Abstract:
Disclosed is a device for regulating the pressure and/or flow of a gas stream, which device comprises a housing ( 9, 109 ) which is provided with a pressure-regulating chamber ( 4, 104 ), at least part of whose wall comprises a diaphragm ( 10, 110 ), which diaphragm ( 10, 110 ) is subjected, on the side remote from the pressure-regulating chamber ( 4, 104 ), to an adjustable prestressing force, the pressure-regulating chamber comprising an inlet opening ( 3, 28, 128 ) for a gas and an outlet opening ( 5, 29, 129 ) for a gas, it being possible for at least one of the openings ( 3/5, 28/29, 128/129 ) to be completely or partially closed off with the aid of a displaceable closure member ( 15, 115 ) which is connected to the diaphragm ( 10, 110 ) in such a manner that the position of the closure member is dependent on the displacement of the diaphragm.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     (Not applicable.) 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device for regulating the pressure and/or the flow of a gas stream, which device comprises a housing which is provided with a pressure-regulating chamber, at least part of whose wall comprises a diaphragm, which diaphragm is subjected, on the side remote from the pressure-regulating chamber, to an adjustable prestressing force, the pressure-regulating chamber comprising an inlet opening for a gas and an outlet opening for a gas, it being possible for at least one of the openings to be completely or partially closed off with the aid of the diaphragm. This means that the extent to which the diaphragm bends is dependent, on the one hand, on the instantaneous pressure in the pressure-regulating chamber and, on the other hand, on the stress which is applied to the diaphragm with the aid of the prestressing means, wherein the diaphragm is actively connected to a pressure chamber for a gas, which pressure chamber is provided with has an inlet opening for a gas and an outlet opening for a gas for setting the pressure in the pressure chamber for the purpose of applying the prestressing force. 
     A device of the abovementioned type is known in the prior art. The device may be used, for example, to regulate a gas stream which is at a relatively high pressure down to a gas stream at a lower pressure. The position of the closure member is linked to the bending of the diaphragm. Consequently, the pressure of the gas stream which leaves the pressure-regulating chamber via the outlet opening will be determined by the position of the diaphragm in a starting position. The known device can be used to reduce the pressure of a gas stream to a desired level. The pressure of the gas stream which will leave the pressure-regulating chamber at the outlet opening will be dependent on the size of the inlet opening which is left open by the closure member. The more the closure member closes off the inlet opening, the lower the pressure flowing out of the outlet opening of the pressure-regulating chamber will be. 
     The above mentioned device is (i.a.) known from U.S. Pat. No. 4,798,521. From this document a device is known for regulating the pressure in a container. In addition to the mentioned elements, the known device comprises means for measuring possible differences in the pressure in the pressure chamber and the device&#39;s outlet opening, which differences can used for regulating the pressure in the pressure chamber. 
     BRIEF SUMMARY OF THE INVENTION 
     An important drawback associated with devices known from the prior art is that it still is impossible to accurately set the position of the diaphragm. In practice the switching time of the valves inside the inlet opening and the outlet opening will not be infinitesimal. There will always be a physical limitation which limits the accuracy of the control. 
     The object of the present invention is to provide a device of the type mentioned in the introduction with which it is possible to accurately set the position of the diaphragm. It is also desirable for it to be possible to adjust a position of the diaphragm once it has been set, in a relatively simple manner. 
     These objects are achieved, in the present invention, in that the inlet opening is provided with a flow restriction. Therewith it is possible that outlet opening is provided with a flow restriction. 
     The use of a pressure chamber in which a gas is kept under pressure allows the position of the diaphragm in the starting position, and therefore the position of the closure member in the inlet opening of the pressure-regulating chamber, to be adjusted with the aid of a gas pressure. By increasing or reducing the pressure in the pressure chamber, the position of the diaphragm can be fixed as desired. 
     Because of the presence of the restrictions at both the inlet opening and the outlet opening it is possible to control the flow to and from the pressure chamber with a much higher accuracy then before. 
     According to the invention it is further possible that the side of the diaphragm which is remote from the pressure-regulating chamber adjoins the pressure chamber. Therewith it is possible that the inlet opening and the outlet opening of the pressure chamber are provided with a remotely controllable shut-off valve. 
     Therewith the position of the diaphragm can be altered by altering the pressure in the pressure-regulating chamber. 
     These measures ensure, in a very simple manner, that the pressure in the pressure chamber can be increased or reduced. The remotely controllable shut-off valves allow the setting of the pressure in the pressure-regulating chamber to be coupled, for example, to measuring means which are accommodated elsewhere in the device. 
     According to the present invention, it is possible for the device to be provided with means for measuring the pressure of the gas stream, which measuring means are arranged in the vicinity of the outlet opening of the pressure-regulating chamber. It is also possible for the device to be provided with means for measuring the pressure of the gas stream, which measuring means are arranged in the vicinity of the inlet opening of the pressure-regulating chamber. In this case, it is advantageous for the device to be provided with regulating means which are actively connected to, on the one hand, the means for measuring the gas pressure and, on the other hand, the remotely controllable shut-off valves of the pressure chamber. 
     These measures ensure that the pressure or the flow of the gas stream which leaves/flows into the pressure-regulating chamber can be monitored. By additionally coupling this pressure measurement to the remotely controllable shut-off valves, it is possible for any deviations in the measured pressure of the gas stream to be directly translated into a change in the position of the diaphragm. 
     According to the invention, it is also possible for the diaphragm to be connected, via a coupling member, to a second diaphragm, the said second diaphragm adjoining the pressure chamber, and that side of the diaphragm which is remote from the pressure-regulating chamber adjoining a second pressure chamber, the pressure-regulating chamber being in communication, via a restriction, with a feed line for a gas, and the second pressure-regulating chamber being in open communication with the said feed line. 
     This measure allows the present invention to be used for setting a diaphragm, with both its sides adjoining a feed line for a gas stream. The first side of the diaphragm adjoins a closed space which contains an outlet opening and is connected to the feed line via a restriction. The other side of the diaphragm adjoins a closed space which is in free communication with the feed line. If flow takes place from the feed line, via the restriction, to the outlet opening of the closed space on the first side of the diaphragm, the presence of the restriction will cause there to be a pressure difference across the diaphragm. This pressure difference determines the position of the diaphragm and hence the extent to which the outlet opening is closed off. The equilibrium position about which the diaphragm will move can be set, by means of the measures described above, with the aid of the said pressure chamber, it being possible to vary the pressure in the pressure chamber. At least one wall of the pressure chamber is formed by a second diaphragm which is connected, via a coupling member, to the diaphragm which is connected on both sides to the feed line. 
     The present invention also relates to a gas chromatograph provided with the above mentioned device. 
     The device according to the present invention is especially suited to be used in a gas chromatograph. Firstly because at both sides of the diaphragm a gas is present, diffusion through the material of the diaphragm will be limited to a minimum. Further it is possible to connect both the inlet opening of the pressure-regulating chamber and the inlet opening of the pressure chamber to one and the same feed line. That means that on both sides of the diaphragm the same gas will be present. In the gas chromatograph it is possible to add a substance to be examined to the gas flow when the pressure of the gas flow has been decreased from a relatively high pressure to a relatively low pressure, i.e. downstream of the device according to the present invention. The result of this will be that possible loss of material to be examined will be prevented. 
     In a second aspect, the present invention relates to a method for regulating the pressure or a flow of a gas stream, in which the gas stream to be regulated is fed from an inlet chamber, via an inlet opening, to a pressure-regulating chamber, at least part of whose wall is formed by a diaphragm, the pressure in the pressure-regulating chamber being regulated by adjusting the size of the inlet opening of the pressure-regulating chamber with the aid of a closure member which is actively connected to the diaphragm in such a manner that a change in the level of displacement of the diaphragm causes a change to the extent to which the closure member closes off the inlet opening, the diaphragm being subjected to a prestressing force, with the aid of which a specific positioning is imposed on the diaphragm. 
     The method according to this invention is characterized in that the said prestressing force is applied by a pressurized gas in the pressure chamber, the starting position of the diaphragm being set by setting the pressure of the gas in the pressure chamber. 
     According to the present invention, it is possible for the gas stream to be discharged from an outlet opening of the pressure-regulating chamber. In this case, it is advantageous for the pressure of the gas stream to be measured at least periodically in the vicinity of the outlet opening of the pressure-regulating chamber, and for the measured value to be compared with a desired value which is dependent on the starting position of the diaphragm, and for the pressure in the pressure chamber to be increased or reduced on the basis of this comparison by feeding or discharging gas to or from the pressure chamber. 
     This measure makes it possible to keep the pressure in the gas stream which leaves the pressure-regulating chamber as close as possible to the desired value. In principle, the device is designed in such a way that any deviations from the desired pressure in the gas stream emerging from the pressure-regulating chamber caused by variations in the position of the diaphragm can be eliminated by the device itself. Any undesirable residual variations can be effectively eliminated by means of the method according to the invention. 
     Furthermore, it is possible, according to the invention, for a volume of gas to be fed to the pressure chamber, during or after which process a different volume of gas is discharged from the pressure chamber. 
     The effect of this measure is that during use of the device according to the invention there is no problem with so-called dead spaces. If an insufficient volume of gas were to be fed to the pressure chamber, the diaphragm might react in a non-linear manner to this addition of gas. By ensuring that the volume of gas which is supplied is always greater than a specific threshold, and that a certain volume of gas is discharged during or immediately after this volume of gas has been supplied, it is ensured that, on balance, small volumes of gas can be fed to the pressure chamber, in other words that the pressure in the pressure chamber can be adjusted very accurately without there being problems with dead spaces. 
     According to the invention, it is advantageous if the pressure in the pressure chamber is allowed to gradually increase or decrease. 
     For certain applications, it may be advantageous to allow the pressure of the gas stream which leaves the pressure-regulating chamber to gradually increase or decrease. For example, in the case of a gas chromatograph, it may be that in the event of variations in pressure, different elements are separated out of the gas stream in a column which may be positioned in a line which is connected to the device according to the present invention. If the pressure in the pressure chamber is now gradually varied, the pressure of the gas stream leaving the pressure-regulating chamber will also vary. These variations may benefit the separating capacity of the column. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 shows a device for regulating the pressure or the flow of the gas stream according to the prior art; 
     FIG. 2 shows a device for regulating the pressure in a gas stream according to a preferred design; 
     FIG. 3 shows a diagrammatic overview of a gas chromatograph in which the device according to the present invention is arranged; 
     FIG. 4 shows a diagrammatic overview of possible input and output parameters of a pressure control computer useful in the gas chromatograph illustrated in FIG. 3; 
     FIG. 5 diagrammatically shows the feed of a gas stream to the pressure chamber; 
     FIG. 6 shows a possible embodiment of the device according to the present invention, in a miniaturized form; 
     FIG. 7 diagrammatically shows the present invention in the form of a “backpressure” regulator; 
     FIG. 8 is a schematic view of the operation of a pressure control module useful in the gas chromatograph illustrated in FIG. 3; 
     FIG. 9 is a schematic view of the operation of a fuzzy pressure controller useful in the gas chromatograph illustrated in FIG. 3; and 
     FIG. 10 shows a possible variant design of the device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a device  1  by means of which it is possible to regulate the pressure of a gas stream. The device in accordance with FIG. 1 is known in the prior art. 
     The device in accordance with FIG. 1 comprises a gas inlet chamber  2  which is connected, via an inlet opening  3 , to a pressure-regulating chamber  4 . In addition to the inlet opening  3 , this pressure-regulating chamber also comprises an outlet opening  5 . The inlet chamber  2  forms a passage which is provided with means  6  for connecting a gas line, for example. The means  6  may, for example, comprise a nut. The outlet opening  5  of the pressure-regulating chamber  4  is connected to a passage  7  which is provided with means  8  for connection of a gas line, for example. 
     On the top side, in the position shown in the figure, the pressure-regulating chamber  4  is closed off by means of a flexible member or diaphragm  10 . On its top side, the diaphragm  10  is connected to a spring  11 . The spring  11  can be used to apply a stressing force to the diaphragm  10 . The extent of the stressing force exerted by the spring  11  on the diaphragm  10  is dependent on the setting of the setscrew  12  which is actively connected to the top side (in the position shown in the figure) of the spring  11 . 
     On the underside, the diaphragm  10  is connected to a closure member  15 . The closure member  15  is coupled to the diaphragm  10  in such a manner that the position of the closure member  15  is dependent on the bending of the diaphragm  10 . 
     It can be seen in FIG. 1 that the closure member  15  is connected, on the underside, to a spring  17 . This spring  17  ensures that the closure member  15  is positioned correctly in the outlet opening  3  of the pressure-regulating chamber by the interaction of the diaphragm  10  and the spring  17 . 
     The device  1  according to the prior art operates as follows: 
     The setscrew  12  and the spring  11  are used to set a specific spring pressure on the diaphragm  10 . The spring pressure acting on the diaphragm  10  sets the position of the closure member  15  in the feed opening  3 . Then, the inlet chamber  2  is connected to a relatively high-pressure line. Via the passage  7 , the discharge opening  5  can be connected to a line in which it is desired to have a gas stream at a constant pressure. The gas stream from the inlet chamber  2  to the pressure-regulating chamber  4  will exert a pressure on the underside of the diaphragm  10 . The pressure which is built up in the pressure-regulating chamber  4 , on the one hand, and the pressure which is exerted by the spring  11 , on the other hand, together determine the position of the diaphragm  10 . In this case, the higher the pressure in the pressure-regulating chamber  10  becomes, the greater the distance between the diaphragm  10  and the inlet opening  3  of the pressure-regulating chamber  4  will be. As a result, the closure member  15  will be pulled upwards, so that the inlet opening  3  will be closed off further. Since the passage is closed off further, the gas stream from the inlet chamber  2  to the pressure-regulating chamber  4  will decrease. As a result, the pressure in the pressure-regulating chamber  4  will fall, with the result that the diaphragm  10  will move slightly downwards. As a result, the opening formed in the feed opening  3  will increase in size again, so that the pressure in the pressure-regulating chamber  4  can increase again. It will be clear that coupling the diaphragm  10  to the closure member  15  will result in an automatically established equilibrium in the pressure-regulating chamber  4 . The level of this equilibrium pressure in the pressure-regulating chamber  4 , and hence the level of flow from the chamber  4 , can be set with the aid of the setscrew and the spring  11 . The equilibrium pressure which will prevail in the pressure-regulating chamber  4  will ensure a flow of gas through the outlet opening  5  and the adjoining passage  7  which is at an essentially constant pressure. 
     The device  1  for regulating the pressure of a gas stream according to the prior art can be used in a gas chromatograph. For a chromatograph of this nature to operate correctly, it is important that it is possible for the gas stream which is to be analyzed to be forced through a column, for example, at a pressure which is easy to set and constant. The device  1  according to the prior art is therefore installed in the feed line of a column of this nature. 
     A significant drawback of the device  1  according to the prior art is that it is necessary for a pressure to be continuously exerted on the diaphragm  10  with the aid of the spring  11 . Moreover, the diaphragm  10  cannot be accurately set with the aid of the spring  11  and the setscrew  12 . A further drawback is that the diaphragm  10  may cause diffusion to occur. Pressurized gas will be present in the pressure-regulating chamber  4 . Depending on the material of the diaphragm  10 , it is possible that certain components of the gas in the pressure-regulating chamber  4  may diffuse through the diaphragm  10 . This means that these constituents will disappear from the gas stream and will not leave the pressure-regulating chamber via the outlet opening  5 . If the device  1  according to the prior art is used, for example, for a gas chromatograph, the occurrence of diffusion may mean that the measurements taken will be unreliable. 
     FIG. 2 shows an exemplary embodiment of the device  20  for regulating the pressure of a gas stream according to the present invention. The device  20  comprises a housing  9  in which an inlet chamber  2  is incorporated. Via an inlet opening  3 , this inlet chamber  2  is connected to the pressure-regulating chamber  4 . On its top side (in the position shown in the figure), the pressure-regulating chamber  4  is closed off by means of a flexible member  10 . The pressure-regulating chamber  4  is connected to a passage  7  via an outlet opening  5 . The inlet chamber  2  can be connected to a connection line for a gas, for example, with the aid of connection means  6 . With the aid of connection means  8 , passage  7  can be connected to, for example, a discharge line for gas. On the top side of the diaphragm  10 , the device according to the present invention comprises a pressure chamber  21 . This pressure chamber  21  comprises an inlet opening  22  and an outlet opening  23 . The inlet opening  22  and the outlet opening  23  can be connected to a feed line  24  for gas and a discharge line  25  for a gas, respectively. Remotely controllable closure members  26  and  27  may be arranged in the lines  24  and  25 , respectively. In the device  20 , measuring means  30 , which can be used to measure the pressure of the gas in the vicinity of the outlet opening  5 , are arranged in the vicinity of the outlet opening  5 . These pressure-measuring means  30  are actively connected to a control unit  31 . This control unit may, for example, contain features which compare the values measured by the means  30  with desired or set values. The control unit  31  is in turn actively connected to the remotely controllable shut-off valves  26  and  27 . 
     The device  20  according to the present invention functions as follows: 
     With the aid of the attachment means  6 , a gas line containing a gas which is at a relatively high pressure can be connected to the inlet chamber  2 . Using each of the attachment means  6 .  8 , a discharge line for discharging a gas can be attached to the passage  7 . In this line, it is possible to generate a gas stream which is at a relatively constant pressure. The gas flows towards the pressure-regulating chamber  4  via the inlet chamber  2  and the inlet opening  3 . The gas stream then leaves the pressure-regulating chamber  4  via the outlet opening  5  in the passage  7 . Just as in the device according to the prior art, the inlet opening  3  can be closed off with the aid of a closure member  15  which is actively connected to the diaphragm  10 . In this case, the higher the pressure in the pressure-regulating chamber  4  becomes, and the more the diaphragm  10  is displaced, the smaller the free flow passage for the gas from the inlet chamber  2  towards the pressure-regulating chamber  4 , via the inlet opening  3 , will become. Just as in the prior art, an equilibrium pressure, and therefore an equilibrium flow, will be automatically built up in the pressure-regulating chamber  4 . This means that a gas stream which is at an essentially constant pressure will leave the pressure-regulating chamber  4  via the outlet opening  5 . In the device  20  according to the invention, the equilibrium level of the pressure which is set in the pressure-regulating chamber  4  is not dependent on a spring pressure, but rather on a pressure which is built up in a pressure chamber  21  on the opposite side of the diaphragm  10 . This means that the pressure of the diaphragm  10  is essentially determined, on the one hand, by the pressure in the pressure-regulating chamber  4  and, on the other hand, by the pressure in the pressure chamber  21 . Like the pressure-regulating chamber  4 , the pressure chamber  21  is provided with an inlet opening  22  and an outlet opening  23 . As has been stated, the inlet opening  22  may also be connected to a gas line  24 . A closure member  26  may be arranged in this gas line  24 . A similar arrangement applies to the outlet opening  23 , to which a gas line  25  can be coupled. A closure member  27  can be arranged in this gas line  25 . 
     When it is desired to set the pressure in the pressure chamber  21 , the shut-off valves  26  and  27  can be opened and closed as desired and gas can be fed to or discharged from the pressure chamber  21  with the aid of the lines  24  and  25 . 
     In use, the pressure of the gas which prevails in the discharge passage  7  will be periodically or continuously measured with the aid of the measuring means  30 . This measurement information will be transmitted to the control unit  31 . The control unit  31  is actively connected to the shut-off valves  26  and  27  in the lines  24  and  25 . If, for example, it is established by the measuring means  30  that the pressure of the gas which is flowing out of the pressure-regulating chamber  4  is too high, the pressure in the pressure chamber  21  can be reduced by opening the shut-off valve  27  in the line  25  for a certain time. As a result, gas will be able to escape from the pressure chamber  21 , with the result that a new equilibrium pressure can be established in the pressure-regulating chamber  4 . 
     It should be noted that the discharge line  25  is generally able to flow out freely to the environment. 
     The advantage of the device  20  according to the present invention is that the position of the diaphragm  10  can be adjusted with a relatively high degree of accuracy. If desired, the gas feed via the inlet opening  22  of the pressure chamber  21  can be used to feed gas until the correct pressure is reached in the pressure-regulating chamber  4 . In this case, the periodic measurement of the pressure in the discharge passage  7  can be used as an input signal for adjusting the pressure in the pressure chamber  21 . 
     An additional advantage is that the pressure in the pressure chamber  21  can be changed, for example periodically or gradually. Applications are known, for example in the case of gas chromatographs, in which it is advantageous if the pressure of the gas stream which is fed to a chromatograph increases or decreases, for example. In the event of a varying pressure, it will be possible to separate different components by means of the detection means which are generally coupled to the column which is used in a chromatograph (not shown). By periodically varying this pressure of the gas which is fed to the chromatograph, it is possible to carry out numerous refined measurements. 
     FIG. 3 diagrammatically depicts the use of a device  20  according to the invention which is employed in a gas chromatograph. From a source (not shown), a gas stream is fed towards the inlet chamber  2 . As explained in FIG. 2, the inlet chamber  2  can be closed off from the pressure-regulating chamber  4  with the aid of the closure member  15 . The pressure which is built up in the pressure-regulating chamber  4  on the underside of the diaphragm  10  and the pressure which is built up in the pressure chamber  21  on the top side of the diaphragm  10  together determine the position of the diaphragm  10 , and hence the position of the closure member  15  in the inlet opening  3  between the inlet chamber  2  and the pressure-regulating chamber  4 . Via the outlet opening  5 , a gas stream which is at an essentially constant pressure will flow through the passage  7 . Since a constant pressure is ensured, the volume of the flow will also be constant. This stream which is at an essentially constant pressure is fed from the passage  7  towards an injector  32 . With the aid of this injector, the gas stream is fed, for example, to a column chroinatograph which is diagrammatically indicated by  33 . This column chromatograph may, for example, comprise a coiled glass tube in which a separating medium is arranged. The gas stream emerging from the column is then fed to detection means which are diagrammatically indicated by  34 . The detection means may be coupled to a processing unit, such as a PC 35 . This PC may also serve, for example, to control the temperature regulation of the chromatograph. This is diagrammatically indicated by the line T. The PC 35  can also be used to control the control unit  31  which is used to regulate the pressure in the pressure chamber  21 . The pressure in the pressure-regulating chamber  20  is regulated as described with reference to FIG.  2 . 
     FIG. 3 further shows that the pressure regulating chamber  4  is provided with a valve for relieving the pressure, pressure relief valve  72 . The path at the output of pressure-regulating chamber  4  sometimes exhibits a high flow restriction, attrubutable to the presence of a long column having a small internal diameter. Because of this high (flow) restriction the speed for regulating from a relatively high pressure to a relatively low pressure is limited. Pressure relief valve  72  enables a part of the redundant gas flow, to be released through flow restriction  70 . 
     Pressure relief valve  72  also serves as a pressure safety valve. When because of malfunctioning or leakage the pressure in the pressure regulating chamber  4  is too high, the control unit  31  will react, by opening pressure relief valve  72 . Therefore, possible damage to the system can be prevented. 
     Moreover, FIG. 3 shows, that the inlet which is connected to the inlet chamber  2  is the same as the inlet connected to the valve  26 . That mean that the gas that is being used for regulating the pressures in both the chamber  4  and  21  comes from the same source. When used as a gas chromatograph normally a stable gas flow is established, before adding the medium to be examined to the gasflow, upstream of the column. 
     Moreover in FIG. 3 it shows that between the respective valve  26  and  27  and the pressure chamber  21  flowrestrictions  41 ,  42  are present. These valves have at least a certain minimal switching time, therefore it is possible that when the valves are opened an amount of gas is being transported through the valve that, in respect of the volume of the pressure chamber, is too large in order to obtain the preferred control characteristics. By adding the restrictions at both the inlet and outlet opening of the pressure chamber  21  an accurate control can be established. 
     Alternatively a so called “padding” (not shown) can be used. This padding can be positioned inside the opening of the valve connected to the inlet opening or oulet opening of the pressure chamber. Because of the presence of the padding the volume between the valve sealing and the restriction can be partially filled. Therefore, even a smaller amount of gas having a relatively high pressure will be transported through the valve, thereby increasing the accuracy of the pressure control. 
     If it is desired to adjust the pressure in the pressure-regulating chamber  4 , and therefore the pressure of the gas stream which will be guided out of the passage  7  of the device  20 , gas has to be discharged from or fed to the pressure chamber  21  with the aid of the shut-off valves  26  and  27 . If it is desired to accurately adjust the pressure in the pressure chamber  21 , it is preferable to use small volumes of gas which are fed to or discharged from the pressure chamber  21 . Owing to the volume of the pressure chamber  21  itself, there will inevitably be a certain volume of dead space. This means that feeding or discharging a small volume of gas from the pressure chamber  21  will not have any effect on the position of the diaphragm  10 , and hence on the ultimate pressure in the pressure-regulating chamber  4 . The regulating arrangement illustrated in FIG. 4 5  can be used to avoid this “dead space” being formed. If the pressure in the pressure chamber  21  is to be increased, a relatively large volume of gas is fed into the pressure chamber via the shut-off valve  26 . This is indicated by the line IN. At the same time, a slightly smaller volume of gas is released from the pressure chamber  21  via the shut-off valve  27 . This is indicated by the line OUT. The net result is that a relatively small volume of gas will be fed to the pressure chamber  21 . This is indicated by the line IN (RESULT). 
     In practice, it is, for example, possible, when setting the pressure in the pressure chamber  21 , firstly to opt for supplying gas in a few large steps via the shut-off valve  26 . When the vicinity of the desired setpoint is reached, the setting of the pressure can be refined using the method illustrated in FIG.  5 . 
     It can be seen from FIG. 3 that a restriction  41  is arranged between the shut-off valve  26  and the inlet opening of the pressure chamber  21 . A similar restriction  42  is also arranged between the outlet opening of the pressure chamber  21  and the shut-off valve  27 . These restrictions  41  and  42  are to be regarded as “delay means” for the gas stream. In order to be able to correctly and accurately regulate the gas stream fed into the pressure chamber  21  and the gas stream discharged from the pressure chamber  21 , it is advantageous to position a filter-like retention member in the line from the shut-off valve  26  and in the line to the shut-off valve  27 . This retention member may be likened to a resistor in an electrical line. The restrictions  41  and  42  may, for example, be formed by sintered material. The gas stream is allowed through but delayed by a porous, spongy structure of the sintered material. 
     FIG. 4 depicts which parameters will be fed to the “pressure control computer”, PC  35 , shown in FIG.  3 . The incoming signals e.g. can be used for the flow set, the gas viscosity, the pressure out, the ambient pressure, the diameter and length of the column connected to the pressure-regulating chamber  4  and/or the set oven temperature. All these parameters can be forwarded to the “pressure control computer”, PC  35 , which sends signals to the control valves subsequently to establish the required pressure (Pset). 
     The device  20  according to the present invention is suitable in particular for very small applications. The design of the device  20  means that it can be miniaturized relatively easily. One exemplary embodiment is a device  20  made of silicon, for example, using etching techniques. 
     In FIG. 6, the inlet chamber  2  is situated on the top side of the diaphragm  10 . The lines illustrated in the figure will in practice have a thickness of a few μm. The pressure chamber  21  is situated on the underside of the diaphragm  10  in the device  20 . The shut-off valves  26  and  27  are respectively formed by flexible closure lips which are shown on the left and right in the figure. 
     The present invention refers to the use of the device  20  according to the present invention for forming a stream of gas which is at an essentially constant pressure from a feed gas stream which is at a relatively high pressure. The structure which has already been discussed with reference to the figures mentioned above may, however, also be employed, with a minor adaptation, as back pressure regulator. This means that in this case the inlet is formed by the passage  7  which will serve as the feed passage. From the passage  7 , the gas stream flows into the pressure-regulating chamber  4 . In this case too, the position of the diaphragm  10  is determined by the pressure which prevails in both the pressure-regulating chamber  4  and the pressure chamber  21 . The description of the figures mentioned above refers to the opening between the passage  2  and the pressure-regulating chamber  4  decreasing in size as the pressure in the pressure-regulating chamber  4  increases. It can be seen from FIG. 6 7  that in the device  60 , which is intended to regulate a back pressure regulator, the outlet opening  29  between the pressure-regulating chamber  4  and the passage  2  increases in size as the pressure in the pressure-regulating chamber  4  increases. In practice, this will mean that when a gas stream is supplied via the passage  7  and the outlet opening  28 , this gas stream can be fed to the pressure-regulating chamber  4  at an essentially constant pressure and with an essentially constant flow. Like the device  20  discussed above, the device  60  is equipped with measuring means  30 , which can be used to measure the pressure of the gas stream in the passage  7 . These measuring means  30  are actively connected to the control means  31 , with the aid of which the shut-off valves  26 ,  27  can be operated. 
     In FIG. 8 schematically the outlook over the pressure control computer is shown, which can be used in the device and the method according to the present invention. The pressure control computer is provided with electronics, such as a single chip micro controller and a high resolution A/D converter. The micro controller can by means of a serial interface communicate with any other instrument. By means of interface, parameters for pressure control can be set and the actual value of the pressure can be established. Every pressure control computer can monitor several pressure controls, completely independently. Moreover every pressure control computer has a known address, therefore several modules can be monitored in parallel by means of the same ire interface. 
     During calibration of the device, the values for calibration of the pressure sensors can be forwarded to the pressure control computer and automatically the off-set-values are determined. This calibration can be executed with reference to any reference-pressure. In the software these values can be used to correct the off-set automatically and to calculate the right pressure values. 
     The software present in the pressure control computer comprises a control algorithm, based on the use of fuzzy logic. As inputs for the fuzzy pressure controller (FPC) both the absolute variation of the actual pressure with respect to the said point and the speed of the pressure change can be used. Also other inputs such as the ambient temperature and the ambient pressure can be used as an input. The output of the fuzzy pressure controller determines how the valve should be controlled. 
     The advantage of the fuzzy pressure controller is that it is not necessary to make a mathematical model of the behaviour of the device and the influence of the valves in the entire pressure-range. Building such a mathematical model in practice is very awkward, because the model strongly depends of on the ambient conditions, the actual work pressure ends the variable restrictions in the system. The fuzzy pressure controller is based on the fact that both the measured values and the set values will be divided by intervals, which overflow. By means of a fuzzy rule base the measured values will be examined and the right value for correction will be generated, wherein the fuzzy pressure controller will be working in a fully adaptive mode. That means that the ambient conditions, the non lineair behaviour of the device and the valves will be automatically compensated in the fuzzy process controller, therefore establishing a simple way for obtaining the required performance within the total pressure-range. This is schematically shown in FIG.  9 . In the center of FIG. 9, the fuzzy pressure controller is shown, being connected to a fuzzy rule base. As input signals of the fuzzy pressure controller are used the actual pressure and the pressure setpoints. Moreover an other input is also possible. As output of the fuzzy pressure controller a correction-output is sent to a valve controller. From this value, signals are forwarded for correctly controlling the valves. 
     In practice it appears that the switching time of the valves is not in infinitesimal. It will always be a physical limitation, whereby the accuracy of the control will be limited. This can be minimized by controlling the valves in combination as has been described with reference to FIG.  5 . 
     The fuzzy process controller uses besides the input and output valve also a so-called vent valve or pressure relief valve. This vent valve is an extra outlet opening and can be used to quickly decrease the pressure. The vent valve is controlled by the fuzzy pressure controller, when the difference in the set values, the set point and the actual pressure exceeds a certain value. Moreover the fuzzy process controller comprises an internal safety, which prevents that the pressure can exceed a certain critical value. As soon as an actual pressure is detected above the maximum acceptable pressure, the outlet opening and the vent valve are opened for quickly decreasing the pressure. This is necessary for protecting the downstream system. 
     The pressure control module can work stand alone and take care of a programmed and constant flow regulation. The several parameters for the pressure regulation, can be read from a known memory or can be introduced by means of a serial interface. The required pressure profile can automatically or by means of an external interface be started. This means that in combination with the pressure regulating device as described above a “stand-alone” unit can be created, forming a universally usable pressure-flow regulator. 
     FIG. 10 shows a device  100  which can be used to regulate the flow of a gas stream. 
     Two diaphragms  110 .  111  are arranged in the device  100  in accordance with FIG.  10 . The first diaphragm  110  is positioned between a second pressure chamber  112  and a pressure-regulating chamber or flow chamber  104 . The flow chamber  104  and the second pressure chamber  112  are both connected to a feed line  107  for a gas stream. The second pressure chamber  112  is in open communication with this feed line  107 . Via a restriction  108 , the flow opening of the flow chamber  104  is connected to the feed line  107 . The flow chamber  104  has an outlet opening  109 , which can be closed off with the aid of a member  115 , and an inlet opening  128 . When gas flows out of the outlet opening  109 , a higher pressure will prevail in the second pressure chamber  112  than in the flow chamber  104 . The reason for this is that the gas stream is delayed in the restriction  108 . The pressures which prevail in the second pressure chamber  112  and the flow chamber  104 , respectively, together determine the position of the membrane  110 , and hence the position of the closure member  115  with respect to the outlet opening  102 . In the same way as that discussed above with reference to FIGS. I to  6 , the position of the member  115  will fluctuate around an equilibrium position. 
     The equilibrium position of the member  115 , which is coupled to the diaphragm  110  via a coupling piece  116 , can be set with the aid of a second diaphragm  111 . This second diaphragm  111  is connected to the outer wall of the second pressure chamber  112  with the aid of a spring  118  and to diaphragm  110  by member  115 . The second diaphragm  111  forms a wall of a pressure chamber  121 . The pressure in this pressure chamber  121  can be regulated by selectively allowing gas to flow into the pressure chamber  121  via the shut-off valve  126  and the inlet opening  122  or by allowing gas to escape from the pressure chamber  121  via the outlet opening  123  and the shut-off valve  127 . The equilibrium position of the member  115  which is attached to the diaphragm  110  is determined as a function of the pressure in the pressure camber  121 . 
     The position depicted in FIG. 10 allows the position of the member  115  with respect to the outlet opening  102 , and hence the flow through this outlet opening  102 , to be instantaneously regulated. To this end, a pressure gauge  130  is arranged in the feed line  107 . This pressure gauge  130  is actively connected to a control unit  131 . This control unit  131  in turn controls the shut-off valves  126  and  127 . 
     The devices  20 ,  60 ,  100  discussed above are particularly suitable for portable chromatographs. The reason for this is that the devices do not require much power. Power is only required to change the setpoint of the devices, in which event power will be required in order to be able to cause gas to flow into or be discharged from pressure chamber  21 . Therefore, there is no need for a constant current in order to keep the diaphragm  10  in position. 
     A further advantage of the above mentioned device is that the valves in principle are closed. Only when regulating is necessary, i.e. when the pressure in the pressure chamber has to be amended, energy is needed for actuating the valves. That means that the system is able to function with low energy consumption. 
     A further advantage of the above mentioned device is that the valve in principle are closed. Only when regulating is nessecary, i.e. when the pressure in the pressure chamber has to be amended, energy is needed for actuating the valves. That means that the system is able to function with low-energy consumption. 
     The device  20 ,  60 ,  100  according to the present invention will be suitable for gas streams of from 0.1 ml to 100 ml per minute. The volume of injection gas used may be 20 microlitres per minute. 
     It will be clear from the above description that the devices  20 ,  60 ,  100  according to the present invention operate via a cascade arrangement. The mechanism by which the shut-off valve  15  is mechanically connected to the diaphragm  10  means that adjustment of the opening between the inlet passage  2  and the pressure turbulence chamber  4  will entail an analogue regulation which adjusts itself automatically about an equilibrium value. This equilibrium value itself can be set with the aid of the measuring means  31  which are able to control the shut-off valves  26  and  27 . 
     Normally, the accuracy of a pressure regulator is equal to that of the pressure sensor itself. Due to the analogue regulation of the pressure in the pressure-regulating chamber  4 , the device  20 .  60 ,  100  is much more accurate. The resolution which is usual in the prior art is ±1 kPa. 
     The device  20 ,  60 ,  100  makes it possible to achieve a resolution of 1/100 kPa. In the device  20 ,  60 ,  100  according to the present invention, the setpoint can be set with a similar degree of accuracy. Owing to the analogue control of the device itself, the. device will be automatically regulated about the setpoint with an accuracy which may reach a level of 1/100 kPa. 
     This represents an important advantage, particularly for use in gas chromatographs. In use, it is, of course, important that the desired gas flow through the gas chromatograph can be set accurately. However, keeping a gas flow constant once it has been set is even more important for the gas chromatograph to operate successfully. As has been explained above, this high level of accuracy can be achieved using the device  20 .  60 .  100  according to the invention. 
     One of the additional advantages of the device  20 ,  60  according to the present invention is that maintaining a gas pressure on both sides of the diaphragm allows diffusion of the gas through the diaphragm to be limited to a minimum. If the same pressurized gas is maintained on both sides of the diaphragm, there will be no diffusion. Depending on the application, a suitable material for the diaphragm may, for example, be silicone rubber. 
     In order for the flexible properties of the diaphragm to act appropriately, the diaphragm may be of slightly concave design.