Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Patent
1987-01-27
1989-08-01
Noland, Tom
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
204401, 204408, G01N 2730, G01N 2738, G01D 1800
Patent
active
048523852
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a new and improved construction of a maintenance device for at least partially automatic cleaning and calibration of a probe containing a measured value transmitter.
In its more specific aspects, the present invention particularly relates to a new and improved construction of a maintenance device for at least partially automatic cleaning and calibration of a probe containing a measured value transmitter and which probe containing the measured value transmitter is part of a measuring device for continuously monitoring biological or chemical processes. Such processes are continuously monitored by measuring analytical parameters in a fluid medium. The probe contains a sensor which is removable from the fluid medium to be investigated, and a guide device for holding and guiding the sensor of the probe which contains the measured value transmitter, between an operative position and a maintenance position. The probe further contains a shut-off device for shutting off the probe from the fluid medium to be investigated.
In general, the aforementioned probes contain, for example, electrochemical sensors, such as pH electrodes, particularly single-rod electrode assemblies, and are used for monitoring biological or chemical processes, particularly fermentation processes. It is disadvantageous here that, in practice, the aforementioned sensors only have a limited service life and their indication is subject to change in the course of time, namely for the following reasons: voltage in the case of pH and redox electrodes, and deactivation in the case of redox electrodes; and
The interferences caused thereby hitherto have rendered more difficult and partially impossible the continuous monitoring of biological and chemical processes because they lead to a considerable falsification of the measured values and the frequently necessary removal and replacement of the sensor brings about an interruption of the process course.
In order to eliminate the interferences arising due to the contamination mentioned as reason 1. hereinbefore, continuous or discontinuous cleaning methods have been proposed or used in the past. These include: membrane; against the sensor or electrode membrane; or ultrasound.
The aforementioned cleaning methods have several disadvantages. Thus, for example, the pH value is highly falsified using the cleaning method mentioned hereinbefore as method 1.1, and the cleaning agent generally is diluted by the fluid medium. The consumption of cleaning agent also is relatively high. The cleaning method mentioned hereinbefore as method 1.2, generally only works for loosely adhering contaminants which is why this method can only be used to a limited extent. In addition, the pH value is also falsified in this case. The cleaning method mentioned hereinbefore as method 1.3, is associated with great mechanical complexity and, in the case of abrasive media, with high wear of the moving parts. Ultrasound cleaning requires a relatively large constructional volume and, in addition, cannot be used in areas with an explosion hazard due to the high energy output. Besides the disadvantage that the aforementioned cleaning methods require relatively large constructional volumes and are not suitable for small or restricted installation dimensions, there is added the further disadvantage that their effectiveness is not always guaranteed at high pressures.
The elimination of errors which are caused in the course of time by the reasons mentioned hereinbefore as reasons 2. and 3., requires regularly repeated cleaning and calibration operations using at least two calibration solutions and corrections at the measuring instruments. The operations necessary for the elimination of these errors require a time expenditure of a few hours to several weeks, depending on the type of fluid medium to be investigated, the type of the contaminants, and the magnitude of the occurring electrode drift. However, this means that these operations result in considerable impairment of the process
REFERENCES:
patent: 3625850 (1971-12-01), Arrington
patent: 4260950 (1981-04-01), Hadden et al.
patent: 4299495 (1981-11-01), Sawakata et al.
patent: 4336232 (1982-06-01), Moritz
Patent Abstracts of Japan; vol. 6, No. 229, (1107) p. 155; published Nov. 16, 1982; (English Abstract of Japanese Patent Publication 57-132053 dated Aug. 16, 1982).
Dr. W. Ingold AG
Kleeman Werner W.
Noland Tom
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