WO1991014932A1 - Sampling device - Google Patents

Abstract

A device for controlled withdrawal of samples of fluid substances, in particular of liquids from a process, comprises a pump (10) which is connected on the inlet side with a suction line (11) for intake of the fluid substance and on the outlet side with a pressure line (12) connected through a three-way valve (13) to a sampling tube (15). The other end of the sampling tube (15) is connected through a second three-way valve (14) to a discharge line (16), so that the test substance can be withdrawn continuously throughout the process, conveyed through the sampling tube (15) and returned to the process. The third inlet of the first valve (13) is connected to a compressed gas source (18), and the third inlet of the second valve (14) is connected to a withdrawal line (19). If the valves (13, 14) are reversed so that the pump (10) can no longer deliver the substance to be sampled through the sampling tube (15), the volume in the sampling tube (15) is acted on directly by compressed gas and conveyed to an analytical device (23).

Description

 Sampling device

The invention relates to a sampling device according to the preamble of claim 1.

In the case of a large number of technical-chemical processes, samples of a substance arising or treated in the process have to be taken at relatively short intervals to monitor and / or control them and fed to an analysis device. This can be accomplished by removing an appropriate amount of the substance by hand, which is, however, labor-intensive. A sample quantity suitable for the investigation can also be removed by means of a pump. However, the problem arises that on the one hand the accuracy in the metering of the sample quantity depends on the pump or its control, and on the other hand volumes contained in the pump and in its supply and discharge lines from an early stage originate from their sampling process, and are therefore not representative of the nature of the substance currently present. From DE 24 41 844 AI, US 3,789,670, DD 133 998, DE 89 11 570 UI, GB 2 030 963 A and GB 2 010 778 A, sampling devices are known, all of which have the disadvantage that at least parts of the sample that can be taken can come from an earlier sampling process.

A sampling device is known from US Pat. No. 3,083,577 which comprises a piece of pipe through which a fluid can flow and which can be closed off by valves at the end.

Pipes lead into the pipeline in the vicinity of the valves and can be shut off via further valves. To take the sample, close the end valves on the pipe section and open the other two valves. The sample can then be conveyed out of the pipe section using compressed air. This sampling device is disadvantageous in that a certain residual volume always remains in the pipe section.

From US 4,628,749 a sampling device is known, as described in the preamble of the main claim. The sample container is emptied by gravity, so that complete emptying is also not possible.

The invention has for its object to develop a device of the type mentioned in such a way that an exactly reproducible amount of a current sample can be removed in a simple manner.

This object is achieved by a device for the controllable removal of samples of fluid substances from a process, comprising pump devices which are connected on the input side to a suction line, to which the fluid substances can be supplied and on the output side are connected to a pressure line. controllable valve devices, by means of which the pressure line can be connected to a sample container and via which the sample container can be connected to a discharge line, by means of the pump device which is removed from the process by and through feed the sample conveyed material back to the process, and sample ejection devices to discharge the contents of the sample container through a sampling line for further use. This device is characterized by the fact that the sample container is designed as a sample tube, that the sample ejection devices comprise compressed gas devices and that the valve devices comprise two separate valve devices which are designed in this way and are connected to the sample tube, that in a first valve position it is constantly connected to the pressure line and the discharge line and through which the fluid can flow, in a second valve position its first end can be connected to the pressure gas devices and its second end can be connected to the extraction line, so that a volume contained in the sample tube can be blown out through the sampling line.

An essential point of the invention lies in the fact that the sample tube has a very large length relative to its clear width (inner diameter). As a result, any residual volumes remaining in the valves are very small in relation to the total volume within the sample tube. Furthermore, the sample tube can be easily wound so that the device does not become too bulky.

For taking the sample, it is advantageous if the valve devices each comprise a three-way valve which is connected to the pressure line, the discharge line, the pressure gas device, the sample hose and the sampling line.

By alternately carrying out a flow through with the substance to be removed or with compressed gas, contamination of the device can be effectively prevented.

It follows from the above description that the invention also relates to a method, since the individual elements of the device according to the invention are known per se. Preferred embodiments of the invention are explained in more detail below with the aid of figures. Here show:

Figure 1 shows a first preferred embodiment of the invention, in which the valves used are shown in their two positions.

Fig. 2 is a schematic diagram of the device according to

Fig. 1;

3 shows a circuit diagram of a further preferred embodiment of the invention;

FIG. 4 shows the device according to FIG. 1, but in a further constructive embodiment, as well as its mode of operation;

5 shows a further preferred embodiment of the invention;

Fig. 6 is a schematic representation of part of a

Measuring device for observing the filling status of the sample tube; and

Fig. 7 shows another embodiment of a measuring device for

Monitoring the filling status of the sample tube.

1A and 1B show a first embodiment of the invention. As can be seen from the figures, the device according to the invention comprises a pump 10 which is connected with its suction line 11 to a process line 20 which contains the fluid substance to be examined.

On the pressure side, the pump 10 is connected via a pressure line 12 to a first connection a of a three-way valve 13, the second connection b of which is connected via a sample hose 15 to a second connection b of a second three-way valve 14. The first connection a of the second three-way tils 14 is connected to one end of a discharge line 16, the other end of which is returned to a suitable place in the process.

The third connection c of the first three-way valve 13 is connected to one end of a sampling line 19, the other end of which communicates either with an analysis device or with a transport container for the sample to be removed. The third connection c_ of the second three-way valve 14 is connected to a compressed gas source 18 via a compressed gas line 17. The pressurized gas source 18 supplies a pressurized gas which has no or at least no disruptive influence on the nature of the substance to be examined.

In the position of the valves 13 and 14 shown in FIG. 1A, the substance from the process line 20 is pumped through the sample tube 15 by means of the pump and flows back to the process. If the flow rate, that is to say the time it takes for a partial volume of the substance removed from the process, to pass from the inlet opening of the suction line 11 to the second valve 14 and to fill it completely, is low in comparison to the rate of change of the substance to be monitored, there is a subset of the substance to be investigated in the sample tube 15 and in the valves 13 and 14, the properties of which correspond to those of the substance currently in the process.

As soon as or each time a sample is to be taken, the valves 13 and 14 are switched so that the connections a and b of the valves are no longer connected to one another (see FIG. 1A), but the connections c and b communicate with each other. As a result, the compressed gas source 18 is now connected via the compressed gas line 17 to the contents of the sample tube 15 located between the valves 13 and 14. The pressurized gas thus pushes a precisely defined sample volume 1 through the extraction line 19 to the analysis device. The entire remaining contents of the valves 13 and 14 are also carried along or blown out. The variant of the invention shown in FIG. 2 differs from that according to FIG. 1 with regard to its mode of operation only in that the sample volume 1 is not ejected from the sample tube 15 in a direction opposite to the direction of rotation, but rather the direction of rotation is keeps.

The embodiment of the invention shown in FIG. 3 differs from that according to FIG. 2 in that two / four-way valves are used instead of two / three-way valves. These are connected via a further circulation line 21 in such a way that when a control 22 switches the valves 13 and 14 in order to supply a sample volume to an analyzer 23, the substance conveyed by the pump 10 passes through the circulation line into the discharge line , so that the pump 10 can continue to promote. This avoids an increased load on the pump 10 and at the same time ensures that the content of the sample tube 15 is "up to date" again immediately when switching back to flow.

The sample tube is preferably made very thin and long

3 forms. A sample tube with a clear width (inside diameter) of 3 mm and a length of 1.415 ir is suitable for holding a sample volume of 10 cm. The valves 13 and 14 are equipped with a corresponding flow diameter. If a liquid column of a few mm remains in such a valve, this changes very little in the total sample volume.

The hose formed in this way is preferably wound up to save space. By blowing out with compressed gas, a narrow hose wound in this way can also be completely emptied.

If 20 air bubbles are carried in the process line and these get into the sample tube or air gets into the sample tube in another way and when switching the Valves with trapped in the sample tube, the sample volume is no longer correct.

To solve this problem, an arrangement is described, which is explained in more detail below with reference to FIGS. 4 A-C.

The device shown in FIGS. 4 A-C differs from that of FIG. 1 in that a signal transmitter 24 is attached to one valve 13 and a sensor 25 is attached to the other valve 14. In one embodiment of the invention, which will be explained in more detail below, the signal transmitter 24 or the sensor 25 are suitable for transmitting or receiving ultrasound.

In operation - as shown in FIG. 4 A - the valves 13 and 14 are switched while the pump 10 is running so that the liquid contained therein is removed from the process line 20 and flows through the lines 11, 12, 15 and 16. If a sample is to be taken, a switch is made to the position shown in FIG. 4B, in which the valve 14 the

Compressed gas source 18 connects to the sample tube 15. A check valve 39 is provided directly in front of the valve 14 so that no liquid can be pressed into the compressed gas source 18 at this point due to the pumping action of the pump 10. Thus, no liquid flow takes place in the switch position shown in FIG. 4B.

The signal generator 24 is now supplied with alternating current at the valve 13, so that the valve 13 is set in vibration. An amount of 5 kHz has been found to be suitable as the oscillation frequency. The vibrations generated in this way are passed on in the liquid within the sample tube 15 and reach the other valve 14. This valve 14 is now set in vibration by the incoming vibrations, so that a corresponding measurement signal can be tapped at the sensor 25. Then, if there is an air bubble within the sample tube 15, that is, the sample tube is not completely filled, the passage of the sound waves from the The signal transmitter to the sensor is damped considerably, since the sound wave resistance in liquids is much lower than in air and reflections also occur at the interfaces. In this way it is very easy to determine whether the sample tube 15 is completely filled or not. A major advantage of this measurement method is that the measurement result is largely independent of the type of liquid examined.

In the variant of the invention shown in FIG. 5, a controllable valve 27 is provided in the line 17 upstream of the valve 13 instead of the check valve 39. In this arrangement, when sampling (switching valves 13 and 14 from the position shown in FIG. 1A to the position shown in FIG. 1B), valve 27 is first kept closed, so that the volume contained in sample tube 15 stays there. The measurement described above is then carried out, in which a signal generator 33 excites the signal generator 24 in accordance with signals from the controller 22. The measurement signal from the sensor 25 is amplified via a measurement amplifier 26 and fed to the control 22. Then, when the amplitude of the measurement signal indicates that the sample tube 15 is properly filled, the valve 27 is opened so that gas from the pressurized gas source can reach the sample tube 15 through the line 17 and its content into the sampling line 19 and from there to the analyzer. However, if the measurement shows that there is an air bubble in the sample tube 15, the valves 13 and 14 are switched back again (from the position shown in FIG. 1B to the position shown in FIG. 1A), so that the sample tube is refilled becomes. Then the process described begins again.

What is essential to this concept is the fact that a fully automatic control can take place and a high level of safety is nevertheless guaranteed.

A valve 13 can either be coupled directly to couple the vibrations into the liquid contained in the sample tube 15 vibrate and the vibrations on the valve 14th

(or vice versa) tap. An increased sensitivity of the sensor or an increased efficiency of the signal generator can be achieved if the device shown in FIG. 6 is used. This comprises a pipe socket 32 (eg made of V2A steel) coming from the valve 13 or 14, which has a flattened section. A piezo element 28 (piezo disk) is applied to the surface of this section. The other surface of the piezo disk 28 is covered with a contact 29, so that an alternating current can be fed into the piezo element 29 via connecting wires 30, 31 - then the arrangement acts as a signal transmitter - or a corresponding alternating voltage can be removed - then the arrangement acts as a sensor. As mentioned above, the greatest possible error in this arrangement, which occurs when there is no liquid (in FIG. 6) to the left of the pipe socket 32, is only small, since the length of the unfilled pipe section relative to the total length of the sample hose 15 is very low.

It is also possible to check the filling state of the sample tube 15 by means of an electric current instead of mechanical vibrations. Such an arrangement is shown schematically in FIG. 7. In this arrangement, the signal generator and the sensor 25 are formed by electrodes. The ohmic resistance between the electrodes is a measure of whether the sample tube 15 is completely filled or not. The resistance between the electrodes depends to a large extent on the liquid being examined, its temperature, etc. In order to compensate for this dependency, it is advantageous to use a bridge circuit as shown in

Fig. 7 is shown. A liquid-filled line 38 with electrodes 36 and 37 contained therein is then also used as the reference resistor, this line section forming a loop hanging downward. It can therefore be ensured that the loop is always filled with the liquid to be examined in an air-free manner. The other elements shown in FIG. 7 and their interconnection (Wheatstone bridge) are known per se. Reference number 34 is one Designated alternating voltage source, with 35 a measuring device which transmits a signal from the control 22 corresponding to the alignment error.

Reference list

1 sample volume

10 pump

11 Suction line 12 Pressure line

13 first valve

14 second valve

15 sample tube

16 discharge line 17 compressed gas line

18 compressed gas source

19 Extraction line

20 process management

21 Circulation line 22 control

23 analyzer

24 signaling devices

25 sensors

26 measuring amplifier 27 compressed air valve

28 piezo element

29 contact

30 connecting wire

31 connecting wire 32 tube

33 signal generator

34 AC voltage source

35 measuring device

36 first reference electrode 37 second reference electrode

38 loop

39 check valve

Claims

 // Claims Device for the controllable taking of samples of fluid substances from a process with pump devices (10) which have controllable valve devices (13) on the inlet side with a suction line (11) to which the fluid substances can be supplied and on the outlet side with a pressure line (12) , 14), via which the pressure line (12) can be connected to a sample container (15) and via which the sample container (15) can be connected to a discharge line (16), in order to remove the pumping device (10) from the process and feed material conveyed through the sample container (15) back into the process, and with sample ejection devices (17, 18, 19) in order to discharge the contents of the sample container (15) through a removal line (19) for further use, characterized in that that the sample container is designed as a sample tube (15), the sample ejection devices gen (17, 18), the valve devices comprise two mutually separate valve devices (13, 14), which are designed and connected to the sample tube (15) such that in a first valve position this is constantly connected to the pressure line (12) and the discharge line (16) connected and through which the fluid can flow, in a second valve position with a first end with the pressure gas devices (17, 18) and with a second end with the sampling line (19) can be connected, so that one contained in the sample tube (15) Sample volume (1) can be blown out through the sampling line (19). 2. Device according to claim 1, characterized in that the sample tube (15) comprises a thin tube, the light width of which is very small, in relation to its length. 3. Device according to claim 1, characterized in that the valve devices (14, 15) each comprise a valve with at least three paths. 4. Device according to claim 1, characterized in that the compressed gas devices comprise a compressed gas source (18) for supplying a pressurized inert gas. 5. Device according to claim 1, characterized by a measuring device (24-26) which is connected to the sample tube (15) and is designed such that a measurement signal can be generated which reflects the filling state of the sample tube. Device according to claim 5, characterized in that the measuring device, with the first end of the pro- benschlauches (15) connected signal transmitter (24), the one Signal in the sample volume (1) generated within the sample tube (15) and comprises a sensor (25) connected to the second end of the sample tube (15), which sensor, after passing through the sample volume (1) in the sample tube (15) converted into the measurement signal. 7. Device according to claim 6, characterized in that the signal transmitter (24) and / or the sensor (25) are each mounted on one of the valve devices (13, 14). 8. Device according to claim 6, characterized in that the signal transmitter (24) and / or the sensor (25) are each mounted on a pipe section (32) which directly between the sample tube (15) and the respective valve (13 or 14th ) is arranged. 9. Device according to claim 6, characterized in that the signal transmitter (24) mechanical vibrations or Sound waves generated, and the sensor (25) mechanical Vibrations or sound waves converted into electrical measurement signals. 10. Device according to claim 6, characterized in that the signal generator (24) generates an electrical current, preferably an alternating current, and the sensor determines the strength of the current flowing through the sample volume (1).