characteristics of the ball 
movement such as the position, velocity, and trajectory of the ball as 
well as the time that it takes the ball to return to its equilibrium 
position. The controller analyzes these signal changes to determine the 
magnitude, duration and/or other characteristic of the vibration to 
distinguish between various causes of the vibrations, thus reducing false 
alarms and increasing the effectiveness and utility of the sensor. 
For example, if the sensor 10 is placed in a window or other glass, a minor 
vibration such as may occur due to knocking on the window, thunder, wind, 
or other natural cause may only cause the ball 38 to move slowly and a 
short distance from its equilibrium position and to quickly return to this 
position. In contrast, a more severe vibration such as may occur due to 
glass breakage and/or unauthorized entry into a building or vehicle will 
likely cause the ball to move rapidly and far from its equilibrium 
position and to never return to this position. The controller 68 can be 
programmed to distinguish between these types of vibrations and to trigger 
the alarm only upon detection of certain types of vibrations. 
FIGS. 6 and 7 illustrate another embodiment of the invention that is 
similar to the embodiment shown in FIGS. 1-4, except that it includes 
flush, generally rectangular-shaped contacts 72,74,76,78,80,82,84,86 that 
are not series connected. Rather, the contacts are each connected to a 
resistor 88,90,92,94,96,98,100,102 that is in turn connected to the second 
terminal 14 of the alarm system 16. In this embodiment, each resistor has 
a different resistive value so that the controller can determine which 
contact the ball is touching. 
FIGS. 6 and 7 also illustrate a method of constructing the circuit board 
104 so that it can be formed flat but still conform to the sloped floor of 
the housing 18. Particularly, as illustrated in FIG. 7, the circuit board 
is formed by cutting a series of narrow wedges 106 from a circular circuit 
board to create a series of circumferentially-spaced and centrally 
connected pie-shaped wedges 108. The circuit board is then inserted into 
the housing and pushed down against the floor 44 by a central electrode 
110 having a rounded bottom edge so that the circuit board conforms to the 
sloped floor. 
FIGS. 8-10 illustrate another embodiment of the sensor 10 that includes 
contacts 112,114,116,118,120,122,124,126 that are generally rectangular in 
shape and flush-mounted as with the contacts 72-86 of the embodiment 
illustrated in FIGS. 6 and 7. However, the contacts are series connected 
by a series of conductive elements such as resistors 
128,130,132,134,136,138,140 similar to the embodiment illustrated in FIGS. 
1-5. 
FIGS. 11-13 illustrate yet another embodiment of the sensor that includes a 
housing 141 formed from a pair of intersecting, planar sidewalls 142,144 
that together form an elongated v-shaped channel. A v-shaped circuit board 
155 rests on top of the housing, and contacts 146, 148, 150, 152, 154 are 
formed on the top surface of the circuit board and are interconnected by 
resistors 156,158,160,162. The end contact 156 is connected to an 
upstanding terminal 164. An elongated electrode 166 is formed on the 
surface of the opposite sidewall 144 and is connected to an upstanding 
terminal 168. The terminals 164 and 168 are then connected to the 
terminals 12,14 of the alarm system as described above. A ball 170 is 
positioned in the housing so that it moves linearly across the floor of 
the channel and simultaneously contacts the electrode and at least one of 
the contacts. The ball is biased to an equilibrium position by a magnet 
172 so that the sensor operates in a similar manner as the sensor 
illustrated in FIGS. 2-5. 
Although the invention has been described with reference to the preferred 
embodiments illustrated in the attached drawing figures, it is noted that 
equivalents may be employed and substitutions made herein without 
departing from the scope of the invention as recited in the claims. For 
example, those skilled in the art will appreciate that the resistors may 
be replaced with other conductive elements such as inductors, capacitors, 
etc., that would alter the characteristics of the electrical signal 
passing between the first and second terminals when the ball moves across 
the contacts. Also, although the sensor has been described as being 
particularly useful in alarm systems, it can be used in any application 
where it is desired to monitor vibrations such as in seismic equipment or 
in packaging. 
Having thus described the preferred embodiment of the invention, what is 
claimed as new and desired to be protected by letters patent includes the 
following.