WO1997035190A1 - Measurement device for determining the properties of a liquid - Google Patents

Abstract

The invention concerns a measurement device connected by electric leads to a power supply and a data-processing unit and designed to be immersed in a liquid, for instance ground water, to determine chemical and/or physical properties of the liquid. The device includes, housed in an essentially cylindrical casing, sensors and a data logger (5), the casing being made up of sections connected so that they can be detached from each other in the axial direction (3), viz: at one end of the casing, a section (2) housing the data logger (5), at the other end a pressure-measurement section (4) and, between them, a middle section (3) housing a sensor unit and fitted with through-flow openings (18). Either the pressure-measurement section (4) or the middle section (3) can be attached directly to the section (2) housing the data logger to make a liquidtight seal.

Description

 Measuring device for determining state variables of a liquid medium

The invention relates to a measuring device that can be completely immersed in a liquid medium and that can be connected via electrical lines to a power supply and a data processing device to determine chemical and / or physical state variables of the liquid medium.

In the case of a measuring device (DE-94 04 359.0 Ul), a measuring probe has a cylindrical probe body, into the lower end of which an adapter is inserted which is designed to hold measuring sensors in such a way that cylindrical measuring sensors also have their rear end in the adapter are inserted, whereas their front end - and thus the measuring head - projects downward beyond the adapter piece and the housing edge and is overlapped by a protective grille.

CONFIRMATION COPY However, this arrangement has the disadvantage that, on the one hand, low measurement requirements, for example only the water pressure and thus the level, cannot be taken into account to the extent that this would reduce the costs of the measurement probe. On the other hand, this measuring probe does not offer adaptability to high measuring requirements, for example if five or more system parameters are to be measured.

DE-25 31 784 C2 discloses a measuring arrangement for measuring the temperature and pressure of a medium in boreholes, in which a resistance which changes its electrical resistance value with temperature and a pressure sensor are provided for measuring the pressure which are connected via measuring signal lines to an evaluation unit located outside the borehole. This arrangement is only suitable for recording temperatures and pressure measurements. Adaptability to high measurement requirements, for example if five or more system parameters are to be measured, cannot be achieved with this measurement arrangement.

A combination probe for exhaust gas measurements on gas and oil heating systems is known from DE 80 26 460 U1, in which a double jacket tube with an inner jacket and an outer jacket and a thermocouple are provided. to This probe is not suitable for determining any measured values in liquid media.

The invention is based on the problem of creating a device for measuring the nature of liquid media, which can be expanded from an inexpensive probe for detecting the water pressure to a most complex measuring device for detecting various parameters.

The invention solves this problem with the features of claim 1. With regard to further refinements, reference is made to claims 2 to 18.

A high degree of variability of the measuring device is achieved through the optional mounting of a pressure measuring housing part receiving the pressure measurement either directly onto the housing part receiving the data logger or with the interposition of an intermediate housing part enclosing a sensor unit.

Because the pressure measuring housing part can be mounted directly on the housing part receiving the data logger, a very cheap basic measuring device, which can be expanded at any time, is made available when there is an exclusive demand for a pressure measurement - possibly even combined with a temperature measurement . The sensor unit can be equipped particularly advantageously with a plurality of sensors, all of which have their sensor head in one measuring plane, both the number of sensors installed and their arrangement in the sensor unit being variable.

As a result, the measuring device cannot only be expanded from a pressure measuring device to a multiple measuring device, but the type of measurements can be adapted to the needs of the users at any time.

This simple expandability and variability of the measuring device is additionally supported if the sensors are equipped with memory chips which transmit a factory calibration and a self-detection of the respective measuring sensor to the data logger. This means that the sensors can not be calibrated on site.

In order to reduce the costs for the user, the sensors can be disassembled after replacement, so that the used measuring electrode can be released from its mechanical holder and electrical contact and the latter can be provided with a new measuring electrode. Further advantages result from the following description and the drawing. The drawing shows:

1 shows a cross section through a measuring device according to the invention with housing parts mounted to one another and with a mounted pressure measuring area and a mounted sensor unit,

2 shows a cross section through the housing part receiving the data logger,

3 shows a cross section through the intermediate housing part,

4 shows a cross section through the pressure measuring housing part,

5 shows a cross section of the pressure measuring area,

6 shows a cross section of a measuring device for pressure and temperature measurement without an assembled intermediate housing part and without a sensor unit,

7 shows a cross section of the housing part accommodating the data logger with the sensor unit inserted and the pressure measuring area installed, but without the intermediate housing part and the pressure measuring housing part, 8 shows a cross-sectional detailed illustration of the upper end of the sensor unit.

In particular, the measuring device 1 comprises a housing part 2 for receiving the data logger 5, an intermediate housing part 3 for receiving the sensor unit 6 and a pressure measuring housing part 4 for receiving the pressure measuring area 7. The housing part 2 has an analogous conclusion on its lower edge 8 the intermediate housing part 3 on its lower edge 9, so that the pressure measuring housing part 4 can be mounted both on the lower edge 8 of the housing part 2 receiving the data logger 5 and on the lower edge 9 of the intermediate housing part 3 receiving the sensor unit 6.

The data logger housing 2 is provided at its upper end, ie connected to the lines leading to the outside, with an end cap 11 which is placed on the upper edge 10 of the housing part 2 receiving the data logger 5 and is provided with reliable protection against it by a sealing body 14 provides penetrating liquids. The sealing body 14 has two sealing seats 12 and 13, which are filled with O-rings and thereby bring about the required tightness. In the middle of the sealing body 14 there is the plug-in projection 15 for the assembly of the outwardly leading and not shown ten cable, which serves on the one hand as a data line and on the other hand as a supply line for the measuring device 1.

The cable can either be cast on, in order to represent a cost-effective and tight solution, or it can, as in the case shown here, be plugged on, so that cables of different lengths can optionally be installed and exchanged for one another. The energy supply is expediently located outside of the measuring device and can be lowered as a battery pack below the surface of the earth, for example when the measuring device is lowered in a level tube for groundwater measurement.

The data logger 5 represents a cylindrical component, in the interior of which there is essentially an analog-digital converter, which converts the incoming and incoming data as analog voltages into digital measurement signals, as well as an intermediate memory in which the digitized data are stored, as well as a possibility of forwarding the stored data to an externally connected computer. The addressing and control components required for carrying out measurement programs and forwarding measurement data are implemented either in hardware or software in the data logger 5. Furthermore, in the data logger 5 there can be one unit for calculating one that is still available Battery or an accumulator removable - residual energy may be arranged.

In the area of the housing part 2 receiving the data logger 5 facing away from the plug 15, there is an attachment on the lower edge 8 for mounting the intermediate housing part 3 or the pressure measuring housing part 4. The connection between the individual housing parts can, for example, be via a Screw threads occur so that the individual housing parts must be rotated against each other for assembly, or also by a fastening in which the housing parts remain stationary relative to one another, for example a union nut or another known way of fastening a plurality of pipe sections to one another.

Since the device has to be used frequently for groundwater measurement through level pipes with a diameter of generally 2 ", it is necessary to keep the outside diameter of the measuring device 1 small and to take this into account when connecting the housing parts 2, 3 and 4 .

At its end facing the data logger, the intermediate housing part 3 has an internal thread 16 which is connected to the external thread 8 'of the housing part 2 provided for receiving the data logger 5. At the end of the intermediate housing part 3 facing away from the data logger there is an external thread 17 with the same dimensions as the external thread 8 'of the housing part 2. Furthermore, the intermediate housing part 3 has inflow openings 18 which have an elongated shape and whose longitudinal axis is parallel to the longitudinal axis of the cylindrical measuring device 1. In addition, there are 3 round openings 19 distributed over its circumference on the intermediate housing part.

The pressure measuring housing part 4 has at its upper end 20 an internal thread 21 which, when mounted on the intermediate housing part 3 with the external thread 17 of the intermediate housing part 3 and when mounting the pressure measuring housing 4 on the housing part 2 receiving the data logger 5, with the external thread winch 8 'of the housing part 2 is connected.

Furthermore, the pressure measuring housing part 4 has an opening 22 on the underside through which the medium to be measured can come into contact with the pressure measuring region 7.

The pressure measuring area 7 comprises in particular a pressure sensor 23, which is usually designed as a piezo element, which is arranged in a complete component 24 and is connected to a flange 26 in a liquid-tight manner via a joint 25, the flange 26 having two sealing seats 27 and 28 has, which are filled with O-rings. In order to enable a pressure measurement with reference to the external air pressure, a pressure compensation line can be led to the pressure measuring area 4 together with the electrical lines on the other hand is connected to the air on the earth's surface.

FIG. 6 illustrates how the pressure measurement area 7 is mounted in the pressure measurement housing part 4 and this is mounted directly on the housing part 2 surrounding the data logger 5. On the housing side, the internal thread 21 of the pressure measuring housing part 4 is screwed to the external thread 8 'of the housing part 2 receiving the data logger. In the housing, the pressure measuring area 7 with its flange 26 is pressed into a sealing part 29 designed similarly to the sealing body 14 on the upper side of the measuring device 1, the tightness being ensured by O-rings inserted in sealing seats 27 and 28. The sealing part 29 is, on the one hand, sealed against the wall of the housing part 2 by O-rings also located in sealing seats 30 and 31. In order to prevent longitudinal displacement of the sealing part 29, a spacer sleeve 32 is mounted on the inside in the housing part 2 and clamped on the one hand with the lower end of the data logger 5 and on the other hand with the sealing part 29, so that both the spacer sleeve 32 and the sealing part 29 and the pressure measuring area 7 have a tight fit in the respective housing part. It is of course also possible to support the sealing part 29 directly at the lower end of the data logger 5 and to reduce the overhang of the housing part 2. Such an arrangement shown in FIG. 6 represents a minimal measuring device, wherein a temperature sensor can additionally be mounted in the pressure measuring housing part 4. In addition, no further sensors can be attached in this arrangement, so that a pure level measuring device is available, with the corresponding price advantages and small housing dimensions.

In order to convert such a level measuring device into a multiple measuring device, the pressure measuring housing part 4 is first unscrewed, then the pressure measuring area 7 with its flange 26 is pulled out of the press fit, the sealing part 29 and the spacer sleeve 32 are removed, so that an upper part Measuring device part, as shown in Fig. 2, is available for further inclusion of parts. A sensor unit 6 is now inserted on the underside of the housing part 2 and engages with its plug connections 33 in sockets provided on the data logger 5 and thereby ensures contacting of the sensor element 6. On the underside, the pressure measurement area 4 is inserted into a receptacle 34 formed on the sensor element 6 by means of its flange 26, as shown in FIG. 7. The electrical contacting of the pressure measuring area 4 takes place via cables which are guided in a liquid-tight manner in a tube 35 of the sensor unit 6 and which can be separated for converting the device via an adapter plug (not shown). The sensor unit 6 inserted into the sockets at the lower end of the data logger 5 by means of a plug movement seals the housing part 2 to the data logger by means of two O-rings in the sealing seats 36 and 37. The sensor unit 6 is mounted independently of the intermediate housing part 3. The measuring device being converted in FIG. 7 is completely surrounded by the intermediate housing part 3 and the pressure measuring housing part 4 in FIG. 1.

The sensor unit 6 is shown in detail in FIG. 8 and essentially comprises at least one body 38 which holds the sensors 39 in a liquid-tight manner and which in turn is fitted in the housing part 2 in a liquid-tight manner by means of its outer sealing seats 36 and 37. Arranged on the body 38 is a spacer pin 40, which represents the stop when the sensor unit 6 is inserted into the underside of the data logger 5.

The sensor unit 6 comprises a plurality of sensors 39 which are mounted side by side in the body 38 of the sensor unit 6, have essentially the same dimensions and are therefore all effective in one measuring plane. Even if two such bodies 38 form a sensor unit, they lie opposite each other, so that the measuring heads 41 of the sensors used are essentially in one measuring plane. The sensors 39 can each be replaced individually, which takes account of their different mounting and facilitates maintenance. In addition, the sensors 39 can be plugged in in any arrangement, and it is possible that individual sensor locations are not occupied, so that in each case only the required sensors 39 have to be used and further sensors that are not required for a specific measurement are not be unnecessarily exposed to aging.

The individual sensors 39 have an essentially two-part construction, which makes it possible to separate the actual measuring electrode 42 from a sleeve 43 surrounding it in its neck area, so that the measuring electrode 42 can be replaced without, therefore, the must destroy the entire sensor. The sleeve 43 has in its neck area 44 windows 45 which allow access to the electrical connections of the measuring electrode 42 and which also serve to fill a sealing and holding paste into the space between the sleeve 43 and the measuring electrode 42 can, so that the measuring electrode 42 is kept liquid-tight and parallel in the sleeve 43. A lateral filler opening 45 'can be provided in a supportive manner for better distribution of the sealing and holding paste. Furthermore, the windows 45 serve to be able to remove the sealing compound again and through the windows 45 the space between the measuring electrode 42 and To be able to pressurize sleeve 43 with a medium under pressure, thereby driving out the sealing paste and making sleeve 43 available for receiving a new measuring electrode 42.

After inserting a new measuring electrode 42 into the sleeve 43, the electrical connections of the sleeve 42 to the extensions 33 'of the plug 33 are first soldered through the windows 45 before the sealing compound is then filled through these windows 45. This method makes it possible not to use the entire sensor 39 after use, e.g. in the pH measurement can only be a few weeks, must be destroyed, but the expensive - mostly metallic - sleeve must be reinserted immediately.

The sleeve 43 seals the sensor 39 against the body 38 of the sensor unit 6 by means of the O-rings mounted in the sealing seats 46 and 47, so that here too no liquid can reach the plug connections 33.

It is possible to additionally equip individual sensors 39 with a temperature measurement, which causes little additional effort and can be desirable for special requirements.

For the greatest possible flexibility in the use of sensors 39, sleeve 43 can be provided in the area of window 45 a memory chip can be arranged, which transmits both the type of sensor 39 and thus the parameter to be measured in each case to the data logger and also carries factory calibration data, which are transmitted to the data logger 5 before the start of a series of measurements and from this each measured value can be assigned as a correction factor. This eliminates the need for on-site calibration, and no changes - not even the software - need to be made on the data logger 5 when the plug 39 is changed or plugged in additionally.

For particularly precise measurements, the data logger 5 can recognize a mutual influence of state variables of the system and correct incorrect measurements resulting therefrom. For example, a high nitrate content in the groundwater can change the density and thus the measured pressure. Since the data from the pressure measurement alone would indicate an incorrect water level, these are provided with a correction factor which is adapted to the high nitrate content.

It can be particularly advantageous here not to connect the individual sensors 39 to the data logger 5 via plugs 33, but rather to transmit the measurement data via an inductive coupling and thus without contact. For this purpose, a data carrier 5 emits a carrier wave Modulation is evaluated as a measurement signal by the signals transmitted by the sensors 39.

Both ion-selective electrodes 42 are available for the sensors 39, in particular for measuring the content of nitrations, oxygen ions, chloride ions, ammonium ions, calcium ions and further alkaline earth metal ions, which are provided at any time with additional electrodes 42. for measuring other ions can be added, as well as measuring cells for determining the redox potential, the electrical conductivity and the turbidity of the medium. There is also the possibility of arranging a light guide in the cable supplying the measuring device 1 and thus stimulating molecular vibrations or rotations by means of excitation light of defined energy and thus detecting the corresponding molecules. This method is intended in particular for the detection of hydrocarbons, especially polycyclic aromatic hydrocarbons (PAHs), which include, for example, benzenes, toluenes and xylenes, which occur, for example, in the area of the leachate of landfills and whose detection is of great importance .

Since the measuring device 1 is to be used not only in groundwater, spring water or flowing water, but also in leachate areas of landfills, that is to say in very aggressive media, it is necessary to very completely stable against corrosion. For this purpose, the use of a high-alloy steel with a high chromium and nickel content as well as titanium and molybdenum admixtures, such as is available with the X 6 CrNiMoTi 17 12 2 (material number 1.4571). It is important that all parts that are in contact with the medium - apart from the sensors 39 - are made of such a corrosion-resistant material. Since the housing must also meet high mechanical stresses, it must be as compact as possible, which is supported by the arrangement of the sensors 39 in one plane. Furthermore, the entire measuring device 1 must be explosion-proof (intrinsically safe).

It goes without saying that the variability of the measuring device 1 is not limited solely to a different number and arrangement of sensors 39, but that the measuring programs can also be selected as desired, e.g. the query times and gaps between the measurements. These can be set individually for each sensor 39 by external programming of the data logger 5 as required.

Claims

Expectations: 1. Completely immersible in a liquid medium and connectable via electrical lines with an energy supply and a data processing device for determining chemical and / or physical state variables of the liquid medium, for example of the groundwater, with integrated in an essentially cylindrical housing th sensors and a data logger (5), the housing in the axial direction of three detachably connectable parts, namely a housing part (2) receiving the data logger (5) at one end, a pressure measuring part (4) and one has an intermediate housing part (3) enclosing a sensor unit and provided with inflow openings (18), the pressure measuring housing part (4) or the intermediate housing part (3) optionally being liquid-tightly mountable directly on the housing part (2) receiving the data logger. 2. Measuring device according to claim 1, characterized in that the sensor unit can be inserted into the intermediate housing part and seals this by means of O-rings arranged in sealing seats to the data logger. 3. Measuring device according to one of claims 1 and 2, characterized ge indicates that the Druckmeßgehäuseteil both on the housing part housing the data logger and on the interposer housing part is liquid-tight and its electrical contact is made via cables that can be guided in the intermediate housing part in a liquid-tight manner . 4. Measuring device according to one of claims 1 to 3, characterized ge indicates that the pressure measuring housing part additionally comprises a temperature sensor which is contacted analogously to the pressure measurement. 5. Measuring device according to one of claims 1 to 4, characterized ge indicates that the intermediate housing part can be mounted independently of the sensor unit and can be connected via a molded thread to a molded part on the housing receiving the data logger. 6. Measuring device according to one of claims 1 to 5, characterized ge indicates that it has liquid-tight plug-in connections to the data logger, and that the sensor in- unit comprises several insertable sensors which are effective in one measuring plane. 7. Measuring device according to claim 6, characterized in that the plug-in sensors are each provided with a memory chip which carries at least one correction factor of the measurement data determined by a factory calibration and transmits it as initialization of a series of measurements to the data logger. 8. Measuring device according to one of claims 6 and 7, characterized ge indicates that the memory chips of the sensor unit carry a record identifying the type of sensor and the measurement value to be recorded in each case. 9. Measuring device according to one of claims 6 to 8, characterized in that the arrangement of the sensors in the sensor unit is variable. 10. Measuring device according to one of claims 6 to 9, characterized ge indicates that a different number of sensors can be used in the sensor unit. 11. Measuring device according to one of claims 6 to 10, characterized in that the sensors are each individually replaceable. 12. Measuring device according to one of claims 1 to 11, characterized in that the sensors each have a cylindrical sleeve which is fixedly connected to their electrical connecting element and which partially gives a measuring electrode and in which the measuring electrode is liquid-tight but detachably held. 13. Measuring device according to claim 12, characterized in that the measuring electrode in the sleeve is held in a sealing compound and the outside of the sleeve has at least one O-ring arranged in a sealing seat. 14. Measuring device according to one of claims 6 to 13, characterized in that the sleeve has a neck provided with windows, the window having access for soldering the measuring electrode connections, for filling and removing sealant and an opening for applying filled sealant with a pressure medium represent. 15. Measuring device according to one of claims 6 to 14, characterized in that the sensor unit in its opposite end regions has two mutually opposite insertion levels for sensors, the measuring electrodes of the sensors arranged opposite one another essentially lying in a common measuring plane. 16. Measuring device according to one of claims 1 to 15, characterized in that the data logger takes into account a mutual influencing of various state variables of the medium and can provide measurement values with a correction. 17. Measuring device according to one of claims 6 to 16, characterized in that sensors with ion-selective electrodes for measuring the pH, the nitrate content, the oxygen content, the chloride ion content, the ammonium ion content and the content of positive calcium ions and the water hardness as well as the content of further ionized particles, sensors with measuring cells for determining the redox potential, the electrical conductivity and the turbidity are also provided, and measurements using molecular excitation by excitation light of defined energy are feasible. 18. Measuring device according to one of claims 6 to 17, characterized in that the electrical contacting of the sensors is contact-free via inductive coupling.