DE202009014978U1 - Online measuring system for pH values in soils - Google Patents

Abstract

Online measuring system for pH values in the soil, characterized in that the commercial pH combination electrode is split into two separate electrodes: in a pH glass electrode (positive pole) and a separate Ag / AgCl reference electrode (negative pole) to the lifetime of the reference electrode to extend to almost unlimited time.

Description

One of the key features of the protected soil is its pH. This is of crucial importance for soil fertility and for the risk of leaching of pollutants into the groundwater. To determine the pH, soil samples are usually taken in the field, which must first be dried in the laboratory, mortared and sieved to a grain size of 2 mm. Subsequently, the treated sample is mixed with aqueous salt solutions or with water to form a suspension in which the pH is then determined with a pH combination electrode (source: eg. Schlichting, E., Blume, H.-P., Stahr, K. (1995): Bodenkundliches Praktikum; Blackwell Wissenschaftsverlag, 2nd edition, 295 pp. ).

Problem 1

• a) der Aufwand bei der bisherigen Vorgehensweise hoch ist, die Messwerte durch die Aufbereitung der Bodenproben beeinflusst werden können und zudem lediglich eine Momentaufnahme darstellen.
• b) handelsübliche pH-Elektroden als sogenannte Einstabmessketten konzipiert sind. Bei diesen Elektroden wird die zur Messung des pH-Wertes erforderliche Glaselektrode (Pluspol) mit einer Referenzelektrode (Minuspol) zu einer Messkette vereinigt. Die enthaltene Referenzelektrode ist mit einer Kaliumchloridlösung gefüllt, welche zur Gewährleistung des elektrischen Kontakts zwischen Glaselektrode (Plus) und Referenzelektrode (Minus) stetig durch das Diaphragma, eine Öffnung im Elektrodenschaft, an das zu messende Medium abgegeben wird und so nach und nach verbraucht wird. Dieser stetige Verlust von Elektrolytflüssigkeit während der Messung verkürzt die Lebensdauer solcher Einstabmessketten erheblich, so dass sie für den Dauereinsatz im Boden nicht geeignet sind.

The protection specified in claim 1 invention is based on the problem that

• a) the effort in the previous procedure is high, the measured values can be influenced by the preparation of the soil samples and also represent only a snapshot.
• b) commercially available pH electrodes are designed as so-called combination electrodes. In these electrodes, the glass electrode (positive pole) required for measuring the pH is combined with a reference electrode (negative pole) to form a measuring chain. The contained reference electrode is filled with a potassium chloride solution which, to ensure electrical contact between the glass electrode (plus) and the reference electrode (minus), is continuously discharged through the diaphragm, an opening in the electrode shaft, to the medium to be measured and thus gradually consumed. This steady loss of electrolyte fluid during the measurement shortens the life of such combination electrodes considerably, so that they are not suitable for continuous use in the ground.

Solution 1

This Problem is solved by the commercial pH electrode is split into two separate electrodes: into a pH glass electrode (positive pole) and a separate Ag / AgCl reference electrode (Negative pole). This structure allows the loss of electrolyte the reference electrode as a major cause of aging a conventional pH combination electrode from the rest Separate test setup.

The The reference electrode of the new pH-online system is electrotechnical identical to the reference electrode of a commercial pH combination electrode. But it achieves an almost unlimited life, Although the liquid KCl inner electrolyte from the diaphragm can escape, but there does not leak directly into the material to be measured (bottom) and consumes quickly, but by the diaphragm with a so-called salt bridge is surrounded. This salt bridge consists of a chemically stabilized KCl gel, which controls the diffusion rate of the KCl from the diaphragm of the reference electrode extremely slows down, nevertheless, the electrochemical contact between the reference electrode and the ground guaranteed. This construction slows down the loss of potassium chloride from the reference electrode by a multiple and thus enables continuous use of the measuring system in the ground without appreciable aging of the reference system. To compensate for the over long periods also in this structure occurring electrolyte loss It is also possible, both the KCl filling the reference electrode as well as the gel filling of the salt bridge to renew. As for this maintenance only the Reference electrode must be expanded and maintained, is a Disassembly of the actual pH glass electrodes avoided and a Disturbance of the pH value by installing and removing the sensors prevented.

Problem 2

Of the in claim 2 protection invention is based on the problem that pH levels in the soil vary widely in the horizontal and vertical directions can. To adequately adjust the pH of a site Therefore, several pH electrodes are required. conventional Need pH combination electrodes with permanently installed reference electrode in this case, a separate connection for each measuring point on the meter. This circumstance increases the metrological Expense especially when the data is not only measured but should also be recorded with data loggers. commercial Laboratory devices for automatic measurement and recording of pH levels are cumbersome and costly, so the Multiple determination of pH in soil in situ unusual is.

Solution 2

This problem is solved by a specially developed data acquisition module, which is connected to a data logger and allows online monitoring of pH values in the field by the automatic data transmission. Up to 7 glass electrodes as well as one or more reference electrodes can be connected to this data acquisition module at the same time, so that a multiple determination of the pH values of a soil depth and / or the pH measurement in different soil depths with different pH values is possible is. As long as the pH glass electrodes (positive pole) and reference electrodes (negative pole) are electrically connected via the bottom water, up to seven pH values can be measured simultaneously with a single reference electrode.

Of the extremely high input resistance of the new data logging module above a teraohm also allows the measurement of redox potentials via the same reference electrode, so that multiple pH values and multiple redox potentials in a circuit are measurable online.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• Schlichting, E., Blume, H.-P., Stahr, K. (1995): Bodenkundliches Praktikum; Blackwell Wissenschaftsverlag, 2nd edition, 295 p. [0001]

Claims (2)

Online measuring system for pH values in the soil, characterized in that the commercial pH combination electrode is split into two separate electrodes: in a pH glass electrode (positive pole) and a separate Ag / AgCl reference electrode (negative pole) to the lifetime of the reference electrode to extend to almost unlimited time. Online measuring system according to protection claim 1, characterized that a specially developed pH / ORP measurement acquisition module a data logger is connected and by the automatic Data sent a simultaneous online monitoring of several pH values and redox potentials in the terrain allowed.