CA2009069A1 - Electrode array for meter reading device - Google Patents

Abstract

IMPROVED ELECTRODE ARRAY FOR METER READING DEVICE
ABSTRACT
An electrode array and substrate for use in an appara-tus for remotely monitoring the position of a rotatable member, relative the substrate on which the array is dis-posed, as the rotatable member is rotated about an axis of rotation. The array includes a substrate composed of a three-layer composite having first and second surfaces, a plurality of spaced-apart, excitable electrodes defining a center portion disposed on the first surface, an aperture in the substrate located in the center portion for receiving an axle, a center electrode in the center portion, at least partially circumscribing the aperture, a guard composed of a first conductive strip disposed in the center portion on the first surface spaced apart from and located between the spaced apart excitable electrodes and the center electrode.
The array further includes a second conductive strip dis-posed on the second surface of the substrate composite in electrical communication with the center electrode, a third and fourth conductive strips in electrical communication with the guard, the third and fourth conductor strips disposed on the second surface of the three-layer substrate composite, spaced apart from and positioned laterally on opposite sides of the second conductive strip and the substrate three-layer composite includes a middle metal layer in electrical communication with the guard.

Description

~a -1- 2~9069 IMPROVED ELECTRODE ARRAY FOR METER READING DEVICE
BACKGROUND OF THE INVENTION

This invention relates to a humidity resistant appara-tus for determining the orientation of a rotatable meter hand relative to a dial spaced apart from the meter hand.
More particularly, the invention is concerned with an electrode array used to create a current signal (amplitude) that is subsequently used to identify the position of a meter hand relative to a dial face, without significantly altering the interior structure or wiring of a meter.

GENERAL DESCRIPTION OF THE PRIOR ART

A prior art remote meter reading device (see Figure 3), sold by Siecor Corporation under Part Number SE200, uses an electrode array like that shown in Figures 1 and 2 in combination with a high pass filter technique, otherwise known as a transimpedance amplifier, to sense the position of a meter's hand. Once this is done, it encodes the reading and sends it over a cable in ASCII form to an interface device, like a TIU-100 (Telephone Interface Device also sold by Siecor Corporation) where the reading can be used for monitoring power usage and customer billing. It employs a four-layer PC Board and a microprocessor, analog and digital circuitry and five encoder dial arrangements.
Each ~encoder dial uses an electrode array of ten pads (exeitable electrodes), arranged around an inner ring, each pad coinciding with one of the ten meter hand positions.
The excitable electrodes or pads and inner ring are made of copper PC board metalization connected to electronic cir-cuitry. To sense the position of the meter hand, a pulse or waveform is generated and routed to a predetermined one of 082989.PA: Improved Electrode Array for Meter Readin9 Device, ~. Bruce Bonnett, Page 2 -2- 2009~69 the ten pads on the dial being tested. If the meter hand of this predetermined dial is located over the pad being tested, it acts like an additional capacitor in parallel to capacitance already formed between excitable electrode and a center electrode. When the meter hand is over the pad being excited, the capacitor formed conducts the high frequency pulses to the inner ring (center conductor) while sharply attenuating lower frequencies, most of which are noise.
Since the capacitance thus formed is small, the frequency corner (frequencies below the corner are attenuated and frequencies above the corner are passed) created by the capacitance and the first stage of an amplifier connected thereto is approximately 159KHz. When the meter hand is not present, the frequency corner is approximately 640KHz. When a meter hand is not over the pad being excited, only stray capacitance exists, through the PC board and the relatively long air path from the excitable electrode pad to the inner ring or center conductor. This prior art encoder makes use of the difference in frequency corners by sending a signal of approximately 130KHz to 175KHz to the pad being measured or analyzed. If the meter hand is not there, the resultant signal output by the first stage of the high performance wide bandwidth amplifier is very small. If the meter hand is over the pad, the resultant signal is relatively large.

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DESCRIPTION OF PRIOR ART APPARATUS
Shown by element 1 of Figure 1, is a cross sectional view of an excitable electrode pad array forming a part of the previously identified prior art Siecor SE200 Encoder.
It has a center electrode 2 and guard 3, all on the same surface, disposed between a meter dial face and a rotatable 08Z989.PA: Improved Electrode Array for Meter Reading Device, ~. Bruce Bonnett, Page 3 " _ ` -- 2009~69 meter hand. Element 1 of Figure 2 is a plan view of the cross sectional view shown in Figure 1. Element 6 is a meter backboard and on top of the meter backboard is element 7, a meter dial face. Disposed over meter dial face 7 is plate 8, a substrate. Meter dial face 7 and substrate 8 can be combined o~ one substrate. On the uppermost surface of substrate 8, there is disposed center electrode 2, guard 3 and center electrode 2. It will be noted that center electrode 2 at least partially circumscribes and is spaced apart from axle 5. Spaced apart from center electrode 2 is guard member 3 and spaced apart from guard member 3 is the electrode array 4-1 through 4-10. Note like element numbers of Figure 2. Excitable electrodes 4-1 through 4-10 repre-sent the ten readable positions that can be read by the encoder. Attached to axle 5 and rotatable about axle 5 is hand 9-10. It will be noted that metal portion of hand 9-10 (the under surface) is spaced apart from axle 5 and its uppermost portion is coated by a plastic or a dielectric 10.

Referring now to the prior art electrode array of Figure 2, electronic guard 3 is connected to a constant DC
voltage (not shown) through leads, X and Z. Lead Y trans-mits current from center electrode 2 to process circuitry.

,Reference is now made to Figure 3, showing a prior art encoder circuit (process circuitry). Element 21 is a square wave generator and is connected through leads 22, 23, and 24 and to dials 7, of which there are five in number and have a structure like that of Figures 1 and 2. Through leads 25, dials 7 are connected to multiplexer 12. In some instances, amplifiers (op-amps) 11 are inserted between dial 7 and 082989.PA: Improved Electrode Array for Meter Reading Device, U. Bruce Bonnett, Page 4 .~

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multipleXer 12 as shown. Each dial is connected through leads 26 and 27, to DC reference voltage 20, and to transimpedance amplifier 13 via lead 27. Multiplexer 12 is connected to transimpedance amplifier 13 by lead 28.
Bandpass filter 14 is connected through lead 29 to transimpedance amplifier 13. Peak-to-peak detector 15 is connected to bandpass filter 14 through lead 30. Analog to digital converter 16 is connected to the peak-to-peak detector 15 by lead 40 and to microprocessor 17 through lead 41. Smart box 18, a transmitter and receiver, is connected to microprocessor 17 through lead 42 and through lead 43 to central office 19.
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The above-described circuit of Figure 3 works as follows: The transmitter-receiver (smart-box) 18 is adapted to receive a signal from central office 19 and is responsive to the signal to activate the microprocessor 17 to control 4 the AC voltage source 21 so that any given electrode 4-1 to4-10 of any given dial may be excited upon command. When hand 9-10 is over electrode 4-6 (note Figure 1), a capaci-tance is created and proportional current flows off of the center electrode 2, greater than there would have been in the absence of a hand 9-10. DC reference voltage source 20 supplies a steady DC bias voltage (E) to each guard member 3, as~sociated with each dial by means of leads X and Z. By means of transimpedance amplifier 13, voltage (E) is applied to each central electrode. The DC reference voltage source 20 also supplies voltage (E) to the non-inverting input port of the transimpedance amplifier 13. Because of the virtual ground characteristics of transimpedance amplifier 13, the inverting output port of transimpedance amplifier 13 is held 082989.PA: Improved Electrode Array for Meter Reading Device, ~. Bruce Bonnett, Page 5 : ' ~3 _5_ 2~Q9 ~6 essentially at voltage (E). Thus, the negative input port of transimpedance amplifier 13 is at the same voltage as the non-inverting input port.

Multiplexer 12, under the control of microprocessor 17, determines whlich current from which central electrode of which dial is allowed to pass onto lead 28. This current (IX) is the current created by the charge existing between the excited electrode central electrode and hand 9-10.
Obviously, IX is changing as the dial hand moves. Current IX passes on to lead 28 through transimpedance amplifier 13 which converts such a current into a low voltage (EX), such voltage arising out of the capacitance coupling of the dial hand and the excited electrode. E is the constant bias voltage on lead 27 applied to the non-inverting input port of transimpedance amplifier 13. The difference of these two voltages appear on lead 29 when referenced to E. Band pass filter 14 is used to filter out any noise and the sum of EX
plus E, minus the noise, appears on lead 30. Peak-to-peak detector 15 strips out the voltage associated with bias voltage E and converts it to an equivalent analog DC voltage denoted EXPP. Such voltage is the function of the capaci-tance coupling of meter hand 9-10, center electrode 2, and its associated excited electrode and appears at the analog digit~l converter 16, which converts it to a microprocessor usable digital word. This digital word is read by a micro-processor 17 and is stored until the same process is per-formed for all 50 excitable electrode-center electrode pairs, ten pairs per dial and five dials. Microprocessor 17 then processes this information to determine the five dial hand positions (ten positions possible for each dial) for 082989.PA: Improved Electrode Array for Meter Reading Device, W. Bruce Bonnett, Page 6 ~ 20Q9~69 '' the meters previously described and subsequently transmits this "meter reading" to the "smart box" 18 via lead 42, which in turn transmits the "meter reading" to the central office 19 by means of lead 43.

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BRIEF DESCRIPTION OF THE INVENTION
The invention is an electrode array used with an apparatus for remotely monitoring the position of a rotatable member (a dial hand), relative to a substrate spaced apart from the dial hand, as the dial hand is rotated by an axle about an axis of rotation. The array composed of spaced apart excitable electrodes (pads) are disposed on one .~ .
surface of the substrate facing the dial hand delimiting a center portion, a center electrode on the substrate on the same substrate surface as the excitable electrodes in the center portion, spaced apart from the axle, dial hand and the spaced apart electrodes. The substrate array consists of a three-layer composite having first and second surfaces with the spaced apart excitable electrodes defining a center portion on the first surface of the substrate. The sub-strate contains an aperture located in the center portion, the aperture being designed for receiving an axle, which delimits an axis of rotation for a meter hand attached to terminal end of the axle. The center electrode, at least partially circumscribing the aperture and a guard, composed of a first conductive strip is disposed in the center portion on the first surface of the three layer composite.
The guard at least partially circumscribes the aperture, and is spaced apart from and located between the spaced apart `~ excitable electrodes and the center electrode. Also includ-ed is a second conductive strip disposed on the second 082989.PA: Improved Electrode Array for Meter Reading Device, U. Bruce Bonnett, Page 7 ._ ~7- 2~ 0~g surface of the three layer substrate composite substrate, in electrical communication with the center electrode and a third and fourth conductive strip also disposed on the second surface of the three-layer composite substrate in electrical communication with the guard. The third and fourth conductive strips are disposed on the second surface, which is the exposed surface of the third layer of the three-layer composite, spaced apart from and positioned laterally on opposite sides of the second conductive strips.
The middle layer of the three-layer composite substrate is a metalized layer that is in electrical contact with the guard and electromagnetically shields or isolates the two outer layers of the three-layer composite substrate. With respect to the prior art apparatus, more particularly Figures 1 and 2, the hand pattern sought by this apparatus has a large capacity for coupling between the excited pads, the central electrodes, or receiver section. The instant invention provides an improved electrode pattern that reduces the baseline, stray, or parasidic capacitance in the electrode array used with the prior art apparatus. It was found by applicant that t:his improved performance could be brought about by the improved electrode array as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a cross sectional view of a prior art excitable electrode (pad~ array having a center electrode and a guard, all disposed between a meter dial face and a rotatable member (dial hand).

FIGURE 2 is a plan view of a prior art single electrode array including a central electrode and a guard.

. 082989.PA: Improved Electrode Array for Meter Reading Device, U. Bruce Bonnett, Page 8 .

8- 2~ 69 FIGURE 3 is a schematic of a prior art circuitry employed by prior art encoders.

FIGURE 4 is a plan view of the electrode array of the invention.

FIGURE 5 is a cross sectional view of the invention shown in Figure 4 along liens A-A of Figure 4.

FIGURE 6 is a cross sectional view of the invention shown in Figure 4 along lines B-B of Figure 4.

FIGURE 7 is a cross sectional view of the invention shown in Figure 4 along lines C-C of Figure 4.

DETAILED DESCRIPTION OF THE INVENTION
The invention is shown in plan view in Figure 4 and a cross sectional view in Figures 5, 6, and 7, with Figures 5, 6, and 7 being cross sectional views along A-A, B-B, and C-C
respectively of Figure 4. It is to be understood that the array shown in Figures 4, 5, 6., and 7 is to be substituted for the array shown as element 1 in Figures 1 and 2, along with the addition of axle 5 and meterhand 9-10. Axle 5 is to be received in aperture 73 and is affixed to a meter hand 9-10, which extends over receiving electrode 2, guard 3, and at least partially over excitable electrodes 4-1 through 4-10.

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Viewing Figure 4, it is to be noted that there is a plurality of spaced apart, excitable electrodes 4-1, 4-2, ``' 082989.PA: l~proved E~ectrode Array for Meter Reading Device, ~. Bruce Bonnett, Page 9 - ~ 20aso6s ' _9_ 4-3, 4-4, 4-5, 4-6, 4-7, 4-8, 4-9, and 4-10. Each one of these electrodes is affixed to a substrate which is made up of layers 74, 76, and 77. Layers 74 and 77 are made of fiberglass impregnated with a suitable resin. Layer 76 is a metalized conductive layer. Excitable electrodes 4-1 through 4-10 leach contain and are in electrical contact with a feed through. For example, excitable electrode 4-1 contains feed through 50, excitable electrode 4-2 contains feed through 51, excitable electrode 4-3 contains feed through 52, excitable electrode 4-4 contains feed through 53, excitable electrode 4-5 contains feed through 54, excitable electrode 4-6 contains feed through 55, excitable electrode 4-7 contains feed through 56, excitable electrode 4-8 contains feed through 57, excitable electrode 4-9 contains feed through 58, and excitable electrode 4-10 contains feed through 59. The purpose of these feed throughs is to create an electrical path from a particular excitable electrode on the uppermost surface of Figure 5 to a particular excitable electrode interconnect to another surface (for example lowermost surface of substrate of Figure 5). For example, excitable electrode 4-3 contains feed through 52, which places excitable electrode 4-3 in electrical communication with excitable electrode intercon-nect 67. In like manner, feed through 57 is in electrical comm~nication with excitable electrode 4-8 and excitable electrode interconnect 62. All other feed throughs connect a particular excitable electrode with a receiving electrode interconnect as shown. All excitable electrode intercon-nects (elements 60-69) are metalized strips that are elec-trically conductive. Excitable electrode interconnect 67, shown by a dotted line in Figure 4, is the same excitable .

082989.PA: Improved Electrode Array for Meter Reading Device, ~. Bruce Bonnett, Page 10 ~ l 200g~69 ~

electrode interconnect 67 shown in cross section in Figure 5. Element Z is a conductive strip connected to guard 3 by feed throughs 71 and 72 and is connected to a constant potential like that of element 20 of Figure 3. Element Y is a conductive strip forming a receiving electrode intercon-nect disposed on the bottom of layer 77 and is electrically connected to center electrode 2 by feed through 70. It will be noted that in Figure 4 interconnects for the center electrode, guard and excitable electrodes are shown in dotted lines. Circumscribing aperture 73 is receiving or central electrode 2 and circumscribing and spaced apart from receiving electrode 2 is guard 3. It will be noted that guard 3 is in electrical communication with feed throughs 71 and 72 and receiving, or center electrode 2, is in electri-cal communication with feed through 70. Feed throughs 71 and 72 are in electrical communication with conductive strips z-Z. See Figures 2 and 4. This places guard 3 in electrical contact with conductive strips Z-Z. Feed through 70 is in electrical contact with central electrode 2 and conductive strip Y, which is for connection with constant voltage source 20.

To operate the apparatus as above described, an AC
voltage signal is applied to each excitable electrode 4-1 through 4-10 via the excitable electrode interconnects 60 through 69. Capacitance is induced between the receiving electrode and the excitable electrode that is excited with the AC voltage. The magnitude of this capacitance is dependent on the presence or absence of the meter hand 9-10 over each excitable electrode. For example, see Figure 1.
The current in the receiving or center electrode 2 is thus 082989.PA: Improved E~ectrode Array for Meter Reading Device, U. Bruce Bonnett, Page 11 ~, ~ C~ 1 2009069 ~

also dependent upon this capacitance. This current is then carried to a current measuring device (see Figure 3) via the receiving electrode interconnects 60 through 69. Guard 3 reduces unwanted capacitance coupling between receiving electrode 2 and the excitable electrodes 4-1 through 4-10.
Metalized layer 76 also acts as a guard. Viewing Figures 7, it will be appreciated that feed throughs 71 and 72 are not only in electrical communication with guard 3 and metalized strips Z, but are also in electrical communieation with metalized layer 76. It will be remembered that the metalized layers Z are connected to a source of constant potential, such as element 20 of Figure 3. Thus, metalized layer or guard 76 provldes a shield and reduces unwanted capacitance coupling between the excitable electrodes 4-1 through 4-10 and the reeeiving or center electrode intercon-nect, namely the metalized strip Y. Metalized strips Z in the lowermost layer reduces unwanted capacitance coupling between the receiving, or eenter electrode interconnect X
and the excitable electrode interconnects 60 through 69.

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Claims (7)

1. An electrode array comprising:

(a) a substrate having first and second surfaces;

(b) a plurality of spaced apart excitable elec-trodes defining a center portion disposed on the first surface of the substrate;

(c) an aperture in the substrate located in said center portion for receiving an axle;

(d) a center electrode at least partially circum-scribing the aperture and a guard, composed of a first conductive strip, both said center electrode and guard disposed in said center portion on said first surface, said guard spaced apart from and located between the spaced apart excitable electrodes and the center electrode; and, (e) second, third and fourth conductive strips, said second conductive strip disposed on said second surface and in electrical communica-tion with the center electrode and said third and fourth conductive strips in electrical communication with said guard said third and fourth conductive strips disposed on said second surface, spaced apart from and posi-tioned laterally on opposite sides of said second conductive strip.

2. The electrode array of Claim 1 further including a D.C. reference voltage potential in electrical communication with the guard and center electrode for supplying essentially the same D.C. reference voltage to both.

3. The electrode array of Claim 1 wherein said sub-strate contains a first feed through device that electrically connects said center electrode on said first surface to said second conductive strip on said second surface.

4. The electrode array of Claim 3 wherein said sub-strate further contains second and third feed through devices that electrically connects said guard on said first surface to the third and fourth conductive strips on said second surface.

5. The electrode array of Claim 1 further including in combination a rotatable axle received in said aperture and a meter hand affixed to a terminal portion of said axle.

6. The electrode array of Claim 4 wherein said sub-strate is composed of a first layer of dielectric material, a second layer of conductive material, and a third layer of dielectric material and wherein said second and third feed through devices are in electrical contact with said second layer of conductive material.

7. The electrode array of Claim 6 further including a D.C. reference potential in electrical communication with said second and third feed throughs.