Abstrict A gas flow meter includes a cylinder closed at its upper end and
slidably supported within a bearing ring. The cylinder side wall
is provided with openings. A gas flow is directed into the interior
of the cylinder which causes it to rise with respect to the bearing
ring and permitting the gas to flow out of the area of the openings
exposed above the bearing. During a constant flow of gas through
the cylinder the flow rate can be measured by the distance which
the cylinder has moved upwardly as indicated on a fixed marker positioned
adjacent to the cylinder. An electrical signal is also provided
by means of an electrical sensor positioned axially within the cylinder.
Claims What is claimed is:
1. A gas flow meter comprising a base, a pair of telescoping coaxial
cylinders having a common vertical axis, one of said cylinders being
axially movable with respect to the other cylinder and said other
cylinder being fixed with respect to said base, said movable cylinder
having a cap at its upper end, means for mounting the cylinders
in close sliding engagement so that gas flow may not pass therebetween,
said base being arranged to support the movable cylinder in its
lowermost position, means for directing gas to the inner of the
cylinders, one of the cylinders having a vertically extending opening
in it side wall to allow an increasing flow of gas to pass therethrough
as the movable cylinder is lifted by the differential pressure of
the gas flow through the meter, means defining an outlet for directing
gas flow out of the meter when it has passed through said opening,
a variable sensor element having a fixed portion thereof mounted
to said base, said sensor element including a moveable member connected
to the cap of said movable cylinder and extending downwardly therefrom
along the vertical axis of and within the cylinder, said movable
member of the sensor element being arranged to move axially along
said fixed portion of the sensor element, electrical circuitry connected
to said sensor element to produce an output signal directly proportional
to the amount of lift of the movable cylinder and the gas flow through
the meter, an indicator element mounted to the top of the movable
cylinder, and a linear scale fixed with respect to the base and
extending upwardly from the indicator element when the indicator
element is in its lowermost position and directly adjacent to the
indicator element and parallel to the cylinder axis to provide a
visual indication of gas flow through the meter.
2. A gas flow meter according to claim 1 wherein said movable member
of the sensor element comprises an electrically conductive member
having a pair of downwardly projecting ends, one end engaging said
fixed sensor element portion and the other end engaging an electrical
contact to complete a circuit through said electrical circuitry.
3. A gas flow meter according to claim 1 wherein said indicator
element comprises a portion of said cap.
4. A gas flow meter according to claim 1 wherein said fixed portion
of the variable sensor element comprises a longitudinally tapered
contact strip of conductive material on an insulating board and
wherein said movable member of the sensor element comprises a conductive
member with a first projecting end for establishing electrical contact
with said contact strip at positions longitudinally therealong,
said insulating board having a second contact strip mounted thereon,
and said conductive member having a second projecting end for continuous
sliding contact with said second contact strip to complete a circuit
to said electrical circuitry.
5. A gas flow meter according to claim 4 wherein said movable member
of the sensor element comprises a U-shaped member depending from
said cap with said first and second projecting ends extending downwardly
and adapted to engage said first and second contact strips on opposite
sides of the insulating board about the longitudinal axes of the
cylinders.
6. A gas flow meter according to claim 1 wherein said variable
sensor element comprises a capacitive transducer including a conductive
structure spaced outwardly of the vertical axis and fixed with respect
to said base and wherein said movable member thereof comprises a
conductive member extending along said vertical axis.
7. A gas flow meter according to claim 6 wherein said fixed portion
of the variable sensor element comprises a coaxial cylinder and
said movable member thereof comprises a rod.
8. A gas flow meter according to claim 1 wherein said fixed portion
of the variable sensor element comprises an inductive transducer
including a coil extending coaxially of the cylinders and fixed
with respect to said base and wherein said movable member of the
sensor element comprises a conductive member extending axially of
the coil.
9. A gas flow meter comprising a base, a pair of telescoping coaxial
cylinders having a common vertical axis, one of said cylinders being
axially movable with respect to the other cylinder and said other
cylinder being fixed with respect to said base, means for mounting
the cylinders in close sliding engagement so that gas flow may not
pass therebetween, said base being arranged to support the movable
cylinder in its lowermost position, means for directing gas to the
inner of the cylinders, one of the cylinders having a vertically
extending opening in its side wall to allow an increasing flow of
gas to pass therethrough as the movable cylinder is lifted by the
pressure differential of the gas flow through the meter, means defining
an outlet for directing gas flow out of the meter when it has passed
through said opening, a variable sensor element positioned axially
within one of said cylinders, said sensor element including a member
dependingly attached to the movable cylinder at the vertical axis
thereof and arranged to move axially with respect to the variable
sensor element as the movable cylinder is lifted, and electrical
circuitry connected to said sensor element to produce an output
signal proportional to the amount of vertical displacement of the
movable cylinder and the gas flow to said outlet, said variable
sensor element including a contact strip of conductive material
on an insulating board, said dependingly attached member comprising
a conductive member with a first projecting end for establishing
electrical contact with said contact strip at positions longitudinally
therealong, said insulating board having a second contact strip
mounted thereon, and said dependingly attached member having a second
projecting end for continuous sliding contact with said second contact
strip to complete a circuit to said electrical circuitry.
10. A gas flow meter according to claim 9 wherein said movable
member has an axially extending passage therein and a cap across
its upper end and wherein said dependingly attached member comprises
a U-shaped member depending from said cap with said first and second
projecting ends extending downwardly and adapted to engage said
first and second contact strips on opposite sides of the insulating
board.
11. A gas flow meter comprising a base, a pair of telescoping coaxial
cylinders having a common vertical axis, one of said cylinders being
axially movable with respect to the other cylinder and said other
cylinder being fixed with respect to said base, means for mounting
the cylinders in close sliding engagement so that gas flow may not
pass therebetween, said base being arranged to support the movable
cylinder in its lowermost position, means for directing gas to the
inner of the cylinders, one of the cylinders having a vertically
extending opening in its side wall to allow an increasing flow of
gas to pass therethrough as the movable cylinder is lifted by the
pressure differential of the gas flow through the meter, means defining
an outlet for directing gas flow out of the meter when it has passed
through said opening, a variable sensor element positioned axially
within one of said cylinders, said sensor element including a member
dependingly attached to the movable cylinder at the vertical axis
thereof and arranged to move axially with respect to the variable
sensor element as the movable cylinder is lifted, and electrical
circuitry connected to said sensor element to produce an output
signal proportional to the amount of vertical displacement of the
movable cylinder and the gas flow to said outlet, said variable
sensor element comprising a capacitive transducer including a conductive
structure spaced outwardly of the vertical axis and fixed with respect
to said base, and said dependingly attached member comprising a
conductive member extending along said vertical axis.
12. A gas flow meter according to claim 11 wherein said variable
sensor element comprises a coaxial cylinder and said dependingly
attached member comprises a rod.
13. A gas flow meter comprising a base, a pair of telescoping coaxial
cylinders having a common vertical axis, one of said cylinders being
axially movable with respect to the other cylinder and said other
cylinder being fixed with respect to said base, means for mounting
the cylinders in close sliding engagement so that gas flow may not
pass therebetween, said base being arranged to support the movable
cylinder in its lowermost position, means for directing gas to the
inner of the cylinders, one of the cylinders having a vertically
extending opening in its side wall to allow an increasing flow of
gas to pass therethrough as the movable cylinder is lifted by the
pressure differential of the gas flow through the meter, means defining
an outlet for directing gas flow out of the meter when it has passed
through said opening, a variable sensor element positioned axially
within one of said cylinders, said sensor element including a member
dependingly attached to the movable cylinder at the vertical axis
thereof and arranged to move axially with respect to the variable
sensor element as the movable cylinder is lifted, and electrical
circuitry connected to said sensor element to produce an output
signal proportional to the amount of vertical displacement of the
movable cylinder and the gas flow to said outlet, said movable cylinder
having an axially extending passage therein and including a cap
at its upper end, said dependingly attached member being secured
to the cap to depend therefrom adjacent the cylinder axis, and said
dependingly attached member having a pair of downwardly projecting
ends one end engaging a fixed portion of said variable sensor element
and the other end engaging an electrical contact to complete a circuit
through said electrical circuitry.
14. A gas flow meter comprising a base, a pair of telescoping coaxial
cylinders having a common vertical axis, one of said cylinders being
axially movable with respect to the other cylinder and said other
cylinder being fixed with respect to said base means for mounting
the cylinders in close sliding engagement so that gas flow may not
pass therebetween, said base being arranged to support the movable
cylinder in its lowermost position, means for directing gas to the
inner of the cylinders, one of the cylinders having a vertically
extending opening in its side wall to allow an increasing flow of
gas to pass therethrough as the movable cylinder is lifted by the
pressure differential of the gas flow through the meter, means defining
an outlet for directing gas flow out of the meter when it has passed
through said opening, a variable sensor element including an electrically
conductive strip positioned axially within the fixed one of said
cylinders, said sensor element further including an electrical contactor
dependingly attached to the upper end of the movable cylinder so
as to extend downwardly adjacent the vertical axis thereof and arranged
to contact and slide along the conductive strip as the movable cylinder
is lifted, and electrical circuitry connected to said conductive
strip to produce an output signal proportional to the amount of
vertical displacement of the movable cylinder and the gas flow to
said outlet.
15. A gas flow meter according to claim 14 wherein said opening
is in a cylindrical wall of the movable cylinder.
16. A gas flow meter according to claim 15 wherein said opening
comprises a series of vertically spaced openings in the cylinder
wall.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to gas flow meters, and more particularly,
it pertains to gas flow meters of an electro-mechanical type wherein
the differential pressure of gas flow through a pair of telescoping
members elevates one of the members with the amount of such elevation
being used as a gauge of the flow rate.
2. Description of the Prior Art
Gas flow meters as used by telephone companies provide some unique
problems with regard to their construction. To prevent moisture
damage to the individual telephone wires within the telephone cables,
the cables are typically filled with dry air under pressure. In
the event of a small break in the waterproof sheath surrounding
the telephone wires, the pressurized dry air flows outwardly through
the break preventing water penetration and continually drying the
broken surfaces, but it is imperative that such leaks be detected
and repaired early enough to prevent water damage to the cables
and the telephone wires therein. Gas flow meters are thus used to
measure the amount of gas flowing at many locations along the lengthy
cable network and are continuously monitored in order to determine
the location and severity of the break through which the air is
leaking.
A long standing problem in the maintenance of such pressurized
cable systems has been the search for a reliable low cost pressure
meter for accurately sensing and indicating the relatively low rates
of gas flow through such systems. Various transducers are available
for measuring such gas flow through enclosed systems including devices
which measure pressure drop across a structure presenting a known
resistance to the flow of gas, rotation of a vane-like structure
immersed in the gas, momentum transfer from the moving gas to a
fixed body immersed therein, the positive displacement of pistons
or nutating disks designed to allow a fixed volume of gas to pass
from inlet to outlet during each compressive or rotational cycle
of the piston or disk, and vertical displacement of a ball or other
device moving upwardly within a transparent tube whose internal
diameter increases with height and in which flow is directed upwardly
(such device commonly being known as a "rotometer").
One particular type of flow meter which has been used for the reading
of gas flow in pressurized cable systems is the telescoping member
or floating piston type wherein flow through the meter creates a
differential pressure to lift one member of a pair relative to the
other thereby exposing an ever-increasing opening to the flow of
gas. In such devices the amount of motion will be directly related
to the amount of gas flow through the meter. For example, a device
of such type is shown in my prior U.S. Pat. No. 4528858. As shown
in this patent, the movable member may have an electrical contactor
connected thereto to provide a continuous electrical signal to a
remote monitor.
Another example of a variable area gas flow meter utilizing the
floating piston or telescoping member construction is shown in prior
U.S. Pat. No. 3691834 to deFasselle et al. In the meter disclosed
in this patent, a floating piston contains an upper plate which
is adapted to slide along a marked post thereby providing a visual
reading of gas flow through the meter.
As shown in further prior patents to deFasselle et al, U.S. Pat.
Nos. 4489614 and 4787253 the floating number may be connected
to a sensing member so as to provide a continuous electrical output
signal indicative of gas flow through the meter.
SUMMARY OF THE INVENTION
With the present invention a gas flow meter is provided which is
relatively simple in structure and therefore inexpensive to produce
and yet which is highly reliable in providing both a visual signal
indicative of flow through the meter as well as an electrical signal
directly proportional to the gas flow through the meter.
In general, the gas flow meter of the present invention includes
a pair of telescoping cylinders with an opening, or series of openings,
being provided in one of the cylinders so that as the differential
pressure across the meter causes one of the cylinders to be elevated
with respect to the other an ever increasing opening is provided
to allow increased gas flow through the meter. Thus, the degree
of elevation of the movable cylinder is directly indicative of the
amount of gas flow through the meter.
It is a unique feature of the present invention that this flow
is metered by means of a sensing member the movable portion of which
depends axially from the movable cylinder to minimize the lateral
force or moment acting upon such cylinder as a result of the friction
necessarily introduced by the sliding contact between the movable
and stationary portions of the sensing member thereby reducing the
tendency of the cylinder to bind and providing an output free of
the variable frictional forces which plague many of the prior art
devices.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded isometric view of the gas flow meter of the
present invention.
FIG. 2 is a central section through the gas flow meter of the present
invention with the movable cylinder being shown in a raised position
to permit gas flow through the meter and with the uppermost and
lowermost positions of such movable cylinder being shown in dashed
lines.
FIG. 3 is a section taken along line 3--3 of FIG. 2.
FIG. 4 is a partial section taken generally along line 4--4 of
FIG. 3 and showing the rear side of the pc card and the sensing
member.
FIG. 5 is a central section similar to FIG. 2 but showing a second
embodiment of the gas flow meter of the present invention.
FIG. 6 is a further central section similar to FIGS. 2 and 5 but
showing a third embodiment of the gas flow meter of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1 a gas flow meter 20 embodying the present
invention is there shown in exploded view with the various components
thereof being separated for ease of illustration. The meter will
be seen to include a base 22 which, in the operation of the meter,
is adapted to be mounted in a vertical position (by appropriate
fasteners through the holes 21 at the four corners of the base)
so that its central cylinder block portion 23 projects forwardly
from lower and upper base sections 25 24 mounting the base to receive
gas inflow and outflow, respectively. A movable or floating cylinder
26 is slidably guided by means of a bearing ring 27 within a chamber
15 35 of the cylinder block 23 so that it may freely slide axially
on the surface of the bearing ring. An upper cover 28 of transparent
plastic materail is secured to the top of the cylinder block 23
and the upper section 24 of the face along a narrow edge 29 and
similarly, a lower cover or housing 30 is secured to this cylinder
block and lower portion 25 of the face along a narrow edge 31. It
will be noted that the lower base section 25 includes a forwardly
projecting portion 25a at the lower end thereof to which is attached,
by means of a pair of screws 33 a pc board 32 containing the electrical
sensor and electrical circuitry elements of the apparatus. The pc
board is arranged to be mounted to the base so that it will project
upwardly through the cylindrical chamber 35 in the cylinder block
23 and axially within the movable cylinder 26.
The float cylinder 26 will be seen from FIG. 1 to include a top
cap 38 from which depends an electrical contactor 36 adapted to
make engagement with a resistive potentiometer contact strip 37
on a flat face of the pc board 32. As also can be seen in FIG. 1
the wall of float cylinder 26 is provided with a plurality of vertically
arranged openings 34 which permit passage of gas through the cylinder
when the cylinder is elevated. A visual indicator pole 40 is mounted
atop the cylinder block 23 parallel to the axis of the float cylinder
26 and is adapted to receive and guide the float cylinder by means
of a notch 39 in a radially projecting flange 38a at the lower periphery
of the cap 38.
In operation, gas flow will be directed through an entry port 41
in the lower base section 25 and thence into the interior of the
float cylinder 26 which, in the absence of any gas pressure, will
be in its lowermost position with the flange 38a of cap 38 resting
atop the bearing ring 27. As gas pressure increases to initiate
the flow of the gas through the meter, the cylinder 26 will be lifted
from the bearing ring 27 thus allowing gas to pass through the uppermost
portion of the uppermost of the openings 34 in its side wall, into
the upper chamber of the meter and out through a port 42 in the
upper base section 24. Although individual openings 34 are cut into
the cylinder 26 rather than a single continuous vertical opening
so as to increase the rigidity and strength of the cylinder, it
will be noted that such openings 34 are continuous in the vertical
direction so that each unit of elevation of the tube will expose
a corresponding unit of area of the openings 34 permitting a corresponding
increase in flow of gas through the meter. The cylinder 26 will
continue to rise after gas flow is initiated until a sufficient
number of openings 34 or a portion thereof are elevated above the
bearing ring 27 to permit flow through the cylinder 26 at the system
flow rate, i.e. the flow rate which is to be measured between input
and output ports 41 42. Flow connections may be made with the passages
defining ports 41 and 42 (FIGS. 2 and 3) by any conventional means
as, for example, by means of a pair of nipples having o-ring seals
for sealing engagement with the walls of the passages.
As can be seen from FIGS. 2 and 3 the float cylinder 26 is arranged
for sliding engagement only at the bearing ring 27. The float cylinder
26 is constructed of a polished stainless steel and the bearing
ring of metallic material is precisely machined to provide clearance
between cylinder 26 and ring 27 which is typically two thousandths
of an inch or less. It is critical that this fit be loose enough
to assure free movement of cylinder 26 with minimal friction and
yet close enough to prevent any passage of gas between the outer
face of the cylinder and the bearing ring 27 so that all flow must
pass within the cylinder and out through the openings 34 to assure
accuracy of the flow measurement. As can be seen from FIGS. 2 and
3 the axial passageway 35 within the cylindrical block 23 is very
closely spaced from the outer surface of the float tube so as to
insure the alignment thereof but so as to impose no continuous frictional
forces thereon.
As can best be seen in FIG. 3 the cap 38 totally encloses the
upper end of the float cylinder 26 so as to prevent any passage
of gas therefrom. The cap is made of an insulating plastic material
so that there will be no conduction between the electrical contactor
36 and the metallic cylinder 26 and bearing ring 27. This electrical
contactor will be seen to be U-shaped in form with two parallel
and downwardly extending legs 36a, 36b which are closely spaced
about the vertical axis A of the cylinder block 23 and float cylinder
26. The contactor is mounted within an inner hub 46 at the center
of the cap and is rigidly secured thereto. At their lower ends,
each of the depending arms 36a, 36b is provided with a radially
inwardly directed projection 50 which is thus springingly engaged
with the associated contact strips on the pc board 32.
The pc board 32 and the electrical circuitry 60 carried thereby
are adapted to provide an output current through leads 62 out of
the meter through a passageway 63 in base section 25a and connector
64 and to remotely located gauges whereby the gas flow can be continuously
monitored. As previously mentioned, the pc card is mounted to the
base section 25a by means of a pair of screws 33 so that it extends
in a plane exactly passing through the central axis A of the float
cylinder 26. As can be seen in FIG. 1 the screws 33 serve to mount
the pc board against a flat surface 55 with a second surface 54
of the base section extending at a right angle to surface 55 to
position the side edge of the pc board so that the resistive potentiometer
strip 37 on the pc board will be precisely positioned adjacent the
center of the cylinder 26. The screws 33 also provide the electrical
connection between the electrical leads 62 and the electrical circuitry
60 (see FIG. 3). The contactor 36 serves to complete a circuit from
the resistive potentiometer strip 37 to a printed contact strip
53 on the backside of the pc card (FIG. 4) connected to the electrical
circuitry 60 through the pc card as shown. The resistive potentiometer
strip 37 is connected with the electrical circuitry 60 at its bottom
end (FIG. 3) and is further connected to the circuitry through a
parallel printed contact strip 52 at the other end. The resistance
value provided by the resistive potentiometer strip 37 between the
contactor 36 and circuitry 60 will thus be determined by the position
at which the projection 50 of contactor leg 36a contacts the strip
along the length thereof. While there are numerous circuits utilizing
a resistive potentiometer to provide a linear current output proportional
to the movement of the mechanical slider portion of the resistive
potentiometer element, a particularly useful circuit is disclosed
in my co-pending application entitled "Circuit for Generating
a Current Linearly Proportional to Displacement of a Movable Member",
Ser. No. 44020 filed on even date herewith. The disclosure of
this application is hereby specifically incorporated by reference
into the disclosure of the current application. It will be seen
that the resistive potentiometer strip 37 is tapered from bottom
to top so that as the float cylinder 26 moves upwardly the current
controlled by the strip 37 will increase proportionately when it
works with the electrical circuitry of the aforesaid copending patent
application.
It is an important feature of the present invention that the variable
sensing element, i.e., the contactor 36 and the associated resistive
potentiometer strip 37 be located at or closely spaced about the
vertical axis A of the float cylinder 26 (FIG. 3) so that there
are minimal lateral forces imposed on the cylinder tending to introduce
inaccuracies into the readings as the cylinder 26 moves between
its uppermost and lowermost positions (FIG. 2).
Another important feature of the present invention is the provision
for both a visual as well as an electrical indication of gas flow
through the meter. The visual indication is provided by the inclusion
of the visual indicator pole 40 in the upper chamber of the meter
within the transparent cover 28 so that the flow rate can be visually
read at the same time that an electrical signal is sent to a remote
monitoring point from the circuitry 60. As can be best seen in FIG.
2 the pole 40 is marked off in uniform increments (each indicative
of a particular flow rate) with the lower edge of the flange 38a
of cap 38 being the movable marker which provides the visual reading.
It will be recognized that the pole 40 thus provides a dual function
of both indicating the flow rate as well as guiding the movable
cylinder 26 and preventing its rotation (by means of the notch 39
within the flange 38a).
A second embodiment 20A of the invention is shown in FIG. 5 wherein
it will be seen that the basic mechanical structure of the meter
is generally the same, with like parts to the first described embodiment
being given like reference numbers, but with the variable sensor
element being different from the sensor element of the first described
embodiment. In the flow meter 20A of FIG. 5 the resistive potentiometer
sensing structure and its associated circuitry have been changed
to a variable capacitive sensing means with associated circuitry.
This has necessitated some minor changes in the telescoping cylinder
mechanical arrangement. Thus, a conductive metal cap 138 covers
the top of the float cylinder 26 and centrally attached to the
cap to extend downwardly therefrom along the cylinder axis A is
a metallic rod 70. Positioned axially within the cylinder 26 is
a fixed metallic cylinder 72 which is securely fastened by screws
73 as shown to a forwardly projecting segment 25b of the lower base
section 25. The cylinder is precisely positioned about the axis
A by its securement within a notch 74 in the vertical face 75 of
the lower base projection 25b. The fixed cylinder 72 is electrically
connected to electrical circuitry 60a (as shown) and a second electrical
connection to the circuitry 60a is made, as shown, through a passage
76 in base cylinder block 23 to the bearing ring 27. It will thus
be appreciated that one side of a conductive circuit passes through
the bearing ring 27 metallic cylinder 26 and metal cap 138 to
the depending rod 70 while the other side of the circuit is made
directly to the fixed tube 72 from the circuitry 60a. As the float
cylinder 26 rises from its support on the bearing ring 27 it will
be appreciated that the capacitance between downwardly projecting
rod 70 and the upwardly projecting tube 72 will be reduced since
a decreased flux path is provided. This variable capacitor structure
is electrically connected to an electrical circuit 60a as aforedescribed
so that the circuitry can provide an output current signal which
is linearly proportional to the amount of movement of the capacitive
rod 70. While there are numerous circuits designed to provide such
a result, a particularly useful circuit is disclosed in my prior
U.S. Pat. No. 3869676 issued Mar. 4 1975. The disclosure of
the aforementioned patent is hereby specifically incorporated by
reference herein.
As can further be seen in FIG. 5 the electrical circuitry 60a
is mounted on a pc card 77 which is individually affixed to the
flat vertical face 75 of the lower base section projection 25b by
means of a pair of screws 78. The screws also serve to make the
electrical connection between the circuitry 60a and the lead wires
62 which are connected through a threaded connector plug 64 to remote
monitoring circuitry adapted to receive a linear current signal
indicative of flow through the meter as measured by the changing
capacitance due to the upward movement of rod 70.
A third embodiment of the present invention is shown in FIG. 6
wherein an inductive sensor, rather than a resistive or capacitive
sensor, is disclosed as the variable sensing means of the present
invention. In the apparatus 20B there shown, the movable cylinder
26 its upper cap 138 and downwardly depending sensor rod 70 may
be similar in structure to the corresponding elements of gas flow
meter 20A (FIG. 5). The lower base section 25 is similar to that
of gas flow meter 20A (FIG. 4) and includes a vertical face 75 extending
adjacent the axis A of the movable cylinder 26. A tube 80 of insulative
material is fixedly mounted within the movable cylinder 26 and about
the axis A thereof, and a coil 82 extends along the length thereof
adjacent to the sensor rod 70 in its lowered position. The tube
80 is fixed to the vertical face 75 within the notch 74 thereof
by means of screws 76 as shown. If the cylinder 26 and/or the central
rod 70 are made of a ferrous metal, then, as the cylinder 26 rises
under increasing flow through the meter, the inductance in the coil
82 will correspondingly decrease thereby making the decrease in
inductance a measure of the amount of motion in the float cylinder
26. If the cylinder 26 and/or the central rod 70 are made of a non-ferrous
metal, then, as the cylinder 26 rises under increasing flow through
the meter, the inductance in the coil 82 will correspondingly increase
thereby making the increase in inductance a measure of the amount
of motion in the float cylinder 26.
In order to measure this inductance, the ends of the coil are directed
to an electrical circuit 60b (as shown) which is mounted on a pc
card 88 that is attached to the face 75 by means of a pair of screws
78. As with the previously described embodiments, such screws 78
also serve to connect the electrical circuitry 60b with the electrical
leads 62 for communication with a remote monitoring point through
the connector plug 64. While various circuits may be used to provide
a linear output current signal proportional to the movement of the
sensor rod 70 and the change in inductance induced thereby, a particularly
useful series of circuits may be found in the Electrical Engineers
Handbook, McGraw Hill, Second Edition, 1982 by D. G. Fink and D.
Christianson (FIG. 1748 A through E).
Although the best modes contemplated for carrying out the present
invention have been herein shown and described, it will be apparent
that other modifications and variations may be made without departing
from what is regarded to be the subject matter of the invention. |