U.S. patent number 3,691,843 [Application Number 05/071,420] was granted by the patent office on 1972-09-19 for condition responsive apparatus.
This patent grant is currently assigned to Dresser Industries, Inc.. Invention is credited to Randall Goff, Joseph E. Gorgens, William A. Heske.
United States Patent |
3,691,843 |
Gorgens , et al. |
September 19, 1972 |
CONDITION RESPONSIVE APPARATUS
Abstract
Apparatus responsive to sensed magnitude of a variable condition
input to provide an output drive for operative connection to a
recorder, counter, or the like. The apparatus includes a control
operative in response to condition changes by discreet
bidirectional movement from a force balance null position at which
sensing means for emitting correlated bidirectional signals to the
output drive are at a nonemitting signal level.
Inventors: |
Gorgens; Joseph E. (Trumbull,
CT), Heske; William A. (Fairfield, CT), Goff; Randall
(Weston, CT) |
Assignee: |
Dresser Industries, Inc.
(Dallas, TX)
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Family
ID: |
22101212 |
Appl.
No.: |
05/071,420 |
Filed: |
September 11, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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859246 |
Sep 17, 1969 |
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732472 |
Apr 12, 1968 |
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565857 |
Jul 18, 1966 |
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Current U.S.
Class: |
73/701; 73/733;
73/705 |
Current CPC
Class: |
G01R
17/08 (20130101) |
Current International
Class: |
G01R
17/00 (20060101); G01R 17/08 (20060101); G01l
007/04 () |
Field of
Search: |
;73/398,388BN,411,382
;137/82 ;346/31,32,33 ;318/18,480 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Woodiel; Donald O.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a streamline continuation of application Ser.
No. 859,246 filed Sept. 17, 1969, now abandoned, which is a
continuation of application Ser. No. 732,472 filed Apr. 12, 1968
now abandoned, which is a continuation-in-part of application Ser.
No. 565,857 filed July 18, 1966, titled "Condition Responsive
Apparatus," and now abandoned.
Claims
What is claimed is:
1. A fluid pressure sensitive condition responsive apparatus
comprising; control means adapted for movement in one direction
from a null-position in response to a force change from an
increasing fluid pressure and adapted for movement in another
direction from a null-position in response to a force change from a
decreasing fluid pressure, sensing means comprising a pair of
spaced apart sensing elements located defining a null-position
therebetween for said control means to move relative thereto and
operable to provide a first differential signal in response to
movement of said control means in said one direction away from said
null-position and a second differential signal in response to
movement of said control means in said another direction away from
said null-position, differential amplifier means receiving signals
from said sensing means to emit an amplified signal correlated and
proportional thereto, bidirectional drive means receiving signals
from said amplifier and adapted to generate a motion force in a
first direction in response to a received signal correlated with
said first signal of said sensing means and a motion force in an
opposite direction in response to a received signal correlated with
said second signal of said sensing means, feedback means including
substantially linear spring means connected between said
bidirectional drive means and said control means, said feedback
means being responsive to said generated motion forces to return
said control means to said null-position in opposition to the force
change incurred thereby, and output means operable in conjunction
with said feedback means for connection to external means to be
operative thereby.
2. A condition responsive apparatus according to claim 1 wherein
said control means includes a variable condition responsive Bourdon
tube connected to produce movement thereof in response to changes
in the variable condition.
3. A condition responsive apparatus according to claim 1 wherein
said sensing means comprises a linear differential transducer
energized to its respective signal providing levels in response to
the respective movement of said control means.
4. A condition responsive apparatus according to claim 1 wherein
said sensing means comprises dual elements separately energized to
their signal providing levels in response to the respective
movement of said control means.
5. A condition responsive apparatus according to claim 4 wherein
said control means comprises a slitted vane movable interposed
between a light source and said dual elements which comprise
photoelectric cells.
6. A condition responsive apparatus according to claim 1 wherein
said sensing means comprises a pneumatic detector means and said
bidirectional drive means comprises a reversible air motor.
7. A condition responsive apparatus according to claim 6 wherein
said pneumatic detector means comprises a first pair of aligned
spaced apart nozzles adapted for connection to an air supply, and
said control means comprises a vane member adapted for movement in
the gap between said spaced apart aligned nozzles.
8. A condition responsive apparatus according to claim 7 wherein
said vane member is adapted for longitudinal movement between said
aligned nozzles and said pneumatic means further comprises
pneumatic relay means responsive to pressure changes in said
nozzles produced by movement of said vane member and adapted to
provide said first signal for driving said reversible air motor in
one direction and said second signal for driving said reversible
air motor in the opposite direction.
9. A condition responsive apparatus according to claim 7 wherein
said feedback means comprises a linear spring connected between
said vane member and said reversible air motor.
10. A condition responsive apparatus according to claim 9 wherein
said linear spring is attached to a threaded support member which
threadedly engages a threaded drive member connected for rotation
with said reversible air motor.
11. A condition responsive apparatus according to claim 7 wherein
said pneumatic detector means further comprises a second pair of
spaced apart aligned nozzles adjacent said first pair of aligned
nozzles and adapted for connection to an air supply, said vane
member is adapted for transverse movement in the gaps between said
first and second pairs of aligned nozzles and said pneumatic means
further comprises pneumatic relay means responsive to pressure
changes in said nozzles produced by movement of said vane member
and adapted to provide said first signal for driving said
reversible air motor in one direction and said second signal for
driving said reversible air motor in the opposite direction.
12. A condition responsive apparatus according to claim 11 wherein
said pneumatic detector means comprises a pneumatic amplifier means
for amplifying said first and second signals before application to
said reversible air motor.
13. A condition responsive apparatus according to claim 1 wherein
said control means comprises bidirectional rotational means and
said feedback means comprises a torsional spring means connected
between said control means and said bidirectional drive means.
14. A condition responsive apparatus according to claim 1 wherein
said sensing means comprises an electrical detector means and said
bidirectional drive means comprises a reversible electric
motor.
15. A condition responsive apparatus according to claim 14 wherein
said control means comprises a magnetic element adapted for
movement in response to the variable condition, and said electrical
detector means comprises a normally balanced circuit adapted in
response to movement of said magnetic element to provide said first
signal for driving said reversible electric motor in one direction
and said second signal for driving said reversible electric motor
in the opposite direction.
16. A condition responsive apparatus according to claim 1 wherein
said control means comprises a differential pressure responsive
device adapted for fluid communication connection with regions of
different pressure, and a movable member adapted to provide said
bidirectional movement in response to changes in the differential
pressure existing in the connected regions.
17. A condition responsive apparatus according to claim 16 wherein
said sensing means comprises a pneumatic detector means and said
bidirectional drive means comprises a reversible air motor.
18. A condition responsive apparatus according to claim 17 wherein
said pneumatic detector means comprises a first pair of aligned
spaced apart nozzles adapted for connection to an air supply, and
said movable member comprises a vane member adapted for movement in
the gap between said spaced apart aligned nozzles.
19. A condition responsive apparatus according to claim 18 wherein
said vane member is adapted for longitudinal movement between said
aligned nozzles and said pneumatic means further comprises
pneumatic relay means responsive to pressure changes in said
nozzles produced by movement of said vane member and adapted to
provide said first signal for driving said reversible air motor in
one direction and said different signal for driving said reversible
air motor in the opposite direction.
20. A condition responsive apparatus comprising; a light source, a
vane having slit and adapted for bidirectional movement from a
null-position past said light source in response to a variable
condition, dual photoelectric cells separately energized to their
signal providing levels by light received from said source through
said vane slit in response to appropriate movement of said vane,
said cells providing a first signal in response to movement of said
vane in one direction from said null-position and a second signal
in response to movement of said vane in the other direction from
said null-position, bidirectional drive means actuated by said cell
signals and adapted to generate one motion in response to said
first signal and a different motion in response to said second
signal, feedback means comprising a linear spring connected between
said bidirectional drive means and said vane, said feedback means
being responsive to said generated motion to return said vane to
said null-position, and output means actuated concomitantly with
said feedback means for connection to external means to be
operative thereby.
21. A condition responsive apparatus according to claim 20
including compensating means to offset spring non-linearity through
changes in the helix angle thereof.
22. A condition responsive apparatus according to claim 20 wherein
said output means is connected to a digital counter readout means
adapted to record movement of said drive means.
23. A condition responsive apparatus according to claim 20 in which
the signals provided by said cells are differential signals and
there is included a differential amplifier to receive said cell
signals and emit an amplified signal correlated and proportional to
said received signals for actuating said bi-directional drive
means.
24. A condition responsive apparatus according to claim 23
including compensating means to offset spring non-linearity through
changes in the helix angle thereof.
25. A condition responsive apparatus according to claim 23 wherein
said output means is connected to a digital counter readout means
adapted to record movement of said drive means.
26. A condition responsive apparatus comprising; a light source, a
vane having a slit and adapted for bidirectional movement from a
null-position past said light source in response to a variable
condition, dual photoelectric cells separately energized to their
signal providing levels by light received from said source through
said vane slit in response to appropriate movement of said vane,
said cells being connected in a normally balanced circuit and
providing a first signal in response to movement of said vane in
one direction from said null-position and a second signal in
response to movement of said vane in the other direction form said
null-position, an amplifier including a conjoined stabilizer
circuit and receiving said cell signals to emit amplified signals
thereof, bidirectional drive means actuated by said amplifier
signals and adapted to generate one motion in response to an
amplified second signal, feedback means connected between said
bidirectional drive means and said vane, said feedback means being
responsive to said generated motion to return said vane to said
null-position, and output means actuated concomitantly with said
feedback means for connection to external means to be operative
thereby.
27. A condition responsive apparatus according to claim 26 in which
said stabilizer circuit comprises a phase lag network.
28. A condition responsive apparatus according to claim 26 in which
said stabilizer circuit comprises a phase lead network.
29. A condition responsive apparatus according to claim 26 in which
said stabilizer circuit comprises a phase lead-lag network.
30. A condition responsive apparatus according to claim 26 in which
said amplifier emits an amplified signal correleated and
proportional to the signal differential from said photoelectric
cells.
31. A condition responsive apparatus according to claim 26 wherein
said output means is connected to a digital counter readout means
adapted to record movement of said drive means.
32. A condition responsive apparatus according to claim 26 in which
the signals provided by said cells are differential signals and
said amplifier is a differential amplifier to emit amplified
signals correlated and proportional to the cell signals received
thereat.
33. A condition responsive apparatus according to claim 32 in which
said stabilizer circuit comprises a phase lag network.
Description
BACKGROUND OF THE INVENTION
The field of art to which this invention relates comprises, for
example, devices which provide an indication or control operation
in response to a particular variable condition such as fluid
pressure, temperature, fluid flow, motion, weight, etc.
It is known in the prior art to employ unidirectional force balance
devices for the above purposes which are responsive to an
interruption of a signal by whatever means. Exemplifying that type
of device in the prior art is U.S. Pat. No. 2,921,595 in which a
galvanometer positions a vane or baffle in interrupting relation
between a pair of axially aligned nozzles one of which normally
discharges and the other of which normally receives a constant air
supply. Prior systems of this basic type have suffered from various
individual and common disadvantages such as complex construction,
high cost, limited useful range, unreliability, inaccuracy,
etc.
SUMMARY
This invention relates generally to apparatus responsive to changes
in a given variable condition. As compared to such prior art
devices, the apparatus hereof is relatively simple and inexpensive
yet will more reliably sense a given variable condition and either
furnish accurate indication of the magnitude of the sensed variable
condition or effect a desired control function in response
thereto.
In accordance with this invention, a primary feature is the
provision of a condition responsive apparatus wherein the
bidirectional movement of a variable condition responsive control
mechanism is acknowledged by a sensing means. When activated, the
sensing means provides an amplified signal to selectively energize
a bidirectional feedback drive to restore the control mechanism to
a given null-position at which the drive is deenergized. Movement
of the drive can be used to actuate a suitable readout device which
either provides an indication of the variable condition or performs
a control function in response thereto. This null-balance and
bidirectionally controlled apparatus permits an extremely accurate
sensing and/or indication of the variable condition. The apparatus
can be operably electronic, electric, fluidic and where of the
latter type has the additional advantage of not requiring
electrical input or explosion proofing.
It is therefore an object of the invention to provide novel
apparatus responsive to changes in a given variable condition.
It is a further object of the invention to provide a novel
condition responsive device capable of operating a control function
in analogue correlation to condition changes.
It is a further object of the invention to provide a device in
accordance with the last recited object in which operational
sensitivity can be either fluidic, electric, or electronic.
It is a still further object to provide novel condition responsive
apparatus in accordance with the aforesaid objects having a high
level of accuracy and reliability as compared to such prior art
devices without associated construction complexity and high
fabrication costs.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a preferred pneumatic
embodiment of the invention;
FIG. 2 is a graph illustrating the pressure-vane deflection
characteristics of the sensing device shown in FIG. 1;
FIG. 3 is a partial schematic representation of a modified readout
device for use with the embodiment of FIG. 1;
FIG. 4 is a schematic representation of a differential pressure
responsive control mechanism for use with the embodiment of FIG.
1;
FIG. 5 is a partial schematic representation of another invention
embodiment utilizing a torsional feedback arrangement;
FIG. 6 is a schematic representation of a modified pneumatic sensor
for use with the embodiment shown in FIG. 1;
FIG. 7 is a schematic representation of another invention
embodiment utilizing an electrical sensor and drive means;
FIG. 8 is a schematic representation of another invention
embodiment utilizing electronic sensing and drive means;
FIG. 9 is a schematic circuit diagram for the embodiment of FIG.
8;
FIG. 10 is a fragmentary schematic of optional mechanical features
for enhanced performance versatility; and
FIG. 11 is a side illustration of FIG. 10 as viewed from the
position 11--11 thereof.
Referring now to FIG. 1, there is shown a pneumatically operative
condition responsive apparatus according to the present invention
including the controller 11 which includes the vane member 12
connected to the conventional Bourdon tube 13 by the lever arm 14.
Associated with the controller 11 is the sensing device 15
including a first pair of spaced apart, aligned nozzles 16
connected between the low pressure air supply 17 and the pneumatic
relay 18 by the air supply tube 19. The sensing device 15 includes
a second pair of spaced apart, aligned nozzles 21 also connected
between the air supply 17 and the pneumatic relay 18.
Formed within the pneumatic relay 18 are the hollow actuating
chambers 23 and 24 which communicate with the air supply tubes 19
and 22 and are separated from the valve chambers 25 and 26 by the
flexible membranes 27 and 28. Attached to the membranes 27 and 28
are the valve stems 31 and 32 which seat in the valve channel 33
communicating with the high pressure air supply 34. The compression
springs 35 bias the valve stems 31 and 32 away from the valve
channel 33 in opposition to the forces applied to the membranes 27
and 28 by the air pressure within the actuating chambers 23 and 24.
Connecting the reversible drive air motor 36 with the valve
chambers 25 and 26 are the air supply tubes 37 and 38.
The feedback mechanism 41 connects the controller 11 with the
reversible air motor 36 and includes the linear spring 42 having
ends attached to the end of the Bourdon tube 13 and the internally
threaded support member 43 which engages the externally threaded
lead screw 44. The stabilizing guide bar 45 passes through an
aperture in the support member 43 so as to permit relative vertical
movement therebetween. Mounted between the spur gear 46 on the
reversible air motor 36 and the spur gear 47 of the feedback
mechanism 41 is a speed reduction spur gear assembly 48. The bevel
gear face 49 of the spur gear 47 drives the lead screw 44, the
digital display counter 51 and the digital printing counter 52
through the associated bevel gears 53. Attached for vertical
movement with the support 43 is the transcribing pen 54 positioned
for contact with the strip chart 55. The paper tape 56 is adapted
with a conventional actuating mechanism (not shown) for periodic
contact with the digital printing counter 52 so as to receive
impressions imposed by the raised digital wheels 57.
For operation of the invention embodiment shown in FIG. 1, the
Bourdon tube 13 is connected so as to be deflected in the
well-known manner by changes in a given variable condition such as
pressure. The Bourdon tube deflection moves the attached vane
member 12 transversely within the gaps between the first and second
pair of aligned air nozzles 16 and 21. Responsive to movement of
the vane member 12, the sensing device 15 actuates the reversible
air motor 36 which, through the feedback mechanism 41, returns the
vane member 12 to a given null-position which can be, as shown,
symmetrically spaced between the nozzles 16 and 21. The operation
can occur, for example, in the following manner: upon a variable
condition change which produces an upward movement of the Bourdon
tube 13 and attached vane member 12, the resultant reduction of air
flow from the air supply 17 into the air supply tube 19 will
provide a reduced pressure air signal within the actuating chamber
23. The reduction in air pressure exerted against the flexible
membrane 27 will permit the compression spring 35 to actuate the
valve stem 31 proving air communication between the high pressure
air supply 34 and the air supply tube 37 thus amplifying the
original signal provided by the air supply tube 19. Responsive to
the amplified air signal, the reversible air motor 36 will drive
the spur gear 46 in a counterclockwise direction causing clockwise
rotation of the speed reduction gear 48. This in turn will produce
counterclockwise rotation of the spur gear 47 and bevel face 49 and
clockwise rotation of the lead screw 44 thereby causing downward
movement of the associated support member 43. The corrective
movement will continue until a sufficient force is exerted via the
linear feedback spring 42 to pull the Bourdon tube 13 into a
position wherein the attached vane member 12 is again in its
null-position. At this time, the air pressure in the supply tube 19
and communicating chamber 23 will again be sufficient to force the
valve stem 31 into seating engagement with the valve channel 33
thereby deactivating the air motor 36. Similarly, a change in the
variable condition causing a downward movement of the Bourdon tube
13 and attached vane member will provide a different reduced
pressure air signal in the supply tube 22 and activating chamber
24. In this case, the valve stem 32 is activated to produce air
communication between the air supply 34 and the supply tube 38 for
driving the reversible air motor and connected spur gear 46 in a
clockwise direction. Thus, the speed reduction gear 48 will be
driven in a counterclockwise direction, the bevel face gear 49 in a
clockwise direction and the lead screw 44 in a counterclockwise
direction. The resultant upward movement of the support member 43
will reduce the tension applied to the Bourdon tube 13 by the
feedback spring 42 allowing the attached vane member 12 to return
to its null-position. Again, the return to null-balance is
accompanied by a pressure increase in the supply tube 22 and
actuating chamber 24 so as to close the valve 32 and deenergize the
air motor 36.
Because of the force balance system provided by the linear feedback
spring 42, the linear movement of the attached support member 43
required to maintain the null-balance is an analog function of the
variable condition which produces movement of the Bourdon tube 13.
Accordingly, the degree of movement experienced by the reversible
motor 36, the reduction gear 48, the bevel gear 49 and the lead
screw 44 are also analog functions of the sensed condition. Thus,
the visible indications exhibited by markings of the transcribing
pen 54 on the strip chart 55, the digital display on the counter 51
and the printed illustration pressed on the tape 56 by the printing
counter 52 are direct measurements of the variable condition being
monitored.
FIG. 2 is a graph illustrating the relationship between the
vertical deflection of the vane member 12 and the nozzle pressure
of the nozzles 16 and 21 with vane deflection in inches .times.
10.sup..sup.-3 plotted as the abscissa and nozzle pressure in
pounds per sq. in. plotted as the ordinate. The particular plotted
values shown were obtained utilizing a supply pressure of 20 psi
which is a typical instrument air supply pressure. Obviously, the
use of other supply pressures would establish different sets of
nozzle curves. Curve A represents the vane deflection-nozzle
pressure characteristic for the nozzle on supply tube 19, curve B
represents the vane deflection-nozzle pressure characteristic for
the nozzle on supply tube 22 and the point C represents the
null-balanced position of the vane member 12. Thus, for example, at
zero deflection the vane member 12 is in a position to totally
obstruct air flow into the supply tube 22 and to permit transfer of
about 10.2 psi pressure into supply tube 19 while at a position
about 5.5 .times. 10 .sup..sup.-3 inches higher the vane member 12
will completely obstruct flow into the supply tube 19 and will
permit transfer of about 10.2 psi pressure to the supply tube
22.
The compression springs 35 are selected to balance an air pressure
in the chambers 23 and 24 corresponding to the null-balance point C
and deflection of the vane member 12 in either direction will
effect a pressure reduction within one of the chambers 23 or 24
thereby actuating the corresponding valve stem, as described above.
Thus, the measured movement of the reversible air motor 36 which
returns the vane member 12 to the null position C after a change in
the variable condition sensed by the Bourdon tube 13 is not a
function of the vane deflection-nozzle pressure characteristics of
the individual nozzles 16 and 21. It will be obvious that this
allows a substantially greater accuracy of measurement than that
obtained by prior art devices which utilize a vane produced nozzle
pressure change to directly actuate an indicator device. In such a
system, the accuracy of the measurement is dependent upon the
linearity of the vane deflection-nozzle pressure characteristic of
the system and, as shown in FIG. 2, nozzle pressure in a typical
system is not a directly linear function of vane deflection.
In addition to providing measuring accuracy, the embodiment of FIG.
1 has the particular advantages of requiring neither an electrical
power input nor an explosion proofing. Furthermore, the arrangement
wherein the vane 12 is mounted for transverse movement between the
nozzles reduces the possibility of vibration-produced contact and
associated mechanical wear of these parts.
It will be appreciated that a conventional Bourdon tube, as shown
in FIG. 1, has a relatively low spring rate enabling it to be
restored to a null-position. Also, the spring rates of conventional
Bourdon tubes are in a magnitude range that can be balanced by
reasonably sized feedback springs. In other applications and
embodiments, however, one may utilize a control element, such as a
large diaphragm motor valve, having an extremely high spring rate.
For these cases, it can be desirable to use between the control
member and sensing means an additional spring member (not shown)
for converting movement of the control device into a suitable force
which could be balanced with a feedback spring of reasonable size.
Also, in the embodiment of FIG. 1, it will be understood that the
described operation simply requires relative movement between the
vane member 12 and nozzle pairs 16 and 21. Thus, one could adopt an
analogous arrangement wherein the vane is stationary and the nozzle
pairs mounted for movement in response to changes in the variable
condition.
FIG. 3 shows a modified invention embodiment wherein components
identical to those shown in FIG. 1 are given the same reference
numerals. As in the embodiment of FIG. 1, the reversible air motor
36 drives the lead screw 44 and the digital display counter 51.
However, in this embodiment the angular displacement .theta..sub.i
of the display counter drive shaft 61 is fed into the differential
gear 62 which also receives through the bevel gears 63 the angular
displacement .theta..sub.s of the drive shaft 64 connected to the
reference counter 65. Attached to the drive shaft 64 is the handle
66 with which the counter 65 can be set to a desired reference
point. The output shaft 67 of the differential gear 62 delivers an
output angular displacement of (1/100 )(.theta..sub.s -
.theta..sub.i ) to the actuator spring 68 via the pulley 69 and
connecting belt 70.
The actuator spring 68 can be used to actuate a variety of
conventional control devices (not shown) such as valves, rheostats,
switching arrays, etc. Typically, such control devices can be
actuated in response to a change in a sensed condition, as
indicated by the display counter 51, to restore the condition to a
given reference value set by the reference counter 65.
FIG. 4 shows another modification wherein components identical to
those shown in FIG. 1 are given the same reference numerals. As in
the embodiment of FIG. 1, movement of the vane member 12 is sensed
by a sensing circuit (not shown) which drives a reversible motor
(not shown) operatively connected to the lead screw 44 and linear
feedback spring 42. However, the controller 11 of FIG. 1 is
replaced by the controller 71 which includes as its primary element
the differential pressure cell 72. Separating the high pressure
chamber 73 and the low pressure chamber 74 is the center support 75
straddled by a pair of flexible membranes 76 spaced apart by the
spacer rod 77. Pivotally connected to the differential pressure
cell 72 at a fulcrum point 78 is the lever arm 79 having at one end
a notch 81 which seats the end of the force pin 82 attached to the
lower flexible membrane 76. The opposite end of the lever arm 79 is
attached to the vane member 12 by the support arm 83 which is
pivoted at 84 and adjustably secured by the slot and screw assembly
85 so as to allow vertical positioning of the vane member 12.
Supported by the lever arm 79 between the fulcrum point 78 and the
vane member 12 is the internally threaded collar 86 which engages
the spindle 87 at an externally threaded mid-portion 88. The
spindle 87 has one end rotatably attached to the feedback spring 42
and an opposite end connected to the handle 89. The supply tubes 91
provide fluid communication between the differential pressure
chambers 73 and 74 and the high and low pressure regions on
opposite sides of the flow restrictor 92 within the fluid
transmission pipe 93.
Except for the controller 71, the operation of this embodiment is
identical to that described for the embodiment of FIG. 1. After
setting a desired null-position for the vane member 12 with the
adjusting assembly 85 and providing a desired tension for the
feedback spring 42 by adjustment of the spindle 87 within the
collar 86, the controller 71 functions in the following manner: an
increased flow rate in the fluid transmission pipe 93 will increase
the pressure differential across the membranes 76 by increasing the
pressure in the chamber 73. This will cause a downward movement of
the membranes and attached force pin 82 causing clockwise rotation
of the lever arm 79. The resultant upward movement of the vane
member 12 will produce the control operations described in
connection with the embodiment of FIG. 1. As above, the actuated
reversible air motor 36 will, through the feedback spring 42,
increase the downward force applied to the lever arm 79 by the
shoulder 90 of the collar 86. Consequently, the vane member 12 will
be moved downwardly until it reaches the set null-position at which
time the control operations will stop. Similarly, a reduced flow
rate in the transmission pipe 93 will reduce the pressure in
chamber 73 permitting the force exerted by the feedback spring 42
to cause counterclockwise rotation of the lever arm 79. The
resultant downward movement of the vane member 12 will again
produce energization of the reversible air motor in a direction
which reduces the tension applied to the feedback spring 42 and
thereby again restores the vane member 12 to its null-position.
The readouts obtained in this embodiment by, for example, the
display counter 51, the printing counter 52 or the strip chart 55
will bear a non-linear dependency to the flow rate in the
transmission pipe 93. However, a linear measurement of flow can be
obtained by extracting the square root of the sensed differential
pressure with suitable feedback devices such as tapes and contoured
drums or a non-linear screw pitch on the lead screw. It will be
apparent that input controllers other than the Bourdon tube 13
shown in FIG. 1 and the differential pressure cell 72 shown in FIG.
4 can be effectively utilized with the present invention. Other
examples of suitable control elements include differential pressure
diaphragms for flow measurements, magnetic drag cups for speed
measurements, weight through-springs for load or weight
measurements, displacement through-springs for position
measurement, bellows and diaphragms for pressure and temperature
measurements, bimetal elements for temperature and flow
measurements, etc. One can also sense changes in electrical current
by using as a control device an electrical coil mounted for
movement in a constant magnetic field.
FIG. 5 shows another invention embodiment wherein components
identical to those shown in FIG. 1 are again given the same
reference numerals. This embodiment is similar to that shown in
FIG. 1 except that the linear feedback mechanism 41 is replaced by
a torsional feedback arrangement 95. The controller comprises the
control shaft 96, supported for rotation by the bearing surfaces
97, and the arm 98 which is adapted to sense a given variable
condition, for example weight W. Also secured to the shaft 96 is an
oppositely directed arm 99 which terminates with the vane member
12. The inner end of the torsional feedback spring 103 is attached
to the control shaft 96 while the outer end thereof is secured to
the feedback arm 102 which rotates with the output shaft 101 of the
reversible air motor 36.
The operation of this embodiment is again similar to that described
for the embodiment of FIG. 1. A change in the variable condition
produces rotation of the shaft 96 and connected arm 99 to move the
vane member 12 transversely in the gaps between the nozzles 16 and
21. This energizes the reversible air motor 36 via the pneumatic
amplifier relay 18 and the produced direction of motor rotation is
such as to change the torque applied to the shaft 96 by the
feedback spring 103. The corrective operation continues until the
vane member 12 has been returned to an original null-position.
Thus, feedback arrangements other than those provided by a linear
feedback spring such as that shown in FIG. 1 are possible. Still
other suitable feedback mechanisms will include lead-screw cams,
tape drives, arrangements utilizing non-linear screw pitches or
equivalent means to provide a non-linear measurement of movement,
etc.
FIG. 6 shows another embodiment of the invention in which elements
identical to those shown in FIG. 1 are again given the same
reference numerals. In this embodiment the sensing device 15 of
FIG. 1 is replaced by a modified pneumatic sensor 111 which
includes only a single pair of spaced apart, aligned nozzles 112
and 113. Each of the nozzles 112 and 113 is connected to a high
pressure air supply 114 by supply tubes 115 and 116 having flow
restrictors 117 and 118. Also connected to the supply tubes 115 and
116 on both sides of the flow restrictors 117 and 118 are the
pneumatic volume relays 119 and 121 which communicate with the
reversible air motor 36 via the actuating air tubes 122 and 123.
The vane member 124 is attached to the Bourdon tube 13 so as to be
moved thereby longitudinally in the gap between the aligned nozzles
112 and 113.
During typical operation, the vane member 124 will assume a
null-position mid way between the nozzles 112 and 113 establishing
equal given pressures within the supply tubes 117 and 118. At this
given pressure the volume relays 119 and 121 will remain closed and
the reversible motor 36 deenergized. However, upon a change in the
variable condition, the Bourdon tube 13 will, for example, move
upwardly causing the vane member 24 to move toward the nozzle 112
thereby raising the pressure in the supply tube 117. The increased
pressure will open the volume relay 119 and energize the reversible
motor 36 for rotation in a direction which will cause, as described
in connection with FIG. 1, the application of an increased tension
on the feedback spring 42. This restoring operation will continue
until the vane member 124 is returned to its null-position.
Similarly, an opposite change in the variable condition will
produce a downward movement of the Bourdon tube 13 causing the vane
member 124 to move toward the nozzle 113. The resultant pressure
increase in the supply tube 118 will open the volume relay 121 and
energize the reversible motor 36 for rotation in an opposite
direction thereby reducing the tension applied to feedback spring
42 and allowing the vane member 124 to again return to its
null-position.
FIG. 7 shows still another embodiment of the invention wherein
components identical to those shown in the preceding figures are
given the same reference numerals. In this embodiment, the
pneumatic sensors are replaced with the electrical sensor 131 and
the vane control members are replaced by the magnetic slug 132
connected between the Bourdon tube 13 and the linear feedback
spring 42. The electric sensor 131 includes a voltage divider 130
magnetically coupled with the slug 132 and having a first inductive
coil 133 connected between ground and the alternating current
voltage supply 140 by an amplifier 134 and the windings 135 of the
reversible electric servo motor 136. Also connected between voltage
supply 140 and ground are the second inductive coil 137 of the
voltage divider 130, the amplifier 138 and a second set of motor
windings 139 which are wound oppositely to the windings 135. The
electric servo motor 136 is connected to the feedback spring 42
with suitable mechanisms (not shown) similar to those shown in the
preceding figures.
During operation of this embodiment, the magnetic slug 132 will
normally assume a null-position wherein the inductive impedances of
the coils 133 and 137 are balanced, the oppositely wound windings
135 and 139 are equally energized and the motor 136 deactivated. A
movement of the Bourdon tube 13 and attached magnetic slug 132,
caused by a change in a sensed variable condition, will introduce a
relative impedance change in the coils 133 and 137 to unbalance the
electrical sensor circuit 131. Thus, for example, a relative
impedance increase of the inductive coil 133 will reduce the
current flow in the first winding 135 relative to that drawn by the
oppositely wound winding 139.
This will produce rotation of the servo motor 136 in a direction
causing the mechanically connected feedback spring 42 to exert a
restoring force on the slug 132 and attached Bourdon tube 13. The
operation will continue until the magnetic slug 132 has been
returned to its null-position. Similarly, a movement of the
magnetic slug 132 which causes a relative impedance increase of the
inductive coil 137 will result in a relatively higher current flow
through the winding 135 and produce an opposite direction of motor
rotation. This rotation will again effect a return of the magnetic
slug 132 to null-position and balancing of the electrical sensing
circuit 131. Obviously, other types of electrical error detectors
such as strain gauges, semi-conductor devices, differential
transformers, etc. could be utilized in this embodiment.
FIGS. 8 and 9 show still another embodiment of the invention
wherein components identical to those shown in the preceding
figures are given the same reference numbers. In this embodiment
the pneumatic sensors are replaced with components adapted for
electronic operation.
The error detector for this embodiment includes a vane here
designated 150 and having an intermediately located transverse slit
151 with a width dimension in the direction of movement of about
0.005- 0.015 inch. When in the null-balance position, the slit is
in optical alignment between constantly energized lamp 152 and an
intermediate position relative to dual photocell elements 155 and
156 producing a constant but minimal illumination on each. By
virtue of the balanced bridge circuit formed by resistors 157 and
158 intermediately biased to ground, a zero voltage differential
exists across the inputs to the amplifier-stabilizing network
generally designated 159 that includes a high gain amplifier 160.
Moving the light beam off center in either direction by a position
shift of slit 151 unbalances the bridge causing the amplifier to
drive D.C. servo motor 164. The motor direction is effective
through lead screw 44 and feedback spring 42 to return the slit to
its null-position at which the light beam rebalances the
bridge.
In order to provide smooth operation of the device and avoid
mechanical instability as a result of increased system sensitivity
from high gain setting of the amplifier 160, a stabilizer circuit
161 is provided as shown in FIG. 9 that includes an adjustable
potentiometer 162 for shunting feedback current to ground for gain
adjustment. Also provided as part of this network is booster
current circuit 163 for the amplifier. This instability sought to
be avoided usually takes the form of lead screw oscillation or
resonance in the feedback spring. By electrically compensating the
system for the dynamic response characteristics of these elements,
high apparatus sensitivity with good stability is obtained.
Many techniques are known for stabilizing servo systems including a
phase lead network, a phase lead-lag network, motor velocity
feedback, a phase lag network and the like. In a preferred
embodiment there is employed as shown a per se convention phase lag
network which is frequency sensitive with high overall amplifier
gain. This was found to provide superior stability with less
criticality of component values.
As a further operating refinement in connection with this
embodiment, the gearing in the feedback loop can be completely
eliminated. In accordance herewith, this is effected by employing a
frameless direct drive servo motor 164 placed operatively around
the lead screw 44 selected of fine pitch. The counter drives under
these circumstances is taken directly from lead screw 44 via an
appropriate coupling or timing belt connection as most suitably
accommodates the particular counter employed. Other refinements
and/or variations should be apparent including the substitution of
A.C. components for the D.C. components shown. Likewise while the
error detector is shown as a dual element photocell, it can be any
motion sensing device such as a linear variable differential
transformer, a strain gauge transducer, a potentiometric type
transducer, or the like.
Referring now to FIGS. 10 and 11, there is illustrated further
operative mechanical features which singularly or collectively can
optionally be employed on any of the aforementioned embodiments
hereof. These features include a span adjustment designated 168, a
temperature compensator designated 169, and a linearized rotator
170 for lead screw 44.
Span adjustment permits change in the effective force exerted by
the Bourdon tube 13 in response to a given change in condition
pressure. This is achieved by the adjustment mechanism 168
interposed between the sealed end of the Bourdon tube and spring 42
permitting axial displacement of the tube end relative to the axis
of screw 44 and to the theoretical rotational center of the tube.
The mechanism includes an elongated vane span arm 174 supporting
vane 12 or 150 and having a flexure pivot support at one end via
leaf springs 175 and 176. At an intermediate location along the arm
length it receives feedback spring 42 secured thereto. Integrally
extending upward from the span arm is a fold-over flange 177 having
an elongated adjustment slot extending generally parallel to the
arm length. Spaced from the latter flange is a comparable flange
178 secured to the end of Bourdon tube 13. Supported in slidable
overlying relation to each of these flanges are span slides 180 and
181 joined by flexure leaf spring 186 and having elongated
adjustment slots 182 overlying the corresponding flange slots
through which to be secured in presettable position to their
respective flanges via screws 183. By this means, transverse
relocation of the tube end relative to the axis of screw 44 can be
easily and simply set for any appropriate and plausible operative
span response.
Since Bourdon tube motion cannot always be constructed precisely
parallel to the feedback spring axis, some motion perpendicular to
that axis occurs which, of course, is not balanced by the feedback
spring. The flexure therefore provided by spring 186 assures that
the Bourdon tube returns to its starting position without imposing
undue and unwanted strain on the other components.
Temperature compensation via compensator 169 may be desired where
the apparatus is subject to wide temperature variations. For these
purposes, it is preferable at the onset to minimize compensation
requirements by using a feedback spring having a spring rate
substantially unaffected by temperature changes. This is
accomplished by employing spring materials such as Ni-Span C and
ISO-Elastic being trademarks respectively of International Nickel
Co. and John Chatillan & Sons.
To temperature compensate for indication shift-requiring a "zero"
position change of the servo, there is as provided herein
interposed between span arm 175 and vane 150 a bimetallic strip 187
which compensatingly reorients the null-position of slit 151
relative to photocells 155 and 156. Strip motion with temperature
can be adjusted by an appropriate resetting of the clamping screw
188. It is obvious that a thermistor could be used in place of one
of the bridge resistors 157 or 158 to also compensate for
temperature changes occuring there.
The use of the linearizing rotator 170 is necessary where lead
screw rotation and consequently spring rate is required to reflect
a highly precise more exact linear function of pressure in the
Bourdon tube or other sensing element. This is operative in
accordance herewith by providing guided angular displacement of
support member 43 as it advances vertically in response to lead
screw rotation. Guide 45 is eliminated such that as the support
member moves vertically, a guide pin 190 extending laterally from
the side of support 43 engages a vertical contoured cam slot 191 in
a stationary cam plate 192. This provides compensation to the
spring rate by adding or subtracting from the affect of lead screw
rotation offsetting spring nonlinearity occasioned by a changing
helix angle. The precise required cam pitch is of course dependent
on the spring geometry characteristics.
Obviously, many modifications and variations of the present
invention are possible in light of the above teachings.
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