US 3555368 A
Description (OCR text may contain errors)
Jan. 12, 1971 c. E. ATK INS CAPACITY SENSING MEANS FOR AUTOMATIC FLUSHING SYSTEMS AND THE LIKE 2 Sheets-Sheet 1 Filed Dec, 154. 1968 WW 7 ATTORNEYS Jam-12, 1971 c ATKlNs 3,555,368 CAPACITY SENSING MEANS FOR AUTOMATIC FLUSHING SYSTEMS AND THE LIKE Filed Dec. 13, 1968 2 Sheets-Sheet z TlE'4- INVEN OR 54a 5 70M:
ATTORNEYS gM M iww United States Patent 3,555,368 CAPACITY SENSING MEANS FOR AUTOMATIC FLUSHING SYSTEMS AND THE LIKE Carl E. Atkins, Montclair, N.J., assignor to Wagner Electric Corporation, a corporation of Delaware Continuation-impart of application Ser. No. 592,825, Nov. 8, 1966. This application Dec. 13, 1968, Ser. No. 795,381
Int. Cl. H01h 47/22 US. Cl. 317-146 18 Claims ABSTRACT OF THE DISCLOSURE A body sensing apparatus for automatic flushing systems having a fiat conductive plate and a conductive mesh screen, mounted parallel to the plate, mounted on or in a wall or partition which may divide one urinal from another. The plate and screen detect the body capacity of the user and energize an electrical circuit operate a flush valve after the user leaves the facility.
This application is a continuation-in-part of application Ser. No. 592,825 filed on Nov. 8, 1966 by Carl E. Atkins now abandoned.
This invention relates to automatic devices which include flush valves in sanitary systems. The invention has particular reference to a form of body sensing arrangement having high sensitivity and the capability of sensing a person who may stand within an extensive adjoining space.
This invention is an improvement over the flushing system described and claimed in US. Pats. No. 3,314,081 and No. 3,339,212 which issued to Carl E. Atkins and Robert L. Ziolkowski upon applications Ser. No. 369,543, filed May 22, 1964, and Ser. No. 473,608, filed July 21, 1965, respectively both assigned to the owner of the present invention.
The automatic operation of flushing valves in urinals and other sanitary facilities is desirable for many reasons. Some autmoatic systems have used a conductive plate mounted above the facility to sense the presence of a person by the added capacity formed by the persons body. This arrangement works well for adults but sometimes fails to work when the facility is used by short people. The present invention uses an improved sensing arrangement which includes a flat conductive plate placed at the side or in front of the place where a person stands when using the facility. The plate may be enclosed within a wall or a partition which separates one facility from another. A conductive screen of a plurality of rods are placed adjacent to the plate and insualted from it. The capacity between the plate and the cream has a low value because of the open spaces in the screen mesh or because of the spaces between rods. However, the capacity between the screen or rods and a person standing some distance from the screen is about the same as the capacity between a person and a solid plate. This arrangement is quite sensitive can be made to detect the presence of a person at a considerable distance.
One of the objects of this invention is to provide an improved automatic flushing device which avoids one or more of the disadvantages and limitations of prior art arrangements.
Another object of the invention is to increase the sensitivity of capacity operated devices.
Another object of the invention is to insure that the presence of a person will be sensed electrically even through the person may stand some distance from the sensing device.
Another object of the invention is to insure that both short and tall persons can opreate the flushing system.
3,555,368 Patented Jan. 12, 1971 In accordance with the present invention, a body sensing system has been devised which may be concealed in a wall mounted adjacent to a urinal or other sanitary facility. The system employs a capacity sensing means to detect the body capacity of the user and includes electric circuit means responsive to the change of capacity of operating a fiush valve after the person has left the urinal. The system includes a flat conductive plate and a conductive mesh screen or other open conductive arrays mounted parallel to the plate. The plate and the screen are mounted on or in a wall or partition which may divided one urinal from another. The present invention includes all the circuit components present in the above mentioned applications.
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.
FIG. 1 is a schematic diagram of connections showing how the sensing screen is coupled to a pair of output terminals which may be connected to a flush valve or to a motor which operates a flush valve.
FIG. 2 is a scheamtic diagram of connections of an alternate coupling means where the circuit components are mounted some distance from the sensing means.
FIG. 3 is an isometric view of one type of urinal employing an alternate type of capacity sensing means.
FIG. 4 is a top view of the facility shown in FIG. 3.
FIG. 5 is a cross sectional view of the facility shown in FIG. 3 and is taken along line 55 of that figure.
FIG. 6 is a schematic diagram of connections showing two alternate schemes of connection to balance the capacity effects introduced by a grounded Water curtain in the facility.
Referring now to FIG. 1, the system includes a flat plate 10 which is mounted alongside the position where a user may stand. The plate may be quite extensive and have dimensions two feet wide by four feet high. A conductive screen 11 is mounted parallel to the plate 10 and may be set about one-half inch from the plate. This sensing device includes a distributed capacity 12 between the screen 11 and ground which in this case may be the floor or the usual plumbing fixtures which are conductive. When a person stands before the facility his body also forms a capacity 13 between the screen and ground and it is this added capacity that operates the circuit and causes the valve to flush after the person leaves the. facility.
A perforate screen has been indicated in FIGS. 1 and 2 because this type of electrode is convenient to use and because it covers a large area. However, many other types of electrodes may be used. Several small plates, a plurality of rods mounted either horizontally or vertically, serve the purpose equally well.
An oscillating circuit is connected to the plate 10 and the screen 11, this oscillating circuit including a small neon lamp 14 and also two resistors. 15 and 16 which are connected in series between the plate 10 and a ground connection. One of the lamp electrodes is connected to an adjustable contact 17 which slides on aresistor 18 connected between resistors 15 and 16. Resistor 18 may be bridged by an additional resistor 20 but this is not always necessary. The other terminal of the lamp 14 is connected to the screen 11. The screen 11 is also connected to a conductor 21 in series with a limiting resistor 22. The conductor 21 is connected to a source of negative potential which in this case is furnished by a diode 23 and a capacitor 24. These components are connected to power supply terminals 25 and 26 which are to be connected to an alternating current power system of about 117 volts. The system of connections described above is an oscillator and includes a first capacity 19 between the plate and the screen 11. A second capacity 12 is formed between the screen 11 and ground. Both these capacitors are charged when conductor 21 is supplied with a negative potential. As the charge is applied through resistor 22, the voltage across the lamp terminals increases until the firing voltage is reached, then the lamp conducts and the potential across its terminals is reduced below the lamp sustaining potential. This action allows capacitor 19 to discharge to produce a current pulse in resistor which moves in the direction of arrow 27. The discharge of capacitor 12 produces a similar current pulse in resistor 16 but in an opposite direction as indicated by arrow 28. If resistors 15 and 16 are equal and if capacities 12 and 19 are equal, there will be no alternating voltage applied across the end terminals of resistors 15 and 16.
When a person steps up to the urinal an added capacity 13 is connected between the screen 11 and ground conductor 30. This causes the oscillator to present an unbalanced series of pulses to resistors 15 and 16. In this case the pulses through resistor 16 will be greater than the pulses applied to resistor 15 and a negative voltage will be applied to the upper end of resistor 15. There may be a wide variety of coupling circuits connected between resistors 15 and 16 and an output set of terminals 31 and 32 which are to be connected to a load circuit. The coupling circuit described herein comprises two transistor amplifiers 33 and 34, a semiconductor switching circuit 35, a first relay 36 and a second relay 37. These major components are interconnected so as to provide a very definite program of operations.
The first amplifier, transistor 33, has its emitter connected in series with a resistor 38 to the ground conductor 30. The emitter is also coupled to the base of transistor 34 through a capacitor 40. The collector of transistor 33 is connected to a voltage divider which includes resistors 41 and 42. The base of transistor 34 is connected to a voltage divider which includes resistors 43 and 44 on one side and resistor 45 on the ground side, thereby partially stabilizing the voltage on the base. The emitter of transistor 34 is connected directly to the ground conductor while the collector is connected to the negative conductor 21 in series with resistor 43. The collector of transistor 34 is coupled through a small capacitor 46 to a double transistor switching means 35. This switch includes a first p-n-p transistor 47 having its emitter connected to the alternating current supply in series with a resistor 48. The second n-p-n transistor 50 has its emitter connected to the ground conductor 30. This switching combination has the base of each transistor connected to the collector electrode of the other transistor with the base of transistor 50 connected to the coupling capacitor 46. The base of transistor 50 is also connected to an automatic bias circuit including a resistor 29 and a capacitor 39. This circuit has been described in application Ser. No. 550,765, filed May 17, 1966, by Carl E. Atkins, which was abandoned in favor of application Ser. No. 755,507 filed on Aug. 20, 1968 by the same inventor. Negative pulses from supply line 21 connected to terminal 25 leak through the emitter-collector electrodes of transistor when the Zener voltage is exceeded and charge capacitor 39. The charge on this capacitor builds up until the Zener voltage of transistor is reached. Additional voltage leaks to grounded conductor 30.
The output of the double transistor switching means 35 is coupled through a diode 51 to a winding 52 of relay 36. The winding is shunted by a large capacitor 53 so that it may operate on discrete pulses without causing the armature to chatter. The armature of relay 36 is connected directly to terminal 25 of the alternating current supply. When the relay is not actuated, an upper set of contacts 54 is closed, thereby sending current through a resistor 55 and a lamp 56 to the other side of the supply terminal. When the relay is actuated, a lower set of contacts 57 is closed and alternating current is applied to conductor 58 which is connected to the collector electrode of transistor 60 and through diode 61 to the winding 62 of the second relay 37. This relay winding is also shunted by a large capacitor 63 so that it may operate without chattering when discrete pulses are applied to the winding.
Relay 37 also includes an armature connected directly to terminal 25 of the alternating current supply. When the relay is actuated the normally open contacts 64 are closed and terminal 25 of the supply is then connected to terminal 31 of the load circuit. At the same time, the alternating current supply is connected by means of conductor 65 to winding 52 in series with a limiting resistor 66 and a diode 67.
Transistor 60 has its collector connected directly to conductor 58 and its base is coupled to a delay circuit 68 which includes a first capacitor 76 and a second capacitor 71. Capacitor 70 is connected across resistors 72, 73, and 74, these resistors being connected in series with each other. Capacitor 71 is connected across resistors 73 and 74. "A diode 75 is connected between line 58 and the junction of capacitor 70 with resistor 72. The purpose of this delay circuit will be described later.
The operation of this circuit is as follows:
It is evident that the oscillating circuit which includes lamp 14 and the chargeable capacitors, oscillates all the time, starting as soon as the negative voltage is applied to conductor 21. When there is no person adjacent screen 11, there is substantially no output applied to the base of transistor 33 because the output voltages are balanced. No pulses are applied to transistor 34 and no pulses are applied to the semiconductor switch 35, therefore the switch is not conductive and the first relay 36 receives current through resistor 48 and diode 51 so that it is actuated and the armature is pulled down closing contacts 57 as shown in the drawing. The lamp 56 is not lighted but current is applied to conductor 58 and to the delay circuit 68. Negative current pulses now flow through diode 75 to charge capacitor 70 to about volts and to charge capacitor 71 to about 40 volts. Since the base of transistor 60 is connected to the mid-point of resistors 73 and 74, its base is maintained at a slight forward potential, transistor 60 is conductive and by-passes current around winding 62 or relay 37, and contacts 64 remain open. The values of resistors 72, 73 and 74 and of capacitors 70 and 71 are arranged so that it takes about five seconds for these capacitors to Charge to a negative voltage which applies a small negative voltage to the base of transistor 60 and thereby shunts the current around winding 62 and permits contacts 64 to open and cut off the voltage to the load terminals. This five seconds time interval is chosen because it takes about five seconds for the flushing operation. It is obvious that any time interval can be produced by such a circuit to accommodate other desired operations.
Now let it be assumed that a person steps up to the' sanitary facility and the capacity of his body is added to the capacity 12 which normally exists between the screen and ground. This added capacity, Which may be only 3 picofarads, causes considerable change in the oscillating circuit and the current through resistor 15 is considerably less than the current through resistor 16. Negative pulses are thereby applied to the first transistor base and these pulses are amplified and negative pulses are applied through capacitor 40 tothe base of the second transistor 34. This produces amplified positive pulses which are applied through capacitor 46 to the switch combination, causing it to conduct and short circuit the winding 52 of relay 36, thereby opening contacts 57 and closing contacts 54. This action removes the alternating current volt age from conductor 58 and lights lamp 56.
When voltage is removed from conductor 58, capacitors 70 and 71 discharge through resistors 72, 73 and 74 in about twelve seconds and apply a more positive voltage to the base of transistor 60 to make it non-conductive. However, current cannot be applied to winding 62 or relay 37 because contacts 57 are open and therefore contacts 64 remain open and the load is not energized. As long as the first relay 36 is unactuated, the second relay cannot operate. This means that as long as the person stands adjacent to screen 11, the load is not actuated and there is no flushing operation.
Now let it be assumed that the person leaves the facility and thereby removes the added capacity 13 and restores the oscillating system to its normal condition. Now there is no voltage applied to the transistor switch 35, the switch is non-conductive, and the first relay winding 52 receives current, thereby turning ofi lamp 56 and applying alternating current voltage to conductor 58 and negative pulses to winding 62, thereby operating the relay and closing contacts 64. The load is now supplied with power and the flushing motor (not shown) is actuated causing a flushing operation. The motor continues to operate for about five seconds until capacitors 70 and 71 are charged to a voltage which applies a negative -volt bias to the base of transistor 60. This causes the transistor to conduct and short current away from winding 62 to open contact 64 and cut off current to the motor.
The above circuit could be operated to flush prematurely if the person stepped away and then returned within five seconds. If this happened, the double transistor switch would then be conditioned to pass current and normalize the first relay. In order to make sure that this does not occur, an additional circuit is provided. This circuit includes conductor 65, resistor 66, and diode 67. As long as contacts 64 are closed, current is supplied from terminal through contacts 64, over conductor 65 and diode 67, to relay winding 52, thereby maintaining contacts 57 closed regardless of the condition of switch combination 35. This permits the load motor to continue working for the allotted five seconds to complete the flushing operation. This interlocking circuit guards against flooding due to the person moving about. Also, a second person may step up to the facility within seventeen seconds without causing premature operation. If there were no interlock circuit, flushing could start again and cause undesirable wetting.
The circuit shown in FIG. 2 is an alternate arrangement of the sensing means. It is the same as the sensing means shown in FIG. 1 except that a conductive concentric cable 76 is used to shield the conductor 77 which connects the screen 11 to one terminal of the lamp 14. The cylindrical shield 78 is connected to the plate 10 at one end and to the base of the first transistor 33 at the other end. This type of connection may be necessary when the operating circuitry must be mounted some distance from the sensing plate and screen. The effect of the addition is to increase the capacity between the plate and screen. The charging current and the discharge current are both increased but the circuit can easily be re-balanced by a shift of contact point 17 or by alternating either of resistors 15 or 16. The operation of such a circuit is the same as the circuit shown in FIG. 1.
Referring now to FIGS. 3, 4, 5 and 6, there is shown an alternate facility 80, made of porcelain or similar material and having a fiat back portion and extending side portions 81 and 82. This shape makes possible an alternate array of capacity sensing electrodes enclosed in the facility and not visible to the user. A solid conductive back plate 10A (corresponding to plate 10 in FIG. 1) forms a part of the sensing system and compensates for the introduction of a grounded water curtain. Two conductive rods 83 and 84 take the place of the mesh in FIG. 1. Because of the positions of these sensing electrodes, it is necessary to make allowance for the water curtain 91 which may be present during the use of the facility. Since the water flows into a metal drain pipe, the curtain is grounded and a considerable capacity is thereby introduced between the shield and ground 30. An additional capacity 92 is introduced between the rods 83 and 84.
6 The distributed capacities between the rods and ground are shown in FIG. 6 as capacities 85 and 86.
In most installations of this type, the control circuit should be mounted at a distance from the facility where it cannot be wetted and where it is difficult for a user to harm it. Such an installation generally calls for a shielded cable 76 as shown in FIGS. 2 and 6, having a central conductor 77. A small distributed capacity is always present in such a line and this capacity is made a part of the oscillation circuit by connecting the discharge lamp 14 between the concentric conductor 77 and the midpoint between the two resistors 15 and 16. When the lamp 14 discharges, part of the current pulse travels over conductors 87 and 77 to rods 83 and 84, through disdistributed capacities 85 and 86, to the grounded conductor 30, resistor 16, to the other side of the lamp 14. Another portion of the discharge travels over conductors 87 and 77, then through the cable capacity 88, to conductor 90, resistor 15, and the other side of the lamp. If these were the only discharge paths, an adjustment of resistor 16 can be made to balance the voltage drops and the output (with no person near the rods) would be substantially zero.
The water curtain 91 is sometimes present and is always grounded. There is a definite small capacity 92 between the sensing rods 83, 84 and the water curtain 91. When this capacity increases, the discharge pulses from the lamp 14, over conductor 77, increase and the voltage drop across resistor 16 increases, thereby increasing the output signal. This capacity 92 shunts capacities 85 and 86 tends to lower the sensitivity. This defect may be partially compensated by placing the shield 10A directly behind the water curtain to introduce a larger capacity between the shield and ground. When switch 94 is moved to its upper position as shown in FIG. 6, capacity 93 shunts a portion of the discharge current which would normally travel through resistor 15 from the cable covering, through capacity 93, to the ground conductor and resistor 16.
The presence of a man, represented by capacity 13, increases the discharge current through resistor 16 and causes an unbalance voltage which is amplified and utilized in the manner explained above in connection with FIG. 1.
Another type of compensation may be obtained by connecting the switch blade 94 to its lower terminal. Then one portion of the discharge current from the lamp passes through the cable, over conductor 77 to the sensing rods 83 and 84, through capacitors 92 and 93 to a portion of resistor 16 and to the other side of the lamp. Resistor 15 may be adjusted so that there is no output when there is no capacity 13 (man) in front of the rods. When capacity 13 is added, the discharge current flowing through the lower part of resistor 16 provides the desired unbalance voltage and an output signal is produced.
It will be obvious that the above system of components can be adjusted to produce either a positive or a negative system of discharge pulses. If such a change is made, the number of amplifying stages may be changed to produce the same signal for the load coupling circuit, or the coupling circuit which activates the relays to energize the load may be reversed.
A highly important feature of the present invention comprises the use of the energized shielding members 10 in FIGS. 1 and 2, and 10a in FIG. 6, in association with the antenna members 11 in FIGS. 1 and 2, and "83 and 84 in FIG. 6. If such shielding members were not used, the residual (no-signal) capacitance to ground of the antenna members 11, 83 and 84 alone would be quite large, on the order of 80 to picofarads, due to the unavoidable close proximity of these antenna members to grounded elements of the urinal or sanitary facility in which the antenna members are installed, e.g. water pipes and flush valves. The increment of capacitance to ground added by the person using the facility is only 1 picofarad or less. Thus the change in the capacitance to ground of the antenna members alone caused by the presence of the person using the facility would amount to only one or two percent maximum, and such a small signal would cause such severe problems of poor sensitivity and stability as to make the device virtually impractical.
The shielding members and 10a are physically interposed between the antenna members 11, 83 and 84 and the grounded elements of the sanitary facility and are driven by application of a potential from the associated circuit, and thereby interrupt flux lines between the antenna members and the grounded elements of the sanitary facility to reduce the residual capacitance to ground of the antenna members to about to picofarads. In this way, the small increment of capacitance added by the body of the person using the facility is made to represent a greater percentage of the residual capacitance of the antenna members to ground to provide a stronger signal which increases the sensitivity and stability of the associated circuit. It is true that there will be a large added capacitance to ground of the shielding members 10 and 10a. However, these capacitances are remote from the detection zone in which the antenna members are operative to sense the added capacitance of the users body, and thus such added capacitances will not interfere with the necessary detection by the antenna members of the presence of the person in the position for use of the sanitary facility. Moreover, the capacitance between the antenna members 11, 83 and 84 and the shielding members 10 and 10a can be relatively large without causing any disadvantage or problems since these capacitances remain fixed and are connected to the associated circuit and can be compensated for or balanced by adjustment of other circuit components such as resistors 15, 16, 18 and 20. Accordingly, the use of shielding members interposed between the antenna members and nearby grounded elements and energized by application of a potential to reduce the residual capacity to ground of the antenna members provides substantial advantages and benefits in the invention and makes the disclosed device for control of sanitary facilities commercially practical.
The advantages of the present invention, as well as certain changes and modifications to the disclosed embodiments thereof, will be readily apparent to those skilled in the art. It is the applicants intention to cover all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.
What is claimed is:
1. In a capacitance-responsive circuit operative to provide an output which varies in response to changes in detected capacitance, said circuit including first and second capacitance which include a common first plate, the improvement comprising: (1) electrically-conductive antenna means formed by said common first plate of said first and second capacitances, a second plate of said first capacitance being formed by an object to be detected, and (2) electrically-conductive shielding means operative to form a second plate of said second capacitance and to shield said antenna means from grounded elements, said antenna means being disposed between said shielding means and any object within the utilization range of said antenna system so as to prevent any substantial capacitive coupling between said shielding means such object.
2. The antenna system according to claim 1 wherein said antenna means consists of a perforate screen.
3. In a capacitance-responsive circuit operative to provide an output which varies in response to changes in detected capacitance, said circuit being operative to control a valve for regulating the flow of water and including first and second capacitances including common first plate means, the improvement comprising an antenna system comprising 1) electrically-conductive antenna means formed by said common first plate means of said first and second capacitances, a second plate of said first capacitance being formed by an object to be detected, and (2) electrically-conductive shielding means operative to form a second plate of said second capacitance and to shield said antenna means from grounded structural elements, and further operative to compensate for variations in capacitance to ground of said antenna means caused by said fiow of water between said antenna means and said shielding means.
4. The antenna system according to claim 3 further comprising (1) a coaxial cable having an inner conductor and an outer conductor, said inner conductor being electrically connected to said antenna means, and (2) switching means operative to selectively connect said shielding means to said outer conductor or to an alternate point in said capacitance-responsive circuit.
5. The antenna system according to claim 3 wherein said antenna means comprises first and second spaced rods.
6. The antenna system according to claim 3 wherein said shielding means comprises a solid plate.
7. The antenna system according to claim 3 further comprising encasement means having a surface on which said water flow occurs, said encasement means being operative to separate and insulate said antenna means and said shielding means.
8. The antenna system described in claim 1 further comprising a coaxial cable having an inner conductor and an outer conductor, said inner conductor being electrically connected to said antenna means and said outer conductor being electrically connected to said shielding means, said coaxial cable forming an increment of said second capacitance and serving to connect said antenna means and said shielding means to the remainder of said capacitanceresponsive circuit.
9. Capacity sensing means for detecting the presence of an object comprising a conductive plate; a conductive element mounted in spaced relation to said plate and insulated therefrom to establish a substantially fixed capacity therebetween; said conductive element having an area less than one-half of the conductive plate; a ground conductor spaced from the element and defining a space in which the presence of said object is to be detected, said element being positioned to establish a substantially fixed capacity between it and the ground conductor; a source of alternating current electric power connected directly to said element and coupled through impedances to the ground conductor and to the conductive plate for charging said capacities between the plate, the element, and ground; said impedances connected so as to produce substantially no signal When an object is not present in said defined space, but producing an electrical signal when an object to be detected is in said defined space and thereby changes the capacity between the conductive element and ground.
10. Capacity sensing means as claimed in claim 9 wherein said signal is applied through an amplifier system to a relay to actuate the relay and thereby connect electrical power to a load.
11. Capacity sensing means as claimed in claim 10 wherein said amplifier system includes a timing circuit for deactuating the relay after a predetermined period of actuation.
12. Capacity sensing means as claimed in claim 11 wherein a coupling circuit is provided for preventing deactuation of the relay during said predetermined period of actuation.
13. Capacity sensing means as claimed in claim 12 wherein said relay operates a pair of contacts which connect the load to an alternating current power supply, said coupling circuit including a connection in series with a rectifying diode which connects one of the load contacts to an actuation circuit to maintain the power supply connected to the load for said period of actuation.
14. A capacity sensing means for detecting the presence of an object comprising a conductive plate; a conductive element mounted in spaced relation to said plate and insulated therefrom; a ground conductor also insulated from the plate and the element; said conductive element and ground conductor forming a first capacitor; the conductive plate and conductive element forming a second capacitor; and oscillator including a non-linear discharge device having one terminal of said device connected to said conductive element by means of a concentric line within a cylindrical shield; the other terminal of said discharge device connected to the mid-point of a voltage divider, one end of which is connected to the ground conductor; the other end of the voltage divider connected to the shield and to said conductive plate; said voltage divider providing two current paths for the oscillator currents, one of said paths including said first capacitor, the other of said paths including said second capacitor and the capacity created by the concentric line and its shield; said first and second resistors adjusted so as to produce substantially no signal at their ends when an object is not present, but to produce an electrical signal when an object is adjacent to the conductive element and thereby adds additional capacity to the capacity between the conductive element and ground.
15. A capacity sensing means as claimed in claim 14 wherein said oscillator is a relaxation oscillator and the non-linear discharge device is a gas-filled lamp.
16. A capacity sensing means as claimed in claim 14 wherein said voltage divider is connected to an amplifier, a rectifier, and a relay for connecting a load circuit to 10 a source of alternating current power when an object is positioned adjacent to said conductive element.
17. A capacity sensing means as claimed in claim 14 wherein said conductive plate is positioned adjacent a grounded water curtain, thereby creating a capacity therebetween, said capacity acting to divert part of the current flowing through the second capacitor to the ground conductor.
18. A capacity sensing means as claimed in claim 14 wherein said conductive shield is connected to a midpoint in the second resistor.
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3,201,774 8/1965 Vemura 340258(C) 3,218,623 11/1965 Buntenbach 340258 3,314,081 4/1967 Atkins et a1 410 0 3,333,160 7/1967 Gorski 317-146 3,339,212 9/1967 Atkins et al 4l00 3,366,847 1/1968 Burns et a1. 317146 0 LEE T. HIX, Primary Examiner US. Cl. X.R.