Pumps – With signal – indicator – or inspection means
Reexamination Certificate
1999-03-17
2001-03-27
Freay, Charles G. (Department: 3746)
Pumps
With signal, indicator, or inspection means
C417S068000
Reexamination Certificate
active
06206646
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and to a sensor for the detection of cavitations in accordance with the respective independent patent claim and to an apparatus containing a sensor of this kind.
By a cavitation one understands a sudden cavity formation such can arise for example when in liquid ring vacuum pumps—these are pumps which use a liquid as an auxiliary means for the production of a vacuum—the previously evaporated liquid condenses very rapidly or even abruptly. In liquid pumps of this kind a mechanical impact or striking on the blade or blades of the blade wheel between which the gas is located arises through a cavitation of this kind. This results in a more or less minor damage to the blades in each cavitation, through which the blade wheel and thus the pump becomes unusable with time.
Now it is often the case in industrial uses that the pumps are located at a place where they cannot be continually monitored without further ado as to whether and how often such cavitations arise. Moreover, the pumps also produce a certain operating noise during operation (even without cavitations occurring), which can at times be quite considerable, so that it can be difficult even in a monitoring of the pumps by the operating personnel to recognize whether and at what frequency such cavitations now arise.
Since on the other hand cavitations can lead to damage of the pump with time, as already explained above, such cavitations should be avoided or at least detected in order that corresponding measures can be taken (e.g. the operating parameters can be changed) in order to prevent a continuous arising of such cavitations.
SUMMARY OF THE INVENTION
In accordance with the invention a space to be monitored is monitored by means of a sensor which is capable of learning. In this, a state in which cavitations arise in any case in the space to be monitored is produced at least once (afterwards a save can be made) during a learning process for the duration of a first time interval. After the completion of the first time interval a state is produced for the duration of a second time interval in which cavitations do not in any case arise in the space to be monitored. In each of the two time intervals the sensor learns which signals correspond to cavitations and which signals correspond to non-cavitations respectively in the space to be monitored. After the completion of this learning process the sensor investigates the signals arising during operation in the space to be monitored as to whether predeterminable criteria, which are derived from the learned signals for the cavitations and non-cavitations respectively, have been fulfilled and decides on this basis whether a cavitation has arisen in the space to be monitored or not and produced a corresponding output signal. In this way the sensor can itself first “learn” what is a cavitation and what is not (in particular it naturally also gets to know the noise of the operation without cavitations) and then decides after a learning phase whether cavitations arise or not. The reliability of this is decidedly high. Thus the corresponding pump can be set up at a place where a continuous monitoring is not possible. If during the operation of the pump the sensor recognizes that cavitations arise it can trigger an alarm when appropriate so that the operating personnel can take corrective measures and damage to the blades and hence to the pump can be avoided.
A sensor which is designed as a pressure sensor can be used for this in an advantageous embodiment, and the pressure is monitored in the space to be monitored. Pressure sensors are available today in various embodiments and can directly deliver an output signal which represents the pressure. In principle, however, other sensors, such as for example acoustic sensors, also come under consideration.
In the space to be monitored the absolute pressure as well as the pressure change can be monitored, in particular, of course, both. This is especially advantageous for the learning process because the latter can then proceed as follows. In the learning process a pressure drop which is greater than a predeterminable minimum pressure drop can first be produced in the space to be monitored. Then when a predeterminable pressure at which cavitations arise in the space to be monitored in any case is reached or dropped below respectively, the sensor for the first time interval is triggered. The sensor now “learns” in this first time interval what a cavitation is. After the completion of the first time interval a pressure increase is produced again which is greater than or equal to a predeterminable minimum pressure increase and the sensor is triggered for the second time interval as soon as the minimum pressure increase is reached or exceeded and a predeterminable pressure is reached or exceeded. The sensor then “learns” in this second time interval what a “non-cavitation” is. After this learning phase the operation of the pump can then take place.
In a further development of this variant the sensor is not triggered in the learning process for the first time interval until the further drop in the pressure is less than a predeterminable threshold value. It is thus waited until the pressure drop is practically completed. After the end of the first time interval the sensor is triggered for the second time interval when the increase in pressure is greater than a predeterminable threshold value. Since the operation is preferably carried out at low vapor pressures, in the event of a correspondingly large pressure increase the pressure practically immediately lies above the vapor pressure (and in any case no cavitations arise).
In an advantageous embodiment variant of the method in accordance with the invention the sensor determines for different criteria how high the probability is when the respective criterion is fulfilled that a cavitation has arisen and that subsequently the sensor decides as a result of all criteria and the associated probabilities whether a cavitation has arisen or not and produces the corresponding output signal. Sensors of this kind typically use the principles of “fuzzy logic”.
The object is also satisfied by means of a sensor which is capable of learning. In this a state in which cavitations arise in any case in the space to be monitored is first produced in the space to be monitored during a learning process for the duration of a first time interval. In this, first time interval the sensor learns what a cavitation is. After the completion of the first time interval a state in which cavitations do not arise in any case in the space to be monitored is produced in the space to be monitored for the duration of a second time interval. In this second time interval the sensor learns what a “non-cavitation” is. Now the sensor comprises means which in each of the two time intervals store the signals which correspond to the cavitations and the non-cavitations respectively in the space to be monitored. Furthermore, the sensor comprises means which investigate the signals arising in the space to be monitored during operation as to whether predeterminable criteria which are derived from the learned signals for the cavitation and the non-cavitation respectively are fulfilled as well as means which decide on this basis whether a cavitation has arisen or not in the space to be monitored and which then produce a corresponding output signal. With a sensor of this kind a pump can be monitored with high reliability, even when operating personnel cannot continually be on site. If cavitations arise, then an alarm can be triggered when appropriate as a result of the sensor output signal so that the operating personnel can take measures which prevent damage to the blades and hence to the pump.
In an advantageous exemplary embodiment the sensor has means for the determination of the pressure in the space to be monitored; it is thus executed as a pressure sensor. In a further development it has means for the determination of the pressure as well as the pressure change in the space to be monit
Freay Charles G.
Gray Michael K.
NSB Gas Processing AG
Townsend and Townsend / and Crew LLP
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