US2618288A - Pneumatic instrument - Google Patents

Description

Nov. 18, 1952 A. R. CATHERON PNEUMATIC INSTRUMENT Filed March 14, 1951 BLAST INPUT FLEXIBLE FIG.

ATTO EYS Patented Nov. 18, 1952 {UNITED STATES PATENT OFFICIE PNEUMATIC INSTRUMENT Allan R. Catheron, Foxboro, Mass., assignor to The Foxboro Company, Foxboro, Mass a corporation of Massachusetts Application March 14, 1951, Serial-No. 2l 5,58l

action device for use in such instruments.

Such instruments use condition sensing elements responsive to value changes in the variable conditions, and the response of the sensing element to the condition change is transmitted to an action device in the instrument for operating a recording, indicating, or control unit.

It is an object of this invention to provide a new and improved device of this nature.

The device of this invention is inexpensive, compact, and accurately effective with small forces, and is in thev form of a balance arrange ment which is productive of a pneumatic operatin output force proportionally representative of the sensing element response to the variable condition change.

Illustrative embodiments of this invention are shown-in the accompanying drawings, in which: Fig-ure-I'is a-diagrammatic illustration of a double nozzleand flapper pneumatic device; and Figure-II shows an alternate flapper structure.

The embodiment of this invention as shown in Figure I is an arrangement fo controlling the temperature of a process.

As will be explained, temperature variations in the process are made to control an input to the-process. This is done by translatin the response of athermometer in the process into movement of a valve in the input, and this translation is accomplished by a pneumatic action 'devi-Ce; in this instance comprising a flapper, a pair of nozzles, and a pneumatic relay. Referring to Figure I, at the lower left, a proc- This thermometer other suitable type maybe used.

Connected to the thermometer H is a tube I2 through which the response to temperature variation is travelled to produce movement in a spiral Bour-don tube l3. 'Secured to the spiral Bourdon tube to receive its movement, is a connector [4, including a coil spring [5. This connector is secured to a lightweight flapper it which is .pivoted at l? so that the Bourdon movement results in pivoting movement of the flapper. The coil spring l5, as will be seen, allows opposing forces to be applied to the flapper without causing undesirable movement in the spiral Bourdon tube.

Associated with the flapper l6 at points removed from the pivot ii, there is a pair of nozzles l8 and it. These nozzles are aimed at the flapper in such a manner that pneumatic flow from the nozzles will be directed against the flap- August 21, 1946, Serial No. 692,102. speaking, there i is a pneumatic :path through the 2 per, and the'movement of the flapper about its pivot .willvary the interception relation of'the flapperand theflow so as to release o restrict pneumaticflow from the nozzles. The nozzles are designated, according totheir functions, as a bleed nozzle at l8, and a blast, nozzle at The bleednozzle is so called because the pneumatic fioworpressure therein is a minor or throttling flow or pressure, variedby movement of the flapper. The blast nozzle is so called because the pneumatic flow or pressur therein connected to a pneumatic relay, generally indicated at-2EJ. The construction and operation of thistype of pneumatic relay is shownand described in the pending patent application for a Controller (inventor, Hoel L. Bowditch), filed Generally relay through which a substantial pneumatic operating pressure may be travelled. This path is opened orwclosed, partially-or fully, through the movement-of ao'diaphragm, with the diaphragm movement controlled by a minor, orthrottling A pneumatic, pressure.

As shown in. Figure Lthe-relay 20 is provided,

atthe top,'with a pneumaticpressure input 2|.

The relay has a power chamber 22 and a secondary chamber 23, with the pressure input having unrestricted access .to the power chamber 22 and restricted access'to the secondary chamber 23 through :a restrictor passage 24. There is a *passagenbetween these chambers, as at 25, which :is closed off by a diaphragm 26. Thediaphragm From the passage 25, between the chambers 22 and 23 and extending into neither, there is an output passage 29. Thus, with th valve 21 open, an unrestricted pneumatic path is provided through the "relay by Way of the input 2|, power chamber 20, chamber passage'25, and the output passage 29. At the bottom of the relay there is a passage from the inside of the diaphragm, as at 39, operable as a bleed to atmosphere.

Referring again tothenozzles, the bleed nozzle I3 is connected by'a tube 3| to the relay sec- The temperature or the process in the tank It is controlled by a heating or cooling medium applied to the process through the-pipe line 34, with this application controlled by the valve 33.

In the operation of the device, the flapper may be moved toward the bleed nozzle M3 by a temperature change in the process tank l0. Asthe flapper approaches the bleed nozzle, it restricts the pneumatic flow therefrom. As this flow is restricted, pressure builds up in the relay 20, in the secondary chamber 23, resulting in movement of the diaphragm 26and in opening the valve formed by the passage 25 and valve unit said nozzles and said flapper achieve a particular position relation, with said relay output pressure available as a working pressure which is propor- 2. In a pneumatic action structure combining a proportioning device and a simple on-ofi device for use in instruments as described, a movable flapper, a nozzle for directing a pneumatic flow against said unencumbered flapper, means responsive to changes in a variable condition for moving said flapper to vary the flow from said nozzle, a diaphragm operated pneumatic relay 21. A pneumatic pressure from the power chamlated to the Bourdon movement resulting from temperature changes in the process tank II].

This proportion is variable by adjustment of the nozzles with respect to the flapper and each In this instance the blast nozzle tube 32 other. is indicated as being flexible, and the blast nozzle may be adjusted toward or away from the flapper pivot l1. As the blast nozzle approaches alignment with the pivot H the proportion relation is reduced, and with the blast nozzle in direct alignment with thepivot l!, the proportion becomes a one to one relation. When the blast nozzle is in direct alignment with the pivot H, the blast has no effect on the flapper l6, and the device becomes a simple on-off action device. Under these conditions, the device is operated simply by themovement of the flapper I6 in closing or opening the nozzle l8 and consequently the pipe line valve is operated only from full'on to full oiT positions, or the reverse.

Referring to Figure II, it is simply a showing of an alternate flapper design with the pneumatic blast from the blast nozzle applied to a This output pressure i proportionally re- 7;;

connected to said nozzle and operable by changes in said pneumatic flow to produce a single pneumatic output pressure from said relay, a second 7 nozzle arranged to direct said relay output pres- 'sure, in the form of a, pneumatic blast, against said flapper in opposition to the variable conditioh action thereon, with said blast being wholly controlled by the relation of said flapper to said bleed nozzle, and said flapper'movement being controlled from said relay solely by said pneu- 'matic blast, whereby said nozzlesa-nd said flapper achievea balance relation,- with said relay output pressure available as a working pressure proporsulting in zero proportion, with saidpneumatic blasthaving no efiect on the movement or posi- 3. Apparatus for controlling the value ofa variable process condition by regulating the flow of a fluid affecting said condition, comprising-in combination, a first nozzle,-means for supplying a restricted flow of air under pressure to-said nozzle to cause a jet'of air to issue therefrom, a

selected contour in the flapper to increase the blast effect onthe flapper. As an example of the various contourswhich may be used a semicylinder is shown. I Y i 1 Iclaim: Y 1. In a pneumatic action device for use in instruments as 'described, a nozzle, meansfor producing a pneumatic flow through said nozzle, an unencumbered flapper mounted in the path of;

said pneumatic flow for movement with respect to said nozzle so as to vary said flow, means for producing such movement of said flapper in re-j;

sponse to changes: in a variable condition, a diafrom said relay, and a second nozzle arranged toja.

direct said relay output pressure against. said flapper in the form of a pneumatic blast in opposition to variablezcondition movement of said flapper, with saidblast. being wholly controlled by the relation of said flapper to said bleed nozzlellt; and said flapper movement being controlled from said relay solely by said pneumatic blast, whereby Number ment with respect to said nozzle to vary the flow of air 'therethrough, means responsive I to the value of said condition connected to said flapper to move the same and thereby vary the air flow through'said nozzle and the pressure in back of the nozzle, a pneumatic relay connected to said nozzle and having a. movable diaphragm com- 'municating with said nozzle back pressure and operated thereby to regulate a pneumatic supply to produce a relay output pressure, a second nozzle connected to said relay output pressure "and positioned adjacent to said flapper to direct "a pneumatic blast against the flapper in opposi- "tion to the condition-responsive movement of the (flapper whereby the flapper'is maintained in operative position with respect to said flrst'nozzle,

and regulating means responsiveto said relay output pressure for regulating the flow' of said :fluid. s I

ALLAN R. CATHERON.

REEERENGES CITED The following referencesare'of record in the file of this patent:

UNITED STATES, PATENTS Date 2,053,797 7 King Sept. 8, 1936 2,436,451 Rosenberger -Feb. 2c,f194s

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