US3625239A

US3625239A - Transfer element for a measuring or control device

Info

Publication number: US3625239A
Application number: US782633A
Authority: US
Inventors: Horst Bader
Original assignee: JC Eckardt AG
Current assignee: JC Eckardt AG
Priority date: 1967-12-22
Filing date: 1968-12-10
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: GB1255023A; DE1807712B1; CH463833A; FR1588045A

Abstract

A transfer element for a measuring or control device which is operated by the flow of a pressure medium, in which a jet apparatus of a type known as such is employed for bringing at least two fluid-pressure values into operative association with each other which may be applied by separate conduits so as to serve selectively as a main jet pressure, as a back pressure, or as a suction pressure and may be controlled by a throttle valve in each conduit.

Description

United States Patent lnventor Appl. No.

Filed Patented Assignee Priority TRANSFER ELEMENT FOR A MEASURING OR Horst Bader Stuttgart-Fasanenhof, Germany Dec. 10, 1968 Dec. 7, 1971 J. C. Eckardt A.G. Stuttgart-Fasanenhof, Germany Dec. 22, 1967 Switzerland CONTROL DEVICE 12 Claims, 9 Drawing Figs.

U.S. Cl

Int. Cl Field of Search Reierences Cited UNITED STATES PATENTS 3,128,040 4/1964 Norwood 3,159,168 12/1964 Reader 137/815 3,250,469 5/1966 Colston 137/815 X 3,388,713 6/1968 Bjornsen l37/8l.5 3,444,878 5/1969 Mayer 137/815 3,459,206 8/1969 137/8 1 .5 3,467,122 9/1969 l37/8l.5 3,473,545 10/1969 137/815 Primary Examiner-Samuel Scott Almrne v-Craig, Antonelli & Hill ABSTRACT: A transfer element for a measuring or control device which is operated by the flow of a pressure medium, in which ajet apparatus ofa type known as such is employed for bringing at least two fluid-pressure values into operative association with each other which may be applied by separate conduits so as to serve selectively as a main jet pressure, as a back pressure, or as a suction pressure and may be controlled by a throttle valve in each conduit.

PATENTEDIJEB Han 1625239 SHEET 1 0F 3 INVENTOR Mr 8905,?

BY 5 72M ATTOR NEYS PATENTED DEB 71971 SHEET 2 OF 3 INVENTOR flak? R5081? ATTORNEKT The present invention relates to a new use of a jet apparatus of a general type known as such and to improvements in such an apparatus to permit it to be used as a transferring and control element in or for a measuring or control device which is operated by the flow of a pressure medium by bringing at least two pressure values into operative association with each other which are applied to the jet apparatus to be used thereon selectively as the main jet pressure, as the back pressure, or as the suction pressure of this apparatus. The invention relates further to a transfer element for a measuring or control device which is operated by a pressure medium and comprises a jet apparatus and a throttle valve or a restriction in the main pressure line, in the back-pressure line, and in the suction-pressure line of this apparatus. The term jet apparatus" as used in connection with the present invention includes all apparatus which operate by the well-known induction principle or Bernoulli's law, such as suction jet pumps which are operated by a fluid, Venturi tubes, ejectors which are also called jet compressors and are operated by air, and steam injectors.

' Although it is known in a flapper-nozzle system of a pneumatic control device with mechanical comparing elements to employ a so-called ejector in place of a fixed restriction the ejector serves in such a case merely for improving the linearity of the characteristic of the flapper-nozzle system, but does not carry out the function ofa transfer element.

The application of the fluid-pressure-operated transfer element in accordance with the invention has the advantage of resulting in a space-saving mechanism for dealing with the pressure values in measuring and control devices. This is due to the fact that a series of mechanical components of the known devices may be omitted. This will become apparent from the following description.

The known types of measuring and control devices such as pneumatic controllers and transmitters are provided with mechanical comparing elements in the form of diaphragm capsules (resilient tubes or bellows) or the like which have the purpose of first transforming the pressure values into forces and movements. Several of these mechanical elements act upon a comparing element which may, for example, consist of a pivotable lever or a rocker, a ring, or a wobble plate. Such a comparing element is moved in accordance with the pressure values. A part of this comparing element serves as a flapper in a flapper-nozzle system which converts the movements of this comparing element back into a pressure value which usually is then conducted to a pneumatic amplifier (relais). The flappernozzle system comprises an outlet nozzle to which the pressure medium is supplied from a constant source thereof via a fixed restriction and from this nozzle the pressure medium flows against the flapper and then to the atmosphere.

Each of these known principles of transforming pressure values may generally be regarded as a mechanical comparing element for controlling a flapper-nozzle system. Such a mechanical comparing element necessarily has to be of a construction which requires numerous components as well as considerable space, and because ofits spring-mass system it forms an oscillatory system with one or several degrees of freedom which may lead to undesirable oscillations.

The present invention has the object to overcome these disadvantages and it consists primarily in the discovery that the jet apparatus which are known in fluid mechanics for other purposes are especially suitable to be employed as transfer elements for fluid-actuated measuring and control devices if the corresponding pressure values are supplied to the jet apparatus as a main jet pressure, as a back pressure, or as a suction pressure. depending upon the particular purpose of the device. The present invention has among others the advantage that mechanical comparing elements and flapper-noz2le systems are no longer required and that all components may be eliminated which were previously required for first converting the pressure values into forces and movements and for then reconverting the latter into a pressure value. On the conelement according to flow of the pressure medium which depends upon the pressure values of the latter.

now carried out by the transfer element which has only two components namely the jet apparatus and the throttle valve or valves or restrictions to which, if required a third component may be added in the form of an amplifier. These components are connected to each other by chan els or pipes in the particular manner as required.

The transfer element according to the invention may be further applied with advantage, for example, in connection with computing apparatus which are operated by a pressure medium. The known computers of this type, for example, root-extracting mechanisms, produce the mathematically necessary dependence of the pressure values upon each other by mechanical means such as cam plates, l-cosa)-gears, toggle-joint gears, and the like. These mechanical means may be replaced by the transfer element according to the invention if the transfer element is adjusted so as to serve as a function generator and is inserted, for example, into the feedback path of an amplifier. For this adjustment, the'transfer element is provided with further adjustable throttle valves or restrictions. Such transfer elements may also be inserted into the feedback path of an apparatus which is equipped with a mechanical comparing element so that a combination of the transfer element according to the invention with mechanical comparing systems of a known type will thus be attained. If such a combination is employed, the mechanical root-extracting mechanisms as mentioned above may be omitted.

In order to adapt the jet apparatus as a transfer element to the ranges of the pressure values, it is provided with the throttling valves as previously mentioned which may be adjustable and may be selectively located in the mainjet line, in the backpressure line, and in the suction-pressure line of the apparatus.

The features and advantages of the present invention and its manifold applications will become further apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which FIG. 1 shows a diagrammatic longitudinal section of a transfer element according to the present invention which comprises ajet apparatus and throttle valves;

FIG. 2 shows a symbolic illustration of the transfer element according to FIG. 1;

FIGS. 3 to 7 respectively show different families of characteristics which may be attained by means of the transfer element according to the invention;

FIG. 8 shows a circuit diagram of the transfer element in its arrangement as a function generator in the feedback path ofa pneumatic-mechanical measuring and control device which may be employed, for example, for root extracting; while FIG. 9 shows a circuit diagram of several transfer elements according to the invention in a fluid-actuated controller.

FIGS. l and 2 of the drawings illustrate a jet apparatus of a type known as such which is enclosed in a housing I as indicated diagrammatically and consists ofa nozzle 2 at the end of the main pressure or jet line 3, a suction chamber 4 at the end of the suction line 5, and a back-pressure chamber 6 which is located behind the narrowest cross-sectional area of flow at the end of the back-pressure line 7. The apparatus is further provided with another pressure line 8 which terminates into the back-pressure line 7. The main pressure line 3 is controlled by an adjustable throttle valve w the suction line by an adjustable throttle valve w and the back-pressure line 7 by an adjustable throttle valve w which connects the back-pressure chamber 6 with the atmospheric pressure p,,. The additional pressure line 8 is likewise controlled by an ad justable throttle valve W In addition, the apparatus is pro vided with connecting lines 9, l0, and I] which connect the main pressure line 3 with the back-pressure line 7 or the suction line 5 with the back-pressure line 7, respectively. The connecting lines 9, l0, and 11 are likewise equipped with adjustable throttle valves W W and w In the jet apparatus the main pressure p the suction pressure p and the back pressurep occur. These three pressures together with the geometric dimensions of the jet apparatus determine the amounts of the pressure medium with which this apparatus is operated and they are mutually dependent upon each other. The apparatus which is used as a transfer element is connected to the pressures x, y, z, and p, which form the input and output valves of the transfer element.

It is now the object of the invention to provide additional relations between these pressures and to render them further dependent upon each other so as to permit a conventional jet apparatus to be employed for its new use as a transfer element in measuring and control devices.

As may be seen in FIGS. 1 and 2, this may be attained in two different manners:

The inner pressures p 2 and p are brought by throttle valves first into a further relationship to each other and second into a dependence upon the outer pressures x, y, z, and p to which the transfer element is connected.

The outer throttle valves w W). w and W then serve primarily for adapting the transfer element to the preset pressure ranges and to the operating point of an adjacent loop element of a control circuit, for example, an amplifier, whereas the inner throttle valves W W and W are primarily adapted to produce different kinds of families of characteristics of the transfer element.

This results in a large selection of variables and parameters First, there are the outer pressures .t, y, and 2 available as input and output variables, while the pressure 12,, serves primarily as a parameter which usually is maintained at a constant value, for example, at atmospheric pressure. For the parameter adjustment, all throttle valves may be employed, that is, the inner as well as the outer throttle valves.

Aside from the pressure signals .r, y, and z, it is also possible to employ the pressures p and p as independent variables, that is, as input values, as parameters, and also as dependent variables, that is, as the output values.

FIG. 3 illustrates the family of characteristics of a jet apparatus of a conventional type which is operated with compressed air. The pressure P in the suction chamber of the apparatus is indicated as being dependent upon the given value y, while the back pressure p p etc. which is adjusted by the throttle valve W serves as parameter. This family of characteristics also corresponds to that of the transfer element according to the invention if the throttles in the connecting lines 9, I0, and II are closed. It indicates that, with the exception of the marginal curves l2 and 13, all other characteristics are nonlinear curves which are generally unsuitable for associating a certain suction pressure p with the value y.

If, however, as shown in FIG. 4, for the same jet apparatus the value .r is employed which is dependent upon the suction pressure p,-. a series of straight lines will result and the position and inclination of the individual lines, for which the pressure in the back-pressure chamber p p likewise serves as parameter, may be determined by the adjustment of the throttle valves w and w A part of the objects of associating two pressure values with each other may therefore be solved already by an arrangement in which the associated pressure values are connected to the transfer element according to the invention as a value .t or as a back pressure, respectively.

In FIG. 5, the family of characteristics of the suction pressure 1 is indicated in relation to the value y. This results when in the jet apparatus according to FIGS. 1 and 2 not only the throttle valves w,, w,,, w,, and w, are employed for the parameters adjustment but also the throttle valve W Depending upon the position of the throttle valve W the characteristics now result in a series of straight lines which, contrary to those in FIG. 4, are downwardly inclined and permit the new transfer element to be used, for example, like the arrangement according to FIG. 4 as a negative feedback in a feedback path ofa measuring and control device.

FIG. 6 shows the family of characteristics which results when the throttle valves w w,-, w (or W and w are effective, while the throttle valves w and w remain closed. De-

pending upon the position of throttle valve w different parabolic associations result between the suction pressure p and y, so that this arrangement may be used with great advantage in the feedback path of a root-extracting measuring instrument.

FIG. 7 shows the family of characteristics p in relation to the value y. This set of curves may be regarded as the reverse to the parabolas of FIG. 6. It results when aside from the outer throttle valves w W W and possibly w also the throttle valve w is employed for the parameter adjustment, while the throttle valves w and W31 remain closed. This arrangement in which the formation of the different curves likewise depends upon the position of the throttle valve WM; may be employed, for example, when a square association of the pressure values is required, for example, in computers or the like.

From the examples as previously described it is apparent that the new transmitting element may be employed for a multitude of different purposes, especially also when a combination of the parameter adjustment is effected by means of the throttle valves w and w or w relative to each other and together with the outer throttle valves w W W and W FIG. 8 shows a circuit diagram of a root-extracting apparatus which may carry out the calculation v= VT... The transfer element 1 is located within the feedback path of an amplifier 15 with a negative feedback.

The transfer element 1 is assumed to be adjusted as described with reference to the family of characteristics according to FIG. 6 and the throttle valve w is therefore also employed as a parameter. This family of characteristics contains a square association between p and y. If by means of a proportional element P which may consist, root-extracting example, ofa lever, a value .t which is proportional to the suction pressure 1,,- acts in opposition to the input value .t',. of the rootextracting apparatus, the desired root-extracting effect will be attained.

In FIG. 8, the comparing device 14 which forms the difference between the values x and x, and conducts to the amplifier a value which is proportional to this difference may be designed as a mechanical comparing device with the result that a combination of the transfer element 1 with a mechanical comparing device is formed. The usual mechanical rootextracting gear is replaced by the transfer element I in which the parameter may be adjusted accordingly.

It is, however, also possible to replace the mechanical comparing device by a comparing device which is operated by a pressure medium. Such a pressure-actuated comparing device may be formed, for example, of a transfer element according to FIGS. I and 2. The values .r and y are then used as independent variables, that is, as input values, and p as output value. This use of the transfer element constitutes a combination of its use in accordance with the previous description of FIGS. 4 and 5. As may be seen by the characteristics according to FIGS. 4 and 5, p increases in proportion to the input signal x and decreases in proportion to the second input signal y. This results in the formula:

If the transfer element I is adjusted so that the values k, and k are equal, p will be in proportion to the difference between the pressure values x and y. This, however, is the effect of a comparing device which is actuated by pressure media.

It will, however, not always be possible to bring the range of values of p,- into conformity with the range of values of p of the input pressure of the amplifier. It is for this reason that, for example, the variable x is not applied directly on the throttle valve WX of the transfer element, but via a further adjustable throttle valve. This case is illustrated in FIG. 9.

The input value x,., acts through the adjustable throttle valve w upon the input pressure signal p, of the amplifier 16. The input value x,. acts through the transfer element la upon the pressure p,,-. This occurs in this case because x determines the main jet pressure of the transfer element Ia and thus the volume of pressure medium which is drawn off the input pressure chamber of the amplifier 16 in which the pressure p prevails. The same arrangement of a transfer element lb with an additional throttle valve is now employed according to FIG. 9 to form a feedback path for the amplifier 16. The output pressure y of the amplifier then acts upon the transfer element lb in such a manner that the pressure y determines the main jet pressure p This has the result that an amount of pressure medium which is proportional to the output pressure y of the amplifier is drawn off the intake pressure chamber which is under the pressure p so that the value p is reduced. This is the effect of a negative feedback. A further pressure value x, is connected through the throttle valve w' to the pressure camber p This throttle valve and the constant pressure signal x, serve for the purpose of adapting the range of values of the pressure p, to the operating point of the amplifier or vice versa.

The arrangement as shown in FIG. 9 illustrates a proportional control device which is actuated by a pressure medium. This apparatus is composed of two pressure-actuated comparing devices and the amplifier 16.

The first comparing device is formed by the transfer element la and the throttle valve w to which the input pressures .r,,, and x are connected. This comparing device serves for determining the deviation of the actual value from the nominal value.

The second comparing device is provided in the feedback path of the amplifier 16.

The proportional range adjustment of the throttle valve W and one or more of the throttle valves of the transfer element la, or by the simultaneous adjustment of the throttle valve w and one or more of the throttle valves of the transfer element lb which is located in the feedback line of the amplifier 16. A fluid-actuated comparing instrument which is designed in accordance with FIG. 9 may be formed ofa transfer element and one additional throttle valve. it may, however, also be formed of two transfer elements according to FIGS. 1 and 2. Other combinations or the replacement of further throttle valves may also be attained by employing transfer elements according to the invention.

It is evident from the foregoing description that the present invention concerns a transfer element for the association of pressure values which may be employed for a multitude of different purposes and may be easily manufactured.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, 1 wish to have it understood that it is in no way limited to the details of such embodiment but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

l. A transfer element for correlating pressures in a measuring or control device which is actuated by the flow of a pressure medium by operatively associating at least two pressure values with each other and comprises ejector means having a nozzle and a venturi arranged coaxially with the nozzle, and means for supplying said pressure values selectively to and employing them in said ejector means as a main jet pressure, as a back pressure, or as a suction pressure.

2. A transfer element as defined in claim 1, wherein the ejector means includes a nozzle, and the flow of the pressure medium leaving the nozzle is substantially symmetrical with respect to the longitudinal axis of the nozzle.

3. A transfer element for a measuring or control device actuated by a fluid pressure medium comprising ejector means having a nozzle and a venturi arranged coaxially with the nozzle, conduits for supplying a main jet pressure, a back pressure, and a suction pressure to said ejector means, and at least one throttling restriction or throttle valve in one of said conduits.

4. A transfer element as defined in claim 3, further comprising a connecting conduit between said main-pressure conduit and said suction-pressure conduit, and a further throttling restriction or throttle valve in said connecting conduit.

5. A transfer element as defined in claim 3, further comprising a connecting conduit betweensaid back-pressure conduit and said suction-pressure conduit and a further throttling restriction or throttle valve in said connecting conduit.

6. A transfer element as defined in claim 3, in which all of said throttling restrictions or throttle valves are adjustable.

7. A transfer element as defined in claim 3, further comprising a back-pressure chamber in said ejector means to which said back pressure is adapted to be supplied. a further conduit for supplying another pressure valve to said back-pressure chamber, and another throttling restriction or throttle valve in said further conduit.

8. A transfer element as defined in claim 7, in which at least one of said throttling restrictions or throttle valves is adjustable.

9. A transfer element as defined in claim 3, further comprising a back-pressure chamber in said ejector means to which said back pressure is adapted to be supplied, a connecting line between said main-pressure conduit and said back-pressure chamber, and a further throttling restriction or throttle valve in said connecting conduit.

10. A transfer element as defined in claim 9, further comprising a connecting conduit between said main-pressure conduit and said suction-pressure conduit with a throttling restriction or throttle valve disposed therein, and a connecting conduit between said back-pressure conduit and said suctionpressure conduit with a throttling restriction or throttle valve disposed therein.

11. A transfer element as defined in claim 10, wherein a back-pressure chamber is provided in said ejector means to which said back pressure is adapted to be supplied, a further conduit for supplying another pressure valve to said backpressure chamber, and another throttling restriction or throttle valve in said further conduit.

12. A transfer element for the correlation of pressures for pressure-medium-operated measuring and controlling devices, comprising ejector means having a nozzle and a venturi arranged coaxially with the nozzle, and at least one throttle restriction disposed in a power stream conduit, and/or in a back-pressure conduit. and/or in a suction-pressure conduit of said ejector means.

# l l 0 l

Claims

1. A transfer element for correlating pressures in a measuring or control device which is actuated by the flow of a pressure medium by operatively associating at least two pressure values with each other and comprises ejector means having a nozzle and a venturi arranged coaxially with the nozzle, and means for supplying said pressure values selectively to and employing them in said ejector means as a main jet pressure, as a back pressure, or as a suction pressure.

5. A transfer element as defined in claim 3, further comprising a connecting condUit between said back-pressure conduit and said suction-pressure conduit and a further throttling restriction or throttle valve in said connecting conduit.

7. A transfer element as defined in claim 3, further comprising a back-pressure chamber in said ejector means to which said back pressure is adapted to be supplied, a further conduit for supplying another pressure valve to said back-pressure chamber, and another throttling restriction or throttle valve in said further conduit.

10. A transfer element as defined in claim 9, further comprising a connecting conduit between said main-pressure conduit and said suction-pressure conduit with a throttling restriction or throttle valve disposed therein, and a connecting conduit between said back-pressure conduit and said suction-pressure conduit with a throttling restriction or throttle valve disposed therein.

11. A transfer element as defined in claim 10, wherein a back-pressure chamber is provided in said ejector means to which said back pressure is adapted to be supplied, a further conduit for supplying another pressure valve to said back-pressure chamber, and another throttling restriction or throttle valve in said further conduit.

12. A transfer element for the correlation of pressures for pressure-medium-operated measuring and controlling devices, comprising ejector means having a nozzle and a venturi arranged coaxially with the nozzle, and at least one throttle restriction disposed in a power stream conduit, and/or in a back-pressure conduit, and/or in a suction-pressure conduit of said ejector means.