CA1277191C - Pneumatic interface apparatus - Google Patents
Pneumatic interface apparatusInfo
- Publication number
- CA1277191C CA1277191C CA000519206A CA519206A CA1277191C CA 1277191 C CA1277191 C CA 1277191C CA 000519206 A CA000519206 A CA 000519206A CA 519206 A CA519206 A CA 519206A CA 1277191 C CA1277191 C CA 1277191C
- Authority
- CA
- Canada
- Prior art keywords
- chamber
- pressure
- pneumatic
- volume
- control means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/1925—Control of temperature characterised by the use of electric means using a combination of auxiliary electric and non-electric power
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
- F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
- F24F11/62—Control or safety arrangements characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
- F24F11/63—Electronic processing
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Fuzzy Systems (AREA)
- Mathematical Physics (AREA)
- Power Engineering (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Fluid-Pressure Circuits (AREA)
- Supply Devices, Intensifiers, Converters, And Telemotors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The interface apparatus of the present invention includes a pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure.
A volume relay has a first chamber coupled to the control means by a pneumatic bus and a second chamber for coupling to a pneumatic transducer to be positionably controlled, the first chamber and the second chamber being in fluid flow isolation one from the other. The volume relay provides a second pressure at its second chamber which has a predetermined relationship to the first pressure. A
substantially constant, confined volume is coupled to the flow control means and to the relay and the flow control means includes means for adjusting the rate of flow of gas from the substantially constant volume to a region of ambient pressure.
The interface apparatus of the present invention includes a pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure.
A volume relay has a first chamber coupled to the control means by a pneumatic bus and a second chamber for coupling to a pneumatic transducer to be positionably controlled, the first chamber and the second chamber being in fluid flow isolation one from the other. The volume relay provides a second pressure at its second chamber which has a predetermined relationship to the first pressure. A
substantially constant, confined volume is coupled to the flow control means and to the relay and the flow control means includes means for adjusting the rate of flow of gas from the substantially constant volume to a region of ambient pressure.
Description
~2~19~
PNEU~TIC INTERFACE APPARATUS
BACKGROUN~ OF THE INVENTION
I'neumatic control of process systems is widely employed wherever the system installation requires rugged components, lo~ered cost, relative ease of installation and troubleshooting and a high degree of controllability.
Examples of such processes which readily lend themselves to pneumatic control include the control of chiller and boiler temperature, steam or air line pressure control, flow control in fluid-transporting pipe systems, tank liquid level control, pH control in chemical processes, and heating, ventilating and air conditioning controls.
Pneumatic control is frequently employed in petrochemical process systems where flammable fluids are often present and may be ignited by electrical control devices. For purposes of illustration, and not by way of limitation, the invention is shown and described in connection with a heating, ventilating and air conditioning system.
~eating, ventilating and air conditioning (HVAC) systems are frequently used in buildings to control the temperature of a conditioned space within the building and ~or energy management purposes. A type of HVAC system includes an air handling unit having a plurality of '~'' -. . . ~ .
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actuator-manipulated dampers for controlling the flow of outdoor air into the building, for controlling the flow of air exhausted from the building and for directing air which is heated or cooled and recirculated. ~ther mechanisms associated with air handling units typically include actuator-manipulated valves for controlling the flow of chilled or heated water through heat exchanger coils disposed in the ductwork for controlling the temperature o~ air 10wing therethrough.
One type of actuator used with such air handling units comprises a spring blased, pneumatic cylinder having i~s rod couple~ to a damper or valve. The cylinder is connected to a source of pneumatic pressure such as a pneumatic bus network formed of small diameter flexible polyeythlene tubing and installed throughout the building. Control is Dy the solution of known algorithms within a pneumatic controller and the generation of analog pneumatic output signals directed to the cylinders.
The relatively recent advent of computerized direct digital control apparatus and the desire of building owners to incorporate such computerized apparatus into new or existing HVAC systems employing low cost, rugged pneumatic actuators requires that a digital-to-pneumatic interface system be employed for receiving digital signals from the control apparatus and translating them to pneumatic signals for cylinder or other actuator positioning. These direct digital controllers may be constructed and arranged to repetitively solve any one or more of several known control algorithms for generating command sigTIals to the interface system and ~or reasons unrelated to the invention, it is often pre~erable to arrange the digital controller to provide command signals which direct the cylinder to undergo a computed change in cylinder pressure rather than to move to a new position as .~ ~ - . ' . .
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, ' ' ' ' ' ' ' ~:77~91 represented by a new absolute pressure. Stated another w~y, it is o~ten preerable to arrange the digital controller and the attached system in a manner such that the ne~1 posit-Lon to be assumed by a cylinder is a function of the duration of the digital output signal oE the controller rather than a unction of the change in c~linder pressure. In commonly employed pneumatic control syster~s, it ~lay also be desir~ble to cause particular cylinders within the system to e~hibit full stroke over pressure ranges which may differ from cylinder to cylinder and commonly employed full stroke pressure ranges are 3-8 psig, ~-13 psig and 13-18 psig.
An example of an interface system useful for controlling the position of a single actuator or for the simultaneous control of the position of several actuators of t~le same size, full stroke pressure range and loading - is shown in United States Letters Patent No. 4,261,50g.
This system includes a pair of two position, electrically -~ctuated solenoid valves for receiving digital signals and controlling the flow of fluid into and out of the actuator. Pneumatic resistors, sometimes termed restrictors, having orifices therethrough typically of a few thousandths of an inch in diameter are disposed in the pneumatic lines for controlling actua~or stroke distance per unit time, i.e., for controlling the slopes of the actuator pressure-time graphs representative of actuator stroke characteristics in both directions of travel.
Another example of an interface device is shown in United States Letters Patent No. 4,440,066 and includes a pair o~ solenoid valves or controlling the ~low of air from a pressure source to a region of indeterminate volume and from the region to an area of ambient pressure. An adjustable ~low ori~ice i8 provided ~or controlling the flow rate to and from an attached actuator, e.g., a cylinder. United States Letters Patent No. 3,266,380 .
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shows the use of a reservoir as an integrating capaci~ance in a pneumatic computing device, unsuitable for interfaced control, which contemplates variable input pressures and which, like the apparatus of the aforementioned U.S.
Patent No. 4,440,066, includes a ~eedback (closed loop) feature.
While interface s~stems of the aforemention~d type have heretofore been satisfactory for the positioning of actuators, they are nevertheless characterized by certain disadvantages. For e~ample, when restrictors are used to control the stroking characteristics of a single actuator or of a group of actuators having the same size, spring range and loading, the restrictor orifice sizes must be selected by e~perimentation at the installation site.
This is so since actuator stroke times are dependent upon actuator size, spring range, loading and the volume of fluid contained within the actuator and the pneumatic interconnections. These parameters are frequently difficult or impossible to determine prior to actual installation. If the HVAC system requires actuator sequencing and incorporates actuators having different volumetric sizes, spring ranges and/or loadings, the system will exhibit highly nonlinear gain characteristics and the control problem ls thereby further complicated.
Using the interface system of the aforementioned V.S.
Patent No. 4,261,5~9 as illustrative, and assuming a plurality of parallel connected disslmilarly-configured actuators to be controlled, the percent change of position will be different for each actuator for a given time during which a solenoid is energized for introducing fluid to or expelling fluid Erom the actuators. This results from the fact that a change in the contained volume of ~luid o~ one actuator will affect the ~troke distance per unit time of other actuators in accordance with the .
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equation of state of an ideal gas. If restrictors are selected ~o control the stroke time of, for example, a small, lightly loaded actuator, the system response will be unacceptably sluggish for positioning larger or more heavily loaded actuators. Conversely, if restrictors are selected for the proper control of actuators of the latter type, system instabilities may result. Even with the addition of a device called a pilot positioner to some or all o the actuators, restrictor selection must be by field experimentation or by measurement and computation of the volume of compressed fluid contained within the pneumatic interconnections and the pilot positioner pressure chamber6.
A further disadvantage of systems of the aforementioned type is that they are susceptible to significant leaks of pneumatic fluid. For example, each pneumatic connection of 1/4 inch tubing typically has a leak rate of approximately 0.1 standard cubic inches per minute (SCIM) at 20 psig while a typical pilot positioner has a leak rate of 0.3 SCIM. In a system including a constant volume reservoir where the system contains a relatively small volume of fluid and/or a large number of connection points and pilot positioners, changes in the control pressure due to leaks within the system and over the time interval between parameter sample times, e.g., conditioned-space temperature sampling times, would be unacceptabl~ large.
Accordingly, an interface system which permits preselection of restrictor orifice sizes irrespective of the configuration of the related pneumatic bus and actuators, which may be used to control actuators havlng a wide variet~ of contained fluid volumes and which may have an adjustment feature permitting its use with actuators which may operate over any one of several pressure ranges would be a significant advance over the prior art.
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~2 ~ 7 SU~ARY OF THE INVENTICN
-In general, the interface apparatus of the present invention includes a pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure.
A volume relay has a first chamber coupled to the control means by the con~ined volume of gas and a second chamber for coupling to a pneumatic actuator to be positionably controlled, the first chamber and the second chamber being in fluid flow isolation one rom the other. The volume relay provides a second pressure at its second chamber which has a predetermined relationship to the first pressure. Means having a substantially constant, confined volume are interposed between the flow control means and the relay and cooperates with the flow control means for determinin~ the slopes of the actuator pressure~time graphs. The flow control means may include means for adjusting the rate of flow o~ the gas from the substantially constant volume to a re~ion of ambient pressure.
It is an object of the invention to provide a new and improved interface apparatus for positionin~ pneumatic actuators which overcomes disadvantages of the prior art.
Another object of the invention is to provide an interface apparatus which permits the preselection of flow controlling restrictors.
Yet another object of the invention is to provide an interface apparatus which provldes actuator positionin~
chAracteristics that are independent of the size or number of actuators connected thereto.
Still another object of the present invention is to provide an interface apparatus which may include means for field adjustment of the rate of flow of a gas from a .
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substantially constant confined volume to a region of ambient pressure.
Anotiler object of the present invention is to provide an interface apparatus which is useul with direct digital controllers.
Yet another object of the present invention is to provide an interface apparatus which results in movement of an actuatln~ cylinder to a new position which is a computed function of the duration of a digital signal from a direct digital controller. How these and other objects of the invention are accomplished will become more apparent from the detailed description thereof taken with the accompanying drawing.
~ESCRIPlION OF THE DRAWING
FIGURE 1 is a graphical depiction of described rise and decay characteristics of the pressure within a substantially constant confined volume of a gas;
FIGURE 2 is a simplified schematic diagram showing the interface apparatus of the present invention in conjunction with an exemplary process control system comprising an air handling unit;, FIGURE 3 is a pictorial schematic diagram of a first embodiment of the interface apparatus shown in FIGURE 2 with portions shown in cross-section and other portions shown in full representation;
FIGURE 4 is a pictorial schematic dlagram of a second embodiment of the interface apparatus of FIGURE 2 with parts broken away, portions shown in cross-section and other portions shown in full representation;
FIGURE 5 i9 a cros~-sectional view of the volume relay portion of the interface apparatus taken in the plane 5-5 of FIGURE 3 and with portions shown in full representation;
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7~ ~9 FIG~RE 6 is a top plan view of a commercial embodiment of the inventive apparatus;
~ lGUKE 7 is a side elevation view of the apparatus of FIGURE 6 taken along the plane 7-7 thereof with portions shown in cross-section and other portions shown in full representation;
~ h ~ is a top plan view of the flexure lever of the apparatus of FIGURE 7;
FIGUR~ ~ ls a side elevation view of the lever of FIGUR~ o taken along the plane 9-9 thereof;
FIGURh 10 ls a cross-section, side elevation view of the center plate of the apparatus with parts added in exploded view, and;
FlGUR~ 11 is an electrical schematic diagram of the apparatus.
DESCRIPTION OF THE PREFERRED EMBODI~ENTS
:
Understanding of the invention will be aided by an explanation of t~e relevant gas law and from the field of applied physics, the equation of state of an ideal gas is expressed as:
pV = I~T
where p = pressure of a gas in a substan-tially rigid, confining volume or vessel;
V = the confined volume of the vessel;
n ~ the number of moles of gas within the vessel;
R = the universal gas constant, and;
T ~ the temperature o~ the gas in K.
From the equation, it will be apparent that if the temperature of the gas confined in the vessel is held constant, a reasonable assumption for this analysis, and , . :.
. . . .
_9_ if the volume of the vessel remains unchanged, the pressure of the ~as will have a direct relationship to the number of moles of the gas confined within the vessel.
Understanding of the invention will also be aided by referral to the graph of FIGU~E 1 which depicts the rise and decay characteristics o~ the gas pressure pre~ailing within a substantially constant, confined volume of gas.
Curve A represents the pressure rise characteristic over time when a gas is introduced into the confined volume from a source of constant pressure, e.g., 20 psig and through a particular flow-restricting orifice. The initial pressure in the volume is assumed to be 0 psig.
Curve B represents the pressure decay characteristic over time when the pressurized gas within the volume is permitted to be expelled from the volume to an area of ambient pressure, e.g., an area at 0 psig, expulsion being through ~ particularly sized ~low-restricting orifice.
~ontrol of gas flow into and out of the volume may be by a pair of normally closed, two position solenoid valves.
Since curves A and B are both nonlinear, it is apparent that ii on~ desires to operate a cylinder over, for example, the range C of 3 8 psig, that generally linear portion of curve A which falls within the range C
has a slope which is dramatically different from the slightly arcuate portion of curve B which falls within range C when ignoring the algebraic sign of the slopes.
Therefore, with a cylinder pressure within range C and rising along curve A, the magnitude of the change in pressure per unit time is different ~rom that o a declining cylinder pressure along curve B and within range C. This may present an unacceptable result if the cylinder is desired to be operated by signals from a digital controller where cylinder positioning i~
preferably by a computed signal dura~ion rhther than by measuring changes in pressure or by other means.
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On the other hand, the slopes of curves A and B in the range D o~ 8-13 psig are substantially equal one to the other if algebraic sign is ignored and this demonstrates that the particular orifice used in the system on which the curves ~re based would likely be satisfactory for cylinder operation over the range of 8-13 psig with a digital controller.
Keferring next to FI~U~E 2, the interface apparatus 10 of the present invention is shown in connection with an exemplary process control system comprising an air handling unit 11 arranged in fluid flow communication with a space 12 to be conditioned. The air handling uni~ 11 includes an inlet duct 13 for introducing outdoor ambient air to the space 12, an exhaust duct 1~ for removing air therefrom and a cross connected return duct 14a coupled between the inlet duct 13 and the exhaust duct 14. Fans 15 are provided for forced air movement. Each duct 13, 14, 14a includes a movable damper 16 disposed therein for controlling the flow of air therethrough. The inlet duct 13 also includes an air cooling coil 17 having chilled water passing therethrough and an air heating coil 1~
having hot water or steam passing therethrough, the coils 17, 18 being provided for controlling the temperature of air ~eing introduced into tne space 12. A chilled water valve 19 and a hot water valve 20 are coupled to the cooling coil 17 and heating coil 18 respectively for modulating the flow o~ liquid through the coils. The air handling unit 11 also includes pneumatic transducers for converting signals to another energy state as, for example, ~rom pneumatic to an electrical or mechanical signal. By way of illustration, such ~ransducers may include a plurality of pneumatic actuators or cylinders 21, each actuator being ~echanically coupled to its associated clamper 16 or valve 20 for controllable .
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positionin~ thereof. The transducers 21 may be coupled to a pneumatic ~s (not shown~ which provides a controlled pneumatic pressure for positioning the actuators 21 and tne associated da~yers 16 and valve 20. A direct digital system controller 27 is coupled to a parameter signalling device such as a therulostat 29 for receiving signals therefrom. ~he system controller 27 periodically samples a syste~ para~eter, e.g., the space ~emperature as signalled by the thermostat 29, compares it with the temperAture set point introduced and established within its computer ~ata base as symbolically represented by the arrow 31, digitally solves a control algorithm and generates digital electronic command signals for controlling a transducer position. For purposes of illustration, the invention will be described in colmection with a pneumatic cylinder 25 connected to the apparatus 10 by a pneumatic bus 26 and it is to be aypreciated that temperature is only one of several possible process system parameters, the control of which will be facilitated with the inventive interfacè apparatus 10 and that the latter is useful in systems for controlling processes wherever pneumatic transducers are employed for parameter control.
Referring next to FIG~R~S 2 and 3, a first embodiment of the interface apparatus lO is connected to an exemplary pneumatic transducer comprisin~ the spring biased, pneumatlcally positioned cylinder 25 coupled to a pivotable air damper 1~ for positioning control thereof.
The apparatus lO includes a pneumatic flow control means 33 which may be coupled to a first source 35 oE compressed fluid such as an air compressor set to a regulated pressure and coupled to the first end 37 of a pneumatic bus 38, the second end 39 of which is open for free fluld e~haustion to atmosyhere. While the regulated pressure may be selected in view of the ratin~s of the various .
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components coupled thereto, a source pressure of about 20 psig is common ~or process control of HVAC systems. A
pair of normally closed, electrically actuated solenoid valves includin~ a first input valve 41 and a second exhaust valve 43 are arran8ed in series for controlling the flow o~ pressuri~ed fluid to and from the substalltially constant, confined volume or vessel 4S
connected trlerebetween. The actuating solenoids of the first valve 41 an~ the second valve ~3 each have their electrical conductors 47 coupled to the system controller 27 for receiving command signals therefrom. Ihe pneumatic flow control means 33 also includes a plurality of restrictors including a first restrictor ~9 disposed in the bus adJacent the first valve 41 and second, third and fourth restrictors 51, 53, 55 respectively, disposed in the end 3~ adjacent the second valve 43. Each restrictor 49, 51, 53, 55 has a longitudinal passage or orifice 57 therethrough for controlling the rate of flow of compressed gas to or from the confined volume 45. Upon actuation of the first valve 41, the first restrictor 45 will permit fluid to restrictively flow from the source 35 to the confined volume 45 while actuation of the second valve 43 will permit fluid to be exhausted from the confined volume 45 through the second restrictor 51, through the third and/or fourth restrictors 53, 55 and thence to atmosphere. The restrictors 53 and 5S may be selected to have fixed orifice si2es which are substantially identical or which differ from one another so as to provide the desired ~lexibility in application.
The restrictors 53 and 55 may be replaced by a vernier adjustable restrictor downstream from the solenoid valve 43 but this arrangement would likely require shop or field calibration, a possibly costly procedure. Restrictors 53, 55 having fixed orifice si~es may be permanently installed or may be of the removable, insertable plug type. In .
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another alternative, the apparatus lO may also be embodied so that the second end 34 includes only a single exhaust port (not shown) having a single restrictor, e.g., restrictor 53 ~ixed therewithin.
Selective actu~tion of the first valve 41 or the secon~ valve 43 thereby facili~ates the regulation of a first pressure within the confined volume 45. When neither valve 41, 43 is actuated, t~le pressure in the volume 45 remains substantially constant ~or reasons set out in greater detail below. It should be appreciated that the interface apparatus 1~ will work equally well, irrespective of w~letller a restrictor 49, 51 is disposed in the bus 38 on the upstream or the downstream side o~ its associated valve 41, 4~ and the restrictor locations depicted are merely ~or illustration.
Keferrin~ to FIG~RES 3 an~ 5, the pneumatic flow control means 33 is coupled by a pneumatic bus 59 to the first input chamber 61 of a volume relay 63, the second output chamber 65 of which is coupled by an output bus 67 to one or ~ore transducers to be positioned such as transducer 25. ~ second source 69 of compressed gas at a substantially co~stant pressure, e.g., ~0 psig, is attached to the second chamber 65 as a pneumatic driver for the transducer 25. The volunle relay 63 includes a resilient diaphragm 71 disposed intermediate the first chamber 61 and the second chamber 65 for maintaining the chambers 61, 65 in fluid flow isolation one ~rom the other. The volume relay 63 is constructed ancl arranged such that the pressure in the second output chamber 65, and therefore in the output bus 67 and the transdLIcer 25, will have a predetermined relationship to the pressure in the first lnput chamber 61, irrespective o~ changes ln the latter.
The volume relay 63 ls preferably constructed and arranged such that the press~lre in the output chamber 65 . ., . ::
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is maintained at a predetermined relationship to that of the input chamber ~1. For reasons o~ simplicity of relay construction and ease of installation, testing and troubleshoo~ing, it is preferred that this relationship be linear and in the ratio of 1:1. It should also be noted that while the flexure of diaphragm 71 will result in slight momentary changes in the volume of gas defined by the ~irst chamber ~1, SUCtl changes are quite small and will have no significant effect upon the per~ormance of the inter~ace apparatus 10. It should be appreciated that in the first embodiment of FIGURE 3, the con~ined volume 45 is that which is enclosed by the ~irst chamber 61 of.
the volume relay 63 and that portion of the buses 38, 59 which is to the ri~ht of the solenoid valves 41, 43 as viewed in FIGURE 3. Other details of one type of volume relay ~3 ~seful in the present invention are shown and described in United States Letters Patent No. 4,207,914 whic~l is incorporated herein by reference.
A second embodiment of the interface apparatus 10 is partially shown in FIGURE 4 and differs from the first embodiment only in that a reservoir 73 is connected in fluid ~low communication with the bus 59. ~olu~etric sizing of the confined volume 45, the "V" component of the ideal gas equation, may be embodied as the aggregate confined volume 45 as described in the ~irst embodiment or, as shown in FIGURE 4, the aggregate volume 45 may additionally include that confined by the reservoir 73 coupled in parallel with the bus as shown or in series therewith.
It should be understood that the inter~ace apparatus 10 may be read~ly configured using available tubing, connector, restrictorl valve and volume relay components.
However, where higher production quantities warrant, the components may be packaged into a single structure having fluid-conductive passages and a confined volume 45 etched : .
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or otherwise formed therewithin. While tooling and design investment will necessarily bP increased with this latter approach, assembly costs will be materially lowered.
When selecting the volumetric size o~ the confined volume ~5, it is preferred that consideration be given to several design parameters selected in view o~ the aforementioned equation of state of an ideal gas. One such parameter is the magnitude of the operative volume of compressed gas de~ined within that portion of the interface ayparatus 10 and which is maintained substantially constant. The operative volume is that total volume 45 o~ compressed gas confined as described in the first embodiment, confined within any reservoir 73 employed and within the first chamber 61 taken together with the volume of any parasitic gas. Parasitic gas is that which resides in those portions of the flow control means 33 between a restrictor 49 or 51 and its associated solenoi~ valve, 41 or 43, respectively. I~ the valves 41, 43 are constructed with resistors incorporated therein, this parasitic volume may ~e practicall~ eliminated.
Another design parameter to be considered is that each of the orifices 57 in the restrictors 49, 51, 53, 55 will have a practical minimum diameter, typically on the order of G.GO5 inch, in order to avoid ori~ice plugging by small particles entrained in the gas and in order to permit manufacture of the restrictors 49, 51, 53, 55 by conventional techniques at low cost. Yet another parameter to be recognized is the leakage rate, if any, of the illustrated pneumatic connection points. This leakage rate may be reduced to a very low v~lue or eliminated entirely by potting the inter~ace apparatus lO with a gas-impervious compound after assembly. Still flnother parameter to be recognized is the desired slopes of the curves A, B which will result upon actuation o~ either of the valves ~1, 43.
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In the ca~e of an interface apparatus 10 having connectlon points char~cterized by small but detectable leaks, the minimum size of the confined volume 45 should preferably be that which will result in a pressure change in the gas contained within the confined volume 45 of less than about 1% over the maximum time interval during which the apparatu6 10 will be maintained in a quiescent state when neither the valve 41 nor the valve 43 is ~ctuated.
~his will normally be the maximum time interval between those consecutive times when the syætem controller 27 will sample a parameter, e.g., a temperature signal, and ~enerate corrective commands. For optimum cylinder positioning accuracy over extended periods of operation, it is pre~erred that this pressure change be limited to 15 one-half of 1% or less. If the interface apparatus 10 is potted to eliminate connection leaks altogether, the controlling parameter for the selection of the minimum cubic containment of the confined volume 45 becomes the desired maximum slopes of the curves A, B computed in view o~ the aforementioned equation and in view of the minimum orifice sizes available or desirable to be used. It is also to be appreciated th&t one of the aspects of the apparatus 10 is an adjustment feature which permits one to select a slope for a particular portion of curve A which coincides with the slope of a portion of curve B, ignoring algebraic sign.
In one embodiment of the invention, short lengths of tubin~ having an internal diameter of 0.0625 inches and a total confined volume of about 0.08 cubic inches were used to connect the solenoid valves 41, 43, a volume relay 63 having a first chamber volume o about 0.13 cubic inches and a reser~oir 73, all as configured in accordance with FIG~RE 4. E'urther, the parasitic volumes of compressed gas totaled approximately 0.006 cubic inches. For a first . .
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pressure source 35 regulated to a ~ressure of 20 psig, a first restrictor 44 orifice adjusted to a computed diameter of 0.00422 inches and a second restrictor 51 orlfice adJu6ted to a computed diameter o~ 0.00485 inches, the cubic confinement o~ the volume was selected to be 2.4 cubic inches and provided highly acceptable system accuracy for temperature sampling times spaced approxlmately three minutes apart.
Referring next to FIGURES 3, 5, 6 and 7, a commercial embodiment of the apparatus 10 is shown to include a generally cylindrical cover 75, an upper body 77, a center plate 7g and a lower body 81. The bodies 77, 81, the plate 79 and the other parts disposed therewithin are cooperatively formed to function in the manner of the volume relay 63 shown in FIGURE 5. A central barbed connection 83 is provided for the connection of a source of air 65 at a substantially constant pressure (FIGURE 3) while a radially disposed connector ~not shown) is provided for connecting to output bus 67 and the cylinder 25 of EIG~P~ 3. The plate 79 and body 81 are internally configured so that source 69 is also permitted to function as the source 35 of FIGURE 3, the supply to the first input valve being through a small filter 85. The first ; input valve 41 and the second exhaust valve 43 are similarly constructed and only the first input valve 41 will be described in detail. Referring additionally to FIGURE~ 8 and 9, the ~irst input valve ~1 includes a supply solenoid 87, a control nozzle ~9 and an extension 91 of a flexure lever 93 which is disposed intermediate the solenoid 87 and the nozzle 89 for controll~bly ~lowing air throu~h the latter. The control nozzle 89 includes an upper truncated cone sectiGn 95 and has a longitudinal passage 97 therethrough which is fitted with a control orifice 99. In ~he preferred embodiment and unlike the more common plastlc orifices 49, 51, 53, 55 having the ., , , . . ,. ~ :
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aforedescribed typical minimum opening therethrough, the orifice ~9 is ~ormed of sapphire and has an aperture nominally of 0.003" therethrough. By using an orifice of this type, ~hrough which air may flow relatively slowly, the physical size of the substantially constant volume 45 may be reduced.
Re~errin~ particularly to FIGU~ES ~, 9 and 10, a 1exure lever 93 is shown to include a ~irst extension 91 and a second extension 101, each extension 91, 101 bein slightly upwardly movable when its associated solenoid is energized. Each extension 91, 101 includes a ~errous armature member 103 and a lower valving button 105. In a preferred embodiment, the button 1~5 is embodied as a generally cylindrical cannister 107 for confining a resilient valving material 1~9, the cannister 107 having a lower opening 111 therethrough for permitting the material lOg to come in direct contact with the cone section 95.
The lever 93 includes a central aperture 113 for receiving the mountin~ post extension 115 of the upper body 77.
~eferring particularly to FIGURE 10, it is pre~erred that the mounting post 117 and its extension 115 define a shoulder 119 therebetween having an angularly sloping surface, a pre~erred angle to be nominally 4. A
pre~erred clamp block 121 has an inside diameter sufficientl~ in excess o~ that of the outside diameter o~
the extension 115 so as to ~reely fit therewith and define a small annular space therebetween. Ihe outer perimeter o~ the clamp block 121 defines a rectangle having a dimension between opposing sides whlch is preferably slightly less than the diameter of the post 117 while the lower lip 123 of the clamp block 121 is chamfered at an angle, slightly in excess of that of the shoulder 119, nominall~ 10. When ~ormed in that manner, there will be two edges of contact between the lip 123 of the clamp `
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-lg-block 121 and the lever 53 and a slight downward force will thereby be exerteci upon the e~tensions ~1, 101, thereby maintaining the valves 41, 43 closed in the absence of solenoid energization. ~ thin spacer shim (not shown~ may be interposed at assembly between each solenoid, as solenoid ~7, and its associated e~tension 91 so as to provide a slight air gap to result in a clean closure of the valves, as valve 41, wherl the solenoid 87 i6 de-energized. The shim is thereupon removed.
Re~erring again to FICURES 3, 4 and 7, in a preferred embodiment, the substantially constant volume 45 of air may be that volume 45' which is confined between the upper body 77 and the cover 75. Provision of the volume 45' in this manner avoids the necessity of including a separate air reservoir 73 and results in certain manufacturing and size economies. As shown in ~IGURE 6, the apparatus 10 may be conveniently constructed to include a pair of mounting ears 125 sized and located to engage the lips of a snap-in mounting track (not shown) for ease of mounting and serviceability.
Referring next to FI~URES 2 and 11, the electrical circuitry of the preferred apparatus 10 may be arranged with diodes 127 as shown so that either the supply solenoid 87 or the exhaust solenoid 129 may be energized from a direct digital controller 27 using DC signals of reversing polarity.
Keferring to the FIGURES and in operation, the digital system controller 27 samples a signal representing a parameter to be controlled such as the signal from the thermostat 2CJ representing actual space temperature, compares it with the desired data base temperature set point, solves a predetermined algorithm and generates a digital command signal for actuating either the first valve 41 or the second valve 43. Upon opening the first valve 41, compressed gas will flow from the source 35 or , ' ' ' ' ~ ', '' ' ' ,:
,,, . , "
, ": '' ,, ~7 ~ ~9 69, depending upon the embodiment, through the ~irst restrictor 49 or orifice 9g and the pressure within the confined volume 45 or 45' will rise at a rate per unit time deter~ined by the par~meters selected as described above. The pressure in the first chamber 61 will thereby be made to exceed that in the second chamber 65 and the diaphragm 71 is caused to ~lex rightwardly as seen in FIGURE 5. The plunger end portion 131 bearing against the check ball 133 will cause a movement of the ball 13~ away from sealing ed~e 135 and a conse~uent opening of the check valve, the area of the opening being generally proportional to the degree of diaphragm flexure.
Compressed gas trom the source 69 will thereby be permitted to flow through the check valvé to the second chamber 65, the output bus 67 and the transducer 25 until the pressure in the second chamber 65 comes to that value indicated by the design ratio oi the relay 63, typically l:i. The diaphragm 71 then returns to position equilibrium and the check ball 133 is returned to sealing-engagement with the edge 135. Any leakage of compressed gas from the connections of the output bus 67 will be sensed by the volume relay 63 which will function as described above to maintain pressure equilibrium.
Similarly, as the second valve 43 is actuated, compressed gas in the confined volume, 45, ~5' will be controllably exhausted through the second restrictor 51 and through one or more restrictors 53, 55 or as further described below, to atmospheric ambient. The pressure in the interface apparatus 10 wlll there~ore decline at a predetermined rate and the resulting difference in pressure between the second chamber 65 and the first chamber 61 will result in flexure of the diaphragm 71 to the le~t as viewed in FIGURE 5. Diaphragm movement will permit the passage 137 to be opened and compressed gas in the second chamber 65, the output bus 67 and the . . ,. ~ ,, .
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transducer 25 to be controllably exhausted to again bring the pressures of the first chamber 61 and the second chamber 65 into ratio equilibrium, whereupon the diaphragm 71 again moves to close passa~e 137.
It will be appreciated from the foregoing that in the embodiments of the apparatus 10 as shown in FIGURES 3 and 4, the size of the orifices 57 in the restrictors 53, 55 and the magtlitude of the con~ined volume 45 may be predetermined. Therefore, one may select restrictors 53 and/or 55 to have orifice sizes which will equalize the unsigned slopes of those portions o~ curves A and B over which it is desired to operate a par~icular cylinder or group of cylinders, e.g., the 3-8 psig portions. If either of the restrictors 53 or 5S is unused, it may simply be capped. In the embodiment of FIGURE 7, the matter of selecting exhaust restrictors is preferably accomplished by providing an insertable, removable restrictor 139 which is sized to slidably fit into the lower body in sealing engagement therewith. Since the a~regate volume of air confined in volume 45' and chamber 61 may be predetermi~ed at the time of design and manufacture, the apparatus 10 may be supplied with a plurality of restrictors 139, preferably three for a typical HVA~ application, each having an orifice of a different cross-sectional area to result in curves A, B
which have su~stantially equal slopes for the pressure range, e.g., 3-8 psig, 8-13 psig or 13-18 psig, over which cylinder 2S i8 desired to be operated.
The minimum ~olumetric 1uid delivery capacity of the sources 35 and/or 69 and the gas flow rate capacity of the relay 63 may be determined in a known manner and in a preferred embodiment, those delivery and flow rate capacities are selected such that the pressure in the second chamber 65 and the output bus 67 coincides with that of the ~irst chamber 61 with no appreciable time - . .
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delay therebetween. Further and in the case of the embodi~erlts of FIGU~ES 3 and 4, it is preferred that the regulated pressure of the second source 69 be closely matched to that of the first source 35.
It is to be appreciated that the interface apparatus 10 will, when con~tructed in accordance with the teaching of the specification, provide an output pressure to the cylinder transducer 25 whicll is a function of the duration of the signal applied to one of the ~alves 41, 43 by the controller 27 and that this result is accomplished without the use oE feedback control. Therefore, cylinder pressure will be unaffected by the length of bus 67 used to connect the transducer 25 to the volume relay 63 or by the functioning of the transducer 25 itself which changes in contained volume over its stroke length. By the selective use of restrictors 53 and/or 55 or by selecting an appropriate restrictor 135 in the embodiment of FIGURE 7, the slope of the operating portions of the curves may also be tailored for the application.
~lile only a few embodiments of the invention have been illustrated and described, it is not intended to be limited thereby but onl~ by the scope of the appended claims.
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PNEU~TIC INTERFACE APPARATUS
BACKGROUN~ OF THE INVENTION
I'neumatic control of process systems is widely employed wherever the system installation requires rugged components, lo~ered cost, relative ease of installation and troubleshooting and a high degree of controllability.
Examples of such processes which readily lend themselves to pneumatic control include the control of chiller and boiler temperature, steam or air line pressure control, flow control in fluid-transporting pipe systems, tank liquid level control, pH control in chemical processes, and heating, ventilating and air conditioning controls.
Pneumatic control is frequently employed in petrochemical process systems where flammable fluids are often present and may be ignited by electrical control devices. For purposes of illustration, and not by way of limitation, the invention is shown and described in connection with a heating, ventilating and air conditioning system.
~eating, ventilating and air conditioning (HVAC) systems are frequently used in buildings to control the temperature of a conditioned space within the building and ~or energy management purposes. A type of HVAC system includes an air handling unit having a plurality of '~'' -. . . ~ .
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27~
actuator-manipulated dampers for controlling the flow of outdoor air into the building, for controlling the flow of air exhausted from the building and for directing air which is heated or cooled and recirculated. ~ther mechanisms associated with air handling units typically include actuator-manipulated valves for controlling the flow of chilled or heated water through heat exchanger coils disposed in the ductwork for controlling the temperature o~ air 10wing therethrough.
One type of actuator used with such air handling units comprises a spring blased, pneumatic cylinder having i~s rod couple~ to a damper or valve. The cylinder is connected to a source of pneumatic pressure such as a pneumatic bus network formed of small diameter flexible polyeythlene tubing and installed throughout the building. Control is Dy the solution of known algorithms within a pneumatic controller and the generation of analog pneumatic output signals directed to the cylinders.
The relatively recent advent of computerized direct digital control apparatus and the desire of building owners to incorporate such computerized apparatus into new or existing HVAC systems employing low cost, rugged pneumatic actuators requires that a digital-to-pneumatic interface system be employed for receiving digital signals from the control apparatus and translating them to pneumatic signals for cylinder or other actuator positioning. These direct digital controllers may be constructed and arranged to repetitively solve any one or more of several known control algorithms for generating command sigTIals to the interface system and ~or reasons unrelated to the invention, it is often pre~erable to arrange the digital controller to provide command signals which direct the cylinder to undergo a computed change in cylinder pressure rather than to move to a new position as .~ ~ - . ' . .
, . . . : ~ .
, ' ' ' ' ' ' ' ~:77~91 represented by a new absolute pressure. Stated another w~y, it is o~ten preerable to arrange the digital controller and the attached system in a manner such that the ne~1 posit-Lon to be assumed by a cylinder is a function of the duration of the digital output signal oE the controller rather than a unction of the change in c~linder pressure. In commonly employed pneumatic control syster~s, it ~lay also be desir~ble to cause particular cylinders within the system to e~hibit full stroke over pressure ranges which may differ from cylinder to cylinder and commonly employed full stroke pressure ranges are 3-8 psig, ~-13 psig and 13-18 psig.
An example of an interface system useful for controlling the position of a single actuator or for the simultaneous control of the position of several actuators of t~le same size, full stroke pressure range and loading - is shown in United States Letters Patent No. 4,261,50g.
This system includes a pair of two position, electrically -~ctuated solenoid valves for receiving digital signals and controlling the flow of fluid into and out of the actuator. Pneumatic resistors, sometimes termed restrictors, having orifices therethrough typically of a few thousandths of an inch in diameter are disposed in the pneumatic lines for controlling actua~or stroke distance per unit time, i.e., for controlling the slopes of the actuator pressure-time graphs representative of actuator stroke characteristics in both directions of travel.
Another example of an interface device is shown in United States Letters Patent No. 4,440,066 and includes a pair o~ solenoid valves or controlling the ~low of air from a pressure source to a region of indeterminate volume and from the region to an area of ambient pressure. An adjustable ~low ori~ice i8 provided ~or controlling the flow rate to and from an attached actuator, e.g., a cylinder. United States Letters Patent No. 3,266,380 .
~ 2'77~
~L
shows the use of a reservoir as an integrating capaci~ance in a pneumatic computing device, unsuitable for interfaced control, which contemplates variable input pressures and which, like the apparatus of the aforementioned U.S.
Patent No. 4,440,066, includes a ~eedback (closed loop) feature.
While interface s~stems of the aforemention~d type have heretofore been satisfactory for the positioning of actuators, they are nevertheless characterized by certain disadvantages. For e~ample, when restrictors are used to control the stroking characteristics of a single actuator or of a group of actuators having the same size, spring range and loading, the restrictor orifice sizes must be selected by e~perimentation at the installation site.
This is so since actuator stroke times are dependent upon actuator size, spring range, loading and the volume of fluid contained within the actuator and the pneumatic interconnections. These parameters are frequently difficult or impossible to determine prior to actual installation. If the HVAC system requires actuator sequencing and incorporates actuators having different volumetric sizes, spring ranges and/or loadings, the system will exhibit highly nonlinear gain characteristics and the control problem ls thereby further complicated.
Using the interface system of the aforementioned V.S.
Patent No. 4,261,5~9 as illustrative, and assuming a plurality of parallel connected disslmilarly-configured actuators to be controlled, the percent change of position will be different for each actuator for a given time during which a solenoid is energized for introducing fluid to or expelling fluid Erom the actuators. This results from the fact that a change in the contained volume of ~luid o~ one actuator will affect the ~troke distance per unit time of other actuators in accordance with the .
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equation of state of an ideal gas. If restrictors are selected ~o control the stroke time of, for example, a small, lightly loaded actuator, the system response will be unacceptably sluggish for positioning larger or more heavily loaded actuators. Conversely, if restrictors are selected for the proper control of actuators of the latter type, system instabilities may result. Even with the addition of a device called a pilot positioner to some or all o the actuators, restrictor selection must be by field experimentation or by measurement and computation of the volume of compressed fluid contained within the pneumatic interconnections and the pilot positioner pressure chamber6.
A further disadvantage of systems of the aforementioned type is that they are susceptible to significant leaks of pneumatic fluid. For example, each pneumatic connection of 1/4 inch tubing typically has a leak rate of approximately 0.1 standard cubic inches per minute (SCIM) at 20 psig while a typical pilot positioner has a leak rate of 0.3 SCIM. In a system including a constant volume reservoir where the system contains a relatively small volume of fluid and/or a large number of connection points and pilot positioners, changes in the control pressure due to leaks within the system and over the time interval between parameter sample times, e.g., conditioned-space temperature sampling times, would be unacceptabl~ large.
Accordingly, an interface system which permits preselection of restrictor orifice sizes irrespective of the configuration of the related pneumatic bus and actuators, which may be used to control actuators havlng a wide variet~ of contained fluid volumes and which may have an adjustment feature permitting its use with actuators which may operate over any one of several pressure ranges would be a significant advance over the prior art.
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~2 ~ 7 SU~ARY OF THE INVENTICN
-In general, the interface apparatus of the present invention includes a pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure.
A volume relay has a first chamber coupled to the control means by the con~ined volume of gas and a second chamber for coupling to a pneumatic actuator to be positionably controlled, the first chamber and the second chamber being in fluid flow isolation one rom the other. The volume relay provides a second pressure at its second chamber which has a predetermined relationship to the first pressure. Means having a substantially constant, confined volume are interposed between the flow control means and the relay and cooperates with the flow control means for determinin~ the slopes of the actuator pressure~time graphs. The flow control means may include means for adjusting the rate of flow o~ the gas from the substantially constant volume to a re~ion of ambient pressure.
It is an object of the invention to provide a new and improved interface apparatus for positionin~ pneumatic actuators which overcomes disadvantages of the prior art.
Another object of the invention is to provide an interface apparatus which permits the preselection of flow controlling restrictors.
Yet another object of the invention is to provide an interface apparatus which provldes actuator positionin~
chAracteristics that are independent of the size or number of actuators connected thereto.
Still another object of the present invention is to provide an interface apparatus which may include means for field adjustment of the rate of flow of a gas from a .
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substantially constant confined volume to a region of ambient pressure.
Anotiler object of the present invention is to provide an interface apparatus which is useul with direct digital controllers.
Yet another object of the present invention is to provide an interface apparatus which results in movement of an actuatln~ cylinder to a new position which is a computed function of the duration of a digital signal from a direct digital controller. How these and other objects of the invention are accomplished will become more apparent from the detailed description thereof taken with the accompanying drawing.
~ESCRIPlION OF THE DRAWING
FIGURE 1 is a graphical depiction of described rise and decay characteristics of the pressure within a substantially constant confined volume of a gas;
FIGURE 2 is a simplified schematic diagram showing the interface apparatus of the present invention in conjunction with an exemplary process control system comprising an air handling unit;, FIGURE 3 is a pictorial schematic diagram of a first embodiment of the interface apparatus shown in FIGURE 2 with portions shown in cross-section and other portions shown in full representation;
FIGURE 4 is a pictorial schematic dlagram of a second embodiment of the interface apparatus of FIGURE 2 with parts broken away, portions shown in cross-section and other portions shown in full representation;
FIGURE 5 i9 a cros~-sectional view of the volume relay portion of the interface apparatus taken in the plane 5-5 of FIGURE 3 and with portions shown in full representation;
'~ "' ' "''' '' : ' ',' ''' ' " ,' '' ', ' .
7~ ~9 FIG~RE 6 is a top plan view of a commercial embodiment of the inventive apparatus;
~ lGUKE 7 is a side elevation view of the apparatus of FIGURE 6 taken along the plane 7-7 thereof with portions shown in cross-section and other portions shown in full representation;
~ h ~ is a top plan view of the flexure lever of the apparatus of FIGURE 7;
FIGUR~ ~ ls a side elevation view of the lever of FIGUR~ o taken along the plane 9-9 thereof;
FIGURh 10 ls a cross-section, side elevation view of the center plate of the apparatus with parts added in exploded view, and;
FlGUR~ 11 is an electrical schematic diagram of the apparatus.
DESCRIPTION OF THE PREFERRED EMBODI~ENTS
:
Understanding of the invention will be aided by an explanation of t~e relevant gas law and from the field of applied physics, the equation of state of an ideal gas is expressed as:
pV = I~T
where p = pressure of a gas in a substan-tially rigid, confining volume or vessel;
V = the confined volume of the vessel;
n ~ the number of moles of gas within the vessel;
R = the universal gas constant, and;
T ~ the temperature o~ the gas in K.
From the equation, it will be apparent that if the temperature of the gas confined in the vessel is held constant, a reasonable assumption for this analysis, and , . :.
. . . .
_9_ if the volume of the vessel remains unchanged, the pressure of the ~as will have a direct relationship to the number of moles of the gas confined within the vessel.
Understanding of the invention will also be aided by referral to the graph of FIGU~E 1 which depicts the rise and decay characteristics o~ the gas pressure pre~ailing within a substantially constant, confined volume of gas.
Curve A represents the pressure rise characteristic over time when a gas is introduced into the confined volume from a source of constant pressure, e.g., 20 psig and through a particular flow-restricting orifice. The initial pressure in the volume is assumed to be 0 psig.
Curve B represents the pressure decay characteristic over time when the pressurized gas within the volume is permitted to be expelled from the volume to an area of ambient pressure, e.g., an area at 0 psig, expulsion being through ~ particularly sized ~low-restricting orifice.
~ontrol of gas flow into and out of the volume may be by a pair of normally closed, two position solenoid valves.
Since curves A and B are both nonlinear, it is apparent that ii on~ desires to operate a cylinder over, for example, the range C of 3 8 psig, that generally linear portion of curve A which falls within the range C
has a slope which is dramatically different from the slightly arcuate portion of curve B which falls within range C when ignoring the algebraic sign of the slopes.
Therefore, with a cylinder pressure within range C and rising along curve A, the magnitude of the change in pressure per unit time is different ~rom that o a declining cylinder pressure along curve B and within range C. This may present an unacceptable result if the cylinder is desired to be operated by signals from a digital controller where cylinder positioning i~
preferably by a computed signal dura~ion rhther than by measuring changes in pressure or by other means.
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On the other hand, the slopes of curves A and B in the range D o~ 8-13 psig are substantially equal one to the other if algebraic sign is ignored and this demonstrates that the particular orifice used in the system on which the curves ~re based would likely be satisfactory for cylinder operation over the range of 8-13 psig with a digital controller.
Keferring next to FI~U~E 2, the interface apparatus 10 of the present invention is shown in connection with an exemplary process control system comprising an air handling unit 11 arranged in fluid flow communication with a space 12 to be conditioned. The air handling uni~ 11 includes an inlet duct 13 for introducing outdoor ambient air to the space 12, an exhaust duct 1~ for removing air therefrom and a cross connected return duct 14a coupled between the inlet duct 13 and the exhaust duct 14. Fans 15 are provided for forced air movement. Each duct 13, 14, 14a includes a movable damper 16 disposed therein for controlling the flow of air therethrough. The inlet duct 13 also includes an air cooling coil 17 having chilled water passing therethrough and an air heating coil 1~
having hot water or steam passing therethrough, the coils 17, 18 being provided for controlling the temperature of air ~eing introduced into tne space 12. A chilled water valve 19 and a hot water valve 20 are coupled to the cooling coil 17 and heating coil 18 respectively for modulating the flow o~ liquid through the coils. The air handling unit 11 also includes pneumatic transducers for converting signals to another energy state as, for example, ~rom pneumatic to an electrical or mechanical signal. By way of illustration, such ~ransducers may include a plurality of pneumatic actuators or cylinders 21, each actuator being ~echanically coupled to its associated clamper 16 or valve 20 for controllable .
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positionin~ thereof. The transducers 21 may be coupled to a pneumatic ~s (not shown~ which provides a controlled pneumatic pressure for positioning the actuators 21 and tne associated da~yers 16 and valve 20. A direct digital system controller 27 is coupled to a parameter signalling device such as a therulostat 29 for receiving signals therefrom. ~he system controller 27 periodically samples a syste~ para~eter, e.g., the space ~emperature as signalled by the thermostat 29, compares it with the temperAture set point introduced and established within its computer ~ata base as symbolically represented by the arrow 31, digitally solves a control algorithm and generates digital electronic command signals for controlling a transducer position. For purposes of illustration, the invention will be described in colmection with a pneumatic cylinder 25 connected to the apparatus 10 by a pneumatic bus 26 and it is to be aypreciated that temperature is only one of several possible process system parameters, the control of which will be facilitated with the inventive interfacè apparatus 10 and that the latter is useful in systems for controlling processes wherever pneumatic transducers are employed for parameter control.
Referring next to FIG~R~S 2 and 3, a first embodiment of the interface apparatus lO is connected to an exemplary pneumatic transducer comprisin~ the spring biased, pneumatlcally positioned cylinder 25 coupled to a pivotable air damper 1~ for positioning control thereof.
The apparatus lO includes a pneumatic flow control means 33 which may be coupled to a first source 35 oE compressed fluid such as an air compressor set to a regulated pressure and coupled to the first end 37 of a pneumatic bus 38, the second end 39 of which is open for free fluld e~haustion to atmosyhere. While the regulated pressure may be selected in view of the ratin~s of the various .
: :" . ' , ,` ' . ' ' ' . ' " "' ' ' ~" . ' ' , ' . ' ~2~
components coupled thereto, a source pressure of about 20 psig is common ~or process control of HVAC systems. A
pair of normally closed, electrically actuated solenoid valves includin~ a first input valve 41 and a second exhaust valve 43 are arran8ed in series for controlling the flow o~ pressuri~ed fluid to and from the substalltially constant, confined volume or vessel 4S
connected trlerebetween. The actuating solenoids of the first valve 41 an~ the second valve ~3 each have their electrical conductors 47 coupled to the system controller 27 for receiving command signals therefrom. Ihe pneumatic flow control means 33 also includes a plurality of restrictors including a first restrictor ~9 disposed in the bus adJacent the first valve 41 and second, third and fourth restrictors 51, 53, 55 respectively, disposed in the end 3~ adjacent the second valve 43. Each restrictor 49, 51, 53, 55 has a longitudinal passage or orifice 57 therethrough for controlling the rate of flow of compressed gas to or from the confined volume 45. Upon actuation of the first valve 41, the first restrictor 45 will permit fluid to restrictively flow from the source 35 to the confined volume 45 while actuation of the second valve 43 will permit fluid to be exhausted from the confined volume 45 through the second restrictor 51, through the third and/or fourth restrictors 53, 55 and thence to atmosphere. The restrictors 53 and 5S may be selected to have fixed orifice si2es which are substantially identical or which differ from one another so as to provide the desired ~lexibility in application.
The restrictors 53 and 55 may be replaced by a vernier adjustable restrictor downstream from the solenoid valve 43 but this arrangement would likely require shop or field calibration, a possibly costly procedure. Restrictors 53, 55 having fixed orifice si~es may be permanently installed or may be of the removable, insertable plug type. In .
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another alternative, the apparatus lO may also be embodied so that the second end 34 includes only a single exhaust port (not shown) having a single restrictor, e.g., restrictor 53 ~ixed therewithin.
Selective actu~tion of the first valve 41 or the secon~ valve 43 thereby facili~ates the regulation of a first pressure within the confined volume 45. When neither valve 41, 43 is actuated, t~le pressure in the volume 45 remains substantially constant ~or reasons set out in greater detail below. It should be appreciated that the interface apparatus 1~ will work equally well, irrespective of w~letller a restrictor 49, 51 is disposed in the bus 38 on the upstream or the downstream side o~ its associated valve 41, 4~ and the restrictor locations depicted are merely ~or illustration.
Keferrin~ to FIG~RES 3 an~ 5, the pneumatic flow control means 33 is coupled by a pneumatic bus 59 to the first input chamber 61 of a volume relay 63, the second output chamber 65 of which is coupled by an output bus 67 to one or ~ore transducers to be positioned such as transducer 25. ~ second source 69 of compressed gas at a substantially co~stant pressure, e.g., ~0 psig, is attached to the second chamber 65 as a pneumatic driver for the transducer 25. The volunle relay 63 includes a resilient diaphragm 71 disposed intermediate the first chamber 61 and the second chamber 65 for maintaining the chambers 61, 65 in fluid flow isolation one ~rom the other. The volume relay 63 is constructed ancl arranged such that the pressure in the second output chamber 65, and therefore in the output bus 67 and the transdLIcer 25, will have a predetermined relationship to the pressure in the first lnput chamber 61, irrespective o~ changes ln the latter.
The volume relay 63 ls preferably constructed and arranged such that the press~lre in the output chamber 65 . ., . ::
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.
is maintained at a predetermined relationship to that of the input chamber ~1. For reasons o~ simplicity of relay construction and ease of installation, testing and troubleshoo~ing, it is preferred that this relationship be linear and in the ratio of 1:1. It should also be noted that while the flexure of diaphragm 71 will result in slight momentary changes in the volume of gas defined by the ~irst chamber ~1, SUCtl changes are quite small and will have no significant effect upon the per~ormance of the inter~ace apparatus 10. It should be appreciated that in the first embodiment of FIGURE 3, the con~ined volume 45 is that which is enclosed by the ~irst chamber 61 of.
the volume relay 63 and that portion of the buses 38, 59 which is to the ri~ht of the solenoid valves 41, 43 as viewed in FIGURE 3. Other details of one type of volume relay ~3 ~seful in the present invention are shown and described in United States Letters Patent No. 4,207,914 whic~l is incorporated herein by reference.
A second embodiment of the interface apparatus 10 is partially shown in FIGURE 4 and differs from the first embodiment only in that a reservoir 73 is connected in fluid ~low communication with the bus 59. ~olu~etric sizing of the confined volume 45, the "V" component of the ideal gas equation, may be embodied as the aggregate confined volume 45 as described in the ~irst embodiment or, as shown in FIGURE 4, the aggregate volume 45 may additionally include that confined by the reservoir 73 coupled in parallel with the bus as shown or in series therewith.
It should be understood that the inter~ace apparatus 10 may be read~ly configured using available tubing, connector, restrictorl valve and volume relay components.
However, where higher production quantities warrant, the components may be packaged into a single structure having fluid-conductive passages and a confined volume 45 etched : .
' , ' ' ,, : .
:
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or otherwise formed therewithin. While tooling and design investment will necessarily bP increased with this latter approach, assembly costs will be materially lowered.
When selecting the volumetric size o~ the confined volume ~5, it is preferred that consideration be given to several design parameters selected in view o~ the aforementioned equation of state of an ideal gas. One such parameter is the magnitude of the operative volume of compressed gas de~ined within that portion of the interface ayparatus 10 and which is maintained substantially constant. The operative volume is that total volume 45 o~ compressed gas confined as described in the first embodiment, confined within any reservoir 73 employed and within the first chamber 61 taken together with the volume of any parasitic gas. Parasitic gas is that which resides in those portions of the flow control means 33 between a restrictor 49 or 51 and its associated solenoi~ valve, 41 or 43, respectively. I~ the valves 41, 43 are constructed with resistors incorporated therein, this parasitic volume may ~e practicall~ eliminated.
Another design parameter to be considered is that each of the orifices 57 in the restrictors 49, 51, 53, 55 will have a practical minimum diameter, typically on the order of G.GO5 inch, in order to avoid ori~ice plugging by small particles entrained in the gas and in order to permit manufacture of the restrictors 49, 51, 53, 55 by conventional techniques at low cost. Yet another parameter to be recognized is the leakage rate, if any, of the illustrated pneumatic connection points. This leakage rate may be reduced to a very low v~lue or eliminated entirely by potting the inter~ace apparatus lO with a gas-impervious compound after assembly. Still flnother parameter to be recognized is the desired slopes of the curves A, B which will result upon actuation o~ either of the valves ~1, 43.
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.
~2~7~19gL
In the ca~e of an interface apparatus 10 having connectlon points char~cterized by small but detectable leaks, the minimum size of the confined volume 45 should preferably be that which will result in a pressure change in the gas contained within the confined volume 45 of less than about 1% over the maximum time interval during which the apparatu6 10 will be maintained in a quiescent state when neither the valve 41 nor the valve 43 is ~ctuated.
~his will normally be the maximum time interval between those consecutive times when the syætem controller 27 will sample a parameter, e.g., a temperature signal, and ~enerate corrective commands. For optimum cylinder positioning accuracy over extended periods of operation, it is pre~erred that this pressure change be limited to 15 one-half of 1% or less. If the interface apparatus 10 is potted to eliminate connection leaks altogether, the controlling parameter for the selection of the minimum cubic containment of the confined volume 45 becomes the desired maximum slopes of the curves A, B computed in view o~ the aforementioned equation and in view of the minimum orifice sizes available or desirable to be used. It is also to be appreciated th&t one of the aspects of the apparatus 10 is an adjustment feature which permits one to select a slope for a particular portion of curve A which coincides with the slope of a portion of curve B, ignoring algebraic sign.
In one embodiment of the invention, short lengths of tubin~ having an internal diameter of 0.0625 inches and a total confined volume of about 0.08 cubic inches were used to connect the solenoid valves 41, 43, a volume relay 63 having a first chamber volume o about 0.13 cubic inches and a reser~oir 73, all as configured in accordance with FIG~RE 4. E'urther, the parasitic volumes of compressed gas totaled approximately 0.006 cubic inches. For a first . .
, . .
- , . . : :
,- , - . :: . , :
. . ~ . . .
, .
.
pressure source 35 regulated to a ~ressure of 20 psig, a first restrictor 44 orifice adjusted to a computed diameter of 0.00422 inches and a second restrictor 51 orlfice adJu6ted to a computed diameter o~ 0.00485 inches, the cubic confinement o~ the volume was selected to be 2.4 cubic inches and provided highly acceptable system accuracy for temperature sampling times spaced approxlmately three minutes apart.
Referring next to FIGURES 3, 5, 6 and 7, a commercial embodiment of the apparatus 10 is shown to include a generally cylindrical cover 75, an upper body 77, a center plate 7g and a lower body 81. The bodies 77, 81, the plate 79 and the other parts disposed therewithin are cooperatively formed to function in the manner of the volume relay 63 shown in FIGURE 5. A central barbed connection 83 is provided for the connection of a source of air 65 at a substantially constant pressure (FIGURE 3) while a radially disposed connector ~not shown) is provided for connecting to output bus 67 and the cylinder 25 of EIG~P~ 3. The plate 79 and body 81 are internally configured so that source 69 is also permitted to function as the source 35 of FIGURE 3, the supply to the first input valve being through a small filter 85. The first ; input valve 41 and the second exhaust valve 43 are similarly constructed and only the first input valve 41 will be described in detail. Referring additionally to FIGURE~ 8 and 9, the ~irst input valve ~1 includes a supply solenoid 87, a control nozzle ~9 and an extension 91 of a flexure lever 93 which is disposed intermediate the solenoid 87 and the nozzle 89 for controll~bly ~lowing air throu~h the latter. The control nozzle 89 includes an upper truncated cone sectiGn 95 and has a longitudinal passage 97 therethrough which is fitted with a control orifice 99. In ~he preferred embodiment and unlike the more common plastlc orifices 49, 51, 53, 55 having the ., , , . . ,. ~ :
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. . ' ' ' .
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aforedescribed typical minimum opening therethrough, the orifice ~9 is ~ormed of sapphire and has an aperture nominally of 0.003" therethrough. By using an orifice of this type, ~hrough which air may flow relatively slowly, the physical size of the substantially constant volume 45 may be reduced.
Re~errin~ particularly to FIGU~ES ~, 9 and 10, a 1exure lever 93 is shown to include a ~irst extension 91 and a second extension 101, each extension 91, 101 bein slightly upwardly movable when its associated solenoid is energized. Each extension 91, 101 includes a ~errous armature member 103 and a lower valving button 105. In a preferred embodiment, the button 1~5 is embodied as a generally cylindrical cannister 107 for confining a resilient valving material 1~9, the cannister 107 having a lower opening 111 therethrough for permitting the material lOg to come in direct contact with the cone section 95.
The lever 93 includes a central aperture 113 for receiving the mountin~ post extension 115 of the upper body 77.
~eferring particularly to FIGURE 10, it is pre~erred that the mounting post 117 and its extension 115 define a shoulder 119 therebetween having an angularly sloping surface, a pre~erred angle to be nominally 4. A
pre~erred clamp block 121 has an inside diameter sufficientl~ in excess o~ that of the outside diameter o~
the extension 115 so as to ~reely fit therewith and define a small annular space therebetween. Ihe outer perimeter o~ the clamp block 121 defines a rectangle having a dimension between opposing sides whlch is preferably slightly less than the diameter of the post 117 while the lower lip 123 of the clamp block 121 is chamfered at an angle, slightly in excess of that of the shoulder 119, nominall~ 10. When ~ormed in that manner, there will be two edges of contact between the lip 123 of the clamp `
. : , . -:
' .. .. : .. ' : .
.
~77~9~
-lg-block 121 and the lever 53 and a slight downward force will thereby be exerteci upon the e~tensions ~1, 101, thereby maintaining the valves 41, 43 closed in the absence of solenoid energization. ~ thin spacer shim (not shown~ may be interposed at assembly between each solenoid, as solenoid ~7, and its associated e~tension 91 so as to provide a slight air gap to result in a clean closure of the valves, as valve 41, wherl the solenoid 87 i6 de-energized. The shim is thereupon removed.
Re~erring again to FICURES 3, 4 and 7, in a preferred embodiment, the substantially constant volume 45 of air may be that volume 45' which is confined between the upper body 77 and the cover 75. Provision of the volume 45' in this manner avoids the necessity of including a separate air reservoir 73 and results in certain manufacturing and size economies. As shown in ~IGURE 6, the apparatus 10 may be conveniently constructed to include a pair of mounting ears 125 sized and located to engage the lips of a snap-in mounting track (not shown) for ease of mounting and serviceability.
Referring next to FI~URES 2 and 11, the electrical circuitry of the preferred apparatus 10 may be arranged with diodes 127 as shown so that either the supply solenoid 87 or the exhaust solenoid 129 may be energized from a direct digital controller 27 using DC signals of reversing polarity.
Keferring to the FIGURES and in operation, the digital system controller 27 samples a signal representing a parameter to be controlled such as the signal from the thermostat 2CJ representing actual space temperature, compares it with the desired data base temperature set point, solves a predetermined algorithm and generates a digital command signal for actuating either the first valve 41 or the second valve 43. Upon opening the first valve 41, compressed gas will flow from the source 35 or , ' ' ' ' ~ ', '' ' ' ,:
,,, . , "
, ": '' ,, ~7 ~ ~9 69, depending upon the embodiment, through the ~irst restrictor 49 or orifice 9g and the pressure within the confined volume 45 or 45' will rise at a rate per unit time deter~ined by the par~meters selected as described above. The pressure in the first chamber 61 will thereby be made to exceed that in the second chamber 65 and the diaphragm 71 is caused to ~lex rightwardly as seen in FIGURE 5. The plunger end portion 131 bearing against the check ball 133 will cause a movement of the ball 13~ away from sealing ed~e 135 and a conse~uent opening of the check valve, the area of the opening being generally proportional to the degree of diaphragm flexure.
Compressed gas trom the source 69 will thereby be permitted to flow through the check valvé to the second chamber 65, the output bus 67 and the transducer 25 until the pressure in the second chamber 65 comes to that value indicated by the design ratio oi the relay 63, typically l:i. The diaphragm 71 then returns to position equilibrium and the check ball 133 is returned to sealing-engagement with the edge 135. Any leakage of compressed gas from the connections of the output bus 67 will be sensed by the volume relay 63 which will function as described above to maintain pressure equilibrium.
Similarly, as the second valve 43 is actuated, compressed gas in the confined volume, 45, ~5' will be controllably exhausted through the second restrictor 51 and through one or more restrictors 53, 55 or as further described below, to atmospheric ambient. The pressure in the interface apparatus 10 wlll there~ore decline at a predetermined rate and the resulting difference in pressure between the second chamber 65 and the first chamber 61 will result in flexure of the diaphragm 71 to the le~t as viewed in FIGURE 5. Diaphragm movement will permit the passage 137 to be opened and compressed gas in the second chamber 65, the output bus 67 and the . . ,. ~ ,, .
. . .
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~Z7~9~L
transducer 25 to be controllably exhausted to again bring the pressures of the first chamber 61 and the second chamber 65 into ratio equilibrium, whereupon the diaphragm 71 again moves to close passa~e 137.
It will be appreciated from the foregoing that in the embodiments of the apparatus 10 as shown in FIGURES 3 and 4, the size of the orifices 57 in the restrictors 53, 55 and the magtlitude of the con~ined volume 45 may be predetermined. Therefore, one may select restrictors 53 and/or 55 to have orifice sizes which will equalize the unsigned slopes of those portions o~ curves A and B over which it is desired to operate a par~icular cylinder or group of cylinders, e.g., the 3-8 psig portions. If either of the restrictors 53 or 5S is unused, it may simply be capped. In the embodiment of FIGURE 7, the matter of selecting exhaust restrictors is preferably accomplished by providing an insertable, removable restrictor 139 which is sized to slidably fit into the lower body in sealing engagement therewith. Since the a~regate volume of air confined in volume 45' and chamber 61 may be predetermi~ed at the time of design and manufacture, the apparatus 10 may be supplied with a plurality of restrictors 139, preferably three for a typical HVA~ application, each having an orifice of a different cross-sectional area to result in curves A, B
which have su~stantially equal slopes for the pressure range, e.g., 3-8 psig, 8-13 psig or 13-18 psig, over which cylinder 2S i8 desired to be operated.
The minimum ~olumetric 1uid delivery capacity of the sources 35 and/or 69 and the gas flow rate capacity of the relay 63 may be determined in a known manner and in a preferred embodiment, those delivery and flow rate capacities are selected such that the pressure in the second chamber 65 and the output bus 67 coincides with that of the ~irst chamber 61 with no appreciable time - . .
~ . ' ' ` ~ ' , . `
: , ~Zt77~3L9~
delay therebetween. Further and in the case of the embodi~erlts of FIGU~ES 3 and 4, it is preferred that the regulated pressure of the second source 69 be closely matched to that of the first source 35.
It is to be appreciated that the interface apparatus 10 will, when con~tructed in accordance with the teaching of the specification, provide an output pressure to the cylinder transducer 25 whicll is a function of the duration of the signal applied to one of the ~alves 41, 43 by the controller 27 and that this result is accomplished without the use oE feedback control. Therefore, cylinder pressure will be unaffected by the length of bus 67 used to connect the transducer 25 to the volume relay 63 or by the functioning of the transducer 25 itself which changes in contained volume over its stroke length. By the selective use of restrictors 53 and/or 55 or by selecting an appropriate restrictor 135 in the embodiment of FIGURE 7, the slope of the operating portions of the curves may also be tailored for the application.
~lile only a few embodiments of the invention have been illustrated and described, it is not intended to be limited thereby but onl~ by the scope of the appended claims.
.
,
Claims (4)
1. A pneumatic interface apparatus for control of process systems comprising:
pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure;
a volume relay having a first chamber coupled to said control means by a pneumatic bus and further having a second chamber for coupling to a pneumatic transducer to be positionably controlled, said first chamber and said second chamber being in fluid flow isolation one from the other, said relay providing a second pressure at said second chamber which has a predetermined relationship to said first pressure;
a reservoir coupled between said control means and said relay, said bus, said relay and said reservoir cooperating to define said substantially constant volume of gas;
said flow control means including means for adjusting the rate of flow of said gas from said substantially constant volume to a region of ambient pressure, including a pneumatic restrictor having an orifice flow passage of a first cross-sectional area, said restrictor being removable from said flow control means and replaceable by a restrictor having an orifice flow passage of a second cross-sectional area.
pneumatic flow control means for controlling the number of moles of a gas confined within a substantially constant volume of gas at a first pressure;
a volume relay having a first chamber coupled to said control means by a pneumatic bus and further having a second chamber for coupling to a pneumatic transducer to be positionably controlled, said first chamber and said second chamber being in fluid flow isolation one from the other, said relay providing a second pressure at said second chamber which has a predetermined relationship to said first pressure;
a reservoir coupled between said control means and said relay, said bus, said relay and said reservoir cooperating to define said substantially constant volume of gas;
said flow control means including means for adjusting the rate of flow of said gas from said substantially constant volume to a region of ambient pressure, including a pneumatic restrictor having an orifice flow passage of a first cross-sectional area, said restrictor being removable from said flow control means and replaceable by a restrictor having an orifice flow passage of a second cross-sectional area.
2. An open loop pneumatic interface apparatus for controlling a pneumatic pressure in a heating, ventilating and air conditioning system and including:
penumatic flow control means for connection to a first source of compressed air at a substantially constant pressure, said first source being connectable at a single point of said flow control means, said flow control means including normally closed first and second solenoid valves, said valves being adapted to receive pulsed electrical input signals from a direct digital system controller, said first valve being energizable for flowing compressed air from said first source to means having a substantially constant confined volume, said second valve being energizable for flowing compressed air from said confined volume to an area of ambient pressure;
said flow control means further including means for adjusting the rate of flow of a gas from said confined volume to said area of ambient pressure, including a pneumatic restrictor means having an orifice flow passage of a first cross-sectional area, said pneumatic restrictor means being removable from said flow control means and replaceable by a pneumatic restrictor means having an orifice flow passage of a second cross-sectional area;
a pressure repeater for providing an analog output pressure, said repeater including a first chamber coupled to said confined volume and a second chamber for connection to a pneumatic cylinder to be positionably controlled, said first chamber and said second chamber being in fluid flow isolation one from the other, said repeater providing a second pressure signal at said second chamber which has a magnitude substantially identical to the magnitude of a first pressure signal at said input means;
said confined volume including a reservoir coupled between said flow control means and said repeater means for controlling the rate of change of said first pressure signal upon energization of said first valve or said second valve;
said second chamber being connectable to a second source of compressed gas at a substantially constant pressure, said flow control means, said first chamber and said confined volume cooperating to define a predetermined, substantially constant volume of gas, thereby resulting in changes in the position of said cylinder which are solely a function of the time of energization of one of said solenoid valves.
penumatic flow control means for connection to a first source of compressed air at a substantially constant pressure, said first source being connectable at a single point of said flow control means, said flow control means including normally closed first and second solenoid valves, said valves being adapted to receive pulsed electrical input signals from a direct digital system controller, said first valve being energizable for flowing compressed air from said first source to means having a substantially constant confined volume, said second valve being energizable for flowing compressed air from said confined volume to an area of ambient pressure;
said flow control means further including means for adjusting the rate of flow of a gas from said confined volume to said area of ambient pressure, including a pneumatic restrictor means having an orifice flow passage of a first cross-sectional area, said pneumatic restrictor means being removable from said flow control means and replaceable by a pneumatic restrictor means having an orifice flow passage of a second cross-sectional area;
a pressure repeater for providing an analog output pressure, said repeater including a first chamber coupled to said confined volume and a second chamber for connection to a pneumatic cylinder to be positionably controlled, said first chamber and said second chamber being in fluid flow isolation one from the other, said repeater providing a second pressure signal at said second chamber which has a magnitude substantially identical to the magnitude of a first pressure signal at said input means;
said confined volume including a reservoir coupled between said flow control means and said repeater means for controlling the rate of change of said first pressure signal upon energization of said first valve or said second valve;
said second chamber being connectable to a second source of compressed gas at a substantially constant pressure, said flow control means, said first chamber and said confined volume cooperating to define a predetermined, substantially constant volume of gas, thereby resulting in changes in the position of said cylinder which are solely a function of the time of energization of one of said solenoid valves.
3. The invention set forth in claim 2 wherein said flow control means includes said first solenoid valve and a first restrictor cooperating therewith for the selective introduction of a restricted flow of compressed gas into said reservoir and said flow control means further includes said second solenoid valve connected to said pneumatic restrictor means for said selective exhaustion of said gas from said reservoir to an area of ambient pressure.
4. The invention set forth in claim 3 wherein said confined volume includes pneumatic conductors interconnect-ing said solenoid valves, said reservoir and said first chamber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79170485A | 1985-10-28 | 1985-10-28 | |
| US791,704 | 1985-10-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1277191C true CA1277191C (en) | 1990-12-04 |
Family
ID=25154540
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000519206A Expired - Fee Related CA1277191C (en) | 1985-10-28 | 1986-09-26 | Pneumatic interface apparatus |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS62106103A (en) |
| AU (1) | AU6074386A (en) |
| BE (1) | BE905670A (en) |
| CA (1) | CA1277191C (en) |
| DE (1) | DE3627164A1 (en) |
| FR (1) | FR2589261A1 (en) |
| GB (1) | GB2182173A (en) |
| IT (1) | IT1197918B (en) |
| NL (1) | NL8602524A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4004519A1 (en) * | 1989-02-17 | 1990-08-30 | Rox Lufttechnische Geraetebau | Combined ventilation and air conditioning system - allows mixing of extracted air with pre-conditioned external air |
| JP2013076858A (en) * | 2011-09-30 | 2013-04-25 | Hitachi High-Technologies Corp | Optical element and shape inspecting apparatus |
| JP2013076806A (en) * | 2011-09-30 | 2013-04-25 | Hitachi High-Technologies Corp | Optical element and method of manufacturing the same |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB714719A (en) * | 1951-01-13 | 1954-09-01 | Taylor Instrument Co | Improvements in pneumatically operated control system |
| US4207914A (en) * | 1977-01-31 | 1980-06-17 | Johnson Controls, Inc. | Fluid relay apparatus |
| US4199101A (en) * | 1979-01-26 | 1980-04-22 | Johnson Controls, Inc. | Multiple load integrated fluid control units |
-
1986
- 1986-07-31 AU AU60743/86A patent/AU6074386A/en not_active Abandoned
- 1986-08-11 DE DE19863627164 patent/DE3627164A1/en not_active Withdrawn
- 1986-09-26 GB GB08623190A patent/GB2182173A/en not_active Withdrawn
- 1986-09-26 CA CA000519206A patent/CA1277191C/en not_active Expired - Fee Related
- 1986-10-08 NL NL8602524A patent/NL8602524A/en not_active Application Discontinuation
- 1986-10-24 IT IT22141/86A patent/IT1197918B/en active
- 1986-10-27 FR FR8614916A patent/FR2589261A1/en not_active Withdrawn
- 1986-10-27 JP JP61253906A patent/JPS62106103A/en active Pending
- 1986-10-28 BE BE905670A patent/BE905670A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BE905670A (en) | 1987-04-28 |
| GB2182173A (en) | 1987-05-07 |
| IT8622141A1 (en) | 1988-04-24 |
| GB8623190D0 (en) | 1986-10-29 |
| AU6074386A (en) | 1987-04-30 |
| JPS62106103A (en) | 1987-05-16 |
| NL8602524A (en) | 1987-05-18 |
| FR2589261A1 (en) | 1987-04-30 |
| IT8622141A0 (en) | 1986-10-24 |
| DE3627164A1 (en) | 1987-04-30 |
| IT1197918B (en) | 1988-12-21 |
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