DE2930364A1 - Leak testing by differential pressure measurement - using controlled displacement body regulating pressure difference between comparison volumes - Google Patents

Abstract

A differential pressure measurement device has two comparison volumes which can be connected to its two measurement chambers. In partic. it is a leak tester with a test object connected to one chamber and a reference object to the other. It gives a quantitative unambiguous leak measurement on faulty test objects such as fuel tanks by simply performing accurate differential pressure measurements. A pressure difference between the measurement chambers arising from a pressure change in the comparison volumes is compensated by varying one or both volumes using a displacement element controlled by the difference pressure. The pressure difference thus remains practically constant during the measurement and the comparison volume, conditional change is measured indirectly from the compensating element, e.g. a piston, displacement.

Description

The invention relates to a differential pressure medium

device with two that can be connected to the separate chambers of the device Comparison rooms. In particular, the invention relates to one based on this principle working leak tester with a test object that can be connected to one measuring chamber or test volume and a comparison object connected to the other measuring chamber or comparison or reference volume.

In the following the invention is mainly based on a leak tester explained without thereby excluding other areas of application of the invention. With With the help of such leak testing devices, leaks or leak points on objects, in which there are liquids or gases during final use, before their Commissioning are discovered so that defective test objects are sorted out know. Such objects can be, for example, lighter tanks, ballpoint pen refills, Carburetor housings, cylinder housings of internal combustion engines, pipe connection parts etc. be.

In the case of Dichtheitsprisgeräter of this type, a method is known in the interior of the container to be tested to one side of a differential device or transducer and a comparison container with a reference volume about the same Grobe is connected to the other side of the measuring device, whereupon both containers with compressed air or the like. filled and then shut off. Then over observed for a long time whether the pressure on the side of the test object drops.

This shows whether there are any leaks or whether the test item is is tight.

All previously known arrangements are used to measure the pressure difference analog differential pressure measuring devices between the reference volume and the sample volume, their Plus and minus pressure sides through an elastic wall, e.g. in the form of a membrane, a spring tube or a column of liquid or the like are separated. The output signal of the differential pressure measuring devices is usually an immediate display, e.g. in the form of a pointer deflection, or an electric or pneumatic Rough, which can be converted into a display in a known manner. Often the Differential pressure is not only displayed, but other signals are obtained from it, with which optical or acoustic warning devices are activated or with which mechanical devices are activated, with the help of which good test specimens be separated from scrap specimens.

For differential pressure gauges with an elastic partition, shows now that every anchorage of the differential pressure is connected with a change in shape the partition, which has the consequence that the volume of the "plus chamber" increases with increasing Differential pressure increases and at the same time the volume of the "minus chamber" decreases.

These This also applies to force-compensating differential pressure gauges or transducers, because here, too, the ring zone between the center of the measuring membrane held by the compensation process and its clamping zone is deformed, apart from the fact that the center of the measuring membrane is also shifted by small amounts due to the compensation process.

In some applications of such differential pressure measuring devices, e.g. for flow or level measurements, is their property when D4fferenzdruck to change or swallow a volume, without essential meaning. However, it has a particularly disadvantageous effect in the case of leak testing devices especially when either small leak rates or small test items or both are to be measured. The differential pressure measured with the known devices does not correspond to the actual values, which leads to incorrect tests leads.

Another disadvantage arises with the previously known leak testing devices through the requirement to have defined differential pressure ratios at the beginning of the measurement to accomplish. The differential pressure measurement should expediently always be the same Differential pressure, preferably start with the differential pressure zero. When locking the reference and test container through valves can, however, because of the short time shift of the two closing processes and at the same time still flowing test fluid a finite one Differential pressure occur between the two container spaces.

Geometric asymmetries of the two valves can therefore also be avoided lead to a finite differential pressure, because, for example, rubber cones that sit on metal lie on top, push yourself in to different depths and thereby the enclosed volume to change a little.

But even if the valves were symmetrical, they could be different The sizes of the reference and test volumes cause a finite differential pressure. This is particularly detrimental in the case of small test objects with a low intrinsic volume.

The invention is based on the task, an accurate Measurement of the differential pressure and thus with leak detection devices To enable the detection of leaks due to leakage losses in the case of faulty test objects in a simple manner.

According to the invention, this object is essentially achieved by that in the case of a device of the type mentioned at the outset, one in the case of pressure changes in the comparison rooms pressure difference to be expected between the measuring chambers due to compensating Changes to the or / andPVclumina of the or / and the comparison rooms by means of at least one movable displacement body controlled by the differential pressure can be compensated in such a way that the differential pressure during the measurement or test although it remains practically constant, its real, the changes in state in the comparison rooms however, the corresponding value can be measured indirectly by adjusting the displacement body is.

What is essential is the idea of the invention, a differential pressure (or Pressure) not to be measured directly, but indirectly by means of a volume compensation. With such an indirect measurement of the differential pressure between two completed Spaces, especially in the case of leak detectors, between a test volume and a Comparison volume, according to one embodiment of the invention, should be the differential pressure with the help of a differential pressure transducer with as little or no directional force as possible thereby constant be held that be changing this Differential pressure of the displacement body into the space with the lower pressure. or / and is moved out of the space with the higher pressure, so that by the Position of the displacement body can be deduced from the differential pressure, which would have occurred if the comparison rooms kept constant volume would have.

The invention can be implemented in various ways and by various means are executed.

According to one embodiment of the invention, there is the displacement body from a piston, which is from one of the differential pressure measuring element, e.g. one between A servomotor controlled by the measuring membrane clamped in the measuring chambers, e.g. by a pneumatic Membrane motor in a communicating with a comparison room or test volume Guide cylinder is displaceable and its displacement movements from a display member removable, e.g. readable on a scale by means of a pointer.

According to the invention, the amount is a change in differential pressure caused by the test process with the aid of the piston made into DJulX, who either pressed into the minus chamber or out of the plus chamber is pulled out; it is also possible according to a variant of the invention, with one or two pistons to simultaneously compress both the minus chamber and the Plus chamber to relax. The movement of the piston or pistons is preferably motorized causes, whereby electric motors or liquid motors or e.g. pneumatic membrane drives can be used for this.

The deviation of the differential pressure from its constant value can be determined by any signals, for example pneumatic, electrical, optical or other signals. Liquid differential pressure gauges can be used to measure and control the constant differential pressure as well as dry ones, e.g. membrane measuring mechanisms, can be used. Furthermore, the differential pressure compensation brought about by the change in volume can be implemented not only in analog, but also digitally. In the latter case, according to the invention, for example, several pistons can be combined, the individually displaced volume of which is graduated in a ratio of 1: 2: 4: 8, etc. With this design of a sealing tester according to the invention, the leocrates of a prefectural container can be taken from the position of a piston that is moved in an analogue manner or from the combination of the positions of pistons that are moved digitally. In the case of the analog piston movement, ole movement of the piston can be read off directly, for example on a scale, or remotely measured at another point using suitable position signal converters. Once the piston diameter has been selected, the signal path of the piston can be adapted to the expected leak rate. With the same leakage volume, a piston with a small diameter will travel a long way and vice versa.

The disadvantage of the known devices that after initial shut-off a finite differential pressure can remain between the two tank spaces, is achieved by the invention thanks to the displacement piston eliminated that first of all the differential pressure zero or a certain other differential pressure is set. The displacement piston will initially make a correction jump relatively quickly move out. Then it will move at the speed at which test gas escapes from the leak. From the time differential quotient of the piston movement, one can therefore refer to the Close leakage flow. The piston position shows the amount of test gas that has escaped.

A volume compensation at constant differential pressure with the help of displacement bodies, which at the same time reduce the test volume and the Increase the reference volume or vice versa, according to the invention, e.g. Ring scales or diving bells can be realized.

Such an embodiment is according to the invention that the Displacement body consists of a diving bell that is immersed in a separating liquid is floating and its liquid-free interior with the one comparison room or reference volume communicated, during the above the level of the separating liquid located room with the other comparison room or

Test volume is in connection, the diving movements of the diving bell detachable from a display member, e.g.

can be read off by means of a pointer on a scale.

Other embodiments of the device are also possible by other resp. to realize equivalent means within the framework of the essential inventive concept. Further features of the invention are also explained in more detail below.

In the drawing the invention is in various embodiments for example illustrated.

Fig. 1 shows schematically a leak detection device with displacement piston, Fig. 2 shows a variant of the device according to Fig. 1 with electrical control of the Displacement piston, FIG. 3 shows a further variant of the device according to FIG. 1 with optoelectronic control of the displacement piston, and Fig. 4 shows schematically a leak tester with a displacement bell.

The differential pressure meter shown in Fig. 1 consists of two Pressure chamber shells 1 and 2, between which a measuring membrane 5 is clamped, which the measuring chamber spaces 1 'and 2' separates from each other. The Meßmemhran 5 is made of membrane plates 4, 4t is supported in its central zone, so it is stiff in this area. the Measuring membrane 3 can be made of thin sheet metal or optionally provided with beads also be made of a soft elastomer such as rubber. The movements the measuring membrane 5 are via a pin 5 in the space 6 of a housing part 6 ' transferred, in which there are facilities with which one for further processing suitable signal is obtained. The space 6 can of course be identical with one of the two measuring chamber spaces 1 'or 2'. When a differential pressure change occurs For example, a pneumatic signal is generated on the measuring membrane 5 as follows: The measuring membrane 5 with its membrane plates 4, 4 presses with its own weight a lever 7 which is rotatably mounted at point 8. A magnet is attached to the lever 7 9 attached whose field through the non-magnetic material wall of the Housing part 6 'penetrates. On the other side of the case wall there is a control lever 10 which is rotatably mounted at point 11.

The lever 10 also carries a magnet 9 ', but in the opposite direction Direction is magnetized so that the two magnets 9 and 9 'repel each other. The lever 10 is balanced by a weight 12, its position is determined by a Scanned air nozzle 13, which cooperates with a baffle 13 'of the lever 10. The tare weight 12 is dimensioned in such a way that a mean output pressure is achieved through a constant inlet throttle 14 and the variable nozzle 15 formed pressure cascade arises, which from an auxiliary energy source 15 via a line 1o with prefxluftkonstantem Pressure is supplied.

The output pressure of the pressure cascade 15, 14 is via the connection line 1s' fed to the pressure chamber 17 of a pneumatic spring motor 18, which has a Rolling membrane 20 drawn over a U-shaped plate 19 and one against the plate 19 acting spring 21 contains. The position of this motor can be adjusted by means of a Plate 19 attached indicator rod 22 with a pointer 25 on a scale 24 read will. On the plate 19 of the pneumatic Spring motor 18 is a Displacement piston 25 attached, which is gas-tight and as low-friction as possible in one Driving cylinder 2o slides and closes a pressure chamber 27.

The differential pressure measuring mechanism is connected to the measuring chamber space via a Line 28 connected to the reference volume V1, while the test volume V2 via a line 29 is connected to the measuring chamber space 2 '. Lines 28 and 29 are via branched lines 30 resp.

31 to a compressed air source Q via shut-off valves 32 or

33 can be connected. These shut-off valves can, for example, be electrical or operated pneumatically. The pressure chamber 27 of the guide cylinder 28 is over a line 34 is connected to the line 31.

Before starting the actual measurement, both volumes V1 and V2 filled up by automatically opening the shut-off valves 32 and 33. After both If the volumes are sufficiently well filled, the shut-off valves 32 and 33 are activated at the same time closed. The measuring process now begins. If there is a differential pressure at the measuring membrane 3 is applied, it will move and over the magnets 9, 9 ' the Adjust control lever 10. if, for example, the pressure in test volume V2 is lower than in the reference volume V1, because the shut-off valves 52 and 3D are not at the same time have closed, then the measuring membrane 7 will move down and thereby Open the air nozzle 15 using the control lever 10. The pressure behind the inlet throttle 14 will fall, and thereby the pressure in the pressure chamber 17 of the pneumatic Spring motor 18.

The spring motor 18 is therefore 21 under the action of the spring for so long Guide the displacement piston 25 into the pressure chamber 27 of the guide cylinder 2o, until that differential pressure occurs again at the measuring membrane 3, which at the beginning the measurement should prevail. If there is now a leak in the test volume V2, then this compensation process take place continuously, with the pointer 25 of the spring motor 18 moves from bottom to top on its scale 24. The scale 24 can be expressed directly in units of volume of the loss of test gas must be calibrated.

Instead of the pneumatic device described above, volume compensation of course also by means of electrical, optical or other means Funds are made.

For example, Fig. 2 shows a simple electrical embodiment. The measuring membrane, which is expediently perpendicular in these heads, acts here is arranged hanging in order to make the dead weights as uninfluenced as possible, over a rod 5t onto an open electrical contact 55. This contact switches via lines) 5, 57 electrical energy that operates an electric motor that then in turn moves the displacement piston so that the differential pressure at the Measuring diaphragm receives the initial value.

The electrical two-position controller formed in this way can also transformed into a three-position controller by a zero zone of the electrical switch will.

Also, by known electrical means, e.g.

Differential transformers, steady electrical signals obtained will.

In FIG. 5, for example, there is a further, optoelectrical embodiment shown. Here the position of the measuring membrane is measured by a light barrier, which consists of a diaphragm 58, which is connected to a measuring membrane, for example Rod 5 is arranged, which moves in a transparent housing 59.

in emanating from a light source 40 and bundled via an lens 41 Depending on the position of the diaphragm 38, the light beam falls on a receiver a. This sends a possibly amplified electrical signal to an electric motor or via another signal converter, which may also be used on a pneumatic one Membrane motor can act. These motors then rehearse the volume compensation. A stabbed light barrier is also advantageous if you place a measuring membrane a liquid column (U-tube) in a manner known per se for measuring the differential pressure used.

In Fig. 4 is a further, simple and advantageous embodiment of the invention.

A transparent vessel 44 is located here in the interior 45 a clear separating liquid 45.

Since the liquid should evaporate as little as possible, one uses expedient e.g. silicone oil. In addition, a diving bell balance is in the vessel 44 arranged.

This consists of a double-armed lever 46, which is in a journal bearing 47 is rotatably mounted. The lever 46 advantageously consists of a closed one Tube so that the entire submersible bell balance is in the separating liquid hover can and despite the journal bearing 47 is hardly subject to any frictional influence. On the left side of the lever 4 is a small diving bell 48 attached while on the right side of the same at the same distance from bearing 47 a similar one, however, the body 49, which is open at the top and bottom, is attached to the lever 4G.

The wall thickness and diameter of the tubular parts of the diving bell 48 and of the body 49 are the same, at least if their axes of symmetry are the same Distance from the bearing 47. This ensures that in the event of a rash Diving bell scales the changing buoyancy forces that act on the diving bell tube wall attack, be compensated. At the end opposite the diving bell 48 A pointer 50 is attached to the lever 46 and plays in front of a scale 51. Of the The angle that the diving bell balance assumes with respect to the vessel 44 can therefore be through the transparent wall of the vessel 44 can be read through. From one source Q of the test fluid, for example air or gas, a pressure line 52 leads a line 53 into the interior 54 of the diving bell 48. Another line 55 leads over a Branch line 5o in the space 43 above the diving bell 48. In the line 55 is a light throttle 57 built in. aside from that are in lines 52 and 55 shut-off valves 58 resp.

59 arranged, which by an auxiliary energy such as e.g.

Know compressed air operated. The line 55 is above the branch line 5 in connection with the reference volume V1. The line 55 is through the vascular space 45 and a line u0 connected to this connected to the test volume V2. Furthermore, with the aid of a lockable filler neck o1, the vessel 44 can be filled with separating liquid 45 should be filled if this is necessary for transport reasons.

With the device described above, the tightness of a test volume V2 carried out as follows: After the container with the test volume V2 on the line 60 has been connected, the shut-off valves 58 and 59 are opened. Through this the reference volume V1 and the test volume V2 fill with the test fluid as Compressed air or compressed gas.

@@@@@@@@@@@@@@ The throttle 57 reduces the pressure in the test volume V2 always be slightly lower than the pressure in the reference volume during the filling process V1.

So there is an overpressure inside the diving bell 48, and the Lever 46 is turned clockwise, until the diving bell 48 may cut the surface of the separating liquid 45. From this moment on, the test fluid enters the space 45 above the separating liquid 45 not only through the pipe 55 but also through the pipe 53.

After about the has set the desired test pressure, the shut-off valve 58 is closed. Now ei4 pressure equilibrates between the reference volume V1 and the test volume V2 instead, until the separating liquid 45 in the interior 54 of the diving bell 48 has the same status as outside. This brings the pointer 5G to its zero point, whereupon the shut-off valve 13 is closed. If the test volume V2 is leaking, so the pressure drops above the diving bell base, and the lever 45 moves in the Clockwise until there is no more differential pressure at the diving bell 48 and thus the liquid levels inside and outside the diving bell 48 are the same are. The position of the pointer 50 can then indicate the size of the leak in the test specimen Close V2.

The movement of the diving bell causes the space above the separating liquid to be i.e. the test volume is reduced, and at the same time the space 54 within the Diving bell 48, i.e. the reference volume, increased. Here is the dimensioning important for diving bell scales.

When the diving bell 48 rises in the separating liquid 45, then at the same time, the body 49 is immersed more deeply in the separation fluid. So that remains the liquid level is constant and the separating liquid does not generate any energy transferred to the scales. In this way, the buoyancy forces in the device are compensated.

The basic idea of the invention, a pressure or differential pressure not to be measured directly, but by means of a volume compensation, can often lead to advantageous solutions for other tasks as well. E.g. occurs when measuring the amount of heat emitted by a Heizwaaserkreisstrom has to determine the temperature difference that flows through this stream a heat exchanger is caused.

According to the invention, by having two closed Brings sensor into the inlet and outlet side of the heating water flow, can because of the after Different gas laws are set Press to gain a particularly large signal through volume compensation. Furthermore the invention is not limited to the exemplary embodiments described and illustrated, but it also includes all variants within the framework of the essential features of the invention.

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Claims (14)

D i f e r e n z p r u c k w e r u s e, especially dense lt 5 -testing device claims: 1. Differential pressure measuring device with two to the separate Measurement chambers of the device connectable comparison rooms, in particular leak testing device with a test object that can be connected to one measuring chamber and one to the other Comparison object connected to the measuring chamber, thereby a indicates there is a pressure difference to be expected in the case of pressure changes in the comparison rooms between the measuring chambers by compensating Veränderunder conditions for the or / and volumes of the and / or the comparison rooms by means of at least one movable one of the differential pressure controlled displacement body can be compensated so that the differential pressure remains practically constant during the measurement or test, its real, the value corresponding to the changes in state in the comparison areas, however, indirectly can be measured by adjusting the displacement body. 2. Apparatus according to claim 1, characterized in that the displacement body consists of a piston (25), which is from one of the differential pressure measuring element, e.g. one between the measuring chambers (1 'and 2') clamped measuring membrane (7) controlled servomotor, e.g. from a pneumatic membrane motor (18) in one with a comparison room or test volume (V2) communicating guide cylinder (26) is displaceable and whose displacement movements can be removed from a display element, e.g. by means of a Pointer (2)) can be read on a scale (24). 3. Apparatus according to claim 1, characterized in that the displacement body consists of a diving bell (43) which is floating in a separating liquid (4) is stored and its fluid-free interior (54) with the one comparison room or reference volume (V1) communicates, during the above the level of the separating liquid (45) located room (4)) with the other comparison room or test volume (V2) is in connection, the diving movements of the diving bell (48) from a display element removable, e.g. readable by means of a pointer (5%>) on a scale (D1). 4. Apparatus according to claim 1 and 2, characterized in that two or more displacement piston provided for a digital differential pressure compensation are. 5. Apparatus according to claim 1 and 2, characterized in that the measuring membrane ()) A nozzle-flapper system (13, 13 ') is actuated, its pneumatic signals be introduced into the pressure chamber (17) of a pneumatic spring motor (18), its membrane (20) or membrane plate (19) connected to the displacement piston (25) is. Device according to claim 1 and 2 or 5, characterized in that daí3 the movements of the measuring membrane (3) by magnets (9, 9 ') on the control system of the servomotor (z.3. 18) are transferred (Fig. 1). 7. Apparatus according to claim 1 and 2 or 5, characterized in that the movements of the measuring membrane (3) electrically through a contact device (35) be transferred to the servomotor of the displacement piston (Fig. 2). 8. Apparatus according to claim 1 and 2 or 5, characterized in that the movements of the measuring membrane (3) by an ostoelectric device free e.g. a light barrier (58 - 42) is transmitted to the servomotor of the displacement piston (Fig. 3). 9. Apparatus according to claim 1 and 2, characterized in that the measuring chamber (1 ') with the reference volume (V1) and the measuring chamber (2') with the test volume (V2) is connected that the volumes (V1, V2) with a pressure medium source (Q) via shut-off valves (32, 3D) can be connected, and that also the pressure chamber (27) of the guide cylinder (20) of the displacement piston (25) is in communication with the test volume (V2). 10. Apparatus according to claim 1 and 5, characterized in that dad in one Vessel (44) a diving bell balance is arranged, the diving bell (48) on a double-armed, pivoted lever (£ 4) is attached, whose the diving bell opposite lever arm carries an open compensating body (49). 11. Apparatus according to claim 1 and 5 or 10, characterized in that the lever (4o) carries a pointer (50) which cooperates with a scale (51), that the vessel (4)) is transparent at least in the pointer scale area, and that the separating liquid (45) is also transparent. 12. Apparatus according to claim 1 and 5bzw. 10, characterized in that the interior (54) of the diving bell (48) is connected to the freezing volume (V1) is that the interior (1!)) of the vessel (44) is above the separating liquid (45) connected to the test volume (V2) and via a shut-off valve (59) to the reference volume (V1) can be connected, and that the volumes (V1, V2) via a shut-off valve (58) a pressure medium source (Q) can be connected. 13. Device for measuring a pressure or differential pressure between two closed spaces, characterized in that the pressure or differential pressure is measured indirectly by a volume compensation. 14. Apparatus according to claim 14, characterized in that da3 for measurement the amount of heat given off by a heating medium flow into the closed rooms of two arranged in the input and in the output of the heating medium flow, with Gas-filled sensors exist, which are caused by different gas pressures Volume changes are compensated.