US3283581A

US3283581A - Transmitter

Info

Publication number: US3283581A
Authority: US
Inventors: Bois Robert C Du; Goff Randall
Original assignee: Dresser Industries Inc
Current assignee: Dresser Industries Inc
Priority date: 1963-11-01
Filing date: 1963-11-01
Publication date: 1966-11-08
Anticipated expiration: 1983-11-08
Also published as: GB1076114A

Description

Nov. 8. 1966 R. c. DU BOIS ETAL 3,283,581

TRANSMI TTER Filed Nov. 1, 1963 INVENTO S ERT C. DUBOIS DALL GOFF ROB RAN ATTORNEY United States Patent G 3,283,581 TRANSMITTER Robert C. Du Bois, Fair-field, and Randall Goff, Weston,

Conn., assignors, by mesne assignments, to Dresser Industries, Inc., Dallas, Tex.

Filed Nov. 1, 1963, Ser. No. 324,596 13 Claims. (Cl. 73363.9)

This invention relates to transducers and more particularly relates to a novel and improved transducer for providing a pneumatic signal over a given pressure range in response to changes in temperature.

One method of providing remote reading or remote control of a changing condition is to provide what is frequently referred to as a transmiter relatively closely to the location of the condition being sensed. An exemplary type of transmitter utilizes a regulated pneumatic pressure supply to provide an air signal which is modulated over a given pressure range, for example between 3 and 15 p.s.i.g., in response to changes in the condition being sensed. This low pressure signal is then transmitted through tubing to a remote location where, for example, a more or less conventional pressure gauge may be utilized to provide an indication of the value of the condition being sensed. The signal pressure is at a relatively low value and is easy to handle by means of small, flexible tubing. Accordingly, such pneumatic transmitters afford good economics and flexibility of installation procedures. However, prior pneumatic transmitters themselves have for the most part been designed for use in process control requiring a degree and type of performance which results in a relatively high cost of manufacture of the transmitter. Accordingly, many less critical applications which are adapted for remote control or remote indication have not employed pneumatic transmitters as the expense thereof could not be justified.

It is the primary object of this invention to provide a novel and improved temperature responsive pneumatic transmitter which is of simplified construction and attendant lower manufacturing cost while at the same time has suflicient accuracy andsensitivity and, in particular, will provide a substantially linear response.

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

FIG. 1 is a plan view of a pneumatic transmitter incorporating the present invention with a portion of the housing being cut away, and with a portion of the instrument being shown in section, in order to reveal internal structure;

FIG. 2 is a cross-sectional view substantially along the line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional view substantially along the line 33 of FIG. 1; and

FIG. 4 is a longitudinal crosssectional view of a portion of the instrument of FIG. 1 illustrating an alternative construction thereof.

With reference to the drawing, and particularly FIGS. 1 and 2, an exemplary pneumatic transmitter incorporating the present invention comprises a generally cupshaped casing 10. Adjustably mounted on the underside of the casing is a plate 12. The plate 12 is held to the casing by a pair of screws 14 which fit through slots in the bottom wall 15 of the casing 10 and are threadably engaged in the plate 12. A cover plate 16 encloses the top of the casing and is held in place by a retaining ring or bezel 18. Depending from the underside of the plate Patented Nov. 8, 1966 12 and fixed thereto in coaxial relation with the casing 10 is a fitting or outlet 20. A portion of the outlet 20 is externally threaded to permit mounting of the same in a well or in the wall of a tank or duct. Depending from the outlet 20 is an elongated cylindrical member or stem 22 closed at its lower end by a plug 24. The stem 22 houses an elongated bimetal coil 26 extending longitudinally within the stern and having one end thereof fixed to the plug 24. The other or upper end of the coil 26 is fixed to one end of a shaft 28 extending generally coaxially of the stem 22. Adjacent the top of the coil 26 the shaft 28 is journalled in a friction bearing 30 which supports the shaft 28 laterally of the side walls of the stem 22. The stem 22, as shown in FIG. 2, extends into a bore extending coaxially of the socket 20. Also received within this bore and a counterbored portion thereof is a bearing 32 which supports the upper end portion of the shaft 28. The bearing 32 is fixed relative to the plate 12 and has a reduced diameter portion 34 extending through an open-ing in the bottom wall of the casing 10. The bottom wall of the casing fits closely about the reduced diameter portion 34, thus providing a pilot for the casing to assure that the same will remain concentric with the shaft 28. The shaft 28 extends beyond the upper end of the bearing 32 and mounted on the upper end of the shaft 28 is a flapper member 36 extending radially of the shaft 28.

Also mounted on the bottom wall of the casing 10 is a manifold 38. The manifold 38 is an elongated block of metal generally rectangular in cross-section. The ends of the manifold extend outwardly of the side wall of the casing 10, and one end of the manifold is provided with an inlet opening 40. The bordering edge portion of the inlet 48 is threaded to receive .a conduit leading from a source of pressure which is preferably regulated. The manifold is further provided with a central passage 42 in one end of which is threaded a throttle screw 44 having a relatively small diameter passage 46 providing communicat-ion bet-ween the inlet 40 and central passage 42. At the other end of the passage 42 the manifold is provided with an outlet opening 48, the bordering edge portion of Which is threaded in order to receive a conduit for conducting outlet air -to a remote position for either a control or indication function. For example, the outlet 48 may be connected to a pressure gauge of the Bourdon tube type.

The manifold is further provided with a branch passage, communicating at one end with the central pasage 42 at a point intermediate the throttle screw 44 and outlet 48. The other end of the branch passage opens outwardly of the manifold. Threadably received within this opening is a nozzle 50 having a passage communicating at one end with the central passage 42 and its other end opening outwardly of the manifold in registry with a portion 52 of the flapper 36. The flapper 36 is preferably fabricated from a strip of flat sheet metal with the portion 52 being deformed out of the general plane of the central portion of the flapper so as to lie in a plane parallel to the axis of the shaft 28. This portion 52 of the flapper is sufficiently wide that it extends beyond the boundaries of the outlet or orifice of the nozzle in all directions. The other end of the flapper is also deformed degrees out of the general plane of the center portion of the flapper and terminates in a turned over portion 54 which is displaced toward the manifold 38. The end 54 of the flapper is normally closed spaced relative to the manifold to proved a stop to a limit movement of the flapper in a counter clockwise direction as viewed in FIG. 1.

In the operation of the device just described, the stem 22 is exposed to the temperature, the value of which it is desired to indicate or control at a remote location. The

inlet of the manifold is connected to a regulated pressurized air supply whereby air will flow through the throttle 46, central passage 42 and out of the outlet 48 to a remote instrument such as a receiver gauge. The air in the passage 42 will also flow outwardly through the nozzle 50 to the interior of the casing. In this connection, the casing is vented by means of spacing between the side wall of the casing and the manifold 38 at the points where the manifold extends out of the casing. This spacing is sufficient to provide a vent greater in area than the discharge orifice of the nozzle to avoid back pressure in the casing. The portion '52 of the flapper 36 overlies the outlet of the nozzle 50 to regulate the air flow from the nozzle. The cross-sectional area of the nozzle, and particularly that of the smaller outlet passage 58 thereof, is greater than the cross-sectional area of the passage 46 in the throttle screw 44. Thus as the flapper portion 52 is moved toward and away from the outlet arifice of the nozzle 50, the pressure within the passage 42 and thus the pressure at the remote location will vary.

The angular position of the flapper 36 about the axis of the shaft 28 is in part determined by the ambient temperature of bimetal coil 26, the upper end of which tends to rotate about the axis of the shaft 28 in response to changes in temperature to which the coil is exposed. Thus as the temperature changes, the bimetal coil will tend to rotate the shaft 28 to move the portion 52 of the flapper toward or away from the nozzle 50, so as to effect an increase or decrease of the pressure within the passage 42 and thus at the outlet 48 of the manifold. In the embodiment being described, the flapper portion 52 is relatively stiff and is not flexed by the air issuing from the nozzle 50. The flapper and nozzle thus form a variable area restriction to control the flow of air from the manifold. The orifice outlet of the nozzle is preferably sharp-edged, and the nominal distance between the outlet orifice and the flapper is quite small, as compared to the diameter of the nozzle outlet orifice. Because of these configurations, the force exerted on the flapper by the air exhausting from the nozzle may be assumed to be equal to the area of the nozzle orifice outlet times the pressure of the air at all positions of the flapper over the nominal range of movement of the flapper. At any given temperature within the nominal range of the transmitter, the torque on the shaft 28 developed by the bimetal coil 26 is balanced by the force on the flapper developed by the air jet from the nozzle 50. Accordingly, with an increase in temperature there will be a corresponding increase in torque developed by the bimetal coil, and this increase will tend to move the flapper toward the nozzle, thereby increasing nozzle pressure until the bimetal torque is again balanced by force on the flapper developed by the air exhausting from the nozzle. As nozzle pressure will be equal to the pressure within the central passage 42 of the manifold and thus the pressure at the outlet 48 of the manifold, the pressure transmitted to the remote location is related directly to the temperature being sensed by the bimetal coil 26.

In a nozzle flapper system where the flapper is positively driven, it is a characteristic of the system that the relationship between output pressure and nozzle to flapper distance is non-linear. This non-linearity would be present in a device of the type described if the flapper movement relative to the nozzle was controlled solely by the temperature induced motion of the bimetal coil. However, in accordance with the present invention, the bimetal coil 26 is fabricated in dimensions and of material selected to provide the coil with a spring rate which is sulficiently low that the temperature induced unrestrained defiection of the nozzle controlling portion of the flapper will, in the absence of nozzle pressure, over the nominal temperature range of the instrument, be sufliciently large as compared to actual flapper movement over the nominal pressure range of the instrument that the output pressure versus temperature sensed relation will be substantially linear. Also, the flapper nozzle system is dimensioned and constructed to provide that a full scale change in output pressure from the manifold may be obtained with a very small movement of the flapper; this coupled with the low spring rate of the bimetal permits full scale movement of the flapper with a very small change in torque. Thus, in accordance with the invention, as the ambient temperature increases, the torque of the bimetal coil will increase tending to rotate the flapper towards the nozzle. However, movement of the flapper towards the nozzle re sults in an increase in the pressure in the nozzle passage and thus the pressure of the air directed at the flapper to tend to rotate the same in the opposite direction and away from the nozzle. The flapper will thus finally be positioned at a point wherein the forces exerted by the bimetal and by the air stream from the nozzle are balanced, providing a force balanced closed loop system incorporating a feed back which provides substantially improved linearity over that obtained when the flapper is driven positively.

In order to provide accuracy and ease of calibration of the instrument, it is important that the nozzle be sharpedged and clean or, in other words, without burrs or nicks. Also it is important that the flapper be squared relative to the nozzle or, in other words, that it be parallel to the general plane of the orifice. An exemplary transmitter incorporating the present invention might utilize a bimetal coil spring having a torque constant of approximately 2.4 X 10 inch. -lbs per degree Fahrenheit with the unrestrained deflection of the bimetal over the nominal temperature range of the instrument of 50 degrees Fahrenheit being approximately 16 degrees. Torque constant is defined as the increase in torque provided by the bimetal coil for a given use in ambient temperature. The spacing of the flapper from the nozzle shall vary a distance on the order of about .001 to .003 over a full output range of the transmitter of from 3 to 15 p.s.i.g. With a nominal distance of approximately 1" between the pivot of the flapper and the center line of the nozzle, the actual range of movement of the nozzle controlling portion of the flapper corresponds to an angular movement of the shaft mounting the flapper of about 0.11 degrees, as compared to an unrestrained movement of about 16 degrees. The unrestrained lineal movement of the nozzle controlling portion of the flapper would be approximately .280" as compared to a movement of about .002" in actual operation. The change in torque of the coil over the nominal output pressure range of the instrument would be approximately 1.2 X 10- inch-lbs. The output orifice of the nozzle should have an area of approximately .001 in. With such an instrument non-linearity between temperature sensed and output pressure should be reduced to something less than 1% which is more than adequate for the purposes for which the instrument is intended.

In the embodiment of the invention just described, the bimetal coil not only acts :as the temperature sensitive driving element for the instrument, but at the same time provides a low spring rate resilient drive of the flapper. While the structure of the embodiment just described will be suitable for most applications, there are certain temperature ranges for which it is diflicult to provide a sufliciently low torque constant for the bimetal coil While at the same time provide the coil with other required characteristics, such as long-term stability. In such cases, the substantial linearity of the system may be preserved by utilizing a construction such as shown in FIG. 4. Here, the bimetal coil 126 develops a larger change in torque, when subjected to the desired full scale temperature change than does the coil 26 previously described. The coil is secured at its lower end to the plug 24. However, a torsion spring 128 connects the upper end of the coil 126 to the shaft 28. The torsion spring has a rate se lected to provide an output torque on the shaft 28 over the nominal temperature range of the instrument which is compatible with the torque exerted on the shaft by the flapper nozzle combination over the output range of say 3 to 15 p.s.i.g For example, if the bimetal coil specifically described above were used for a 200 degree Fahrenheit temperature differential, the change in torque over this temperature range would be approximately 4.8 X- inch.-lbs. .and the unrestrained deflection of the coil and corresponding angular movement of the flapper would be approximately 64 degrees. If it is a system characteristic that a torque change on the flapper of only 1.2 l0- inch-lbs. will provide a full scale change in output pressure, the spring 128- would be selected to provide an output torque of 1.2x l() inch-lbs. irrespective of the torque output of the bimetal 126 over the nominal temperature range of the instrument. For example, the torsional stiffness of the spring might be selected to be approximately 2.5x l0 inch-lbs. per angular degree. In this manner the effective torque output of the total system of the bimetal 126 and spring 128 is maintained at the same level as the coil 26 previously described. While the present embodiment has been described in terms of a coil spring 128, it is within the scope of the invention to use other spring means for the same purpose, such a the torsional resilience of the shaft 28, or a resilient drive of different configuration.

With reference back to FIG. 1, the device includes means for providing an adjustment of the temperature change which will provide a given change in output or nozzle pressure. In this connection, it will be observed that the output pressure of the nozzle 50 acts at a given radius of the shaft 28. By varying the radius at which the nozzle jet acts the relationship of temperature change to output pressure change will also be varied. Accordingly, the manifold 38 is mounted on the bottom wall of the casing 10 by means of screws 62 extending upwardly through elongated slots in the casing with the slots extending generally longitudinally of the manifold. By loosening the screws 62, the manifold may be adjusted longitudinally of itself and radially of the shaft 28. This Will vary the moment arm at which the nozzle pressure acts on the flapper. With a given bimetal coil, the shorter this moment arm the smaller the temperature change required to produce a given output pressure change and conversely the greater the moment arm, the greater the temperature change required to produce a given output pressure change. This adjustment is used to provide for minor adjustments in the instrument for a given bimetal ooil, but is not used to provide for major changes in temperature span, which are made by substitution of bimetal coils having appropriate torque-temperature char acteristics.

The device also includes a coarse and fine zero adjustment to permit setting of the transmitter to provide a specific output pressure at a given temperature. The coarse adjustment is provided by a resilient friction mounting of the flapper on the shaft 28. More particular and with reference to FIG. 3, the flapper 36 is mounted on a hub 64 which is press fit on the shaft 28 so as to be fixed relative thereto. The hub is provided with an axially facing annular shoulder 66 on which is seated the upper side of the flapper 36. The flapper is maintained against the shoulder 66 by a spring washer 68 retained on the hub 64 and pressing against the underside of the flapper. The spring force with which the washer 68 clamp the flapper to the hub is, under normal circumstances, sufficient to maintain the flapper fixed relative to the shaft.

The fine zero adjustment is provided by an eccentric pin 70 having a shaft 72 rotatably received within an aperture in the base plate 12. The eccentric 70 is received within an elongated slot 72 in the bottom wall of the casing 10. The slot 72 extends generally radially of the shaft 28 and the eccentric 70 engages the side walls of the slot. It will be remember that the manifold is secured to the bottom Wall of the casing. Hence, angular adjustment of the eccentric 70 will tend to move the entire casing 10, and thus the manifold 38, about the axis of the shaft 28 and hence vary the spacing between the 6 nozzle and the flapper. The elongated slots in the casing bottom wall which receive the screws 14 holding the casing to the plate 12 permit this angular adjustment of the casing. When the fine zero adjustment has been completed, the screws 14 are retightened to clamp the casing to the plate 12.

While the invention has been described in terms of the specific embodiment shown in the drawing, it will 'be apparent to those skilled in the art that various modifications in the construction of the device could be made without departing from the scope of the invention. In particular, while the temperature responsive driving element has been described in terms of a coil spring directly connected to a shaft which mounts directly for move ment therewith a flapper, it will be apparent that other bimetal springs configurations could be utilized and as mentioned above other means of connecting the bimetal spring in driving relation to a flapper could be utilized while remaining within the overall scope of this invention. Therefore, the foregoing description and accompanying drawing, while including limitations as to a specific embodiment of the invention, are not to be considered as limiting, but rather only as illustrative as to the overall scope of the invention, and the invention is to be limited only by the appended claims.

We claim:

1. A pneumatic temperature responsive transmitter comprising a casing, a flap-per and air nozzle system within said casing, a hollow stem projecting from said casing, temperature-responsive spring means Within said stem including a bimetal element for directly sensing a variable temperature condition, one end of the spring means being directly connected to said flapper to impose a torque thereon in opposition to the force of the air stream from said nozzle, the other end of said spring means being attached to said step, and means transmitting the air pressure in the nozzle system as a measurement of the temperature sensed by the spring means, the overall spring rate of said spring means being that it has an unrestrained temperature induced deflection which is very =la-rge as compared to the angular deflection of the flapper over a predetermined full scale temperature range and produces an actual torque on the flapper across said range which is the same as the change in torque on the flapper by the air stream throughout the system air pressure range.

2. A transmitter according to claim 1, wherein said spring means includes in series, between said stem and flapper, a pair of springs producing different output torques over the full scale temperature range.

3. A pneumatic transmitter comprising a temperature responsive spring means having a portion which deflects in response to changes in temperature, means for providing an output pressure varying over a predetermined temperature range including a nozzle and a flap er rotatably mounted on a shaft for movement toward and away from said nozzle to control the discharge therefrom, said spring means comprising a bimetal coil fixed at one end, and means connecting the other end of said coil to said flapper comp-rising a spring means constructed to provide a predetermined torque on said shaft which is less than the output torque of said bimetal coil over said predetermined temperature range, and said himeta-l coil being constructed to provide an unrestrained movement of the nozzle controlling portion of the flapper over a given temperature range which is large as compared to the actual movement of said portion over said predetermined temperature range.

4. A pneumatic transmitter comprising a spring means having a portion which deflects in response to changes in temperature, means for providing an output pressure varying over a predetermined range including a nozzle, a flapper and a manifold, a shaft mounting said flapper for oscillation relative to said nozzle, said spring means being connected to drive said flapper, said manifold having a passage adapted to be connected at one end to a regulated pressure supply, the other end of said passage being adapted to be connected to a remote instrument, a restriction in said passage, a branch second passage conoonnected at one end to the first passage intermediate said restriction and said other end thereof, said nozzle providing an outlet to atmosphere for the other end of said branch passage, and means mounting said manifold for adjustment longitudinally of said flapper and radially of said shaft, said spring means being constructed to provide an unrest-rained movement of the nozzle controlling portion of the flapper over a given temperature range which is large as compared to the actual movement of said portion over said predetermined pressure range.

5. A pneumatic transmitter comprising a vented casing, a manifold mounted on and within the casing, and having a passage adapted to be connected at one end to a regulated air supply and at the other end to a remote pressure responsive instrument, a flow restriction in said passage, means providing a branch second passage communicating at one end with the first passage intermediate said restriction and other end of said first passage, a nozzle at the other end of said branch passage having a sharp-edged clean discharge orifice communicating with the interior of said casing, a shaft journalled on the casing, a flapper mounted for movement with said shaft and extending parallel to said discharge orifice in closely spaced relation thereto, a hollow stem depending from said casing concentrically of said shaft, and a bimetal coil in said stem, the lower end of the coil being fixed to said stem, means connecting the upper end of the coil to said shaft, said coil having an unrestrained temperature induced angular deflection over the nominal temperature range of the transmitter which is sufiiciently large as compared to the angular deflection of the flapper over the nominal pressure output range of the transmitter that the temperature sensed to output pressure characteristic of the transmitter is substantially linear.

6. In a pneumatic transmitter as described in claim 5, means mounting said nozzle for adjustment longitudinally of said flapper.

7. In a pneumatic transmitter as described in claim 5, means mounting said nozzle for adjustment angularly about the axis of said shaft to vary the spacing of the nozzle and flapper.

8. In a pneumatic transmitter as described in claim 5, said casing having a bottom wall, a plate underlying said bottom wall, an eccentric journalled on said plate g 4 and engaged within a slot in said bottom wall extending radially of said shaft whereby angular movement of said eccentric will effect movement of said plate angularly of and about said shaft, said manifold being secured to said plate for movement therewith relative to said casing.

9. In a pneumatic transmitter as described in claim 5, said manifold extending outwardly of the casing through apertures in the casing, the manifold being at least in part spaced from the bordering edge portion of at least one of said apertures to provide a vent for the casing of a size greater than the area of said discharge orifice.

10. In a pneumatic transmitter as described in claim 5, said means connecting said bimetal coil to said shaft being a coil spring disposed coaxially of said bimetal coil, one of the spring being fixed to the upper end of said coil, the other end of the spring being fixed to said shaft.

11. In a pneumatic transmitter as described in claim 5, said bimetal coil being fixed at its upper end directly to said shaft, said coil being operable to move the flapper toward said nozzle in response to an increase in temperature.

12. In a pneumatic transmitter as described in claim 5, means mounting said flap-per on said shaft comprising a member fixed to the shaft, said flapper being supported on said member, and resilient means yieldable holding said flapper in adjusted position on said member and angularly about said shaft.

13. In a pneumatic transmitter as described in claim 5, said transmitter having a nominal output pressure range of 3-15 p.s.i.-g., the range of movement of the portion of the flapper controlling nozzle discharge being on the order of .00

References Cited by the Examiner UNITED STATES PATENTS 2,829,492 4/ 1958 Klein-man 73-363.9 X 2,877,785 3/1959 Hildeu'brandt 73--388 2,911,991 11/ 1959 Pearl 73-388 OTHER REFERENCES Publication: Republic Data Book No.1001 Pneumatic Transmission, page 17, Republic Flow Meters Co., Chicago 47, Illinos, September 15, 1948.

LOUIS R. PRINCE, Primary Examiner.

D. M. YASICH, Assistant Examiner.

Claims

1. A PNEUMATIC TEMPERATURE RESPONSIVE TRANSMITTER COMPRISING A CASING, A FLAPPER AND AIR NOZZLE SYSTEM WITHIN SAID CASING, A HOLLOW STEM PROJECTING FROM SAID CASING, TEMPERATURE-RESPONSIVE SPRING MEANS WITHIN SAID STEM INCLUDING A BIMETAL ELEMENT FOR DIRECTLY SENSING A VARIABLE TEMPERATURE CONDITION, ONE END OF THE SPRING MEANS BEING DIRECTLY CONNECTED TO AID FLAPPER TO IMPOSE A TORQUE THEREON IN OPPOSITION TO THE FORCE OF THE AIR STREAM FROM SAID NOZZLE, THE OTHER END OF SAID SPRING MEANS BEING ATTACHED TO SAID STEP, AND MEANS TRANSMITTING THE AIR PRESSURE IN THE NOZZLE SYSTEM AS A MEASUREMENT OF THE TEMPERATURE SENSED BY THE SPRING MEANS, THE OVERALL SPRING RATE OF SAID SPRING MEANS BEING THAT IS HAS AN UNRESTRAINED TEMPERATURE INDUCED DEFLECTION WHICH IS VERY