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EP0943805B1 - Process and sensor for cavitation detection as well as a device comprising such sensor - Google Patents

Process and sensor for cavitation detection as well as a device comprising such sensor Download PDF

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Publication number
EP0943805B1
EP0943805B1 EP98810237A EP98810237A EP0943805B1 EP 0943805 B1 EP0943805 B1 EP 0943805B1 EP 98810237 A EP98810237 A EP 98810237A EP 98810237 A EP98810237 A EP 98810237A EP 0943805 B1 EP0943805 B1 EP 0943805B1
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EP
European Patent Office
Prior art keywords
sensor
monitored
pressure
time interval
space
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP98810237A
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German (de)
French (fr)
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EP0943805A1 (en
Inventor
Peter Bucher
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NSB Gas Processing AG
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NSB Gas Processing AG
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Publication date
Application filed by NSB Gas Processing AG filed Critical NSB Gas Processing AG
Priority to AT98810237T priority Critical patent/ATE285037T1/en
Priority to EP98810237A priority patent/EP0943805B1/en
Priority to DE59812383T priority patent/DE59812383D1/en
Priority to US09/270,958 priority patent/US6206646B1/en
Publication of EP0943805A1 publication Critical patent/EP0943805A1/en
Application granted granted Critical
Publication of EP0943805B1 publication Critical patent/EP0943805B1/en
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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04CROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C14/00Control of, monitoring of, or safety arrangements for, machines, pumps or pumping installations
    • F04C14/28Safety arrangements; Monitoring
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04DNON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00Details, component parts, or accessories
    • F04D29/66Combating cavitation, whirls, noise, vibration or the like; Balancing
    • F04D29/669Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for liquid pumps
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04CROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C2270/00Control; Monitoring or safety arrangements
    • F04C2270/78Warnings
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04CROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C2270/00Control; Monitoring or safety arrangements
    • F04C2270/80Diagnostics

Definitions

  • the invention relates to a method and a sensor for the detection of Cavitation according to the respective independent claim, and a device containing such a sensor.
  • Cavitation is a sudden formation of cavities like this can occur, for example, when liquid ring vacuum pumps - these are pumps that look like a liquid Use auxiliary medium to create a vacuum - the previously evaporated Liquid condenses very quickly or even suddenly.
  • Such a cavitation creates a mechanical fluid pump Impact or impact on the blade or blades of the impeller, between which the gas is located. This has one with every cavitation more or less minor injury to the blades resulting in time the paddle wheel and thus the pump becomes unusable.
  • a method is already known from the published patent application DE 35 20 734 A. and a device for operating a centrifugal pump is known, wherein by means cavitation-free operation can be set for a probe.
  • cavitation will damage the pump over time can, as already explained above, avoid such cavitations will be or at least be detected, so that appropriate measures can be taken (e.g. operating parameters can be changed), to prevent the constant occurrence of such cavitations.
  • this task is solved by a procedure like this characterized by the features of the independent process claim is.
  • the space to be monitored monitored using a teachable sensor. Doing this at least once (a saving can then take place) during a learning process for the duration of a first time interval produces a state in which in cavitation will definitely occur in the room to be monitored. To Completion of the first time interval will last for a second Time interval established a state in which to be monitored Hence no cavitation will occur. In each of the two Time intervals, the sensor learns which signals cavitation or which Signals correspond to non-cavitation in the room to be monitored.
  • the sensor examines the im Operation in the signals to be monitored, whether Predefinable criteria that are derived from the learned signals for cavitation or Non-cavitation are derived, fulfilled and deciding on this basis, whether or not cavitation has occurred in the room to be monitored and generates a corresponding output signal.
  • the sensor itself "learns" what is cavitation and what is not (In particular, of course, he also learns the operating noise without Know cavitations) and then decides after a learning phase whether Cavitations occur or not.
  • the reliability is there extremely large.
  • the corresponding pump can also be used on one Place where monitoring is not always possible. If the sensor detects that cavitation is occurring when the pump is operating, If necessary, he can trigger an alarm so that the operating personnel appropriate measures can take and damage the Buckets and thus the pump can be avoided.
  • pressure sensors are in these days Different versions available and can directly Deliver an output signal that represents the pressure. Basically come but also other sensors, such as acoustic sensors, in Consideration.
  • both the absolute pressure and the pressure change are monitored, especially of course both.
  • This is particularly advantageous for the teach-in process because it then follows as follows can expire.
  • the sensor for the first Triggered time interval when falling below or Reaching a predeterminable pressure at which the pressure to be monitored Cavitation definitely occur, the sensor for the first Triggered time interval.
  • the sensor "learns" in this first time interval, what is a cavitation.
  • the pump After the end of the first time interval, again generates an increase in pressure that is greater than or equal to a predeterminable one Minimum pressure rise, and the sensor will be on for the second time interval triggered as soon as the minimum pressure rise is reached or exceeded and a predeterminable pressure is reached or exceeded. The sensor Then “learns” in this second time interval what is a "non-cavitation”. After this learning phase, the pump can then be operated.
  • the senor is used during the learning process triggered for the first time interval only when the further decrease of the Pressure is less than a predetermined threshold. So it’s waiting until the pressure drop is practically complete. After completing the first Time interval, the sensor is then triggered for the second time interval, if the increase in pressure is greater than a predetermined threshold. Since it is preferred to work with low vapor pressures, one is correspondingly large pressure increase the pressure almost immediately above the Vapor pressure (and there are no cavitations in any case).
  • the sensor determines how high for different criteria Fulfillment of the respective criteria the probability is that a Cavitation has occurred, and then due to all Criteria and the associated probabilities the sensor decides whether or not cavitation has occurred and the corresponding Output signal generated.
  • Such sensors typically set the Principles of "fuzzy logic”.
  • the task is also solved by means of a teachable sensor. Doing so in the room to be monitored initially during a teach-in process a state is established for the duration of a first time interval in which Cavitation definitely occurs in the room to be monitored. In this first time interval, the sensor learns what cavitation is. To The first time interval is completed in the room to be monitored for the duration of a second time interval produces a state in which in in any case, no cavitation occurs in the room to be monitored. In During this second time interval, the sensor learns what "non-cavitation" is. The sensor now includes means that in each of the two time intervals Store signals which indicate the cavitations or the non-cavitations in correspond to the room to be monitored.
  • the sensor also includes Means which occur during operation in the room to be monitored Signals then investigate whether predeterminable criteria that result from the learned signals for cavitation or non-cavitation are derived, are fulfilled as well as means that decide on this basis whether to monitoring room a cavitation has occurred or not and then generate a corresponding output signal.
  • a pump can be monitored with high reliability, even if operating personnel cannot be on site at all times. If cavitations occur, an alarm may be triggered based on the sensor output signal so that the operating personnel can take measures that Prevent damage to the blades and thus the pump.
  • the senor has means for Determination of the pressure in the room to be monitored, so it is as Pressure sensor trained.
  • he has both funds for Determination of the pressure as well as the change in pressure in the monitoring room, especially of both, which is especially for the Teaching process can be an advantage. Doing so can change the pressure either by forming the difference between successive measured values of the absolute pressure can be determined, or it can be separate means be provided, the direct measurement of the pressure change enable.
  • the sensor has means for triggering the trigger the sensor for the first time interval during the teach-in process, if in a greater pressure drop is generated in the room to be monitored as a predeterminable minimum pressure drop and if a predeterminable pressure is reached or fallen below, in which in the to be monitored Cavitation definitely occur.
  • the sensor learns what cavitation is and stores it corresponding signals.
  • the sensor comprises means that the Sensor after completion of the first time interval for the second time interval trigger as soon as a pressure rise is generated that is greater than or equal to a predeterminable minimum pressure rise and as soon as a predeterminable one Minimum pressure is reached or exceeded. The sensor learns in this Time interval, which is a non-cavitation and stores the corresponding one Signals off.
  • the means for triggering cause the learning process triggering of the sensor for the first time interval when the further pressure drop is smaller than a predeterminable one Threshold. In other words, this means that a trigger for the first time interval occurs at a practically stable low pressure.
  • the means for triggering the Sensor triggers the sensor for the second time interval when the pressure rises is greater than a predefinable threshold. Because preferably with low Steam pressure is worked, the pressure is accordingly large pressure increase practically immediately above the vapor pressure.
  • the senor comprises means which determine for different criteria how high when the respective one is fulfilled Criterion the likelihood is that cavitation has occurred as well as funds that are based on all criteria and the associated probabilities decide whether cavitation has occurred or not and generate the corresponding output signal.
  • Such sensors typically use the principles of "fuzzy logic”.
  • the subject of the invention is a device in particular a liquid ring pump that has a corresponding sensor includes.
  • Liquid ring pump 1 can be seen the intake manifold 10 and the location 11, on which a pressure transmitter of a cavitation sensor (not shown) can be arranged inside the intake manifold 10.
  • An eccentrically arranged paddle wheel 12 can also be seen (dashed), with the help of which a gas to be pumped (e.g. air at a Vacuum pump) through the intake manifold 10 and the intake slot 100, the are connected to each other, but what in Fig. 1 from the drawing For reasons not recognizable, is sucked in.
  • the direction in which that Gas is pumped is indicated by the arrows G. It is immediate obvious that the paddle wheel 12 is driven clockwise for this purpose must become what e.g.
  • An outlet slot 130 can also be seen in FIG. 1 and an outlet port 13, which are also in communication with each other stand, but which is not visible in Fig. 1 for drawing reasons. Through the outlet slot 130, the pumped gas can again from the Pump are led out.
  • Fig. 2 shows the embodiment of the liquid ring pump 1 according to Fig. 1, however, is in addition to the intake manifold 10, the sensor 2 for Detect cavitations.
  • the ring liquid space R which is concentric to the Pump housing is arranged and shown with a hatched Liquid F is filled.
  • this ring liquid space R that is Paddle wheel 12 arranged eccentrically.
  • the suction slot 100 as well the outlet slot 130 are indicated in Fig. 2 for the mode of operation to better explain such a pump.
  • Another is Opening O for the ring liquid F is indicated. Because it has to - like still will be explained - new liquid F is constantly fed and heated liquid F are discharged.
  • Sensor 2 is provided for the detection of such cavitations.
  • there it is a so-called “learnable” sensor. That means the Sensor 2 is first taught in a teach-in process, which is actually (in terms of signal) corresponds to cavitation, and what does not. To do this of course a condition can be made, in any case Cavitations occur. In this state, sensor 2 must "learn” what is a cavitation. The sensor 2 must also learn what is a "non-cavitation” so that he is able to prevent cavitation from others Distinguish between disturbing noises (such as flow noises, Engine noise, etc.). This is done in a teach-in process, as in following will be described with reference to FIG. 3.
  • the triggering of the sensor 2 for the first time interval t1 in which the Sensor learns what a cavitation (signal-based) is, is now done in such a way that first wait until the pressure level is below the level LO and on the other hand until the further pressure drop is less than one predefinable threshold. If the further pressure drop is smaller than this Threshold (this is in the area of the "kink" at the bottom of the edge 31 the case, which is actually not a sharp kink, but a there is a short, fixed transition Waiting time or triggering can take place immediately.
  • the pressure p (DC component) is approximately in the region 32, which runs horizontally in FIG. 3 constant and cavitation occurs in any case at this pressure level (Alternating component).
  • store in sensor 2 during the first time interval t1 means provided the signals corresponding to the cavitations. at these signals are the alternating component of the pressure (in FIG. 3 not shown), for a definable number of time windows, all lie within the first time interval t1, recorded and is saved.
  • FIG. 4 shows the same signal curve as in FIG. 3, but here an operating state of the pump has been assumed.
  • the triggering of sensor 2 takes place in operation only when the Pressure level (DC component) is below the LO level. this is a necessary - but not sufficient - condition for the occurrence of Cavitations. If the sensor is triggered during operation, there is a Monitoring with the help of sensor 2 until the time interval t3 Pressure level (DC component) is again above LO. Is this the If so, no cavitation and monitoring can occur through the sensor is reset until the level of pressure (DC component) falls below LO again.
  • DC component Pressure level
  • Fig. 5 shows a block diagram of a signal generating unit 21 of the Sensor 2.
  • the transmitter 210 is separated there delivered signal in a switch ("Switch") 211.
  • the two Output signal branches for absolute pressure detection 212 and for cavitation detection ("Cavitation Detection") 213 follow the outputs of the switch 211.
  • the absolute pressure detection 212 the Constant component of the pressure is taken into account during the cavitation detection 213 the alternating component of the pressure is taken into account, for example in the already mentioned frequency range of 500-4000 Hz.
  • such a device is particularly suitable for the Use as a vacuum pump.
  • the quality of the achievable vacuum is thereby determined by the vapor pressure of the liquid F in the liquid annulus F.
  • the device it is also suitable for applications where the monitoring room there is a risk of explosion.
  • the sensor be designed so that the pressure transmitter in the hazardous area is located, but the rest of the sensor outside the hazardous area. Especially for use in The chemical / pharmaceutical industry can do this particularly Be interested.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Measuring Fluid Pressure (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
  • Control Of Non-Positive-Displacement Pumps (AREA)

Abstract

The detection method is carried out using a learning sensor (2) for detecting cavitations in a pump chamber (120) due to rotation of an impeller (12). In two intervals (t1, t2) the sensor learns which signals correspond to cavitations and which correspond to non cavitations. Following the termination of the learning operation. The sensor following the learning operation, decides on the basis of specified criteria, whether in the chamber (120) being monitored, a cavitation exists or not exists, and produces a corresponding output signal.

Description

Die Erfindung betrifft ein Verfahren und einen Sensor zur Detektion von Kavitationen gemäss dem jeweiligen unabhängigen Patentanspruch, sowie eine Vorrichtung enthaltend einen solchen Sensor.The invention relates to a method and a sensor for the detection of Cavitation according to the respective independent claim, and a device containing such a sensor.

Unter einer Kavitation versteht man eine plötzliche Hohlraumbildung, wie sie beispielsweise dann auftreten kann, wenn bei Flüssigkeitsringvakuumpumpen - das sind Pumpen, die sich einer Flüssigkeit als Hilfsmedium zur Erzeugung eines Vakuums bedienen - die zuvor verdampfte Flüssigkeit sehr schnell bzw. sogar schlagartig kondensiert. Bei derartigen Flüssigkeitspumpen entsteht durch eine solche Kaviation ein mechanischer Stoss bzw. Schlag auf die Schaufel bzw. Schaufeln des Schaufelrads, zwischen denen sich das Gas befindet. Dies hat bei jeder Kavitation eine mehr oder weniger kleine Verletzung der Schaufeln zur Folge, wodurch mit der Zeit das Schaufelrad und somit die Pumpe unbrauchbar wird.Cavitation is a sudden formation of cavities like this can occur, for example, when liquid ring vacuum pumps - these are pumps that look like a liquid Use auxiliary medium to create a vacuum - the previously evaporated Liquid condenses very quickly or even suddenly. With such Such a cavitation creates a mechanical fluid pump Impact or impact on the blade or blades of the impeller, between which the gas is located. This has one with every cavitation more or less minor injury to the blades resulting in time the paddle wheel and thus the pump becomes unusable.

Oft ist es nun bei industriellen Anwendungen so, dass die Pumpen sich an einem Ort befinden, wo sie nicht ohne weiteres ständig daraufhin überwacht werden können, ob und wie häufig solche Kavitationen auftreten. Darüberhinaus erzeugen die Pumpen beim Betrieb auch ein gewisses Betriebsgeräusch (auch ohne dass Kavitationen auftreten), welches mitunter recht erheblich sein kann, sodass es selbst bei einer Überwachung der Pumpe durch Operationspersonal schwer sein kann, zu erkennen, ob und in welcher Häufigkeit nun solche Kavitationen auftreten.It is now often the case in industrial applications that the pumps turn on a place where it is not readily monitored whether and how often such cavitations occur. In addition, the pumps also produce a certain amount during operation Operating noise (even without cavitation), which sometimes can be quite significant, so even when monitoring the Pump by surgical personnel can be difficult to tell if and in the frequency of such cavitations.

Aus der Offenlegungsschrift DE 35 20 734 A ist bereits ein Verfahren und eine Einrichtung zum Betrieb einer Kreiselpumpe bekannt, wobei mittels einer Sonde ein kavitationsfreier Betrieb einstellbar ist.A method is already known from the published patent application DE 35 20 734 A. and a device for operating a centrifugal pump is known, wherein by means cavitation-free operation can be set for a probe.

Da Kavitationen mit der Zeit zu Schäden an der Pumpe führen können, wie oben bereits erläutert, sollen solche Kavitationen vermieden werden oder zumindest detektiert werden, damit entsprechende Massnahmen getroffen werden können (z.B. Betriebsparameter verändert werden können), um ein ständiges Auftreten solcher Kavitationen zu verhindern.Because cavitation will damage the pump over time can, as already explained above, avoid such cavitations will be or at least be detected, so that appropriate measures can be taken (e.g. operating parameters can be changed), to prevent the constant occurrence of such cavitations.

Verfahrensmässig wird diese Aufgabe durch ein Verfahren gelöst, wie es durch die Merkmale des unabhängigen Verfahrensanspruchs charakterisiert ist. Bei dem erfindungsgemässen Verfahren wird der zu überwachende Raum mittels eines lernfähigen Sensors überwacht. Dabei wird mindestens einmal (danach kann eine Abspeicherung erfolgen) während eines Lernvorgangs für die Dauer eines ersten Zeitintervalls ein Zustand hergestellt, in welchem in dem zu überwachenden Raum auf jeden Fall Kavitationen auftreten. Nach Abschluss des ersten Zeitintervalls wird für die Dauer eines zweiten Zeitintervalls ein Zustand hergestellt, in welchem in dem zu überwachenden Raum auf jeden Fall keine Kavitationen auftreten. In jedem der beiden Zeitintervalle lernt der Sensor, welche Signale Kavitationen bzw. welche Signale Nicht-Kavitationen in dem zu überwachenden Raum entsprechen. Nach dem Abschluss dieses Lernvorgangs untersucht der Sensor die im Betrieb in dem zu überwachenden Raum auftretenden Signale, ob vorgebbare Kriterien, die aus den gelernten Signalen für die Kavitation bzw. Nicht-Kavitation abgeleitet sind, erfüllt sind und entscheidet auf dieser Basis, ob in dem zu überwachenden Raum eine Kavitation aufgetreten ist oder nicht und erzeugt ein enstprechendes Ausgangssignal. Auf diese Weise kann der Sensor zunächst selbst "lernen", was eine Kavitation ist und was nicht (insbesondere lernt er natürlich auch das Betriebsgeräusch ohne Kavitationen kennen) und entscheidet dann nach einer Lernphase, ob Kavitationen auftreten oder nicht. Die Zuverlässigkeit ist dabei ausgesprochen gross. Somit kann die entsprechende Pumpe auch an einem Ort aufgestellt werden, wo nicht ständig eine Überwachung möglich ist. Erkennt der Sensor beim Betrieb der Pumpe, dass Kavitationen auftreten, kann er ggf. einen Alarm auslösen, sodass das Operationspersonal entsprechende Massnahmen treffen kann und eine Beschädigung der Schaufeln und damit der Pumpe vermieden werden kann.In terms of procedure, this task is solved by a procedure like this characterized by the features of the independent process claim is. In the method according to the invention, the space to be monitored monitored using a teachable sensor. Doing this at least once (a saving can then take place) during a learning process for the duration of a first time interval produces a state in which in cavitation will definitely occur in the room to be monitored. To Completion of the first time interval will last for a second Time interval established a state in which to be monitored Definitely no cavitation will occur. In each of the two Time intervals, the sensor learns which signals cavitation or which Signals correspond to non-cavitation in the room to be monitored. After completing this learning process, the sensor examines the im Operation in the signals to be monitored, whether Predefinable criteria that are derived from the learned signals for cavitation or Non-cavitation are derived, fulfilled and deciding on this basis, whether or not cavitation has occurred in the room to be monitored and generates a corresponding output signal. In this way, the First, the sensor itself "learns" what is cavitation and what is not (In particular, of course, he also learns the operating noise without Know cavitations) and then decides after a learning phase whether Cavitations occur or not. The reliability is there extremely large. Thus, the corresponding pump can also be used on one Place where monitoring is not always possible. If the sensor detects that cavitation is occurring when the pump is operating, If necessary, he can trigger an alarm so that the operating personnel appropriate measures can take and damage the Buckets and thus the pump can be avoided.

Dabei kann in einer vorteilhaften Ausgestaltung ein als Drucksensor ausgebildeter Sensor verwendet werden, und es wird der Druck in dem zu überwachenden Raum überwacht. Drucksensoren sind heutzutage in verschiedenen Ausführungen verfügbar und können direkt ein Ausgangssignal liefern, das den Druck repräsentiert. Grundsätzlich kommen aber auch andere Sensoren, wie beispielsweise akustische Sensoren, in Betracht.In an advantageous embodiment, it can be used as a pressure sensor trained sensor will be used and it will increase the pressure in the monitoring room. Pressure sensors are in these days Different versions available and can directly Deliver an output signal that represents the pressure. Basically come but also other sensors, such as acoustic sensors, in Consideration.

In dem zu überwachenden Raum kann sowohl der absolute Druck als auch die Druckveränderung überwacht werden, insbesondere natürlich beides. Dies ist speziell für den Einlernvorgang von Vorteil, weil dieser dann wie folgt ablaufen kann. Beim Einlernvorgang kann zunächst in dem zu überwachenden Raum ein Druckabfall erzeugt werden, der grösser ist als ein vorgebbarer Mindestdruckabfall. Sodann wird beim Unterschreiten bzw. Erreichen eines vorgebbaren Drucks, bei welchem in dem zu überwachenden Raum auf jeden Fall Kavitationen auftreten, der Sensor für das erste Zeitintervall getriggert. Der Sensor "lernt" nun in diesem ersten Zeitintervall, was eine Kavitation ist. Nach Abschluss des ersten Zeitintervalls wird wieder ein Druckanstieg erzeugt, der grösser oder gleich ist wie ein vorgebbarer Mindestdruckanstieg, und der Sensor wird für das zweite Zeitintervall getriggert, sobald der Mindestdruckanstieg erreicht oder überschritten wird und ein vorgebbarer Druck erreicht oder überschritten wird. Der Sensor "lernt" dann in diesem zweiten Zeitintervall, was eine "Nicht-Kavitation" ist. Nach dieser Einlernphase kann dann der Betrieb der Pumpe erfolgen.In the room to be monitored, both the absolute pressure and the pressure change are monitored, especially of course both. This is particularly advantageous for the teach-in process because it then follows as follows can expire. During the teach-in process, you can start with monitor a pressure drop that is greater than a predeterminable minimum pressure drop. Then when falling below or Reaching a predeterminable pressure at which the pressure to be monitored Cavitation definitely occur, the sensor for the first Triggered time interval. The sensor "learns" in this first time interval, what is a cavitation. After the end of the first time interval, again generates an increase in pressure that is greater than or equal to a predeterminable one Minimum pressure rise, and the sensor will be on for the second time interval triggered as soon as the minimum pressure rise is reached or exceeded and a predeterminable pressure is reached or exceeded. The sensor Then "learns" in this second time interval what is a "non-cavitation". After this learning phase, the pump can then be operated.

In einer Weiterbildung dieser Variante wird der Sensor beim Einlernvorgang für das erste Zeitintervall erst dann getriggert, wenn der weitere Abfall des Drucks kleiner ist als ein vorgebbarer Schwellenwert. Es wird also gewartet, bis der Druckabfall praktisch abgeschlossen ist. Nach Abschluss des ersten Zeitintervalls wird der Sensor für das zweite Zeitintervall dann getriggert, wenn der Anstieg des Drucks grösser ist als ein vorgebbarer Schwellenwert. Da vorzugsweise mit niedrigen Dampfdrücken gearbeitet wird, liegt bei einem entsprechend grossen Druckanstieg der Druck praktisch sofort oberhalb des Dampfdrucks (und es treten in jedem Fall keine Kavitationen auf).In a further development of this variant, the sensor is used during the learning process triggered for the first time interval only when the further decrease of the Pressure is less than a predetermined threshold. So it’s waiting until the pressure drop is practically complete. After completing the first Time interval, the sensor is then triggered for the second time interval, if the increase in pressure is greater than a predetermined threshold. Since it is preferred to work with low vapor pressures, one is correspondingly large pressure increase the pressure almost immediately above the Vapor pressure (and there are no cavitations in any case).

In einer vorteilhaften Ausführungsvariante des erfindungsgemässen Verfahrens legt der Sensor für verschiedene Kriterien fest, wie hoch bei Erfüllung des jeweiligen Krireriums die Wahrscheinlichkeit ist, dass eine Kavitation aufgetreten ist, und dass anschliessend aufgrund sämtlicher Kriterien und der zugehörigen Wahrscheinlichkeiten der Sensor entscheidet, ob eine Kavitation aufgetreten ist oder nicht und das entsprechende Ausgangssignal erzeugt. Solche Sensoren setzen typischerweise die Prizipien der "Fuzzy-Logic" ein.In an advantageous embodiment variant of the invention The sensor determines how high for different criteria Fulfillment of the respective criteria the probability is that a Cavitation has occurred, and then due to all Criteria and the associated probabilities the sensor decides whether or not cavitation has occurred and the corresponding Output signal generated. Such sensors typically set the Principles of "fuzzy logic".

Die Aufgabe wird auch mittels eines lernfähigen Sensors gelöst. Dabei wird in dem zu überwachenden Raum zunächst während eines Einlernvorgangs für die Dauer eines ersten Zeitintervalls ein Zustand hergestellt, in welchem in dem zu überwachenden Raum auf jeden Fall Kavitationen auftreten. In diesem ersten Zeitintervall lernt der Sensor, was eine Kavitation ist. Nach Abschluss des ersten Zeitintervalls wird in dem zu überwachenden Raum für die Dauer eines zweiten Zeitintervalls ein Zustand hergestellt, in welchem in dem zu überwachenden Raum auf jeden Fall keine Kavitationen auftreten. In diesem zweiten Zeitintervall lernt der Sensor, was eine "Nicht-Kavitation" ist. Der Sensor umfasst nun Mittel, die in jedem der beiden Zeitintervalle die Signale speichern, welche den Kavitationen bzw. den Nicht-Kavitationen in dem zu überwachenden Raum entsprechen. Ferner umfasst der Sensor Mittel, welche die im Betrieb in dem zu überwachenden Raum auftretenden Signale daraufhin untersuchen, ob vorgebbare Kriterien, die aus den gelernten Signalen für die Kavitation bzw. Nicht-Kavitation abgeleitet sind, erfüllt sind sowie Mittel, die auf dieser Basis entscheiden, ob in dem zu überwachenden Raum eine Kavitation aufgetreten ist oder nicht und die dann ein entsprechendes Ausgangssignal erzeugen. Mit einem solchen Sensor lässt sich eine Pumpe mit hoher Zuverlässigkeit überwachen, auch wenn nicht ständig Operationspersonal vor Ort sein kann. Treten Kavitationen auf, so kann ggf. aufgrund des Sensorausgangssignals ein Alarm ausgelöst werden, sodass das Operationspersonal Massnahmen treffen kann, die eine Beschädigung der Schaufeln und damit der Pumpe verhindern.The task is also solved by means of a teachable sensor. Doing so in the room to be monitored initially during a teach-in process a state is established for the duration of a first time interval in which Cavitation definitely occurs in the room to be monitored. In In this first time interval, the sensor learns what cavitation is. To The first time interval is completed in the room to be monitored for the duration of a second time interval produces a state in which in in any case, no cavitation occurs in the room to be monitored. In During this second time interval, the sensor learns what "non-cavitation" is. The sensor now includes means that in each of the two time intervals Store signals which indicate the cavitations or the non-cavitations in correspond to the room to be monitored. The sensor also includes Means which occur during operation in the room to be monitored Signals then investigate whether predeterminable criteria that result from the learned signals for cavitation or non-cavitation are derived, are fulfilled as well as means that decide on this basis whether to monitoring room a cavitation has occurred or not and then generate a corresponding output signal. With such a sensor a pump can be monitored with high reliability, even if operating personnel cannot be on site at all times. If cavitations occur, an alarm may be triggered based on the sensor output signal so that the operating personnel can take measures that Prevent damage to the blades and thus the pump.

In einem vorteilhaften Ausführungsbeispiel weist der Sensor Mittel zur Bestimmung des Drucks in dem zu überwachenden Raum auf, er ist also als Drucksensor ausgebildet. In einer Weiterbildung weist er sowohl Mittel zur Bestimmung des Drucks als auch der Druckveränderung in dem zu überwachenden Raum auf, insbesondere von beidem, was speziell für den Einlernvorgang von Vorteil sein kann. Dabei kann die Änderung des Drucks entweder mittels Differenzbildung von aufeinanderfolgenden Messwerten des absoluten Drucks bestimmt werden, oder es können separate Mittel vorgesehen sein, die eine direkte Messung der Druckveränderung ermöglichen.In an advantageous exemplary embodiment, the sensor has means for Determination of the pressure in the room to be monitored, so it is as Pressure sensor trained. In a further education, he has both funds for Determination of the pressure as well as the change in pressure in the monitoring room, especially of both, which is especially for the Teaching process can be an advantage. Doing so can change the pressure either by forming the difference between successive measured values of the absolute pressure can be determined, or it can be separate means be provided, the direct measurement of the pressure change enable.

Gemäss einer Weiterbildung weist der Sensor Mittel zum Triggern auf, die beim Einlernvorgang den Sensor für das erste Zeitintervall triggern, wenn in dem zu überwachenden Raum ein Druckabfall erzeugt wird, der grösser ist als ein vorgebbarer Mindestdruckabfall und wenn ein vorgebbarer Druck erreicht oder unterschritten wird, bei welchem in dem zu überwachenden Raum auf jeden Fall Kavitationen auftreten. In diesem ersten Zeitintervall lernt der Sensor dann, was eine Kavitation ist und speichert die entsprechenden Signale ab. Ferner umfasst der Sensor Mittel, die den Sensor nach Abschluss des ersten Zeitintervalls für das zweite Zeitintervall triggern, sobald ein Druckanstieg erzeugt wird, der grösser oder gleich ist wie ein vorgebbarer Mindestdruckanstieg und sobald ein vorgebbarer Mindestdruck erreicht oder überschritten wird. Der Sensor lernt in diesem Zeitintervall, was eine Nicht-Kavitation ist und speichert die entsprechenden Signale ab.According to a further development, the sensor has means for triggering the trigger the sensor for the first time interval during the teach-in process, if in a greater pressure drop is generated in the room to be monitored as a predeterminable minimum pressure drop and if a predeterminable pressure is reached or fallen below, in which in the to be monitored Cavitation definitely occur. In this first time interval the sensor then learns what cavitation is and stores it corresponding signals. Furthermore, the sensor comprises means that the Sensor after completion of the first time interval for the second time interval trigger as soon as a pressure rise is generated that is greater than or equal to a predeterminable minimum pressure rise and as soon as a predeterminable one Minimum pressure is reached or exceeded. The sensor learns in this Time interval, which is a non-cavitation and stores the corresponding one Signals off.

In einer Weiterbildung bewirken beim Einlernvorgang die Mittel zum Triggern des Sensors eine Triggerung des Sensors für das erste Zeitintervall erst dann, wenn der weitere Druckabfall kleiner ist als ein vorgebbarer Schwellenwert. Mit anderen Worten heisst dies, dass eine Triggerung für das erste Zeitintervall bei praktisch stabilem niedrigen Druck erfolgt. Nach Abschluss des ersten Zeitintervalls triggern die Mittel zum Triggern des Sensors den Sensor für das zweite Zeitintervall, wenn der Druckanstieg grösser ist als ein vorgebbarer Schwellenwert. Da vorzugsweise mit niedrigen Dampfdrücken gearbeitet wird, liegt der Druck bei einem entsprechend grossen Druckanstieg praktisch sofort oberhalb des Dampfdrucks.In a further development, the means for triggering cause the learning process triggering of the sensor for the first time interval when the further pressure drop is smaller than a predeterminable one Threshold. In other words, this means that a trigger for the first time interval occurs at a practically stable low pressure. To Completion of the first time interval triggers the means for triggering the Sensors the sensor for the second time interval when the pressure rises is greater than a predefinable threshold. Because preferably with low Steam pressure is worked, the pressure is accordingly large pressure increase practically immediately above the vapor pressure.

Gemäss einem Ausführungsbeispiel der Erfindung umfasst der Sensor Mittel, die für verschiedene Kriterien festlegen, wie hoch bei Erfüllung des jeweiligen Kriteriums die Wahrscheinlichkeit ist, dass eine Kavitation aufgetreten ist, sowie Mittel, die anschliessend aufgrund sämtlicher Kriterien und der zugehörigen Wahrscheinlichkeiten entscheiden, ob eine Kavitation aufgetreten ist oder nicht und das entsprechende Ausgangssignal erzeugen. Solche Sensoren setzen typischerweise die Prinzipien der "Fuzzy-Logic" ein.According to one embodiment of the invention, the sensor comprises means which determine for different criteria how high when the respective one is fulfilled Criterion the likelihood is that cavitation has occurred as well as funds that are based on all criteria and the associated probabilities decide whether cavitation has occurred or not and generate the corresponding output signal. Such sensors typically use the principles of "fuzzy logic".

Gegenstand der Erfindung ist schliesslich noch eine Vorrichtung, insbesondere eine Flüssigkeitsringpumpe, die einen entsprechenden Sensor umfasst.Finally, the subject of the invention is a device in particular a liquid ring pump that has a corresponding sensor includes.

Im folgenden wird die Erfindung anhand der Zeichnung näher erläutert. Es zeigen in schematischer Darstellung:

Fig. 1
ein Ausführungsbeispiels einer Flüssigkeitsringpumpe,
Fig 2
das Ausführungsbeispiel gemäss Fig. 1, wobei der Flüssigkeitsring und der Sensor zum Detektieren von Kavitationen zu erkennen sind,
Fig. 3
ein Beispiel eines typischen Verlaufs des absoluten Drucks (nur Gleichanteil) während des Einlernvorgangs des Sensors,
Fig. 4
der Verlauf des absoluten Drucks aus Fig.3, mit der Triggerung des Sensors im Betrieb, also mit eingelerntem Sensor,
Fig. 5
ein Blockschaltbild der Signalerzeugungseinheit eines Sensors,
und
Fig. 6
ein Blockschaltbild der Art und Weise der Signalauswertung im Sensor.
The invention is explained in more detail below with reference to the drawing. In a schematic representation:
Fig. 1
an embodiment of a liquid ring pump,
Fig. 2
1, wherein the liquid ring and the sensor for detecting cavitations can be seen,
Fig. 3
an example of a typical course of the absolute pressure (only DC component) during the teach-in process of the sensor,
Fig. 4
the course of the absolute pressure from FIG. 3, with the triggering of the sensor in operation, that is to say with the taught-in sensor,
Fig. 5
2 shows a block diagram of the signal generation unit of a sensor,
and
Fig. 6
a block diagram of the way of signal evaluation in the sensor.

In dem in Fig. 1 dargestellten Ausführungsbeispiel einer Flüssigkeitsringpumpe 1 erkennt man deren Ansaugstutzen 10 und den Ort 11, an welchem ein Drucktransmitter eines Kavitationssensors (nicht dargestellt) im Innern des Ansaugstutzens 10 angeordnet sein kann. Weiterhin erkennt man ein exzentrisch angeordnetes Schaufelrad 12 (strichliert), mit dessen Hilfe ein zu förderndes Gas (z.B. Luft bei einer Vakuumpumpe) durch den Ansaugstutzen 10 und den Ansaugschlitz 100, die miteinander in Verbindung stehen, was aber in Fig. 1 aus zeichnerischen Gründen nicht zu erkennen ist, angesaugt wird. Die Richtung, in welcher das Gas gefördert wird, ist durch die Pfeile G angedeutet. Es ist unmittelbar einleuchtend, dass hierzu das Schaufelrad 12 im Uhrzeigersinn angetrieben werden muss, was z.B. mittels eines (nicht dargestellten) Elektromotors erfolgen kann. Ferner erkennt man in Fig. 1 noch einen Auslassschlitz 130 und einen Auslassstutzen 13, die ebenfalls miteinander in Verbindung stehen, was aber in Fig. 1 aus zeichnerischen Gründen nicht zu erkennen ist. Durch den Auslassschlitz 130 kann das geförderte Gas wieder aus der Pumpe herausgeführt werden.In the embodiment shown in Fig. 1 Liquid ring pump 1 can be seen the intake manifold 10 and the location 11, on which a pressure transmitter of a cavitation sensor (not shown) can be arranged inside the intake manifold 10. An eccentrically arranged paddle wheel 12 can also be seen (dashed), with the help of which a gas to be pumped (e.g. air at a Vacuum pump) through the intake manifold 10 and the intake slot 100, the are connected to each other, but what in Fig. 1 from the drawing For reasons not recognizable, is sucked in. The direction in which that Gas is pumped is indicated by the arrows G. It is immediate obvious that the paddle wheel 12 is driven clockwise for this purpose must become what e.g. by means of an electric motor (not shown) can be done. An outlet slot 130 can also be seen in FIG. 1 and an outlet port 13, which are also in communication with each other stand, but which is not visible in Fig. 1 for drawing reasons. Through the outlet slot 130, the pumped gas can again from the Pump are led out.

Fig. 2 zeigt das Ausführungsbeispiel der Flüssigkeitsringpumpe 1 gemäss Fig. 1, jedoch ist zusätzlich am Ansaugstutzen 10 der Sensor 2 zum Detektieren von Kavitationen zu erkennen. Ausserdem ist schematisch auch der Ringflüssigkeitsraum R zu erkennen, der konzentrisch zum Pumpengehäuse angeordent ist und mit einer schraffiert dargestellten Flüssigkeit F gefüllt ist. Bezüglich dieses Ringflüssigkeitsraums R ist das Schaufelrad 12 exzentrisch angeordnet. Auch der Ansaugschlitz 100 sowie der Auslassschlitz 130 sind in Fig. 2 angedeutet, um die Funktionsweise einer solchen Pumpe besser erläutern zu können. Ferner ist noch eine Öffnung O für die Ringflüssigkeit F angedeutet. Es muss nämlich - wie noch erläutert werden wird - ständig neue Flüssigkeit F zugeführt werden und erwärmte Flüssigkeit F abgeführt werden. Fig. 2 shows the embodiment of the liquid ring pump 1 according to Fig. 1, however, is in addition to the intake manifold 10, the sensor 2 for Detect cavitations. In addition, is also schematic to recognize the ring liquid space R, which is concentric to the Pump housing is arranged and shown with a hatched Liquid F is filled. Regarding this ring liquid space R, that is Paddle wheel 12 arranged eccentrically. The suction slot 100 as well the outlet slot 130 are indicated in Fig. 2 for the mode of operation to better explain such a pump. Another is Opening O for the ring liquid F is indicated. Because it has to - like still will be explained - new liquid F is constantly fed and heated liquid F are discharged.

Die prinzipielle Funktionsweise einer solchen Pumpe, die insbesondere als Vakuumpumpe betrieben werden kann, ist nun wie folgt (siehe Fig. 2): Durch das Drehen das Schaufelrads 12 im Uhrzeigersinn wird das zu fördernde Gas (im Falle der Vakuumpumpe z.B. die Luft aus dem zu evakuierenden Raum) durch den Ansaugstutzen 10 und den Ansaugschlitz 100 in den Raum 120 zwischen der Nabe 121 und den Schaufeln 122 des Schaufelrades eingesaugt. Ist der Bereich des Ansaugschlitzes 100 überstrichen, so ist das zu fördernde Gas in diesem Raum 120 eingeschlossen. Wegen der exzentrischen Anordnung des Schaufelrades 12 in Bezug auf den Ringflüssigkeitsraum R wird dieser Raum 120 in der Aufwärtsbewegung in Richtung auf den Auslassschlitz 130 zu immer kleiner. Dadurch wird das in dem Raum 120 befindliche Gas komprimiert und erwärmt sich und auch die Flüssigkeit F. Erreicht der Raum 120 den Bereich des Auslasschlitzes 130, so kann das komprimierte (erwärmte) Gas durch den Auslassschlitz 130 entweichen.The principle of operation of such a pump, which in particular as Vacuum pump can now be operated as follows (see Fig. 2): By rotating the paddle wheel 12 clockwise becomes the gas to be pumped (in the case of the vacuum pump e.g. the air from the room to be evacuated) through intake manifold 10 and intake slot 100 into space 120 between the hub 121 and the blades 122 of the impeller sucked. If the area of the suction slit 100 is covered, this is the case gas to be extracted included in this space 120. Because of the eccentric arrangement of the impeller 12 with respect to the Ring fluid space R becomes this space 120 in the upward movement in Direction towards the outlet slot 130 to become smaller and smaller. This will in the gas located in the room 120 compresses and heats up and also the Liquid F. If the space 120 reaches the area of the outlet slot 130, the compressed (heated) gas can pass through the outlet slot 130 escape.

Wird nun der Druck in dem Raum 120 niedriger als der Dampfdruck der Flüssigkeit F, weil aus dem zu evakuierenden Raum praktisch keine Luft mehr angesaugt wird, dann kann bei der Zunahme des Volumens des Raums 120 in der Abwärtsbewegung des Schaufelrads 12 Flüssigkeit F in den Raum 120 hinein verdampfen. Wird dann das Gas in der Aufwärtsbewegung wieder komprimiert, weil das Volumen des Raums 120 wieder abnimmt, so kondensiert das Gas schlagartig an den verhältnismässig kalten Flächen der Schaufeln 122 des Schaufelrads 12 - es kommt zu den bereits erwähnten Kavitationen. Im Vakuumbetrieb werden daher Flüssigkeiten mit niedrigem Dampfdruck gewählt, weil dadurch die Güte des Vakuums verbessert wird.If the pressure in space 120 now becomes lower than the vapor pressure of the Liquid F because there is practically no air from the room to be evacuated more is sucked in, then can increase the volume of the room 120 in the downward movement of the paddle wheel 12 liquid F into the room Vaporize 120. Then the gas will move up again compressed because the volume of space 120 decreases again, so the gas suddenly condenses on the relatively cold surfaces of the Paddles 122 of the paddle wheel 12 - it comes to those already mentioned Cavitations. In vacuum operation, liquids with low Vapor pressure selected because this improves the quality of the vacuum.

Zur Detektkon solcher Kavitationen ist der Sensor 2 vorgesehen. Dabei handelt es sich um einen sogenannten "lernfähigen" Sensor. Das heisst, dem Sensor 2 wird zunächst in einem Einlernvorgang beigebracht, was eigentlich (signalmässig) einer Kavitation entspricht, und was nicht. Hierzu muss natürlich ein Zustand hergestellt werden, in welchem auf jeden Fall Kavitationen auftreten. In diesem Zustand muss der Sensor 2 "lernen", was eine Kavitation ist. Der Sensor 2 muss auch lernen, was eine "Nicht-Kavitation" ist, damit er in der Lage ist, Kavitationen von sonstigen Störgeräuschen zu unterscheiden (wie z.B. Strömungsgeräusche, Motorgeräusche, etc.). Dies erfolgt in einem Einlernvorgang, wie er im folgenden anhand von Fig. 3 beschrieben wird.Sensor 2 is provided for the detection of such cavitations. there it is a so-called "learnable" sensor. That means the Sensor 2 is first taught in a teach-in process, which is actually (in terms of signal) corresponds to cavitation, and what does not. To do this of course a condition can be made, in any case Cavitations occur. In this state, sensor 2 must "learn" what is a cavitation. The sensor 2 must also learn what is a "non-cavitation" so that he is able to prevent cavitation from others Distinguish between disturbing noises (such as flow noises, Engine noise, etc.). This is done in a teach-in process, as in following will be described with reference to FIG. 3.

In Fig. 3 ist der Verlauf des absoluten Drucks p (Gleichanteil) über der Zeit t während des Einlernvorgangs in Form einer Kurve 3 dargestellt. Diese weist zunächst einen horizontatlen Verlauf 30 mit einem Pegel HI auf, der Druck p (Gleichanteil) ist also im wesentlichen konstant. Nun wird ein Druckabfall erzeugt, der in der Kurve 3 der abfallenden Flanke 31 entspricht. Detektiert der Sensor 2 einen solchen Druckabfall, der grösser ist als ein vorgebbarer Mindestdruckabfall, das heisst stellt der Sensor 2 fest, dass innerhalb eines Zeitraums Δt der Druck p (Gleichanteil) um einen Wert fällt, der grösser ist als ein vorgegebener Mindestdruckabfall, so weiss er, dass nun gleich ein Zeitintervall folgt, in welchem er lernen wird, was Kavitationen sind und ein weiteres Zeitintervall, in welchem er lernen wird, was "Nicht-Kavitationen" sind.3 shows the course of the absolute pressure p (constant component) over time t shown in the form of a curve 3 during the learning process. This points first a horizontal course 30 with a level HI, the pressure p (DC component) is therefore essentially constant. Now there is a pressure drop generated which corresponds to the falling edge 31 in curve 3. detected the sensor 2 has such a pressure drop that is greater than a predeterminable one Minimum pressure drop, that is, the sensor 2 detects that within a Period Δt the pressure p (constant component) falls by a value that is greater than a given minimum pressure drop, he knows that one now Time interval follows in which he will learn what cavitations are and a further time interval in which he will learn what "non-cavitation" are.

Die Triggerung des Sensors 2 für das erste Zeitintervall t1,in welchem der Sensor lernt, was eine Kavitation (signalmässig) ist, erfolgt nun derart, dass zuerst abgewartet wird, bis der Druckpegel einerseits unterhalb des Pegels LO liegt und andererseits bis der weitere Druckabfall kleiner ist als ein vorgebbarer Schwellenwert. Ist der weitere Druckabfall kleiner als dieser Schwellenwert (dies ist im Bereich des "Knicks" am unteren Ende der Flanke 31 der Fall, der genau genommen eben kein scharfer Knick, sondern ein gekrümmter Übergang ist) so kann entweder noch eine kurze, festgelegte Zeit zugewartet werden oder die Triggerung kann sofort erfolgen. Der Druck p (Gleichanteil) ist in dem Bereich 32, der in Fig. 3 horizontal verläuft, in etwa konstant und es kommt bei diesem Druckpegel in jedem Fall zu Kavitationen (Wechselanteil).The triggering of the sensor 2 for the first time interval t1, in which the Sensor learns what a cavitation (signal-based) is, is now done in such a way that first wait until the pressure level is below the level LO and on the other hand until the further pressure drop is less than one predefinable threshold. If the further pressure drop is smaller than this Threshold (this is in the area of the "kink" at the bottom of the edge 31 the case, which is actually not a sharp kink, but a there is a short, fixed transition Waiting time or triggering can take place immediately. The pressure p (DC component) is approximately in the region 32, which runs horizontally in FIG. 3 constant and cavitation occurs in any case at this pressure level (Alternating component).

Während des ersten Zeitintervalls t1 speichern hierfür im Sensor 2 vorgesehene Mittel die Signale, die den Kavitationen entsprechen. Bei diesen Signalen handelt es sich um den Wechselanteil des Drucks (in Fig. 3 nicht dargestellt), der für eine bestimmbare Anzahl von Zeitfenstern, die alle innerhalb des ersten Zeitintervalls t1 hintereinander liegen, aufgezeichnet und gespeichert wird. Bei der Aufzeichnung bzw. Speicherung werden beispielsweise die Signalanteile im Frequenzbereich von 500-4000 Hz berücksichtigt.For this purpose, store in sensor 2 during the first time interval t1 means provided the signals corresponding to the cavitations. at these signals are the alternating component of the pressure (in FIG. 3 not shown), for a definable number of time windows, all lie within the first time interval t1, recorded and is saved. When recording or saving for example the signal components in the frequency range of 500-4000 Hz considered.

Ist das Zeitintervall t1 abgeschlossen, so wird abgewartet, bis wieder ein Mindestanstieg des Drucks p (Gleichanteil) erfolgt. Da typischerweise bei niedrigem Dampfdruck gearbeitet wird, liegt der Pegel des Drucks p (Gleichanteil) bei einem vorgegebenen Mindestdruckanstieg praktisch sofort wieder oberhalb des Dampfdrucks und es treten keine Kavitationen mehr auf. Beim Erkennen dieses Mindestdruckanstiegs wird daher der Sensor 2 für ein zweites Zeitintervall t2 getriggert. In diesem zweiten Zeitintervall t2 erfolgen keine Kavitationen, und die im Sensor 2 vorgesehenen Mittel speichern die Signale, die einer "Nicht-Kavitation" entsprechen.If the time interval t1 is completed, the system waits until on again The minimum rise in pressure p (constant component) takes place. Because typically at low vapor pressure is worked, the level of the pressure p (Constant component) practically immediately with a given minimum pressure increase again above the vapor pressure and there are no more cavitations. When this minimum pressure rise is detected, sensor 2 is therefore switched on second time interval t2 triggered. In this second time interval t2 no cavitation, and the means provided in sensor 2 store the Signals that correspond to a "non-cavitation".

Nach erneutem Anstieg des Drucks über die Flanke 33 über den Pegel HI erreicht dann der Pegel des Drucks (Gleichanteil) wieder den ursprünglichen Wert, die Kurve 3 verläuft daher im Bereich 34 wieder horizontal, der Druck (Gleichanteil) bleibt also im wesentlichen konstant. Der Einlernvorgang ist somit abgeschlossen. Die Parameter für die Erkennung, welche Signale nun einer Kavitation entsprechen und welche Signale einer "Nicht-Kavitation", können dann abgespeichert werden, sodass bei der nächsten Aufnahme des Betriebs kein neues Einlernen des Sensors mehr erfolgen muss. Selbstverständlich kann jedoch ein solcher Lernvorgang auch erneut durchgeführt werden.After the pressure across edge 33 has risen again above level HI the pressure level (constant component) then reaches the original level again Value, curve 3 therefore runs horizontally again in area 34, the pressure (DC component) therefore remains essentially constant. The learning process is thus completed. The parameters for the detection of which signals now correspond to a cavitation and which signals a "non-cavitation", can then be saved so that the next time the No new teach-in of the sensor has to take place during operation. However, such a learning process can of course also be repeated be performed.

In Fig. 4 ist der gleiche Signalverlauf wie in Fig. 3 gezeigt, wobei hier aber ein Betriebszustand der Pumpe angenommen worden ist. Zur Vereifachung wurde ein gleicher Verlauf des Drucks (Gleichanteil) wie in Fig. 3 angenommen. Die Triggerung des Sensors 2 erfolgt im Betrieb nur, wenn der Pegel des Drucks (Gleichanteil) unterhalb des Pegels LO liegt. Dies ist eine notwendige - aber nicht hinreichende - Bedingung für das Auftreten von Kavitationen. Ist der Sensor im Betrieb getriggert, so erfolgt eine Überwachung mit Hilfe des Sensors 2 so lange (Zeitintervall t3), bis der Pegel des Drucks (Gleichanteil) wieder oberhalb von LO liegt. Ist dies der Fall, so können sicher keine Kavitationen auftreten und die Überwachung durch den Sensor wird wieder eingestellt, bis der Pegel des Drucks (Gleichanteil) erneut unter LO fällt. Die Bedingung, dass zum Triggern im Betreieb der Pegel des Drucks (Gleichanteil) unter dem Pegel LO liegt, ist insofern von Bedeutung, als auch während des normalen Betriebs, also in einem Pegelbereich des Drucks (Gleichanteil), in welchem sicher keine Kavitationen auftreten können, Störgeräusche (z.B. Strömungsgeräusche, Motorgeräusche, etc.) auftreten können, die sonst möglicherweise vom Sensor als Kavitation erkannt werden könnten.FIG. 4 shows the same signal curve as in FIG. 3, but here an operating state of the pump has been assumed. For simplification the same course of the pressure (constant component) as in FIG. 3 accepted. The triggering of sensor 2 takes place in operation only when the Pressure level (DC component) is below the LO level. this is a necessary - but not sufficient - condition for the occurrence of Cavitations. If the sensor is triggered during operation, there is a Monitoring with the help of sensor 2 until the time interval t3 Pressure level (DC component) is again above LO. Is this the If so, no cavitation and monitoring can occur through the sensor is reset until the level of pressure (DC component) falls below LO again. The condition that to trigger in Operating the level of the pressure (DC component) is below the level LO insofar as also during normal operation, ie in a pressure level range (constant component), in which certainly none Cavitation can occur, noise (e.g. flow noise, Engine noises, etc.) that may otherwise come from Sensor could be recognized as cavitation.

Fig. 5 zeigt ein Blockschaltbild einer Signalerzeugungseinheit 21 des Sensors 2. Dort erfolgt die Auftrennung des von einem Transmitter 210 gelieferten Signals in einer Weiche ("Switch") 211. Die beiden Ausgangssignalzweige für die Absolutdruckdetektion ("Pressure Detection") 212 und für die Kavitationsdetektion ("Cavitation Detection") 213 folgen auf die Ausgänge der Weiche 211. Bei der Absolutdruckdetektion 212 wird der Gleichanteil des Drucks berücksichtigt, während bei der Kavitationsdetektion 213 der Wechselanteil des Drucks berücksichtigt wird, beispielsweise in dem bereits genannten Frequenzbereich von 500-4000 Hz.Fig. 5 shows a block diagram of a signal generating unit 21 of the Sensor 2. The transmitter 210 is separated there delivered signal in a switch ("Switch") 211. The two Output signal branches for absolute pressure detection 212 and for cavitation detection ("Cavitation Detection") 213 follow the outputs of the switch 211. In the absolute pressure detection 212 the Constant component of the pressure is taken into account during the cavitation detection 213 the alternating component of the pressure is taken into account, for example in the already mentioned frequency range of 500-4000 Hz.

In Fig. 6 schliesslich ist in einem Blockschaltbild die Art und Weise der Signalverarbeitung im Sensor 2 dargestellt. Das von der Signalerzeugungseinheit ("Signal generating unit") 21 (siehe Fig. 5) kommende kontinuierliche Signal wird in einer Signalaufbereitungsstufe ("Analog Signal Conditioning") 22 aufbereitet und anschliessend einem Analog/Digitalwandler 23 ("A/D") zugeführt. Dessen Ausgangssignal gelangt zu einer Fenstervorgabe- und Speicherstufe 24 ("Windowing & Buffering"), in welcher die Dauer und Anzahl der Zeitfenster festgelegt werden, in denen das Ausgangssignal des A/D-Wandlers tatsächlich gespeichert und weiterverarbeitet wird. Über eine Adaptionsstufe 25 ("Adaptation")und eine dazugehörige Eingabeeinheit 25a ("Adaptation Signal Input") kann Einfluss auf die der Fenstervorgabe- und Speicherstufe 24 nachgeschaltete Diskriminatorstufe 26 ("Discriminator") genommen werden. In dieser Diskriminatorstufe 26 wird für verschiedene Kriterien festgelegt, wie gross bei Erfüllung des jeweiligen Kriteriums die Wahrscheinlichkeit ist, dass eine Kavitation aufgetreten ist. Solche Kriterien können beispielsweise, aber nicht ausschliesslich, sein:

  • Anzahl der Tangenten mit einer Steigung, die grösser ist als eine vorgegebene Mindeststeigung
  • Absolute Grösse der Tangentensteilheit
  • Amplitude der Schwankungen des Druckpegels (Wechselanteil) In der Detektionsstufe 27 ("Detection") schliesslich findet eine Gesamtbewertung sämtlicher Kriterien bzw. der zugehörigen Wahrscheinlichkeiten statt. Dabei kann den einzelnen Kriterien ein unterschiedliches Gewicht zugemessen werden. Die Gesamtbewertung aller Kriterien und der zugehörigen einzelnen Wahrscheinlichkeiten führt schliesslich zu einer Gesamtwahrscheinlichkeit, welche nach Vergleich mit den Vorgaben einer Alarmbedingungs-stufe 28 ("Alarm Conditions") dazu führen, dass von der Detektionsstufe 27 entweder ein Alarm ausgelöst wird oder nicht. Derartige Signalauswertungen, bei denen bei der Erfüllung von einzelnen Kriterien ein bestimmtes Ereignis mit einer bestimmten Wahrscheinlichkeiten eingetreten ist, basieren typischerweise auf den Prinzipien der Fuzzy-Logic.
Finally, FIG. 6 shows the manner of signal processing in sensor 2 in a block diagram. The continuous signal coming from the signal generating unit 21 (see FIG. 5) is processed in a signal conditioning stage 22 and then fed to an analog / digital converter 23 (A / D). Its output signal reaches a window setting and storage stage 24 ("Windowing &Buffering"), in which the duration and number of time windows are defined in which the output signal of the A / D converter is actually stored and processed. The adaption stage 25 (“adaptation”) and an associated input unit 25a (“adaption signal input”) can be used to influence the discriminator stage 26 (“discriminator”) downstream of the window specification and storage stage 24. In this discriminator stage 26 it is determined for various criteria how large the probability that a cavitation has occurred if the respective criterion is met. Such criteria can be, for example, but not exclusively:
  • Number of tangents with a slope that is greater than a specified minimum slope
  • Absolute size of the tangent slope
  • Amplitude of the fluctuations in the pressure level (alternating component) Finally, in the detection stage 27 ("detection"), an overall evaluation of all criteria or the associated probabilities takes place. Different weight can be assigned to the individual criteria. The overall evaluation of all criteria and the associated individual probabilities ultimately leads to an overall probability which, after comparison with the specifications of an alarm condition level 28 ("alarm conditions"), either means that an alarm is triggered by the detection level 27 or not. Such signal evaluations, in which a certain event with a certain probability has occurred when individual criteria are met, are typically based on the principles of fuzzy logic.

Wie bereits erwähnt ist eine solche Vorrichtung besonders geeignet für den Einsatz als Vakuumpumpe. Die Güte des erreichbaren Vakuums wird dabei durch den Dampfdruck der Flüssigkeit F im Flüssigkeitsringraum F bestimmt. Erwähnt werden soll an dieser Stelle noch, dass sich die Vorrichtung natürlich auch für solche Einsatzzwecke eignet, bei denen in dem zu überwachenden Raum Explosionsgefahr besteht. In einem solchen Fall kann der Sensor so ausgebildet werden, dass der Drucktransmitter im explosionsgefährdeten Bereich angeordnet ist, der Rest des Sensors jedoch ausserhalb des explosionsgefährdeten Bereichs. Speziell für den Einsatz in der chemisch/pharmazeutischen Industrie kann dies von besonderem Interesse sein.As already mentioned, such a device is particularly suitable for the Use as a vacuum pump. The quality of the achievable vacuum is thereby determined by the vapor pressure of the liquid F in the liquid annulus F. At this point it should also be mentioned that the device Of course, it is also suitable for applications where the monitoring room there is a risk of explosion. In such a case the sensor be designed so that the pressure transmitter in the hazardous area is located, but the rest of the sensor outside the hazardous area. Especially for use in The chemical / pharmaceutical industry can do this particularly Be interested.

Claims (13)

  1. A method for the detection of cavitations in a space to be monitored, in which method the space to be monitored is monitored by means of a sensor (2) which is capable of learning, wherein at least once during a learning process a state is produced for the duration of a first time interval (t1) in which cavitations in any event arise in the space to be monitored, after the completion of the first time interval (t2) a state is produced for the duration of a second time interval (t2) in which cavitations do not in any event arise in the space to be monitored, and wherein in each of the two time intervals the sensor (2) learns which signals correspond to cavitations and which signals correspond to non-cavitations respectively in the space to be monitored, and that after the completion of this learning process the sensor investigates the signals which arise during operation in the space to be monitored as to whether predeterminable criteria which are derived from the learned signals for cavitation and non-cavitation respectively are fulfilled and decides on this basis whether a cavitation has arisen in the space to be monitored or not and produces a corresponding output signal.
  2. A method in accordance with claim 1 in which a sensor (2) which is formed as a pressure sensor is used and the pressure are monitored in the space to be monitored.
  3. A method in accordance with claim 2 in which the absolute pressure as well as the pressure change, in particular both, is monitored in the space to be monitored.
  4. A method in accordance with claim 3 in which during the learning process a pressure drop (31) is first produced in the space to be monitored which is greater than a predeterminable minimum pressure drop; in that then, when the pressure falls below or reaches a predeterminable pressure at which cavitations in any event arise in the space to be monitored, the sensor is triggered for the first time interval (t1); in that after the completion of the first time interval (t1) a pressure increase (33) is produced which is greater than or equal to a predeterminable minimum pressure increase; and in that the sensor (2) is triggered for the second time interval (t2) as soon as the minimum pressure increase is reached or exceeded and a predeterminable pressure (LO) is reached or exceeded.
  5. A method in accordance with claim 4 characterised in that during the learning process the sensor for the first time interval (t1) is first triggered when the further drop in the pressure is less than a predeterminable threshold value; and in that, after the completion of the first time interval (t1), the sensor (2) for the second time interval (t2) is triggered when the increase in the pressure is greater than a predeterminable threshold value.
  6. A method in accordance with one of the claims 1 to 5 in which the sensor determines for different criteria how high the probability is when the respective criterion is fulfilled that a cavitation has arisen and that the sensor subsequently decides as a result of all the criteria and the associated probabilities whether a cavitation has arisen or not and produces the corresponding output signal.
  7. A sensor (2) which is capable of learning, for the detection of cavitations in a space to be monitored, in which a state is first produced during a learning process for the duration of a first time interval (t1) in which cavitations in any event arise and in which, after the completion of the first time interval (t1), a state is produced for the duration of a second time interval (t2) in which cavitations do not in any event arise in the space to be monitored and wherein the sensor further includes means (26) which investigate the signals arising in the space to be monitored during operation for the fulfilment of predeterminable criteria which are derived from the learned signals for the cavitation and the non-cavitation respectively, as well as means (27) which decide on this basis whether a cavitation has arisen in the space to be monitored or not and then produce a corresponding output signal.
  8. A sensor in accordance with claim 7 which has means (21) for the determination of the pressure in the space to be monitored.
  9. A sensor in accordance with claim 8 which has means (21) for the determination of both the pressure and the pressure change in the space to be monitored, in particular for the determination of both.
  10. A sensor in accordance with claim 9 which has triggering means which trigger the sensor for the first time interval (t1) during the learning process when a pressure drop (31) is produced in the space to be monitored which is greater than a predeterminable minimum pressure drop and when a predeterminable pressure at which cavitations do not in any event arise in the space to be monitored has been reached or dropped below, and which trigger the sensor for the second time interval (t2) as soon as a pressure increase (33) is produced after the completion of the first time interval (t1), which is greater than or equal to a predeterminable minimum pressure increase and as soon as a predeterminable minimum pressure is exceeded.
  11. A sensor in accordance with claim 10 characterised in that, during the learning process, the triggering means which trigger the sensor for the first time interval (t1) during the learning process first trigger the sensor when the further pressure drop is less than a predeterminable threshold value; and in that, after the completion of the first time interval (t1), the triggering means trigger.the sensor for the second time interval (t2) when the pressure increase is greater than a predeterminable threshold value.
  12. A sensor in accordance with one of the claims 7 to 11 which includes means (26) which determine for different criteria how high the probability is when the respective criterion is fulfilled that a cavitation has arisen as well as means (27) which subsequently decide, as a result of all the criteria and the associated probabilities, whether a cavitation has arisen or not and produce the corresponding output signal.
  13. An apparatus, in particular a liquid ring pump (1), containing a sensor in accordance with one of the claims 7 to 12.
EP98810237A 1998-03-19 1998-03-19 Process and sensor for cavitation detection as well as a device comprising such sensor Expired - Lifetime EP0943805B1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AT98810237T ATE285037T1 (en) 1998-03-19 1998-03-19 METHOD AND SENSOR FOR DETECTING CAVITATIONS, AND DEVICE CONTAINING SUCH A SENSOR
EP98810237A EP0943805B1 (en) 1998-03-19 1998-03-19 Process and sensor for cavitation detection as well as a device comprising such sensor
DE59812383T DE59812383D1 (en) 1998-03-19 1998-03-19 Method and sensor for detecting cavitations, and device comprising such a sensor
US09/270,958 US6206646B1 (en) 1998-03-19 1999-03-17 Method and sensor for the detection of cavitations and an apparatus containing a sensor of this kind

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Application Number Priority Date Filing Date Title
EP98810237A EP0943805B1 (en) 1998-03-19 1998-03-19 Process and sensor for cavitation detection as well as a device comprising such sensor

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