Capacitively coupled ohmic resistance position sensor

A position sensor comprises a pair of electrically conducting elongated members having a high ohmic resistance per unit length thereof disposed parallel to one another in a direction defined by the line of displacement of a target member, and a capacitively coupling member disposed adjacent to the pair of electrically conducting elongated members and moving with the target member in the direction of displacement, which capacitively coupling member transmits an alternating electrical signal between the pair of electrically conducting elongated members by a capacitive electrical interaction therebetween, wherein an alternating electrical signal is supplied to the two opposite extremities of one of the pair of electrically conducting elongated members and a phase angle difference between two alternating electrical signals respectively taken off from the two opposite extremities of the other of the pair of electrically conducting elongated members is measured, and the position of the target member is determined as a function of the measured phase angle difference.

FIELD OF INVENTION 
This invention relates to a position sensor that measures the linear or 
rotary position of a target member including an electrically conducting 
member with a sizable surface area that capacitively couples two 
electrically conducting elongated members having a high ohmic resistance 
per unit length thereof, which position sensor has particularly useful 
applications in the construction of a variable area flowmeter, nonrotating 
propeller or turbine flowmeter, liquid level sensor, pressure sensor, 
etc., as well as in determining the position of a mechanical element 
remotely and automatically. 
BACKGROUND OF INVENTION 
There has been a great deal of demand for a linear or rotary position 
sensing apparatus that determines nonintrusively the position of a 
mechanical target member such as a float floating on the free surface of a 
liquid medium, a drag body suspended in the stream of a fluid medium, a 
pointer marking a scale in a dial or bar gauge, a position of a linear or 
rotary actuator, a nonrotating propeller or turbine experiencing a fluid 
dynamic torque, etc., which apparatus provides an inexpensive means for 
automatically or remotely measuring or monitoring the position of the 
mechanical target with a high degree of resolution and a great deal of 
accuracy. Unfortunately, such a position sensing apparatus of high 
performance and low cost is not available at the present time. 
BRIEF SUMMARY OF INVENTION 
The primary object of the present invention is to provide a linear and 
angular position sensing apparatus comprising a pair of electrically 
conducting elongated members of a high specific ohmic resistance disposed 
in a side-by-side parallel relationship, and a capacitively coupling 
member made of an electrically conducting material moving with a target 
member, that capacitively couples the flow of electric current through the 
pair of electrically conducting elongated members, wherein an alternating 
electrical signal is supplied to at least one of the two opposite 
extremities of the first of the pair of electrically conducting elongated 
members and a phase angle of an alternating electrical signal taken off 
from one of the two opposite extremities of the second of the pair of 
electrically conducting elongated members is measured relative to the 
phase angle of one of the two alternating electrical signals taken off 
from the other of the two opposite extremities of the second of the pair 
of electrically conducting elongated members and supplied to the one 
extremity of the first of the pair of electrically conducting elongated 
members, respectively, and the position of the target member is determined 
as a function of the measured phase angle difference. 
Another object is to provide the position sensor described in the 
afore-mentioned primary object of the present invention, wherein the 
alternating electrical signal is supplied to both of the two opposite 
extremities of the first of the pair of electrically conducting elongated 
members, and the phase angle difference between two alternating electrical 
signals respectively taken off from the two opposite extremities of the 
second of the pair of electrically conducting elongated members is 
measured as an electrical variable, from which the position of the target 
member is determined. 
A further object is to provide the position sensor described in the 
afore-mentioned another object of the present invention, wherein the 
position sensor includes a second and third pair of electrically 
conducting elongated members having a construction and function similar to 
those of the first pair of electrically conducting elongated members, 
which are disposed in a side-by-side parallel relationship to the first 
pair of electrically conducting elongated members, and a second 
capacitively coupling member capacitively coupling the second pair of 
electrically conducting elongated members to one another fixedly located 
at one of the two opposite extremities of the combination of the three 
pairs of electrically conducting elongated members and a third 
capacitively coupling member capacitively coupling the third pair of 
electrically conducting elongated members to one another fixedly located 
at the other of the two opposite extremities of the combination of the 
three pairs of electrically conducting elongated members; wherein the 
position of the target member is determined as a function of three phase 
angle differences respectively obtained from the three pairs of 
electrically conducting elongated members. 
Yet another object is to provide the position sensor described in the 
afore-mentioned primary object of the present invention, wherein the 
alternating electrical signal is supplied to only one of the two opposite 
extremities of the first of the pair of electrically conducting elongated 
members, and the phase angle difference between the alternating electrical 
signal supplied to only the one extremity of the first of the pair of 
electrically conducting elongated members and an alternating electrical 
signal taken off from one extremity of the second of the pair of 
electrically conducting elongated members adjacent to the one extremity of 
the first of the pair of electrically conducting elongated member is 
measured, from which phase angle difference the position of the target 
member is determined. 
Yet a further object is to provide the position sensor described in the 
afore-mentioned yet another object of the present invention, wherein the 
the position sensor includes a second and third pair of electrically 
conducting elongated members having a construction and function similar to 
those of the first pair of electrically conducting elongated members 
disposed in a side-by-side parallel relationship to the first pair of 
electrically conducting elongated members, and a second capacitively 
coupling member capacitively coupling the second pair of electrically 
conducting elongated members to one another fixedly located at one of the 
two opposite extremities of the combination of the three pairs of 
electrically conducting elongated members and a third capacitively 
coupling member coupling the third pair of electrically conducting 
elongated members to one another fixedly located at the other of the two 
opposite extremities of the combination of the three pairs of electrically 
conducting elongated members; wherein the position of the target member is 
determined as a function of three phase angle differences respectively 
obtained from the three pairs of electrically conducting elongated 
members. 
Still another object is to provide a linear and rotary position sensing 
apparatus comprising a single electrically conducting elongated member 
with a high specific ohmic resistance and a capacitively coupling member 
moving with a target member in directions parallel to the single 
electrically conducting elongated member, wherein an alternating 
electrical signal is supplied to the capacitively coupling member, and a 
phase angle of an alternating electrical signal taken off from one of the 
two opposite extremities of the single electrically conducting elongated 
member is measured relative to the phase angle of one of the two 
alternating electrical signals taken off from the other of the two 
opposite extremities of the single electrically conducting elongated 
member and supplied to the capacitively coupling member, respectively, and 
the position of the target is determined as a function of the measured 
phase angle difference. 
Still a further object is to provide the position sensor described in the 
afore-mentioned still another object of the present invention, wherein the 
phase angle difference between two alternating electrical signals 
respectively taken off from the two opposite extremities of the single 
electrically conducting elongated member is measured, from which the 
position of the target is determined. 
Yet still another object is to provide the position sensor described in the 
aforementioned still a further object of the present invention, wherein 
the position sensor includes a second and third single electrically 
conducting elongated member disposed in a side-by-side parallel 
relationship to the first single electrically conducting elongated member, 
and a second capacitively coupling member receiving the alternating 
electrical signal fixedly located at one of the two opposite extremities 
of the combination of the three single electrically conducting elongated 
members, which second capacitively coupling member capacitively transmits 
the alternating electrical signal to the second single electrically 
conducting elongated member, and a third capacitively coupling member 
receiving the alternating electrical signal fixedly located at the other 
of the two opposite extremities of the combination of the three single 
electrically conducting elongated members, which third capacitively 
coupling member capacitively transmits the alternating electrical signal 
to the third single electrically conducting elongated member; wherein the 
position of the target member is determined as a function of three phase 
angle differences respectively obtained from the three single electrically 
conducting elongated members. 
Yet still a further object is to provide the position sensor described in 
the afore-mentioned still another object of the present invention, wherein 
the phase angle difference between the alternating electrical signal 
supplied to the capacitively coupling member and an alternating electrical 
signal taken off from one of the two opposite extremities of the single 
electrically conducting elongated member is measured, from which the 
position of the target is determined. 
Additionally another object is to provide the position sensor described in 
the afore-mentioned yet still another object of the present invention, 
wherein the position sensor includes a second and third single elongated 
electrically conducting elongated member disposed in a side-by-side 
parallel relationship to the first single elongated electrically 
conducting member, and a second capacitively coupling member receiving the 
alternating electrical signal fixedly located at one of the two opposite 
extremities of the combination of the three single electrically conducting 
elongated members, which second capacitively coupling member capacitively 
transmits the alternating electrical signal to the second single 
electrically conducting elongated member, and a third capacitively 
coupling member receiving the alternating electrical signal fixedly 
located at the other of the two opposite extremities of the combination of 
the three single electrically conducting elongated members, which third 
capacitively coupling member capacitively transmits the alternating 
electrical signal to the third single electrically conducting elongated 
member; wherein the position of the target member is determined as a 
function of three phase angle differences respectively obtained from the 
three single electrically conducting elongated members. 
Additionally a further object of the present invention is to provide the 
position sensors described in the afore-mentioned objects of the present 
invention, wherein the change of the position of the target is created by 
a fluid dynamic force exerted on the target member by a flow of fluid 
media, and the flow rate of fluid media is determined as a function of the 
position of the target member. 
Additionally a further object is to provide the position sensors described 
in the afore-mentioned objects of the present invention, wherein the 
target member comprises a float floating at the free surface of a liquid 
medium, and the position of the liquid level is determined from the 
position of the target. 
Additionally yet another object is to provide the position sensors 
described in the afore-mentioned objects of the present invention, wherein 
the target member comprises a mechnical pointer included in a dial or bar 
gauge such as a mechanical pressure sensor.

OPERATING PRINCIPLES 
The operating principles of the present invention can be best described by 
referring to FIG. 1. The pair of electrically conducting elongated members 
1 and 2 of a high ohmic resistivity are disposed parallel to one another, 
and a capacitively coupling member 3 moving with a target member, that is 
made of an electrically conducting material, maintains a close 
surface-to-surface proximity relationship with the surfaces of the pair of 
electrically conducting elongated members 1 and 2 for all instants during 
the displacement of the capacitively coupling member 3 following the 
center line of the combination of the pair of electrically conducting 
elongated members 1 and 2. The combination of the pair of elongated 
members 1 and 2, and the capacitively coupling member 3 provides two 
parallel electric circuits connecting the alternating electrical signal 
generator 11 and the device 18 measuring the phase angle difference 
between two alternating electrical signals respectively taken off from the 
two opposite extremities of one of the pair of elongated members 1 and 2, 
that is not physically connected to the signal generator 11, wherein the 
first electric circuit comprises a first portion of the combination of the 
pair of elongated members 1 and 2 located on one side of the capacitively 
coupling member 3, the lead wires 14 and 19 respectively connecting the 
first extremity 12 of the first elongated member 1 to the signal generator 
11 and the first extremity 16 of the second elongated member 2 to the 
phase angle measuring device 18, and the capacitively coupling member 3 
capacitively coupling the electric currents flowing through the pair of 
elongated members 1 and 2 to one another, while the second electric 
circuit comprises a second portion of the combination of the pair of 
elongated members 1 and 2 located on the other side of the capacitively 
coupling member 3 opposite to the one side thereof, the lead wires 15 and 
20 respectively connecting the second extremity 13 of the first elongated 
member 1 to the signal generator 11 and the second extremity 17 of the 
second elongated member 2 to the phase angle measuring device 18, and the 
capacitively coupling member 3. The ohmic resistances of the two parallel 
electric circuits are respectively related to the position x of the 
capacitively coupling member 3 measured from the center section of the 
combination of the pair of elongated members 1 and 2 by equations 
EQU R.sub.1 =.alpha.(L-2x)+R.sub.W1 +R.sub.I, (1) 
and 
EQU R.sub.2 =.alpha.(L+2x)+R.sub.W2 +R.sub.I, (2) 
where .alpha. is the ohmic resistance per unit length of each of the pair 
of electrically conducting elongated members 1 and 2, L is the length of 
the combination of the pair of elongated members 1 and 2, R.sub.W1 and 
R.sub.W2 are the ohmic resistances of the lead wires respectively included 
in the two parallel electric circuits, R.sub.I is the resistance belonging 
to the phase angle measuring circuit included in the phase angle measuring 
device 18. The capacitance of the two parallel electric circuits are 
respectively given by equations 
##EQU1## 
where .beta. is the capacitance between the pair of elongated members 1 
and 2 per unit length of the combination thereof, C is the capacitance of 
the capacitive coupling between the pair of elongated members 1 and 2 
through the capacitive coupling member 3, and C.sub.W1 and C.sub.W2 are 
the capacitances of the lead wires respectively belonging to the two 
parallel electric circuits. When use of Equations (1), (2), (3) and (4) is 
made, it can be easily shown that the phase angles of two alternating 
electrical signals respectively taken off from the two opposite 
extremities 16 and 17 of the second elongated member 2 is given by 
equations 
##EQU2## 
where .omega. is the circular frequency of the alternating electrical 
signal supplied by the signal generator 11. When equations (5) and (6) are 
substituted into the difference formula of the trigonometric functions and 
use of the fact is made that the instrument resistance R.sub.I is much 
greater than the ohmic resistances of the pair of elongated members 1 and 
2 and the connecting lead wires and that the total capacitance belonging 
to each of the two parallel electric circuits has a very small value as 
far as the alternating electrical signal has a frequency of order of kilo 
cycles or less and the combined value of the capacitance between the pair 
of elongated members 1 and 2 and the capacitance of the lead wires is much 
smaller than the capacitance C provided by the capacitively coupling 
member 3, the following equation can be obtained: 
##EQU3## 
Equation (7) can be readily solved for the position x of the capacitively 
coupling member 3, that is related to the phase angle difference by 
equation 
##EQU4## 
In general, the position x of the capacitively coupling member 3 measured 
from the center section of the combination of the pair of electrically 
conducting elongated members 1 and 2 is given by equation 
EQU x=A tan(.phi..sub.1 -.phi..sub.2)-B, (9) 
where A and B are constants intrinsic to the structural arrangement of the 
position sensor. The position S of the capacitively coupling member 3 
measured from one extremity of the combination of the pair of elongated 
members 1 and 2 is given by equation 
##EQU5## 
Equations (9) and (10) are approximate forms of the exact relationship 
between the position of the capacitively coupling member 3 and the phase 
angle difference between the two alternating electrical signals 
respectively taken off from the two opposite extremities of the second 
elongated member 2. The exact relationship between the position of the 
capacitively coupling member 3 and the phase angle difference 
.DELTA..phi.=(.phi..sub.1 -.phi..sub.2) must be obtained empirically by 
calibrating the position sensor rather than deriving theoretically. The 
empirically obtained exact relationship between the position of the 
capacitively coupling member 3 and the phase angle difference .DELTA..phi. 
may be expressed in the form 
EQU s=f(.DELTA..phi.), (11) 
where the specific mathematical relationship defined by the function f must 
be determined empirically by calibrating the position sensor. By using an 
approach parallel to the derivation of equation (9) or (10), it can be 
shown that the position of the capacitively coupling member 3 relative to 
one of the two opposite extremities of the combination of the pair of 
elongated members can be determined by equation of the following form: 
EQU s=g(.DELTA..phi.'), (12) 
where .DELTA..phi.' is the phase angle difference between the alternating 
electrical signal supplied to one of the two extremities of the first 
elongated member 1 and an alternating electrical signal taken off from one 
of the two opposite extremities of the second elongated member 2, wherein 
the two alternating electrical signals are supplied to and taken off from 
those extremities of the pair of electrically conducting elongated members 
located on the same side of capacitively coupling member 3. Of course, the 
specific mathematical relationship g must be determined empirically by 
calibrating the position sensor. The first embodiment of the position 
sensor of the present invention determines the position of the target by 
using the empirically determined equation (11) or (12). It becomes 
immediately evident from the analysis that has led from equations (1), 
(2), (3) and (4) to equations (10) and (11) that a position sensor may 
include a single electrically conducting elongated member and the 
alternating electrical signal may be supplied directly to the capacitively 
coupling member, wherein the position of the target is determined as a 
function of the phase angle difference between the two alternating 
electrical signal respectively taken off from the two opposite extremities 
of the single electrically conducting elongated member or as a function of 
the phase angle difference between the alternating electrical signal 
supplied to the capacitively coupling member and an alternating electrical 
signal taken off from one of the two opposite extremities of the single 
electrically conducting elongated member, which structural combination and 
method define the second embodiment of the position sensor of the present 
invention. It is well known fact that the ohmic resistivity of most 
material changes with changing temperature. In order to compensate for an 
error arising from the change of the specific ohmic resistance of the 
electrically conducting elongated member due to the changing temperature, 
equations (10) and (11) may include a temperature compensating term that 
eliminates the effect of temperature on the measurement of the position of 
the target member. 
The third embodiment of the position sensor of the present invention 
comprises three pairs of electrically conducting elongated members 
disposed in a side-by-side parallel relationship therebetween as shown in 
FIG. 17, wherein the first pair of elongated members has a first 
capacitively coupling member experiencing a displacement in direction 
parallel thereto, the second pair of elongated members has a second 
capacitively coupling member fixedly located at one of the two extremities 
of the combination of the three pairs of elongated members, and the third 
pair of elongated members has a third capacitively coupling member fixedly 
located at the other of the two extremities of the combination of the 
three pairs of elongated members. By using equation (8) it can be shown 
that the position s of the first capacitively coupling member moving with 
a target member can be determined by following equation: 
##EQU6## 
where .DELTA..phi..sub.1, .DELTA..phi..sub.2 and .DELTA..phi..sub.3 are 
the phase angle differences respectively 
obtained from the three pairs of electrically conducting elongated members. 
Equation (13) can be written in the form 
EQU s=p[tan(.DELTA..phi..sub.1 -.DELTA..phi..sub.2), tan(.DELTA..phi..sub.3 
-.DELTA..phi..sub.2)], (14) 
or 
EQU s=q[tan(.DELTA..phi..sub.1 -.DELTA..phi..sub.2), (.DELTA..phi..sub.3 
-.DELTA..phi..sub.2)], (15) 
where the specific functional relationship p and q must be determined 
empirically by calibrating the position sensor. The equivalence 
relationship between equations (11) and (15) immediately shows that the 
position s of the capacitively coupling member can be determined from the 
following equation that is equivalent to equation (12): 
EQU s=y[(.DELTA..phi..sub.1 '-.DELTA..phi..sub.2 '), (.DELTA..phi..sub.3 
'-.DELTA..phi..sub.2 ')], (16) 
where the specific functional relationship y must be determined 
empirically. It is readily recognized that a position sensor comprising 
three single electrically conducting elongated members respectively 
including three capacitively coupling members directly receiving the 
alternating signal also determines the position of the target member by 
using equation (15) or (16). 
It should be understood that the position sensors determining the position 
of the target by equation (15) or (16) measures the position without being 
influenced by the changing ambient condition such as the temperature and 
the surrounding electromagnetic field, while the position sensors 
determining the position of the target by equation (11) or (12) provides 
an economic means for measuring the position with a high degree of 
resolution. 
DESCRIPTION OF ILLUSTRATED EMBODIMENTS 
In FIG. 1 there is illustrated an embodiment of the linear position sensor 
of the present invention comprising a pair of electrically conducting 
elongated members 1 and 2 disposed in a side-by-side parallel relationship 
therebetween, and a capacitively coupling member 3 disposed in a 
relationship allowing a displacement thereof following the center line of 
the combination of the pair of elongated members 1 and 2. Each of the pair 
of elongated members 1 and 2 has a sizable surface area and the 
capacitively coupling member 3 also has a sizable surface area. The 
capacitively coupling member 3 and the pair of elongated members 1 and 2 
maintain a close surface-to-surface proximity relationship therebetween at 
all instants during the displacement of the capacitively coupling member 3 
relative to the pair of elongated members 1 and 2, whereby the 
capacitively coupling member 3 made of an electrically conducting material 
couples the electric currents flowing through the pair of elongated 
members 1 and 2 to one another by means of the electrical capacitance 
thereof. It is desired that the close surface-to-surface proximity 
relationship between the sizable surface area of the capacitively coupling 
member 3 and a section of the sizable surface area of the combination of 
the pair of elongated members 1 and 2 is maintained with a substantially 
constant dimensional tolerance in the gap or interface therebetween, 
whereby the level of the capacitive electrical coupling between the pair 
of elongated members 1 and 2 through the capacitively coupling member 3 
remains at a substantially constant level at all instants. At least one of 
the pair of elongated members 1 and 2 must have a high ohmic resistance 
per unit length thereof, while the position sensor works best when both of 
the pair of elongated members 1 and 2 have the high specific ohmic 
resistance. In the particular illustrative embodiment, the pair of 
elongated members 1 and 2 are respectively built into or supported by two 
flanges or ribs 4 and 5 extending inwardly from the wall 6 of an elongated 
hollow cylindrical member 7. The flanges 4 and 5, and the elongated hollow 
cylindrical member 7 are made of an electrically nonconducting material 
such as a rigid plastic or ceramic material. The displacement of the 
capacitively coupling member 3 following the center line between the pair 
of elongated members 1 and 2 is guided by the edges of the flanges 4 and 5 
having a constant gap therebetween, which edges guide a pair of rollers 8 
and 9 included in the capacitively coupling member 3. The combination of 
the pair of elongated members 1 and 2, the capacitively coupling member 3, 
the pair of flanges 4 and 5, and the elongated hollow cylindrical member 7 
is enclosed within a grounded metallic enclosure 10 providing an 
electromagnetic shielding from the ambient surroundings. The enclosure 10 
may be constructed of a solid sheet or wire mesh made of an electrically 
conducting material. An alternating electrical signal generator 11 
supplies an alternating electrical signal to the two opposite extremities 
12 and 13 of the first elongated member 1 respectively through two lead 
wires 14 and 15. The two opposite extremities 16 and 17 of the second 
elongated member 2 are respectively connected to the two terminals 
included in a device 18 measuring the phase angle difference .DELTA..phi. 
between two alternating electrical signals supplied to the two terminals 
of the phase angle difference measuring device 18 respectively through two 
lead wires 19 and 20. A data processor 21 determines the position of the 
capacitively coupling member 3 as a function of the measured phase angle 
difference .DELTA..phi. between the two alternating electrical signals 
respectively taken off from the two opposite extremities 16 and 17 of the 
second elongated member 2 by using an empirically determined mathematical 
relationship given by equation (11). The specific ohmic resistance of the 
pair of elongated members 1 and 2 can change with the changing 
temperature, when the elongated members are made of a temperature 
sensitive material such as a plastic ribbon of a plastic material 
impregnated with carbon powders. A temperature sensor 22 measuring the 
temperature of the interior space within the metallic enclosure 10 may be 
included as an option, whereby information on the temperature of the pair 
of elongated members 1 and 2 is supplied to the data processor 21 that 
carries out an algorithm compensating for the effect of the temperature 
change on the measurement of the position of the target member due to the 
temperature change. In an alternative design, the lead wire 15 can be 
omitted, and the lead wires 20 connected to one of the two terminals of 
the phase angle difference measuring device 18 can be connected to the 
first extremity 12 of the first elongated member 1 or to the lead wire 14 
supplying the alternating electrical signal to the first extremity 12 of 
the first elongated member 1 after removing the connection of the lead 
wire 20 from the second extremity 17 of the second elongated member 2, 
wherein the phase angle difference measuring device 18 measures the phase 
angle difference .DELTA..phi. ' between the alternating electrical signal 
supplied to the first extremity 12 of the first elongated member and an 
alternating electrical signal taken off from the first extremity 16 of the 
second elongated member 2. The data processor 21 determines the position 
of the target as a function of the measured phase angle difference 
.DELTA..phi.' by using an empirically obtained mathematical relationship 
given by equation (12). Of course, the temperature sensor 22 can be 
included whereby the data processor 21 executes the temperature 
compensating algorithm in determining the position of the capacitively 
coupling member 3 as a function of the phase angle difference 
.DELTA..phi.'. 
In FIG. 2 there is illustrated a cross section of the linear position 
sensor shown in FIG. 1, which cross section taken along plane 2--2 as 
shown in FIG. 1 illustrates with a greater clarity the freely sliding 
engagement between the capacitively coupling member 3 and the flanges 4 
and 5. The capacitively coupling member 3 comprises two planar members 23 
and 24 made of an electrically conducting material such as a metallic 
sheet or plate and connected to one another at the center line between the 
pair of elongated members 1 and 2, and simultaneously sandwich the two 
flanges 4 and 5 in a freely sliding relationship. The capacitively 
coupling member 3 may be mechanically connected to a target member under 
position sensing by a rigid arm 25 laterally extending from the 
capacitively coupling member 3 and through a slitted axially disposed 
opening 26 through the cylindrical walls of the hollow cylindrical 
elongated member 7 and the cylindrical metallic enclosure 10 as shown in 
the particular illustrative embodiment, or may be connected to a target 
member by a connecting rod disposed parallel to the center line between 
the pair of elongated members 1 and 2, and extending through a hole 
included in one end wall of the cylindrical metallic enclosure. The 
slitted axial opening 26 and holes included in the end walls of the 
cylindrical metallic enclosure 10 for routing the lead wires and/or the 
connecting arm or rod are not detrimental to the electromagnetic shielding 
provided by the cylindrical metallic enclosure 10, as the frequency of the 
alternating electrical signal supplied by the signal generator 11 is well 
below the microwave or radio wave frequencies and the openings of 
dimensions much less than the wave length of the alternating electrical 
signal supplied by the signal generator 11 do not degrade the quality of 
the electromagnetic shielding. It should be mentioned that the 
construction of the capacitively coupling member 3 comprising two planar 
members 23 and 24 sandwiching the pair of elongated members 1 and 2 
therebetween is highly preferred, because firstly, it maintains a constant 
level of capacitive coupling independent of a small movement thereof in 
directions perpendicular to the plane including the pair of elongated 
members 1 and 2, as an increase in the gap between one of the two planar 
members 23 and 24 of the capacitively coupling member 3 and one side 
surface of the pair of elongated members 1 and 2 becomes compensated by a 
decrease in the gap between the other of the two planar members 23 and 24 
of the capacitively coupling member 3 and the other side surface of the 
pair of elongated members 1 and 2, and secondly, the two sided close 
surface-to-surface proximity relationship between the capacitively 
coupling member 3 and the pair of elongated members 1 and 2 provides a 
large capacitance that increases the resolution in the position sensing as 
indicated by equation (8). Of course, the rollers 8 and 9 prevent the 
shifting movement of the capacitively coupling member 3 in directions 
parallel to the plane defined by the two flanges 4 and 5 relative to the 
edges thereof. 
In FIG. 3 there is illustrated a cross section of another embodiment of of 
the position sensor comprising a pair of parallel elongated members 27 and 
28, each of which elongated members has a plurality of parallel axial 
grooves. The pair of elongated members 27 and 28 are disposed in such a 
way that the openings of the plurality of parallel axial grooves included 
in each of the pair of elongated members 27 and 28 face one another, and 
are simultaneously engaged in a freely sliding relationship by two sets of 
plurality of flanges included in the capacitively coupling member 29. An 
electrically insulating hollow cylinder 30 having a rectangular cross 
section anchors the pair of elongated members 27 and 28 and guides four 
rollers 31, 32, 33 and 34 included in the capacitively coupling member 29. 
The electrically insulating hollow cylinder 30 also provides the required 
separation between the eletromagnetically shielding enclosure 35 and the 
combination of the pair of elongated members 27 and 28, and the 
capacitively coupling member 29. 
In FIG. 4 there is illustrated a cross section of a further embodiment of 
the position sensor comprising a pair of elongated members 36 and 37 
disposed in a face-to-face relationship therebetween within and anchored 
to an insulating hollow cylinder 38, that is sheathed by a metallic 
enclosure 39. The capacitively coupling member 40 disposed between the 
pair of elongated members 36 and 37 in a freely sliding relationship is 
guided by two rollers 41 and 42. 
In FIG. 5 there is illustrated a cross section of yet another embodiment of 
the position sensor employing a pair of elongated members 43 and 44 
disposed in a T-shaped cross sectional geometry. A capacitively coupling 
member 45 having a T-shaped cross sectional geometry maintains a close 
surface-to-surface proximity relationship with the first elongated member 
43 in a face-to-face relationship and with the second elongated member 44 
in a sandwiching relationship. The capacitively coupling member 45 is 
guided by three rollers 46, 47 and 48. The metallic enclosure 49 
electromagnetically shields the the combination of the pair of elongated 
members 43 and 44, and the capacitively coupling member 45 from the 
conductors, capacitors and electromagnetic field existing outside of the 
metallic enclosure 49. One obvious embodiment of the position sensor, that 
is not shown as an illustrative example, comprises a pair of elongated 
members of circular cylindrical shell geometry disposed in a coaxial 
relationship, and a capacitively coupling member having a shape of 
circular cylindrical ring that fills up the annular space between the pair 
of of elongated members. Of course, the combination of the pair of 
elongated members and the capacitively coupling members must be enclosed 
within a metallic enclosure providing the electromagnetic shielding. 
In FIG. 6 there is illustrated an embodiment of the rotary position sensor 
comprising a pair of elongated members 50 and 51 (elongated member 51 is 
not visible in the particular illustration as it is hidden behind 50) 
disposed circumferentially on a circular cylindrical surface in a 
side-by-side parallel relationship therebetween, wherein the pair of 
elongated members 50 and 51 are supported by by a dielectric cylindrical 
shell 52 that is sheathed by a metallic cylindrical shell 53 having two 
closed ends. The capacitively coupling member 54 having an outer surface 
coinciding with a circular cylindrical surface coaxial to the pair of 
elongated members 50 and 51 is supported by an arm 55 rotatable about the 
central axis 56 of the circular cylindrical surface including the pair of 
elongated members 50 and 51, wherein the outer surface of the capacitively 
coupling member 54 maintains a close surface-to-surface proximity 
relationship with both of the pair of elongated members 50 and 51 during 
all phases of rotary displacement of the capacitively coupling member 54 
about the central axis 56. 
In FIG. 7 there is illustrated a cross section of the rotary position 
sensor shown in FIG. 6, which cross section taken along plane 7--7 as 
shown in FIG. 1 illustrates with a greater clarity the arrangement of the 
pair of elongated members 50 and 51 disposed on a common circular 
cylindrical surface coaxial to the central axis 56, and the capacitively 
coupling member 54 supported by the arm 55 rotatably about the central 
axis 56, wherein the combination of the pair of elongated members 50 and 
51, and the capacitively coupling member 54 is enclosed within a metallic 
enclosure 53. The rotary sensor operates on the same principles as the 
operating principles of the linear position sensor shown in FIG. 1 with 
one exception that the rotary position sensor measures position of a 
target member along the circumference of the circular cylindrical surface, 
while the linear position sensor measures position of a target member 
following a rectilinear line of the displacement of the target member. Of 
course, the angular displacement can be obtained from the circumferential 
displacement provided by the rotary sensor by dividing the circumferential 
displacement by the radius of the circular cylindrical surface defined by 
the pair of elongated members 50 and 51. In this particular illustrative 
embodiment, the rotary displacement of the capacitively coupling member 54 
about the central axis 56 represents the rotary displacement of a target 
member fixedly mounted on the rotary motion transmitting shaft 57 that 
transmits the rotary motion of the rotary motion transmitting shaft 57 to 
the rotary motion of the capacitively coupling member 54 by means of a 
magnetic motion coupler comprising a pair of permanent magnets 58 and 59 
respectively affixed to the two shafts 57 and 56. In an alternative 
design, the rotary displacement of a target member may be mechanically 
coupled to the rotary displacement of the capacitively coupling member 54 
or the capacitively coupling member 54 or the supporting arm 55 may be the 
target itself. The magnetic displacement coupling included in the 
particular illustrative embodiment suggests that the linear displacement 
of the capacitively coupling member 40 or 45 shown in FIG. 4 or 5 may be 
made of a ferromagnetic material and coupled to the displacement of a 
target member including a permanent magnet, that is disposed outside of 
the sealed metallic enclosure 39 or 49. 
In FIG. 8 there is illustrated another embodiment of the rotary position 
sensor comprising a pair of electrically conducting planar members 60 and 
61 of circular annular geometry disposed on a common plane in a concentric 
relationship to a central axis 62. The capacitively coupling member 63 
disposed on a plane closely adjacent to the plane defined by the pair of 
circular annular members 60 and 61, is supported by an arm 64 rotatable 
about the central axis 62, wherein the capacitively coupling member 63 
maintains a close surface-to-surface proximity relationship with both of 
the pair of circular annular members 60 and 61 during all phases of rotary 
displacement about the central axis 62. The rotary position sensors shown 
in FIGS. 6 and 8 determines the rotary position of the capacitively 
coupling member or the rotary position of the arm supporting the 
capacitively coupling member as a function of the phase angle difference 
.DELTA..phi. between two alternating electrical signals respectively taken 
off from the two opposite circumferential extremities of one of the pair 
of elongated or circular annular members that does not receiving the 
alternating electrical signal from the signal generator, or as a function 
of the phase angle difference .DELTA..phi.' between the alternating 
electrical signal supplied to one circumferential extremity of the first 
elongated or circular annular member and an alternating electrical signal 
taken off from one circumferential extremity of the second elongated or 
circular annular member. 
Before proceeding to show a few representative applications of the linear 
and rotary position sensors of the present invention, a number of 
important conditions required to make the position sensor work accurately 
and sensitively should be mentioned. As indicated by equation (8), the 
individual elongated member must have a high specific ohmic resistance and 
the capacitively coupling member must maintain a close surface-to-surface 
proximity relationship with each of the pair of elongated members over a 
sizable surface area in order to provide a high resolution in measuring 
the position of the target member moving with the capacitively coupling 
member. This condition requires that the individual elongated member must 
have a sizable surface area and, consequently, the individual elongated 
member must be made of a material having a high ohmic resistivity into a 
shape of a ribbon or a flat bar, and the capacitively coupling member must 
have a sizable area under a close surface-to-surface proximity 
relationship with a section of the surfaces of the pair of elongated 
members. It is important that the value of the electric capacitance 
associated with the capacitively coupling member remains substantially 
constant. The amplitude of the alternating electrical signal must be 
maintained at a substantially constant level. The phase angle difference 
determining the position of the capacitively coupling member changes very 
acutely as a result of the electrically conducting objects, capacitive 
elements and low frequency alternating electromagnetic field existing in 
the ambient surroundings. Therefore, the assembly including the pair of 
elongated members and the capacitively coupling member must be enclosed 
within an electromagnetically shielding enclosure made of an electrically 
conducting solid sheet or wire mesh , that is well grounded. The position 
sensor works best when the individual electrically conducting elongated 
members and the capacitively coupling member are sheathed, coated or lined 
with a layer of electrically insulating material, whereby the ambient 
media occupying the surroundings of the combination of the pair of 
elongated members and the capacitively coupling member do not alter the 
electrical parameters of the position sensor. When the above-mentioned 
conditions are satisfied, it is not difficult to construct a position 
sensor capable of measuring the position of a target member with 
increments of every one hundredth of an inch, and it is possible to 
construct a position sensor measuring the position with increments of 
every few thousandth of an inch. 
In FIG. 9 there is illustrated a cross section of an embodiment of the 
nonrotating propeller or nonrotating turbine flowmeter that employs the 
rotary position sensor comprising a pair of elongated members 65 and 66 
disposed in a side-by-side parallel relationship on a circular cylindrical 
surface coaxial to the center line 67 of the flow passage 68 having a 
circular cross section. A propeller or turbine 69 is disposed on a cross 
section of the flow passage 68 rotatably about the center line 67 of the 
flow passage 68, wherein a torsion spring 70 provides a bias torque 
countering the fluid dynamic torque exerted on the propeller or turbine 69 
by the fluid media moving through the flow passage 68, which bias torque 
keeps the propeller or turbine 69 at the zero position having a stop that 
prevents the propeller or turbine 69 from experiencing a rotary 
displacement in a direction opposite to the direction of the fluid dynamic 
torque, when the fluid media in the flow passage 68 is stationary. The 
capacitively coupling member 71 of a curved planar geometry maintaining a 
close surface-to-surface proximity relationship with the pair of elongated 
members 65 and 66 is affixed to the tip of one propeller or turbine blade, 
while a dummy capacitively coupling member 72 made of a dielectric 
material is affixed to the tip of the other propeller or turbine blade in 
a diametrically opposite arrangement to the real capacitively coupling 
member 71. The axisymmetric construction of the propeller or turbine 69 
including the real and dummy capacitively coupling members 71 and 72 
provides the structural and fluid dynamic symmetry enhancing the 
performance of the flowmeter. The dielectric sleeve 73 supporting the pair 
of elongated members 65 and 66 is sheathed by a metallic cylindrical shell 
74, which together with two metallic wire meshes 75 and 76 respectively 
covering the inlet and outlet ends of the flow passage 68 provides the 
electromagnetic shielding. The fluid dynamic torque proportional to the 
dynamic pressure, that is equal to one half of the fluid density times the 
square of the fluid velocity, is determined as a function of the rotary 
displacement of the propeller or turbine 69 as a measure of the flow rate 
of the fluid media moving through the flow passage 68, as the velocity of 
the fluid media is readily determined from the measured dynamic pressure 
of fluid flow when the density of the fluid media is known or measured. 
The covering of the inlet and outlet ends of the flow passage 68 with the 
wire meshes 75 and 76 may be omitted by extending the metallic cylindrical 
shell 74 to a greater length in both directions from the propeller or 
turbine 69. FIG. 23 illustrates an end view of a nonrotating propeller or 
turbine disposed within a flow passage in an arrangement similar to that 
employed in the construction of the nonrotating propeller or turbine 
flowmeter shown in the particular illustrative embodiment. 
In FIG. 10 there is illustrated a cross section of an embodiment of the 
variable area flowmeter that employs the linear position sensor comprising 
a pair of elongated members 77 and 78 disposed axially on a circular 
cylindrical surface coaxial to the center line 79 of a tapered flow 
passage 80, wherein the pair of elongated members are respectively 
disposed along the two diametrically opposite halves of the wall of the 
tapered flow passage 80. The capacitively coupling member 81 of a circular 
cylindrical shell or ring geometry under a close surface-to-surface 
proximity relationship with the pair of elongated members 77 and 78 is 
included in a displaceable or movable orifice member 82 of a circular 
cylindrical ring geometry. The coil spring 83 provides a bias force 
countering the fluid dynamic drag force exerted on the diplaceable orifice 
member 82 by the fluid media moving through the tapered flow passage 80. 
The drag force experienced by the displaceable orifice member 82 is 
determined as a function of the linear position thereof. As the drag force 
is proportional to the dynamic pressure of the fluid flow, the velocity of 
the fluid media is determined as a function of the linear position of the 
displaceable orifice member 82. The electromagnetic shielding is provided 
by the metallic circular cylindrical shell 84 and two metallic wire meshes 
85 and 86 respectively covering the inlet and outlet sections of the 
tapered flow passage 80. The pair of metallic wire meshes 85 and 86 can be 
omitted by extending the metallic circular cylindrical shell 84 to a 
greater length. When the variable area flowmeter is installed in an 
up-right vertical position, the coil spring 83 can be omitted as the 
weight of the displaceable orifice member 82 provides the bias force 
countering the drag force exerted on the displaceable orifice member 82 by 
the flow of the fluid media. In an alternative design, the variable area 
flowmeter may have a tapered flow passage between a circular cylindrical 
core of a constant diameter and a tapered outer cylindrical wall coaxially 
disposed to the circular cylindrical core of the constant diameter, 
wherein a pair of electrically conducting elongated members constituting 
the linear position sensor are included in the circular cylindrical core 
of the constant diameter. 
In FIG. 11 there is illustrated another cross section of the variable area 
flowmeter shown in FIG. 10, which cross section taken along plane 11--11 
as shown in FIG. 10 illustrates with a greater clarity the arrangement of 
the linear position sensor comprising the pair of elongated members 77 and 
78 included in the outer cylindrical wall of the tapered flow passage 80, 
and the capacitively coupling member 81 included in the displaceable 
orifice member 82. 
In FIG. 12 there is illustrated a cross section of an embodiment of the 
liquid level sensor employing the linear position sensor comprising a pair 
of elongated members 87 and 88, and the capacitively coupling member 89, 
which combination is disposed in an arrangement similar to the combination 
of the corresponding elements included in the embodiment shown in FIG. 10. 
Of course, the capacitively coupling member of a circular cylindrical 
shell geometry is now included in a float 90 having a centrally located 
vent hole 91, wherein the float 90 floats on the free surface of a liquid 
medium. The metallic enclosure 92 providing the electromagnetic shielding 
has a closed top end 93 and an open bottom end 94 covered with a metallic 
wire mesh 95. The vent holes 96 and 97 are disposed through the enclosure 
wall housing the linear position sensor assembly at a section near the 
closed top end 93. The liquid level is determined by adding a constant to 
or subtracting a constant from the position of the capacitively coupling 
member 89, which constant is determined empirically by calibrating the 
liquid level sensor. It should be understood that, when the liquid medium 
under level measurement is an electrically conducting medium, the 
capacitively coupling member 89 included in the linear position sensor can 
be omitted, as the electrically conducting liquid medium plays the role of 
capacitively coupling the pair of elongated members 87 and 88. 
In FIG. 13 there is illustrated another cross section of the liquid level 
sensor shown in FIG. 12, which cross section taken along plane 13--13 as 
shown in FIG. 12 illustrates with a greater clarity the arrangement of the 
pair of elongated members 87 and 88, and the capacitively coupling member 
89 included in the float 90. 
In FIG. 14 there is illustrated an embodiment of the linear position sensor 
of the present invention, that comprises a single electrically conducting 
elongated member 98 having a high specific ohmic resistance and a 
capacitively coupling member 99 under a close surface-to-surface proximity 
relationship with the single elongated member 98. The position sensor 
works best when the capacitively coupling member 99 is made of a metal , 
and coated or lined with an electrically insulating layer. An alternating 
electrical signal is directly supplied to the capacitively coupling member 
99 through a lead wire 100 physically connected to the capacitively 
coupling member 99, while the phase angle difference .DELTA..phi. between 
two alternating electrical signals respectively taken off from the two 
opposite extremities 101 and 102 of the single elongated member 98 is 
measured. The position of the capacitively coupling member 99 representing 
the position of a target member is determined as a function of the 
measured phase angle difference .DELTA..phi.. It should be understood that 
the combination of the single elongated member 98 and the capacitively 
coupling member 99 must be enclosed within a grounded metallic enclosure 
103. Another embodiment of the position sensor comprising a single 
elongated member can be constructed by modifying the position sensor shown 
in FIG. 1. When the first elongated member 1 and the capacitively coupling 
member 3 included in the position sensor shown in FIG. 1 are made of a 
highly electrically conductive metal, and the side surfaces of the first 
elongated member 1 and one-half of the surface of the capacitively 
coupling member 3 adjacent to the side surfaces of the first elongated 
member 1 have bare surfaces and are under a physical contact therebetween 
whereby the alternating electrical signal is directly transmitted between 
the first elongated member 1 and the capacitively coupling member 3 by the 
electrical conduction, the position sensor shown in FIG. 1 operates on the 
same principles as those of the position sensor comprising a single 
elongated member 98 shown in FIG. 14. In an alternative design of the 
position sensor shown in FIG. 14 or the above-described revised version of 
the position sensor shown in FIG. 1, the lead wires 104 and 15 can be 
omitted and the phase angle difference .DELTA..phi.' between the 
alternating electrical signal conductively supplied to the capacitively 
coupling member and an alternating electrical signal taken off from one of 
the two opposite extremities of the single elongated member can be 
measured, wherein the position of the capacitively coupling member is 
determined as a function of the measured phase angle difference 
.DELTA..phi.'. 
In FIG. 15 there is illustrated an embodiment of the rotary position sensor 
of the present invention comprising a single elongated member 105 disposed 
circumferentially on a circular cylindrical surface coaxial to a center 
line 106. The capacitively coupling member 107 made of a metal and covered 
with an electrically insulating layer and under a close surface-to-surface 
proximity relationship with the single elongated member 105 is supported 
by a metallic arm 108 rotatable about the center line 106, wherein the 
metallic capacitively coupling member 107 and the metallic arm 108 are 
physically connected to one another in a metal-to-metal connection 
conductively transmitting an electric current. An alternating electrical 
signal is supplied to the capacitively coupling member 107 through a 
combination of the arm 108 and a lead wire 109 physically connected to the 
hub of the arm 108 or a metallic spindle rotatably supporting the arm 108. 
The rotary position of the capacitively coupling member 107 or that of the 
arm 108 is determined as a function of the phase angle difference 
.DELTA..phi. between two alternating electrical signals respectively taken 
off from the two opposite extremities 110 and 111 of the single elongated 
member 105. In an alternative mode of operation, the rotary position can 
be determined as a function of phase angle difference .DELTA..phi.' 
between the alternating electrical signal conductively supplied to the 
capacitively coupling member 107 and an alternating electrical signal 
taken off from one of the two opposite extremities of the elongated member 
105. 
In FIG. 16 there is illustrated another embodiment of the rotary position 
sensor that has essentially the same construction as that of the 
embodiment shown in FIG. 15 with one exception. In this particular 
illustrative embodiment, an electrically conducting member 112 having a 
circular annular geometry is disposed coaxially to a center line 113 on a 
plane perpendicular to the center line 113 and the capacitively coupling 
member 114 is disposed on another plane closely adjacent and parallel to 
the plane defined by the electrically conducting member 112. 
In FIG. 17 there is illustrated an embodiment of the linear position sensor 
of the present invention comprising three pairs of electrically conducting 
elongated members disposed in a side-by-side parallel relationship 
therebetween, wherein each of the three pairs of elongated members has 
essentially the same construction and the same operating principles as 
those of the pair of elongated members 1 and 2 included in the embodiment 
shown in FIG. 1. The first pair 115 of elongated members has a 
capacitively coupling member 116 built into or connected to a target 
member, wherein the capacitively coupling member 116 experiences a 
displacement following the center line between the first pair 115 of 
elongated members. The second pair 117 of elongated members has a 
capacitively coupling member 118 fixedly disposed at a first extremity 119 
of the combination of the three pairs of elongated members. The third pair 
120 of elongated members has a capacitively coupling member 121 fixedly 
disposed at a second extremity 122 of the combination of the three pairs 
of elongated members. The alternating electrical signal generator 123 
supplies an alternating electrical signal to both of the two opposite 
extremities of the first of each pair of elongated members, while each of 
three phase angle difference measuring devices 124, 125 and 126 measures a 
phase angle difference between two alternating electrical signals 
respectively taken off from the two opposite extremities of the second of 
each pair of elongated members. The position of the capacitively coupling 
member 116 or that of a target member kinematically coupled to the 
capacitively coupling member 116 is measured as a function of three phase 
angle differences .DELTA..phi..sub.1, .DELTA..phi..sub.2 and 
.DELTA..phi..sub.3 respectively provided by the three phase angle 
difference measuring devices 124, 125 and 126 in accordance with the 
principles described in conjunction with equation (15). In an alternative 
mode of operation, the alternating electrical signal is supplied to only 
one of the two opposite extremities of the first of each pair of elongated 
members, and each of three phase angle differences .DELTA..phi..sub.1 ', 
.DELTA..phi..sub.2 ' and .DELTA..phi..sub.3 ' is taken by measuring a 
phase angle difference between the alternating electrical signal supplied 
to the one extremity of the first of each pair of elongated members and an 
alternating electrical signal taken off from only one of the two opposite 
extremities of the second of each pair of elongated members, wherein the 
one extremity of the first and the one extremity of the second of each 
pair of elongated members are located on the same side of the capacitively 
coupling member associated with each pair of elongated members, wherein 
the position of the capacitively coupling member or that of the target 
member represented thereby is determined as a function of three phase 
angle differences .DELTA..phi..sub.1 ', .DELTA..phi..sub.2 ' and 
.DELTA..phi..sub.3 ' in accordance with the principles described in 
conjunction with equation (16). It should be noticed that, in the 
particular illustrative embodiment, the first of each pair of elongated 
members receiving the alternating electrical signal from the signal 
generator 123 are combined into a single integral assembly having a 
trifurcate cross sectional geometry. In an alternative design, the three 
pairs of elongated members may be electrically as well as physically 
isolated from each other as exemplified by the embodiment shown in FIGS. 
20, 21 and 22. The particular assembly of the three pairs of elongated 
members shown in FIG. 17 is particularly useful, when the first of each 
pair of elongated members assembled into an integral structure having the 
trifurcate cross section, that receives the alternating electrical signal 
from the signal generator 123, is made of a highly conductive metal, while 
the second of each pair of elongated members is made of a material of high 
ohmic resistivity such a ceramic or a synthetic material impregnated with 
carbon powders. 
In FIG. 18 there is illustrated an end view of the position sensor shown in 
FIG. 17. The position sensor shown in FIGS. 17 and 18 works best, when it 
is enclosed within a metallic enclosure providing an electromagnetic 
shielding as explained in conjunction with FIG. 1. 
In FIG. 19 there is illustrated an embodiment of the rotary position sensor 
of the present invention comprising three pairs 127, 128 and 129 of 
elongated members respectively disposed circumferentially on three 
circular cylindrical surfaces coaxial to a common center line 130. The 
combination of the first pair 127 of elongated members and the 
capacitively coupling member 131 is a curved version of the combination of 
the first pair 115 of elongated members and the capacitively coupling 
member 116 included in the embodiment shown in FIG. 17. The combination of 
the second pair 128 of elongated members and the capacitively coupling 
member 132 and the combination of the third pair 129 of elongated members 
and the capacitively coupling member 133 respectively correspond to the 
combination of the second pair 117 of elongated members and the 
capacitively coupling member 118 and the combination of the third pair 120 
of elongated members and the capacitively coupling member 121 included in 
the embodiment shown in FIG. 17. The metallic enclosure 134 surrounding 
the position sensing elements provides the electromagnetic shielding. The 
rotary position sensor shown in FIG. 19 operates on the same principles as 
those of the linear position sensor described in conjunction with FIG. 17. 
In FIG. 20 there is illustrated a cross section of the rotary position 
sensor shown in FIG. 19, which cross section taken along plane 20--20 as 
shown in FIG. 19 illustrates with a greater clarity the coaxially layered 
disposition of the three pairs 127,128 and 129 of elongated members and 
one 131 of the three capacitively coupling members. 
In FIG. 21 there is illustrated a cross section of another embodiment of 
the rotary position sensor comprising three pairs 135, 136 and 137 of 
elongated members and the three capacitively coupling members 138, 139 and 
140. The capacitively coupling member 138 is built into a hollow 
cylindrical collar or ring 141 sliding on the hollow cylindrical member 
142 providing a supporting structure securing the three pairs of elongated 
members. The two stationary capacitively coupling members 139 and 140 are 
respectively disposed fixedly at the two opposite extremities of the two 
pairs 136 and 137 of elongated members. The combination 143 of the keys 
and key ways maintains the proper line up between the first pair 135 of 
elongated members and the capacitively coupling member 138 maintaining the 
close surface-to-surface proximity relationship with the first pair 135 of 
elongated members. It becomes clear from the embodiments shown in FIGS. 12 
and 13 that, in an alternative design, the collar 141 including the 
capacitively coupling member 138 can be disposed within the hollow 
cylindrical member 142 rather than outside thereof, and the exterior 
surface of the hollow cylindrical member 142 can be coated or lined with a 
layer of an electrically conducting material providing the electromagnetic 
shielding. 
In FIG. 22 there is illustrated a cross section of a further embodiment of 
the position sensor comprising three pairs 144, 145 and 146 of elongated 
members assembled into an I-beam structure. The capacitively coupling 
member 147 slides on one of the two flanges of the I-beam structure, while 
the capacitively coupling members 148 and 149 are respectively disposed 
fixedly at the two opposite extremities of the I-beam structure. The 
combination of the I-beam assembly of the three pairs of elongated members 
and the three capacitively coupling members may be enclosed within an 
elongated metallic shell container providing the electromagnetic 
shielding. 
The various embodiments of the position sensor shown in FIGS. 17, 19, 20, 
21 and 22 comprise three component position sensors, one with a 
displaceable capacitively coupling member and the other two with the 
stationary capacitively coupling members, wherein the individual component 
position sensor is the same as or similar to the position sensor shown and 
described in conjunction with FIGS. 1, 6 and 8. It becomes immediately 
clear that a modified versions of the position sensors shown in FIGS. 17, 
19, 20, 21 and 22 can be constructed by using three individual position 
sensors respectively comprising the single elongated member such as that 
shown in FIG. 14, 15 or 16 in place of the three individual position 
sensors respectively including the pair of elongated members. Such a 
modified version of the position sensor comprising the three individual 
position sensors operates on the same principles as those described in 
conjunction with FIGS. 17 or 19. 
In FIG. 23 there is illustrated an embodiment of the liquid level sensor 
employing the linear position sensor comprising three pairs of elongated 
members such as the position sensor shown in FIG. 21. The capacitively 
coupling member 138 built into the collar 141 included in the position 
sensor shown in FIG. 21 now constitutes a float floating on the free 
surface of a liquid medium. It becomes immediately clear from the 
embodiment shown in FIGS. 12 and 13 that the liquid level sensor shown in 
FIG. 23 can be readily modified to the type of liquid level sensor shown 
in FIGS. 12 and 13, that included the float inside of the elongated hollow 
cylindrical member including the three pairs of elongated members rather 
than outside thereof. 
In FIG. 24 there is illustrated a cross section of an embodiment of the 
variable area flowmeter operating on the same principles as those of the 
variable area flowmeter shown in FIG. 10. The variable area flowmeter 
shown in the particular illustrative embodiment employs a linear position 
sensor comprising three pairs 150,151 and 152 of elongated members 
disposed within the outer wall 153 of the tapered annular flow passage 154 
in a coaxially layered arrangement. The capacitively coupling member 155 
associated with the first pair 150 of elongated members is included in the 
displaceable or movable orifice member 156 of a circular cylindrical shell 
or ring geometry. The second and third pairs 151 and 152 of elongated 
members respectively have two stationary capacitively coupling members of 
a circular cylindrical shell geometry, which are fixedly disposed 
respectively at the two opposite extremities of the combination of the 
three pairs of elongated members in an arrangement exemplified by the 
embodiment shown in FIG. 17. 
In FIG. 25 there is illustrated another cross section of the variable area 
flowmeter shown in FIG. 24, which cross section taken along plane 25--25 
as shown in FIG. 24 illustrates the coaxially layered disposition of the 
three pairs 150, 151 and 152 of elongated members and the displaceable 
orifice member 156. 
In FIG. 26 there is illustrated a cross section of an embodiment of the 
nonrotating propeller or nonrotating turbine flowmeter having a 
construction similar to and the same operating principles as those of the 
nonrotating propeller shown in FIG. 9. While the nonrotating propeller 
flowmeter shown in FIG. 9 employs a rotary position sensor comprising a 
single pair of elongated members, the nonrotating propeller flowmeter 
shown in the particular illustrative embodiment employs a rotary position 
sensor comprising three pairs of elongated members built into the wall 157 
of the flow passage 158 having a circular cylindrical cross section, which 
rotary position sensor has the same construction as that of the rotary 
position sensor shown in FIG. 19. The capacitively coupling member 159 is 
affixed to the tip of one propeller blade 160 disposed rotatably about the 
center line 161 of the flow passage 158, wherein a torsion spring provides 
a bias torque countering the fluid dynamic torque exerted on the propeller 
by the fluid media moving through the flow passage 158. 
In FIG. 27 there is illustrated another cross section of the nonrotating 
propeller flowmeter shown in FIG. 26, which cross section taken along 
plane 27--27 as shown in FIG. 26 illustrates the structural arrangement 
including the propeller blade 160 and the torsion spring 162. The cross 
section of the propeller blade 160 has an airfoil geometry having zero or 
a small constant angle of attack over the entire length of the propeller 
blade 160. As the propeller is not rotating, the pitch angle of the 
propeller is not varied from a large value at the root of the propeller to 
a small value at the tip thereof. The zero rotary position of the 
propeller corresponding zero flow of the fluid media may include a stop 
preventing the propeller from experiencing a rotary displacement beyond 
the zero rotary position in a direction opposite to the direction of the 
fluid dynamic torque exerted by the moving fluid media. The flow rate of 
the fluid media is determined as a function of the rotary position of the 
propeller blade 160 measured by means of the rotary position sensor 
included in the wall 157 of the flow passage 158. It is readily recognized 
that the level sensors, variable area flowmeters and nonrotating propeller 
flowmeters shown and described as a few representative applications of the 
position sensor taught by the present invention may employ a position 
sensor comprising a single, or a pair of, or three pairs of elongated 
members. 
In FIG. 28 there is illustrated an embodiment of the pressure sensor 
employing a rotary position sensor comprising three pairs of elongated 
members such as the rotary position sensor shown in FIG. 19. The 
capacitively coupling member 163 corresponds to the capacitively coupling 
member 131 included in the rotary position sensor shown in FIG. 19. The 
difference between two pressures respectively introduced into two bellows 
164 and 165 creates a pivoting displacement of the lever arm 166 that, in 
turn, rotates the arm or pointer 167 of the dial gauge. It is readily 
recognized that the rotary position sensor included in the particular 
illustrative embodiment of the pressure sensor with the electronic 
read-out device can be replaced with a rotary position sensor comprising a 
pair of elongated members such as that shown in FIG. 6 or 8, or with a 
rotary position sensor comprising a single elongated member such as that 
shown in FIG. 15 or 16. It should be understood that various types of the 
conventional visual read-out displays such as the dial gauges and bar 
scales can be converted to an electronic read-out device by incorporating 
the position sensor of the present invention as exemplified by the case of 
the pressure shown in FIG. 28, wherein a position sensor comprising a 
single, or a pair of, or three pairs of elongated members may be employed 
to electrically and automatically measure the linear or rotary position of 
the pointer or indicator representing the value of a physical quantity 
under measurement. 
The three different structural embodiment of the position sensor of the 
position sensor shown and described in conjunction with FIGS. 1 through 28 
can be summarized as follows: The first structural embodiment of the 
position sensor comprising a single elongated member is illustrated in 
FIGS. 14 through 16, wherein the alternating electrical signal is 
conductively supplied to the capacitively coupling member and the phase 
angle difference between two alternating electrical signals respectively 
taken off from the two opposite extremities of the single elongated member 
is measured, and the position of the capacitively coupling member is 
determined as a function of the measured phase angle difference. In a 
modified version, the alternating electrical signal can be supplied to one 
of the two opposite extremities of the single elongated member and the 
phase angle difference between two alternating electrical signals 
respectively taken off from the capacitively coupling member and the other 
of the two opposite extremities of the single elongated member can be 
measured to determine the position of the capacitively coupling member. 
The second structural embodiment of the position sensor comprising a pair 
of elongated members is illustrated in FIGS. 1 through 8, wherein the 
alternating electrical signal is supplied to at least one of the two 
opposite extremities of the first of the pair of elongated members and the 
phase angle difference between two alternating electrical signals 
respectively taken off from the two opposite extremities of the second of 
the pair of elongated members. The position sensor works best when the 
alternating electrical signal is supplied to both of the two opposite 
extremities of the first of the pair of elongated members. When the 
alternating electrical signal is supplied to only one of the two opposite 
extremities of the first of the pair of elongated members, the other of 
the two opposite extremities of the first of the pair of elongated members 
may be grounded. In a modified version, the alternating electrical signal 
is supplied to one of the two opposite extremities of the first of the 
pair of elongated members and the phase angle difference between two 
alternating electrical signals respectively taken off from one of the two 
opposite extremities of the first of the pair of elongated members and one 
of the two opposite extremities of the second of the pair of elongated 
members. This version of the position sensor works best when the two 
alternating electrical signals are respectively taken off from the same 
extremity of the first of the pair of elongated members, to which 
extremity the alternating electrical signal is supplied, and one extremity 
of the second of the pair of elongated members, which one extremity is 
located on the same side of the capacitively coupling member as the 
extremity of the the first of the pair of elongated members receiving the 
alternating electrical signal. The third structural embodiment of the 
position sensor is illustrated in FIGS. 17 through 22, wherein the 
position sensor comprises three individual position sensors respectively 
comprising a single or a pair of elongated members, wherein each of the 
three individual position sensors has the same construction and the mode 
of operation as that defined by the afore-mentioned first or second 
structural embodiment of the position sensor. The first of the three 
individual position sensor has a first capacitively coupling member 
displaceable or movable following the length of the first individual 
position sensor, while the second and third individual position sensor 
respectively have a second and third capacitively coupling members fixedly 
disposed at two opposite extremities of the combination of the three 
individual position sensors, respectively. The position of the first 
capacitively coupling member is determined as a function of the three 
phase angle differences respectively provided by the three individual 
position sensors. It should be understood that, in the actual practice of 
the invention, the phase angle difference or other electrical variable 
representing the phase angle difference such as the tangent or cotangent 
of the phase angle difference can be measured by using an appropriate 
electronic measuring device, and then the position of the target member 
can be determined as a function of the phase angle difference or other 
electrical variable representing the phase angle difference by using an 
empirically obtained mathematical relationship. It is imperative to 
enclose the assembly of the electrically functioning components of the 
position sensor within a grounded electromagnetically shielding enclosure 
and use electromagnetically shielded lead wires in supplying the 
alternating electrical signal and taking off the alternating electrical 
signals providing the phase angle difference. 
While the principles of the inventions have now been made clear by the 
illustrative embodiments shown and described, there will be many 
modifications of the structures, arrangements, proportions, elements and 
materials, which are immediately obvious to those skilled in the art and 
particularly adapted to the specific working environments and operating 
conditions in the practice of the invention without departing from those 
principles. It is not desired to limit the inventions to the particular 
illustrative embodiments shown and described and accordingly, all suitable 
modifications and equivalents may be regarded as falling within the scope 
of the inventions as defined by the claims which follow.