Method and apparatus for electrically determining the presence, absence or level of a conducting medium, contamination notwithstanding

Sensing apparatus is disclosed which allows for the determination of the presence, absence or percentage of a conducting medium such as water, by electronic means. The inventive apparatus negates the effect of a false signal generated by contamination of the sensing apparatus. The inventive sensor comprises three or more sensing members attached to a non-conducting substrate with electronically significant distances between pairs of sensing members. An appropriate electrical circuit is connected to the sensing members which converts signals output from the pairs of sensing members into readings which indicate the presence or absence of a conducting medium, notwithstanding the presence or absence of contamination between the sensing members.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to the field of determining the presence, 
absence or percentage of a conducting medium and in particular to the 
field of electronically sensing the presence, absence or percentage of a 
volume of a conducting medium such as water as distinguished from a false 
reading due to the effect of contamination between sensing electrodes. 
2. Description of the Prior Art 
In the past, electronically determining the existence or non-existence of a 
conducting medium such as water, slurries, sewage, etc. has been achieved 
only with limited success. Typically, a pair of wire electrodes are 
mounted onto a non-conducting substrate which is then immersed into the 
medium to be sensed. Because of the conducting nature of the medium, when 
a signal is output from the electrodes, the signal indicates the presence 
of the conducting medium and vice versa. However, due to contaminants 
which are present in the conducting medium and after a period of time, the 
contaminants build up an electrical path between the electrodes. After the 
build-up of the electrical path by the contaminants, it is not possible to 
distinguish between the presence or absence of the conducting medium 
because the contamination causes the signal from the electrodes to read 
the same. Thus, the reading from the electrodes would always indicate the 
presence of the conducting medium because the sensor cannot distinguish 
between the conducting medium or the contamination. The conducting medium 
can have leaked out or otherwise no longer be present but the electrode 
will still indicate that the conducting medium is present. 
The false reading caused by contamination between electrodes can be 
extremely disadvantageous when the presence of the conducting medium is 
essential to the operation of the system using the conducting medium. For 
example, when the conducting medium is water, which is used in a heat 
exchanger for cooling purposes, the absence of the cooling water can 
permanently damage the system. One can readily envision a situation where 
a water-cooled internal combustion engine fails due to the lack of cooling 
water but the sensing elements indicate that cooling water is present. 
Another example is where the presence of the conducting medium is 
undesirable and requires to be pumped out such as water leakage into a 
boat. A false signal due to contamination would cause the pump to 
continually operate until it bums out. Another example is where the 
percentage of the conducting medium requires an on or off action. 
Contamination would cause the on or off sequence to occur at the wrong 
time. 
In prior art systems involving the detection of a conducting medium by the 
use of electrodes, the common practice is to require periodic cleaning of 
the built-up contamination between the electrodes. However, once the 
contamination does build up, it is difficult to remove and then it builds 
up at a faster rate. Thus, periodic cleaning is not a satisfactory prior 
art solution to this problem. 
The inability of the prior art to successfully eliminate the problem of 
contamination between the electrodes is the main reason why many of the 
present day systems still rely on a mechanical device to sense the 
presence or absence of a conducting medium or the level of the conducting 
medium. Accordingly, a primary objective of the present invention is to 
provide methods and apparatus for electronically deterring the presence, 
absence or percentage of a conducting medium or the level of the same 
whether or not contamination exists between the sensing members. 
SUMMARY OF THE INVENTION 
Electrodes immersed in a volume of water or other conducting medium, do not 
exhibit a resistance to current flow that is proportional to the lineal 
distance between them. Electrodes fully immersed, for example, at four 
inches apart, present a resistance just slightly greater than that when 
the electrodes are one inch apart. This slight difference is not 
electronically significant. If, however, as the inventor has determined, a 
thin layer of a conducting medium (such as contamination) is distributed 
between sensing members, as provided herein, the thin layer of a 
conducting medium will exhibit resistance roughly proportional to the 
lineal distance. The present invention, exploits this phenomena, by 
recognizing that current flow or electrical resistance that is 
proportional to the sensor member lineal distances, must be caused by a 
conducting contamination. If the current flow is roughly the same between 
unequally spaced sensing members, then there must be a volume of the 
conducting medium around the sensing members. Thus, methods and apparatus 
are disclosed for negating the effect of contamination when measuring the 
presence, absence, or percentage of a conducting medium. 
The method and apparatus contemplates spacing at least three elongated 
sensing members across a non-conducting substrate such that the distance 
between one pair of sensing members is greater than the distance between a 
second pair of sensing members, each pair of sensing members may have one 
common sensing member. In practicing the invention, an electric circuit is 
attached to the sensing members whereby the electrical signal from the 
first pair of sensing members is compared to the electrical signal from 
the second pair of sensing members. Significantly different signals are 
obtained when the sensing members are immersed in a conducting medium and 
when they are not immersed in the conducting medium, and when the 
percentage of conducting medium varies regardless of the existence or 
non-existence of contamination between the sensing members. Thus, the 
methods and apparatus employed, negates the effect of a false signal 
generated by contamination and provides a discernable signal generated by 
the presence, absence, or percentage present of the conducting medium. 
In practicing the invention any arrangement of sensing members, able to 
make the discrimination described above, may be connected to a variety of 
electrical comparison circuits to render a different output when a volume 
of conducting material is present as opposed to a thin layer (such as 
contamination). In this way, contamination between unequally spaced 
sensing members, can be negated in order to determine the presence, 
absence or percentage of the conducting medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As required, detailed embodiments of the present invention are disclosed 
herein; however, it is to be understood that the disclosed embodiments are 
merely exemplary of the invention which may be embodies in various forms. 
Therefore, specific structural and functioning details disclosed herein 
are not to be interpreted as limiting, but merely as a basis for the 
claims and as a representative basis for teaching one skilled in the art 
to variously employ the present invention in virtually any appropriately 
detailed structure. 
Reference is now made to the drawings, wherein like characteristics and 
features of the present invention shown in the various figures are 
designated by the same reference numerals. 
FIGS. 1 and 2 schematically illustrate one embodiment of the inventive 
apparatus comprising an electronic probe or sensor 10. Three conducting 
sensing members, 11, 12 and 13, each comprising, for example, a metallic 
strip, are attached to or mounted upon a non-conducting substrate 14. Each 
conducting sensing member 11, 12 and 13 sufficiently extends in length 
across the width of substrate 14, as more fully explained hereinafter. 
Each sensing member 11, 12 and 13 is arranged generally parallel to each 
other with a first lineal distance 15 between members 11 and 12 and a 
second lineal distance 16 between members 11 and 13. Lineal distances 15 
and 16 have a ratio which is electronically significant; that is, a ratio 
which lends itself to detection by electronic means when covered by a 
conducting contaminant, which may alternatively be referred to as a thin 
layer of conducting material. For test purposes, the inventor used a ratio 
of approximately 1 to 4. This ratio provided a resistance ratio whereby 
the resistance in ohms between members 12 and 13 was four times greater 
than the resistance in ohms between members 11 and 12 when the sensor 10 
is covered with a conducting contaminant. Other ratios of approximately 1 
to 2 or greater may also be used. Each sensing member is adapted to be 
connected to an electrical wire or conductor 17, 18, and 19 respectively. 
The length, width, and thickness of substrate 14 in the embodiment of FIGS. 
1 and 2 are not critical to the invention. Thus, the length, width, and 
thickness of substrate 14 may be of any size consistent with its end use. 
Similarly, the width and thickness of sensing members 11, 12, and 13 are 
not critical to the invention and may be of any convenient or practical 
size. The length of sensing members 11, 12, and 13 are advantageously 
approximately equal to the dimension of substrate 14 along which the 
sensing members extend. If it is desirous that the individual lengths of 
sensing members (however many) be less than the width of substrate 14 then 
the length is to be approximately that which produces an electrical signal 
which is in proportion to the lineal distance between sensing members when 
covered by a layer of contaminant resulting from the conducting medium in 
which the sensor 10 is to be used. 
FIG. 3 illustrates another embodiment of the inventive sensor 10. In this 
embodiment two separate substrates 14a and 14b are used. Sensing members 
11a and 12 are attached or mounted onto substrate 14a while sensing 
members 11b and 13 are associated with substrate 14b. Lineal distances 15 
and 16 are respectively associated with substrates 14a and 14b. 
FIG. 4 illustrates another embodiment of the inventive sensor 10. In this 
embodiment, a cut out or slit 21 is provided in substrate 14. Sensing 
member 11 extends substantially across the width of substrate 14. Sensing 
members 12 and 13, however, extend substantially across each leg 22 and 23 
of substrate 14. 
FIG. 5 illustrates an embodiment similar to that of FIG. 4, but without the 
slit 21 and sensing members 11, 12, and 13 do not extend to the edges of 
substrate 14. 
FIG. 6 illustrates an embodiment with multiple sensing members 11, 12, 13, 
24, 25, 26, and 27. Additional wire conductors 28-32 are associated with 
the additional sensing members 24-27. 
FIG. 7 illustrates an embodiment of the inventive sensor 10, which may be 
used as an on/off switch to activate and deactivate a pump. For example, 
the switch can be used with a bilge pump to drain water which accumulates 
in a boat. Substrate 14 comprises a non-conducting material that is 
commonly used in the electronics industry. Sensing elements 11, 12 and 13, 
and 11, 25 and 26 are located in a vertical arrangement on substrate 14 
such that lineal distances 15 and 16 are as described above. Sensing 
members 12 and 13 are vertically arranged on the lower portion of 
substrate 14; while, sensing members 25 and 26 are vertically located on 
the upper portion of substrate 14. For convenience, sensing member pair 26 
and 13, and sensing member pair 12 and 25 are vertically aligned and all 
sensing members are substantially parallel to each other. 
Conducting wires 17, 18, 19, 29 and 31 are connected to sensing members 11, 
12, 13, 25 and 26 respectively. Electronically, sensing element 11 is 
common to each sensing pair 12-25 and 13-26. Conducting wires 17, 18, 19, 
29 and 31 are connected to an appropriate electrical circuit such as those 
described hereinafter, or in accordance with the teachings of those 
described hereinafter which is then connected to a bilge pump in the 
example being described. 
When the water level reaches the height indicated by numeral 27, sensors 
11, 12, and 13 sense that water is present at this level. The lineal 
distance arrangement of sensor members 12 and 13 relative to sensor member 
11 again negates the affect of contamination. Although water is present at 
level 27, the electronic circuit connected to sensor 10 does not activate 
the pump. When the water level reaches level 28, sensor members 11, 25, 
and 26 sense the presence of the water and activate the pump. In 
accordance with the signals emitted by sensor members 11, 12, 13, 25, and 
26 the pump stays on until the water level drops to level 27, then it is 
turned off. In this manner the pump only turns on only when the water 
level reaches level 28, and turns off when the water level drops to level 
27. This prevents the pump from continuous operation which would quickly 
lead to pump failure. 
It is to be noted, in accordance with the above embodiments, that many 
different variations of the inventive sensor 10 are possible. And, 
although it is not possible to show and describe all of the possible 
variations, all of the possible variations are intended to be included 
within the coverage of the present patent. 
FIG. 8 schematically illustrates one simple electronic circuit in using the 
inventive sensor 10 to determine if the sensor 10 is immersed in a body of 
a conducting medium such as water, a slurry, sewage, ground, etc. whether 
or not contamination is present over the sensor 10. The method in FIG. 8 
utilizes the electrical resistance between the sensing members 11, 12, and 
13. When the sensor 10 is out of the water 31 and no contamination covers 
the sensor 10, each ohmmeter 33 and 34 will indicate an infinite 
resistance. Since no external current flows, any circuit would detect this 
condition as: "Nothing Present". When sensor 10, without contamination, is 
immersed in water 31, the reading from each ohmmeter 33 and 34 will be 
approximately the same. When contamination builds up on sensor 10 and it 
is immersed in water 31, each ohmmeter will again read about the same 
resistance. But when the water leaks out of the container (or no water is 
present) and the contamination has built up on sensor 10, the difference 
in the ohmmeter readings will be substantially proportional to the lineal 
distances 15 and 16 between each pair of elements 11-12 and 11-13. Thus, 
if there is infinite resistance, no water is present and there is no 
contamination. If the resistances are closer to one-to-one, water is 
present regardless of the presence or absence of contamination. If the 
resistances are in the ratio of the lineal distances 15 and 16, no water 
is present and contamination has built up. Thus, the arrangement shown in 
FIG. 8 allows for the detection of the presence or absence of water 
regardless of contamination of sensor 10. 
FIG. 9 illustrates another type of electrical circuit utilizing the 
inventive sensor 10, which may be used to determine the presence or 
absence of the conducting medium 31. The circuitry is designed to 
determine differences in current flow between elements 11-12 and 11-13, 
which is accomplished by comparing the voltages produced at outputs 35 and 
36, of comparitor 39. Either the output is zero or a positive value. When 
the output is zero, no conducting medium is present; when the output is 
positive, the conducting medium is present. These outputs are such, 
whether or not contamination is present on sensor 10. Thus, in this 
circuit, the effect of contamination is again negated. 
With further reference to FIG. 9, wires 17, 18 and 19 are electrically 
connected to sensing members 11, 12 and 13 respectively. Wire 18 is 
connected to the junction of resistors 38 and 41 which is the positive 
(noninverting) input 35 of comparitor 39. The negative (inverting) input 
36 of comparitor 39 is connected to the junction of resistors 38 and 42 
and then to wire 19. Wire 17 from sensing member 11 is common. 
The voltage at 35 is derived from the voltage divider consisting of 
resistors 37 and 41. The voltage at 36 is derived from the divider 
consisting of resistors 38 and 42. The values of these resistors are 
selected to make the voltage at input 36 more positive than the voltage at 
input 35, and to present a resistance in parallel with spaces 15 and 16 
that is proportional to these distances. This arrangement gives a zero 
volts output from comparitor 39 with a near infinity resistance between 
sensing members 11, 12, and 13 (normal state). Thus, for purposes of 
explanation, if lineal distances 15 and 16 are in the ratio of one to four 
then the following values may be assigned: resistor 41 is 5k ohms, 
resistor 37 is 20k ohms, resistor 38 is 100k ohms, resistor 42 is 10k 
ohms, and the voltage source is 10 volts. 
When contamination is present, the resulting resistance of lineal distance 
15 is in parallel with resistor 37, while the resistance of lineal 
distance 16 is parallel with resistor 38. The resistance due to 
contamination that exists in the respective spares will have a ratio close 
to the distance ratio. Since the ratio of fixed resistor 37 and 38 is the 
same as the distance ratios of lineal distances 15 and 16, then the lower 
resistances of the parallel combination of contaminated spaces and fixed 
resistors will be in the same ratio, Therefore, the voltage dividers which 
create the voltages at 35 and 36 will produce lower voltages but in the 
same ratio as they were when no contaminants were present. The voltage at 
36 would remain more positive and the output from 39 would be zero volts, 
which again would indicate that no water is present. 
When immersed in the conducting medium 31, lineal distances 15 and 16 
present about the same resistance. Therefore, the voltage at 36 will be 
reduced more than the voltage at 35 since the source resistor 42 is two 
times the value of resistor 41. A higher voltage at 35 compared to that at 
36 produces a positive output from comparitor 39. This indicates that the 
conducting medium is present. 
In accordance then with the circuitry of FIG. 9 and the values assigned as 
stated, the following may be determined. When the sensor 10 is out of the 
conducting medium 31 and no contamination is present, the comparitor 
outputs a zero value indicating the absence of the conducting medium 31. 
When the sensor 10 is out of the conducting medium 31 and contamination 39 
is present, the comparitor outputs a zero value again indicating the 
absence of the conducting medium 31. When the sensor is immersed in the 
conducting medium 31, with or without contamination, the output of 
comparitor 39 is positive indicating the presence of the conducting 
medium. 
Reference is now made to FIG. 10. This is an A. C. version of the same 
circuit as in FIG. 9. This type circuit prevents electrolysis between the 
sensing members. The three sensing members 11, 12, and 13 are coupled to 
the resistor divider networks through capacitors 44, 43, and 45 with 
reactances less than one tenth of the smallest resistor. Two 
rectifier/filters 46 and 47 provide D.C. inputs to the comparitor 39. The 
net results are the same with A.C. currents flowing in the voltage 
dividers and externally, instead of D.C. 
In manufacturing the inventive sensor, the non-conducting substrate 14 may 
be made from a commonly used material such as phenolic or polycarbanate. 
The size and thickness of substrate 14 may be consistent with the 
application for which it is to be used. Thus, it may be as small as one 
millimeter square by 0.01 mm thick, or it may be as large as one meter 
square by one mm thick. Other sizes, larger and smaller may also be used. 
The sensing elements 11, 12, and 13 may be fabricated from any conducting 
material such as copper, gold, steel, aluminum, etc. The elements 11, 12 
and 13 may be electrically deposited or mechanically fixed to the 
substrate 14 by any known method. The thickness of sensing elements 11, 12 
and 13 may also be consistent with the end use of sensor 10. However, the 
length of sensing elements 11, 12 and 13 may be substantially equal to or 
less than the width of the substrate 14, as explained above. Similarly, 
the lineal distances 15 and 16 are arbitrary; however, ratios of 1 to 2 
and greater are suggested. 
In using the inventive sensor 10, many applications are possible. For 
example, a single-three element sensor 10 may be used to determine if a 
container contains a conducting medium. The sensor 10 it may be placed 
flat at the bottom of the container or in a vertical position near the 
bottom of the container. Any of the circuits shown in FIGS. 8, 9 or 10 as 
described above as well as any appropriate alternative circuit maybe used. 
By placing two or more sensors 10, each with their own circuit along the 
depth of the container, or by using multiple sensing members, the sensor 
10 may be used not only to determine the presence or absence of the 
conducting medium but also to determine the level of the conducting medium 
in the container. Moreover, the conducting medium need not be limited to 
water; the invention can be used with any conducting liquid, or with any 
porous medium when rendered conducting by a conducting liquid; e.g. wet 
earth. By appropriate electrical circuitry, the sensor 10 may be used as a 
switch to turn on or turn off a pump. By connecting outputs of the 
comparators 39 of the circuits of FIGS. 9 and 10, to a switch, a simple 
on-off switch may be effectuated. For example, a pump may be turned on 
when the water contacts the sensing elements 11,12, and 13 and turns off 
when the water is no longer in contact with said sensors. 
FIG. 11 illustrates the use of the inventive sensor 10 in conjunction with 
an operational amplifier 48. This arrangement may be used as a switch 
with, for example, a ground sprinkler system, as hereinafter explained. 
The value of resistors 50 and 51 are in the same ratio as lineal distances 
15 and 16. The resistance between sensing member pairs 11-12 and 11-13 
with contamination present on substrate 14, is in proportion to lineal 
distances 15 and 16 respectively. Accordingly, the output of operational 
amplifier 48 is equal to the ratio of lineal distances 15 to 16 when no 
conducting medium is present, whether or not contamination exists between 
sensing members 11, 12 and 13. And, the output of operational amplifier 48 
is less than the ratio of lineal distances 15 to 16 when a conducting 
medium is present, whether or not contamination exists. This circuitry 
will sense the presence of a conducting medium even when its conductivity 
is very low compared to that of the contamination and circuit resistors 50 
and 51. A low conductivity of the conducting medium may, for example, be a 
slight amount of moisture in the ground where the sensor 10 is used with a 
ground sprinkler system. This will result in an output from amplifier 48 
less than the spacing ratio. But when the ground is dry, the output will 
be equal to the spacing ratio. Thus the sensor 10 acts as a very sensitive 
switch. 
Reference is now made to FIG. 12 wherein a sensor 54 comprising a pair of 
sensing members 55 and 56 as described above are spaced apart a distance 
of that of members 11 and 13. These are mounted on a substrate 57 as 
previously described. Sensors 10 and 54 are placed in the ground at the 
approximate same location. Resistor 51 is placed in parallel with the 
contamination resistance, if any, and in parallel with the moisture 
resistance, if any, between members 55 and 56. When a reference voltage 58 
is applied and no moisture is present, amplifier 59 outputs a voltage 
proportional to the resistor 51 and the contamination resistance. Since no 
moisture is present, the ground sensor 10 (FIG. 11) closes switch 61, 
causing capacitor 62 to charge to the output of amplifier 59. If 
contamination builds up over time, the current into amplifier 59 increases 
but the output from sensor 10 will keep switch 61 closed because there is 
no change in the resistor ratio of FIG. 11 so that the output of amplifier 
59 will be lower as will the charge on capacitor 62. 
When a conducting medium or moisture surrounds sensors 10 and 54, the 
output from sensor 10 will be lower, causing switch 61 to open. The charge 
in capacitor 62 will remain that established by the resistance of resistor 
51 and the contamination. The output of amplifier 59 will be lower than 
previously as affected by the added resistance of the moisture. Amplifier 
63 can now compare the original output from amplifier 59 (stored in 
capacitor 62) with the new lower output every time switches 64 and 65 are 
closed. The difference between the two input voltages to amplifier 63 is 
directly proportional to the resistance of the moisture because the new 
current flow is due to the resistance of the moisture. 
The output of amplifier 65 is input to a capacitor 66. The other leg of 
capacitor 66 is attached to a rheostat 67 which allows the setting of a 
preset voltage. When the resistance of the moisture is lower, the output 
of capacitor 66 is negative; when the resistance of the moisture is 
higher, the output of capacitor 66 is positive. This may then be used to 
turn on or turn off a pump at a preset value of the moisture content or 
soil electrical resistance. 
Although particular embodiments of the invention have been shown and 
described in full here, there is no intention to thereby limit the 
invention to the details of such embodiments. On the contrary, the 
intention is to cover all modifications, alternatives, embodiments, usages 
and equivalents as fall with the spirit and scope of the present 
invention, specification and appended claims.