US3814119A

US3814119A - Pneumatic controllers

Info

Publication number: US3814119A
Application number: US00270120A
Authority: US
Inventors: P Bertrand; M Nony
Original assignee: Compteurs Schlumberger SA
Current assignee: Compteurs Schlumberger SA
Priority date: 1971-07-12
Filing date: 1972-07-10
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: ES404684A1; BE785213A; DE2234303A1; FR2150570A1; GB1397966A; IT959945B; FR2150570B1; NL7209526A

Abstract

A pneumatic controller providing an outgoing signal proportional to the magnitude and time integral of the incoming signal comprises a first sealed-beam balance with a rigid beam attached onto a diaphragm defining four chambers, a second sealed-beam balance with two chambers performing the flow relay function, and a pressure balance with two chambers for copying the integral pressure. In the case of a pneumatic controller providing an outgoing signal proportional to the magnitude, time integral and time derivative of the incoming signal, the first sealed-beam balance is preceded by a time derivative stage comprised of a sealed-beam balance with four chambers similar in construction to the first sealed-beam balance.

Description

United States Patent 1191 Bertrand'et a1; 1 51 June 4, 1974 [54] PNEUMATIC CONTROLLERS 3,7l7,l62 2/1973 Prescottm 137/84 [75] Inventors: Pierre Bertrand, Jouy-en-Josas;

Maurice Nony, Billere, both of ft W. France Attorney, Agent, or F1rmW1ll1am R. Sherman, Stewart F. Moore [73] Assignee: Computeurs Schlumberger,

Montrouge, France 57 ABSTRACT [22] Filed: July 10, 1972 A pneumatic controller providing an outgoing signal proportional to the magnitude and time integral of the [21 1 Appl' 270l20 incoming signal comprises a first sealed-beam balance I with a rigid beam attached onto a diaphragm defining [30] Foreign Application Priority Data four chambers, a second sealed-beam balance with July 12. 1971 France 71.25472 chambers Performing e flow relay function, and a pressure balance with two chambers for copying the 52 us. (:1 137/86, 137/84, 137/82 integral Pressure: In the ease of a pneumatic controller [51 1m. (:1. .1 FlSb 5/00 Providing an Outgoing signal proportional to the [58] Field of Search; 137/86, 85, 84,82 niwdez time integral and time derivative of the incoming signal, the first sealed-beam balance is preceded 56] Refere Ci d by a time derivative stage comprised of a sealed-beam UNITED STATES PATENTS balance with four chambers similar in construction to i I the first sealed-beam balance. 3.292.852 l2/l966 Shmskey 137/86 X 3,590,691 7/1971 Prescott 137/82 3 Claims, 16 Drawing Figures R i K 1h 1 I P' 1 F C \l, .L' i i A J} 5 ML; T d 11 B B" 7 PA C PATENTEDJUN 4 924 SHEET 3 [IF 7 FIGS FIG.13

PATENTEDJux 4 1914 SHEET 5 0F 7 FISH fATENTEDJUN 4 I974 4 saw a nr 1 PNEUMATIC CONTROLLERS BACKGROUND F THE INVENTION 1.. Field of the Invention.

This invention relates to pneumatic controller apparatus used for the control of various industrial processes. V

A pneumatic controller can be defined as an apparatus which when supplied, for example from a measuring or like element, with an incoming signal M proportional to the extent to which the value of a variable of a quantity or process to be controlled has deviated from a required value will yield a pneumatic outgoing signal for utilization in a pneumatically operated regulating element adapted to restore the variable to the required value.

2. Description of the Prior Art e The most usual pneumatic controllers are of the PI (proportional integral) type, i.e. providing an outgoing signal proportional to the magnitude and time inte gral of the incoming signal, or the PID (proportional integral derivative) type i.e. providing an outgoing with rubber seals so asto form a system with two 2 a PID pneumatic controller with time derivative action on the incoming signal which has a miniature overall size and costs substantially less than diaphragm pneumatic controllers.

The invention resides in the substitution of the diaphragmstacks byseaIed-beam balance having two or four chambers. Such sealed-beam balance mainly comprises a flexiblediaphragm pressed between two metal plates cutout such that their central portion, forming a beam, is connected tov the peripheralportion of the metal plates by two strips forming a hinge, the plates diaphragm assembly being pressed between two flanges four chambers.

The pneumatic controller of the present invention is either of the PI type or of the PID type with a time derivative stage followed by a PI stage, said Pl stage comsignal proportional tothe magnitude, time integral and time derivativeof theincomin'g signal. The latter are commonly referred to as three-term pneumatic conjtrollers" and are mainly comprised of bellowshaving a' time derivative action on the error or of diaphragms having a time derivative action on the measurement. When bellows are used, the three-term J pneumatic controllers" have a single P-ID stage and an amplifier; in the case of diaphragms, they have aseparate derivative stage D, a PI stage and an amplifier. I

Bellows pneumatic controllers usually comprise a set of four bellows combined with a flapper-pivot assembly. The magnitude adjustment is mechanically set by changing the length of the lever arm. The time derivative action is carried out by introducing a time constant in the negative feedback and the time integral action is carried out by introducing a time constant in the positive feedback.

Diaphragm pneumatic controllers are comprised of a first stack of two diaphragms defining three chambers and performing a time derivative action withv a limited gain and of a second stack of three symmetrically disposed diaphragms defining four chambers and performing a PI action. The four chambers receive in addition to the inhibit signal C and the negative and positive feedback signals, the outgoing signal M of the derivative stage in the case of a PID pneumatic controller or the incoming signal M in the case of a PI pneumatic controller. The magnitude adjustment is made by modifying the positive feedback through a pressure divider bridge connected between the output pressure and the integral pressure, i.e. the delayed output pressure, copied by means of a pneumatic copier with a 1/1 gain. This pneumatic copier is used for eliminating the effect of the magnitude adjustment on the time integraladjustment.

The diaphragm pneumatic controllers, being of a more sophisticated design than that of the bellows pneumatic controllers, have the drawback of being quite complex and, therefore, have a relatively large overall size and high cost.

SUMMARY OF THE INVENTION The object of the invention is to provide for a PI or divider bridge;

prising a sealed-beam balance with four chambers which carry out the PI action, a sealed-beam balance with two'chambers which performs the amplification function without any permanent leak, and a pressure balance with two chambers which copies the'time integral pressure.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the manner in which the foregoing and the other objects ,are attained in accordance with the invention can be understood in detail, a particularly ad-' vantageous embodimentthereof will be described with reference to the accompanying drawings, which form apart of this specification, and wherein FIG. 'I is a schematic diagram of the derivative stage of a PID pneumatic controller;

FIG. 2 is a schematic diagram of the PI stage with its flow relay, its integral pressure copier and its pressure FIG. 3 is a plane view of a PID controller according to the invention;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3; i

FIG. 5 is a sectional view of a hinge taken along line 5-5 of FIG. 11;

FIG. 6 is an exploded view of the flow relay;

FIG. 7 is a sectional view of a sealed-beam taken along line 7-7 of FIG. 6.

FIG. 8 is a sectional view taken along line 8-8 of FIG. 4;

' FIG. 9 is a perspective view of the hinge of a beam (detail D of FIG. 6);

FIG. 10 is a sectional view ofan adjustment knob; FIG. 11 is an exploded view of the PI stage; FIG. 12 is an exploded view of the derivative stage;

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows in a diagrammatic way a time derivative stage which mainly comprises the assembly of a sealedbeam balance with its four chambers a, b, c and d. The

along line incoming signal M is applied to chamber b and the outcomprised of the nozzle B supplied at the supply pressure P through restriction means C The transfer function of the time derivative stage of FIG. 1 is given by the formula:

M'/M 1 T pll (T p/k) in which T,, is the time constant R,, X K,,, and p the Laplace variable of the transfer function. g I

FIG. 2 shows, also in a diagrammatic way, a PI stage which comprises a sealed-beam balance shown generally as E, a pneumatic copier shown generally as R, a flow relay shown generally as D, a pressure supply shown generally as PA and resistors shown generally as capital letters R and C with subscripts.

. P'= s+ 1 P', The transfer function of the assembly is S/M -c=:/ /1 g 1 l)/T,-P

' FIG. 3 and the following represent the embodiment of a PID pneumatic controller accordingto the invention.

FIGS. 3, 4 and 5 show a completely assembled PID pneumatic controller formed by the combination of a timederivative stage 1 and a PI stage 2. These two stages are mechanically secured together by means of screws 3,-and pneumatically connected by means of holes 4 sealed by gaskets 5. The PI stage 2 includes

mouldedpar'ts

6, 7 and 8, a direct-reverse pneumatic switch 9, a knob 10 for selecting the magnitude or proportional action, a knob 11 for the adjustment of the The sealed-beam balance E comprises four chambers a, b, c and d. The set point signal C is applied. to chamber a and the incoming-signal is applied to chamber b. When the pneumatic controller is of the PI type, the incoming signal is the measurement signal M; in the case of a PID pneumatic controller the incoming signal is the outgoing signal M provided by the time derivative stage shown in FIG. 1. A direct-reverse switch, schematically shownby the dotted line, enables one to reverse the direction of the pneumatic controller action. The negative feedback signal S is applied to chamber d and the positive feedback pressure P is applied to chamber c. The feedback pressure P is defined by S (P 0.2) bars The output pressure S is supplied to the chamber d.

The nozzle B operates under a constant differential pressure of 0.2 bars. The pressure P,- is obtained through the filter comprised of resistor R,- and capacitor K and is expressed by:

This pressure P,- is copied with high accuracy by a pneumatic copier R using a very flexible diaphragm m and a nozzle-vane system B" supplied at the pressure P through the resistor C such that l The pressure divider bridge is comprised of the f xed resistor C and the adjustable resistor R This bridge is connected'between S and P,. Its output pressure P is given by:

P (C /R, c.) s (R,/R, c.) P,

integralaction, two beam-diaphragm assemblies 12 and 13 and bored pins 14 for the pneumatic input, output and supply connections.

The beam-diaphragm assembly 12 is pressed between the moulded pieces 6 and 7 by means of screws 15. The crushing of this assembly is limited by bosses 16 of precise height which form part ofthe moulded'piece 6 and surround each screw 15'. Likewise, the beamdiaphra'gm assembly 13 is pressed between, the moulded pieces 7and 8 by screws 17, and the crushing of this assembly is limited by the bosses 18.

The timederivative stage 1 is formed'by'two moulded

pieces

19 and 20 which press a beam-diaphragm assembly 21 by means of screws 22. The crushing of this assembly is limited by bosses 23. A knob 24 permits one to adjust themagnitude of the derivative action.

Referring now to the exploded view of FIG. 6, the I chamber 25 of the moulded piece 7 is supplied with the input pressure. This pressure acts on the beamdiaphragm assembly 13 which is pressed between the

moulded pieces

7 and 8. The sealing isobtained by identical rubber seals 26 and 27. The bosses 18 go through the rubber seals 26 and 27 as well as through theassembly 13; their thickness is calculated so as to provide correct crushing of the seals. The chamber 28 is supplied with output pressure of the flow relay.

The beam-diaphragm assembly 13 is comprised of a flexiblediaphragm 29 disposed between two punched

metal plates

30 and 31. The pattern of these two plates is identical but their thickness is different. Plate 30 is thin and has a constant thickness. Plate 31 is thick and has two machine-finished narrow portions 32 and 33, said portions having been sufficiently thinned so as to be used as a flexible joint. The assembly operates like a rigid beam 34 articulated around the axis 7-7 in the outer edge 35. The rubber seals 26 and 27 are pressed along their outer edge 35 by means of the moulded

pieces

7 and 8 as well as along the axis 7-7 by the

portions

36 and 37 serving as knife-edges.

Referring now to FIG. 7 which is a sectional view of FIG. 6 taken along line 7-7 the knife-

edges

36 and 37 project by a value Y. beyond the facing even surfaces of the moulded

pieces

7 and 8. This extra thickness Y provides a greater crushing of the rubber seals 26 and 27 along line 7-7 than along the remaining part of the surface. The knife-edge 36 has two bulging portions 38 and 3.9 which are used to maintain tightness of the rubberseal 26 in the machine-finished portions 32 and 33 of the thick plate 31.

. The flow relay is of the type without permanent leak with double outlet-inlet valve as can be seen in FIG. 8

which is a sectional .view of FIG. 4 taken along line 8-8. The supply pressure is applied through the chamber 41 formed inside the piece 106. At the rest position, a small spring 42 holds the valve 40 against the admission seat 43. The exhaust towards the open air is accomplished through a seat 44 welded on the beam 34 which has an exhaust groove '45 emerging to the open air at 46. A spring 47 provides a substantially constant offset between the output pressure S prevailing in the chamber 28 and the input pressure P such that by the force of the spring 47. Then, the admission closes. Inversely, if the pressure P decreases, the beam 34 moves down and opens theexhaust, thereby decreasing S until the balance is again reached.

. is supplied with the supply pressure P, through a capil- FIG. 6 also shows the direct-reverse switch which comprises a moulded piece 9, having two

channels

48 and 49, pressed on the moulded piece 7 by means of a screw 51. Sealing is obtained by a gasket 50.

The moulded piece 7 has four

holes

52, 53, 54 and 55 opposite the holes of the gasket 50. The

holes

52 and 53 are supplied with the measurement signal in'the case of a PI pneumatic controller or the corrected measurement signal in the case of a PID pneumatic controller and the set point signal, respectively, and are in communication with the measurement and set point chambers of the pneumatic controller. In the disposition shown in FIG. 6, the measurement and set point signals are applied respectively to the measurement and setpoint chambers of the PI controller (direct direction). A rotation of 90 of the moulded piece 9 causes thechannels .48 and 49 .to apply, on the one hand, the measurement signal to the set point chamber and, on the other hand. .the set point signal to the measurement chamber (reverse direction).

FIG. 11 shows the Pl stage which comprises ,a moulded piece 6, a beam-diaphragm assembly 12 pressed between two identical rubber seals 56 and 57, and another moulded piece 7.

The beam-diaphragm assembly metal plates, a is comprised of a flexible diaphragm 58 attached between two identical punched plates. A thin plate 59 and a thick plate 60. The thick plate 60 hastwo portions (not shown) that are thinned according to an arrangement similar to'that of FIG. 9 in order to decreasethe stiffness of the articulation. The knife-

edges

61 and 62 of the moulded pieces 6 and 7 are identical to those described previously, but bosses 65 (FIG. 5)are provided in the moulded pieces 6 and 7 to prevent the narrow portions 63' and 64 of the rubber seals 56 and 57 from sliding laterally.

The moulded parts 621ml 7 are pressed against each other by screws 15 and the crushing of the rubber seals 56 and 57 is limited by bosses 16 at each screw hole.

sealed

chambers

66, 67, 68 and 69 corresponding to the four chambers a, b, d and c of FIG. 2 which relary (not shown). The vane is comprised of the beam 63, and the output pressure of this nozzle-vane system is applied to the input of the flow relay.

The pre'ssurecopi'er is comprised of the circular portion 71 of the diaphragm 58. An exhaust nozzle 72 is supplied at the pressure P,, through a capillary (not shown)..The input pressure is applied to the chamber 73 of the moulded piece 7; the chamber 73 corresponds to the capacitor K of FIG. 2. The resistors R and R of FIG. 2 are made directly in the

knobs

10 and 11 shown in FIG. 6. A 270 circular groove 85 of decreasing depth is provided in the

knobs

10 and 11. The moulded piece 7 has two spotfacings 83 and 84 receiving the

gaskets

76 and 77 on which the

knobs

10 and 11 are pressed by means of the screws 78 and flexible washers 79 shown in FIG. 10. As also shown in FIG. 10,

the moulded piece 7 has two

holes

81 and 82 opposite the holes 74 and of each gasket, respectively. The hole 74 communicates with the groove 85 of the knob while the hole 75 emerges in the deep circular groove 80 and communicates with the end 103 of the groove by means of a transverse hole 104 having its outer end closed off by a ball and its inner end in communication with in the deep circular groove 80. A conventional device (not shown) prevents the

gaskets

76 and 77 from turning and keeps the

holes

74 and 75 opposite the holes8l and 82 respectively. The pneumatic connection between the

holes

81 and 82 is thus made up of a portion of the groove 85, which portion is more or less long according to the position of the knob.

' The knob 10 is equipped with a dial graduated in (proportional adjustment) and the knob 11 is equipped with a dial graduated in minutes (integral time). It must be noted thatthe grooves 85 of thesetwo knobs are not identical in size. i g

Referring now to FIG. 12, the time derivative stage D designed in accordance with the diagram of FIG. 1 comprises, two moulded

pieces

19 and 20 holding a beam-diaphragm assembly 21 identical to the beamdiaphragm assembly 12 (except for the copier part) between two identical rubber seals 86 and 87. This assembly thus defines four

chambers

88, 89, 90 and 91 corresponding to the four chambers a, b, c and d of FIG. 1 respectively. The volume of the

chambers

88 and 90 forms the capacitor C,,. These two chambers are in communication by a slit in the knife-edge 92. The rigidity of this knife-edge is provided by a moulded wall 93. The beam 95 is used as a vane for the exhaust nozzle 94. The knob 24 is used for the adjustment of the derivative action and is identical to the knob 11 for the adjustment of the integral action. In the case of a PI pneumatic controller the holes 4 of the PI pneumatic controller (FIG. 3) are closed off by balls or by a shutoff plate.

The pneumatic connections between the various parts of the pneumatic controller are established by means of channels (channel 96 of FIG. 11 for example). The sealing of the channels is provided by the seals of the beams (seal 56 of FIG. 11 for example). The communications between the channels are provided by holes, such as 97 (FIG. 11) in the seals and beam, constituting the pneumatic equivalent of a twoside printed circuit board.

The preceding description has shown that each diaphragm stack of the prior art pneumatic controllers is replaced by .a single diaphragm attached on a rigid beam defining'two-or three measurement chambers.

Each beam is held between two moulded pieces pressing rubber seals the crushing of which can be adjusted. A particular embodiment of the articulations enables to obtain both a rigid beam and a flexible and sealed articulation.

The advantages of this embodiment are very important, namely, time saving for both the assembly and adjustment, and consequently saving in cost as-well as a smaller overall size and an easier maintenance.

While only one particular embodiment of the present invention and modes of practicing the invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. An improved pneumatic controller having a first I stage for providing an output signal proportional to the magnitude and time integral of an input signal comprisa first sealed beam balance with a housing and a beam structure defining four chambers; means for applying said input signal to a first one of said four chambers; means for applying a set point signal to a second one of said chambers, said second chamber being located on the opposite side of the beam from said first chamber; output'means for providing an output signal from a third one of said chambers, said third chamber being located on the same side of the beam as said first chamber; said output means including a sealed beam flow-relay; adjustable positive feedback means connected to said output means and to a fourth one of said chambers,

said positive feedback means including a copying I relay; and negative feedback means connected to said output means and said third chamber:

and wherein the sealed beam structures of said sealed beam balance and saidflow relay each comprise a flexible layer;

a thin metal layer disposed on'one side of said flexible layer, and a thick metal layer disposed on the other side of said flexible layer, said metal layers each being formed with openings defining an outer sec tion and an interior section; and first and second narrow bridge portions interconnecting said outer and interior sections along a beam pivot axis, said narrow portions of said thick metal layer having thinned segments to facilitate movement of the interior portionabout said pivot axis.

2. A controller according to claim 1 and wherein said flexiblelaye'r and said metal layers of said beam structure are each formed with openings adjacentthe edges thereof;

and wherein said housing includes protruding bosses located to mate with and pass through said openings in assembling the controller, and fastener means for passing through said bosses and clamping said housing and said be'am structure together, whereby said bosses limit the compression to which the-edges of said beam structure are.

subjected. 3. A controller according to claim 1 further comprising a second stage including a sealed beam balance with a housing and a beam structure defining four chambers; means for applying an input signal toa first one of said four chambers; output means for providing an output signal from a I second chamber,

said second chamber being located on the same side of the beam as said first chamber; third and fourth chambers located on the opposite side of the beam from said first and second chambers; feedback means connected between said output means and said third and fourth chambers, said third and fourth chambers being in communication and said output signal of the second stage being applied as the input signal of the first stage.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,814,119 DATED June t, 197A INVENTOR(S) Pierre Bertrand and Maurice Nony 7 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

IN THE HEADING:

The spelling of the Assignee's name should be Compteurs Schlumber'ger Signed and Scaled this Thirty-first Day of August 1976 A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflarems and Trademarks

Claims

1. An improved pneumatic controller having a first stage for providing an output signal proportional to the magnitude and time integral of an input signal comprising a first sealed beam balance with a housing and a beam structure defining four chambers; means for applying said input signal to a first one of said four chambers; means for applying a set point signal to a second one of said chambers, said second chamber being located on the opposite side of the beam from said first chamber; output means for providing an output signal from a third one of said chambers, said third chamber being located on the same side of the beam as said first chamber; said output means including a sealed beam flow relay; adjustable positive feedback means connected to said output means and to a fourth one of said chambers, said fourth chamber being located on the same side of the beam as said second chamber; said positive feedback means including a copying relay; and negative feedback means connected to said output means and said third chamber: and wherein the sealed beam structures of said sealed beam balance and said flow relay each comprise a flexible layer; a thin metal layer disposed on one side of said flexible layer, and a thick metal layer disposed on the other side of said flexible layer, said metal layers each being formed with openings defining an outer section and an interior section; and first and second narrow bridge portions interconnecting said outer and interior sections along a beam pivot axis, said narrow portions of said thick metal layer having thinned segments to facilitate movement of the interior portion about said piVot axis.

2. A controller according to claim 1 and wherein said flexible layer and said metal layers of said beam structure are each formed with openings adjacent the edges thereof; and wherein said housing includes protruding bosses located to mate with and pass through said openings in assembling the controller, and fastener means for passing through said bosses and clamping said housing and said beam structure together, whereby said bosses limit the compression to which the edges of said beam structure are subjected.

3. A controller according to claim 1 further comprising a second stage including a sealed beam balance with a housing and a beam structure defining four chambers; means for applying an input signal to a first one of said four chambers; output means for providing an output signal from a second chamber, said second chamber being located on the same side of the beam as said first chamber; third and fourth chambers located on the opposite side of the beam from said first and second chambers; feedback means connected between said output means and said third and fourth chambers, said third and fourth chambers being in communication and said output signal of the second stage being applied as the input signal of the first stage.