US3181547A - Pneumatic transmitters - Google Patents

Description

y 1955 J. 5. BENNETT 3,181,547

PNEUMATIC TRANSMITTERS Filed Jan. 22, 1962 F/GZI JAMES STEWART BEN/VET 7' BY AT TORNE Y United States Patent 3,131,547 PNEUMATIC TRANSMKTTERS James Stewart Bennett, Toronto, Gntario, Canada, as-

signor to Moore Products ('10., Philadelphia, Pa, a corporation of Pennsylvania Filed Jan. 22, 1962, er. No. 167,772 6 Claims. (Cl. 13782) This invention relates to pneumatic transmitters and more particularly to a transmitter which transmits a fluid pressure mathematically related to a condition.

It is the principal object of the present invention to provide a pneumatic transmitting device for producing a transmitted pressure which, in one embodiment of the invention, is linearly related to the rate of change of a pressure applied therein.

it is a further object of the present invention to provide a pneumatic transmitting device for producing a transmitted pressure which in another embodiment of the invention is proportional to the time integral of an error signal.

It is a further object of the present invention to provide a pneumatic transmitting device in which a needle valve is employed and provisions are made for compensating for the variation in restrictive effect of the needle valve with changes in the pressure level.

It is a further object of the present invention to provide a pneumatic transmitting device in which a needle valve is employed and a variable volume is provided for compensating for the Variation in restrictive effect of the needle valve with changes in the pressure level.

It is a further object of the present invention to provide a pneumatic relay having a linear relationship between the transmitted pressure and a time function of the input.

It is a further object of the present invention to provide a pneumatic integrating relay in which the output pressure has a linear relationship to the time integral oi. an error signal.

It is a further object of the present invention to provide a pneumatic difierenting relay in which the output pressure has a linear relationship to the rate of change of the input pressure.

Other objects and advantageous features will be apparent from the description and claims.

The nature and characteristic features of the invention will be more readily understood from the following description taken in connection with the accompanying drawings forming part thereof, in which:

FIGURE 1 is a vertical central sectional view of a pneumatic transmitter in accordance with the invention and which is adapted for a difiterenting action;

FIG. 2 is a horizontal sectional view taken approximately on the line 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 1 showing a relay for providing an integrating function; and

FIG. 4 is a horizontal sectional view taken approximately on the line 4-4 of FIG. 3. I

It should, of course, be understood that the description and drawings herein are illustrative merely, and that various modifications and changes can be made in the structure disclosed without departing from the spirit of the invention.

Like numeral refer to like parts throughout the several views.

Referring now more particularly to FIGS. 1 and 2 of the drawings, the fluid pressure transmitter there illustrated has a plurality of units in a stacked assembly which includes an upper housing section 3 with an interior chamber 9 therein having an atmospheric vent it), the chamber 9 being closed at the bottom by an upper diaphragm assembly 12. The upper diaphragm assembly Patented May 4 i955 12 has spaced diaphragms 13 with an interposed central spacer 14 and outer ring 15, and an atmospheric vent 16 extends through the ring from the space between the diaphragms 13.

The chamber 3 has a loading spring 18 therein hearing at one end on the diaphragm assembly 12 at the central spacer l4 and at the other end on a spring abutment 19 carried by an externally accessible threaded adjusting stem 29. The diaphragms 13 have a predetermined area as hereinafter referred to.

An intermediate diaphragm assembly 22 is provided spaced from the diaphragm assembly 12 by an outer spacer ring 23, and by a central spacer 24.

The intermediate diaphragm assembly 22 includes a pair of spaced diaphragms 25 with an interposed central spacer 26, and an outer spacer ring 27, and an atmospheric vent 28 extends through the ring 27 from the space between the diaphragms 25. The effective area of the diaphragms 25 is greater than and preferably a multiple of that of the diaphragms 13 to provide the desired gain as hereinafter pointed out.

A lower diaphragm assembly 30 is provided, spaced from the diaphragm assembly 22 by an outer spacer ring 31 and by a central spacer 32.

The lower diaphragm assembly 30 includes a pair of spaced diaphragms 33 with an interposed central spacer 34 and an outer spacer ring 35, and an atmospheric vent 36 extends through the ring from the space between the diaphragms.

The d-iaphragms 33 may have the same effective area as the diaphragrn 13.

The diaphragms 13, 25 and 33 are connected for simultaneous movement in response to the forces acting thereon by a connector '37 and a biasing spring 38 can be provided for urging the assembly in an opposite direction from that of the loading spring 18. The connector 37 can have a nozzle control face 39 thereon.

A pilot valve section 46 is provided having components of well known type such as are described in US. Patent No. 2,359,236, and with improvements as described in US. Patent No. 2,501,957. The pilot valve section 40 includes a chamber 41 having a shoulder 42 therein providing an abutment for the biasing spring 38 and has a pilot nozzle 43 controlled by the positioning of the nozzle control face 39 with respect thereto. The nozzle 43 has its input side communicating with a chamber 44 which is bounded by a diaphragm 45 urged upwardly by a spring 46 in a fluid delivery chamber 47. The diaphragm 45 can be of any preferred type and advantageously can have a porous central section for fluid discharge such as is shown in the US. patent to C. B. Moore, No. 2,501,957. The diaphragm 45, by its positioning, controls a valve 43 interposed between a fluid supply chamber 49 and the chamber 47.

The chamber 49 has a fluid supply connection so extending thereto. The supply connection 50 is connected to any suitable source of filtered fluid, such as air, under pressure. A fluid connection 51 is provided, connected through a restriction 52 to the chamber 44 and the chamber 41 is connected to the chamber 47 by a fluid connection 53.

The chamber 4'7 has a fluid pressure transmitting connection 54 connected thereto.

A chamber 55 is provided between the upper and intermediate diaphragm assemblies 12 and 22 and a chamber 56 is provided between the intermediate and lower diaphragm assemblies 22. and 30. The effective area of chamber 55 is preferably equal to that of chamber 56.

A signal input pressure connection 59 is provided for the introduction of a signal in the form of gaseous pressure, and for convenience only is shown as carried by ber.

the chamber 56.

The chamber 56 has connected thereto by a passageway 64 a variable volume chamber which'preferably includes a flexible metallic bellows 65 in a protective housing 66. The total volume which includes the volume between the contiguous diaphragms and 33, in the chamber 56, and the volume in the chamber of the bellows 65 is selected according to the stiffness of the bellows 65 which is employed such that the product of the restrictive eflect of the needle valve 63 times the capacitive effect of the volume remains constant at all pressure levels.

The mode of operation will now be pointed out.

Pressure fluid is supplied through the fluid supply connection 50 and the pressure of the fluid delivered past the valve 48 to the chamber 47 and to the delivery connection 54 is determined by the positioning of the diaphragm 45. The positioning of the diaphragm 45 is controlled by the nozzle 43 which nozzle 43 is controlled by the positioning of the connected diaphragm assemblies 12 22 and and the control face '39. The control of a nozzle by a diaphragm is well known in the art and appears at least as early as 1943 in a published paper of C. B. Moore, entitled The Pneumatic Null Balance System Applied to Industrial Instruments, and published by Moore Products Co., Philadelphia, Pennsylvania.

The input pressure signal supplied through the signal input pressure connection 69 is applied through the passageway 61 to the chamber 55 and through the passageway 62 through the restriction 63 to the chamber 56. The pressure in the chamber 41 is the same as that available for delivery.

Under steady state conditions the pressures in the chambers 55 and 56 are equal and oppositely applied and the pressure in the chamber 41 is also constant and is determined solely by the excess force of the loading spring 18 in opposition to the force of the biasing spring 38. If the input pressure is rising the pressure in the chamber 55 will be higher than that in the chamber 56 and the output pressure will increase in proportion to the differential established between the chambers 55 and 56.

In a differentiating relay it is desired that the output pressure be directly proportional to' the rate of change of the input and that a constant rate of change will give a constant output. If the output is constant then the differential pressure between the chambers 55 and 56 must be constant. This constant differential is effective across the restriction '63.

Assuming laminar flow in the restriction 63, the flow into chamber 56 is proportional to the differential and to the mean absolute pressure in the restriction 63. Since the mean of the absolute pressure is rising the flow will also be rising in proportion to the absolute pressure.

The flow into a volume chamber is proportional to the rate of change of pressure and to the volume of the cham- If the volume chamber is so made that its volume is proportional to the absolute pressure then the flow is also proportional to the absolute pressure and this is the same condition that characterizes the flow in restriction 63. The expansion of the volume chamber, including the V bellows 65, thus compensates for the compressibility of the gas in the restriction 63.

The setting of the restriction 63 determines the rate time constant.

Referring now more particularly to FIGS. 3 and 4 of the drawings, the fluid pressure transmitter there illus- The chamber 1&9 has connected thereto a variable volume chamber which includes a flexible metallic bellows in a protective housing 166. The chamber 169 has a loading spring 18 adjustable as before by an adjusting stem 2%.

An intermediate diaphragm assembly 22 and lower diaphragm assembly 36 are provided as before with a connector 3'7, biasing spring 38 and nozzle control face 39.

The pilot valve section 146 has a chamber 41 as before with a diaphragm 45, valve 48, fluid supply chamber 49, chamber 47, and supply connection 56.

The chamber 55, between the upper and intermediate diaphragm assemblies 12 and 22, has the signal input connection 66 connected thereto by the passageway 61.

The chamber 156 between the intermediate and lower diaphragm assemblies 22 and 30 is vented to atmosphere by a vent 67.

The chamber 199 is connected by a passageway 63 to the fluid pressure delivery connection 154 and a fluid connection 69 with a variable restriction 163 therein is provided to the relay output connection 153 which extends to the chamber 41. The variable restriction 163 may be a needle valve.

The total volume which includes the volume in the chamber 109 and the volume in the chamber of the bellows 165, and the volume in the delivery connection 154, is selected, as before, according to the stiffness of the bellows 165 such that the. product of the restrictive effect of the needle valve 163 times the capacitive effect of the volume remains constant at all pressure levels.

The mode of operation will now be pointed out.

Pressure fluid is supplied through the fluid supply connection 5f], the pressure of the fluid delivered past the valve 48 to the chamber 47' being determined by the positioning of the diaphragm 45. The diaphragm 45 is controlled by the nozzle 43 which nozzle 43 is controlled by the positioning of the connected diaphragm assemblies 12, 22 and 30 and the control face 39.

The input pressure signal is supplied through the signal input pressure connection 60 and is applied through the passageway 61 to the chamber 55 to control the position of the diaphragm assemblies 12, 22 and 30 and the control face 39. Y

The pressure, from the chamber 47 is effective immediately through the passageway 53 and in the chamber 41 against the lower diaphragm 33 and will be delayed because of the restriction 163 in reaching the chamber 109.

In an integrating relay it is desired that the output signal be proportional to the linear time integral of the input. For example, a constant input signal applied in the cham-' ber 55 should result in a steadily rising pressure in the connection 154.

The assembly which includes the diaphragm assemblies 12, 22 and 30, will remain in equilibrium so long as the differential pressure between the chambers 41 and 169 balances the constant input in chamber 55. This requires that the differential across the restriction 163 also be constant.

'As previously explained, the rate of flow through such a restriction is proportional to the mean absolute pressure at the restriction. This is also the rate of flow required by a volume subject to a rising pressure such volume having the characteristic that'it is proportional to the absolute pressure.

I claim: W

l. A fluid pressure transmitter comprisinga signalinput connection, a fluid pressure responsive device having a first chamber with a first pressure responsive member therein, a second chamber with 'a second pressure responsive member therein in opposed relation to said first pressure responsive member, and a mechanical connec tion between said members for movement of said members together members' for applying" a signal from said input connection to said device, a fluid connection connecting said chambers to each other, one of said chambers having a variable volume chamber connected thereto, a restriction in said fluid connection providing the sole access to and from said one of said chambers, a fluid supply connection, a fluid delivery connection, a valve interposed between said fluid supply and said fluid delivery connections, and members controlled by said device for controlling said valve.

2. A fluid pressure relay having a source of operating pressure fluid, a fluid pressure signal input connection, a pressure delivery connection, a fluid conduit between said source and said pressure delivery connection, a valve in said fluid conduit for controlling the delivery of fluid to said delivery connection, a plurality of opposed pressure responsive members for moving said valve, a first fluid passageway communicating between said members and having a restriction therein, a second fluid passageway applying a signal from said input connection to one of said pressure responsive members, a closed chamber having means for varying the volume of said chamber in response to the pressure therein, and a third fluid passageway between the other of said members and said chamber.

3. A fluid pressure relay having a first connection to a source of operating pressure fluid, a second connection to a fluid pressure signal, a pressure delivery connection, valve means interposed between said first connection and said pressure delivery connection, pressure responsive means for controlling said valve in response to a signal at said second connection, said means comprising two opposed pressure responsive members connected for simultaneous movement, a first fluid passageway communicating between said members and having a restriction therein, a second fluid passageway applying a signal from said input connection against one of said members, a closed chamber having means for varying the volume of said chamber in response to the pressure therein, and a third fluid passageway between the other of said members and said chamber.

4. A fluid pressure relay having a source of operating pressure fluid, a fluid pressure signal input connection, a valve connected to said source for controlling the delivery of pressure fluid, a pressure responsive device for controlling said valve, said device having a pair of opposed pressure responsive members, a first fluid passageway communicating between said members, and having a restriction therein, a second fluid passageway applying a signal from said input connection to said device, a third fluid passageway from said valve to one of said members, a closed chamber having means for varying the volume of said chamber in response to the pressure therein, a fourth fluid passageway between the other of said members and said chamber, and an output connection for sensing the pressure in the other of said chambers.

5. A fluid pressure transmitter comprising a signal input connection, a first chamber having a first pressure responsive member therein to which said input connection is connected, a fluid pressure responsive device having a pair of opposed chambers with pressure responsive members therein, a mechanical connection between said members for movement of said members together, a fluid connection connecting said chambers having a restriction therein, one of said opposed chambers having a variable volume chamber connected thereto, a fluid supply connection, a valve connected to said fluid supply connection, members controlled by said first pressure responsive member for controlling said valve, and an output connection for sensing the pressure in said variable volume chamber.

6. A fluid pressure transmitter comprising a signal input connection, a signal delivery connection, a fluid pressure responsive device having a first chamber with a first pressure responsive member therein, a second chamber with a second pressure responsive member therein in opposed relation to said first pressure responsive member, and a mechanical connection between said members for movement of said members together, one of said chambers having a variable volume chamber connected thereto, a fluid connection connecting said chambers to each other, a restriction in said connection, providing the sole access to and from one of said chambers, a connection between the other of said chambers and one of said signal connections, a fluid supply connection, a fluid delivery connection, a valve interposed between said fluid supply and said fluid delivery connections, and members controlled by said device for controlling said valve.

References Qited by the Examiner UNITED STATES PATENTS 2,517,051 8/50 Swenson.

2,635,618 4/53 Moore 137-85 2,950,729 8/60 Hortz 13785 3,124,147 3/64 Hallett 137-86 LAVERNE D. GEIGER, Primary Examiner.

MARTIN P. SCHWADRON, M. CARY NELSON,

Examiners.

Claims (1)

1. A FLUID PRESSURE TRANSMITTER COMPRISING A SIGNAL INPUT CONNECTION, A FLUID PRESSURE RESPONSIVE DEVICE HAVING A FIRST CHAMBER WITH A FIRST PRESSURE RESPONSIVE MEMBER THEREIN, A SECOND CHAMBER WITH A SECOND PRESSURE RESPONSIVE MEMBER THEREIN IN OPPOSED RELATION TO SAID FIRST PRESSURE RESPONSIVE MEMBER, AND A MECHANICAL CONNECTION BETWEEN SAID MEMBERS FOR MOVEMENT OF SAID MEMBERS TOGETHER, MEMBERS FOR APPLYING A SIGNAL FROM SAID INPUT CONNECTION TO SAID DEVICE, A FLUID CONNECTION CONNECTING SAID CHAMBERS TO EACH OTHER, ONE OF SAID CHAMBERS HAVING A VARIABLE VOLUME CHAMBER CONNECTED THERETO, A RESTRICTION IN SAID FLUID CONNECTION PROVIDING THE SOLE ACCESS TO AND FROM SAID SAID ONE OF SAID CHAMBERS, A FLUID SUPPLY CONNECTION, A FLUID DELIVERY CONNECTION, A VALVE INTERPOSED BETWEEN SAID FLUID SUPPLY AND SAID FLUID DELIVERY CONNECTIONS, AND MEMBERS CONTROLLED BY SAID DEVICE FOR CONTROLLING SAID VALVE.

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