EP1203886B1 - Method for determining at least one characteristic of a fluid pumped - Google Patents

Abstract

The measuring method uses a heating element (17), e.g. a positive temperature coefficient resistance, inserted in the flow medium for periodic heating of the latter, with comparison of the temperature characteristic of the heating element with predetermined values, for determining at least one material characteristic of the flow medium. An Independent claim for a pump unit with a device for measuring at least one characteristic of the flow medium is also included.

Description

The invention relates to a method for determining at least one property of a medium in the conveying path of a pump unit or for determining the medium itself and a pump unit with a device for carrying out this method.

In centrifugal pump units, the drive motor is often designed as a wet-running motor. The shaft carrying the rotor and the impeller is then guided in bearings, which are usually lubricated by the fluid itself. In addition, in some constructions, the cooling of engine and engine electronics via the pumped medium. Particularly in modern, frequency converter controlled pump units, which run at high speed, constant cooling and lubrication by the pumped medium is of decisive importance, since during dry running an increased bearing wear occurs and eventually other components can be damaged by overheating or even destroyed. Such dry running can occur if the liquid pumped medium fails, d. H. in the conveying path to the pump is air or if the fluid is overheated and there is gas. In addition, the consistency of the pumped medium itself may be important for the cooling and lubricating properties.

The publication EP 0 210 509 A is considered to be the closest prior art.

Against this background, the present invention seeks to provide a method that detects the medium or the medium currently located in the pump unit with little structural effort. In addition, a corresponding pump unit to be created, in which with little structural Expenditure and extensive use of existing components / assemblies such a method can be realized.

The procedural part of this object is achieved by the features specified in claim 1. A suitably designed pump unit is characterized by the features specified in claim 8. Advantageous embodiments of the method according to the invention are specified in the dependent claims 2 to 7 and the pump unit in the dependent claims 9 to 13 and the following description.

The basic idea of the present invention is to provide an electrically heatable heating element in the conveying path of the pump unit, in particular in the pump unit itself, and to heat it periodically, the desired material property of the medium or the medium itself being determined on the basis of the temperature profile of the heating element. The invention proceeds in its simplest form of substantially constant temperatures of the pumped medium, wherein flow velocities of the pumped medium are also neglected to detect, for example, whether in the conveying path of the pump unit conveying fluid, eg. As water is located or air. Since the heating element is subject to a much more intense heat exchange in the environment of liquid than in the vicinity of gas, it can be determined on the basis of the temperature profile of the heating element, either in the heating or in the cooling phase, whether the medium is a liquid or a gas acts. This simplest form of evaluation can be refined depending on the requirements of the application, so that even with changing environmental conditions (temperature, speed) with sufficient reliability, the desired material property of the medium or the medium itself can be determined.

The inventive method is primarily used to prevent dry running of a pump unit, but it can also be used to determine other material properties, such as the concentration of antifreeze in Water or the like, serve. It goes without saying that the process parameters for this purpose are to be adapted in accordance with the substance property or the media to be distinguished.

The device-like structure for carrying out the method according to the invention is comparatively low, since in addition to the required heating element, which is preferably provided in the form of a PTC resistor, essentially only evaluation electronics is needed, which are not made available due to the present day aggregate digital engine electronics available must, but only by implementing appropriate software can be realized.

In order to determine the desired substance property or to detect the respective medium, it is necessary to determine corresponding values beforehand, be it mathematically or experimentally, which are then compared with the measured values, after which the substance property or the medium to be determined is determined as the result become.

Basically, in the simplest form, only the detection of at least one temperature of the heating element at a certain time during or after the heating process is to be detected in order then to determine the substance property or the medium by comparison. In practice, however, it would be more advantageous to detect several temperature values at time intervals, if not even to record the temporal temperature profile.

In order to exclude dry running with sufficient safety, it is expedient to repeat the process according to the invention at suitable intervals, that is to carry out periodically. The distances should be chosen appropriately so that the reliability of the device is sufficiently ensured against dry running.

In the simplest embodiment of the method according to the invention, the temperature at the beginning and at the end of the heating phase or at the beginning and at the end of the cooling phase is determined and determines the temperature difference, for example, to determine whether the heating element is in water or in air. If the values are stored over time, temperature changes of the pumped medium can also be recorded in this simple evaluation. It is expedient to always heat the heating element with a predetermined constant power for a predetermined time and then to allow it to cool down again for a predetermined time. By introducing a constant power and intermediate values can be evaluated before reaching the predetermined time to detect trends early on.

An even more reliable and accurate evaluation allows a development of the method according to the invention, in which the heating element is first heated and then detects the temperature profile of the heating element during a predetermined time after the heating phase and the property of the medium or the medium itself is determined. In this case, according to a development of the method, the temperature values determined during the heating and / or cooling phase can be used to computationally determine in a model calculation, based on the possible different substance properties or media to be determined, how the temperature behavior on the heating element would be without heat supply. For each of the possible material properties or the possible media, a different temperature profile over time is determined. The medium to be determined is then determined by the curve which has the smoothest course. This method is based on the finding that only the medium or only the medium with the existing property will have an almost constant temperature, whereas in the case of deviating media, temperature changes will be calculated that can not be used for thermodynamic reasons.

In principle, in the method according to the invention, temperature changes of the pumped medium or changes in the flow rate can be neglected if they are such that they do not appreciably influence the measurement result. If this is no longer the case, either the temperature of the pumped medium can be detected separately, as well as the flow rate, or, which is preferred, a refined investigation method can be used. For this purpose, the invention preferably provides a four-stage process, wherein within the first stage, the heating element is heated by a predetermined temperature difference. Thereafter, the heating element is heated for a predetermined time with constant but lower power than in the first stage. In the third stage, the heating element is not heated for a predetermined time, i. H. cooled only by the surrounding medium, and in a fourth stage, the heating element is heated so that a temperature profile as in step 2 is formed, but with a constant temperature difference. The power supplied to the heating element in the fourth stage is determined and used as comparison value for determining the medium or the substance property of the medium to be determined. In this case, the stage 2 serves exclusively to detect a possibly changing temperature of the pumped medium in order to ensure a reliable determination of the material properties of the medium or of the medium even without temperature measurement of the medium, even if the temperature changes during the measuring process. If the temperature influence is expected to be low, the corresponding process steps can also be omitted, d. H. The power for heating the heating element by a predetermined temperature difference can be used as a measure of the evaluation.

The pump unit designed to carry out this method will preferably have a PTC resistor as a heating element, which resistor can serve both for heating and for temperature measurement, by determining the voltage / current profile at this resistor during heating and this resistance in the cooling phase as a measuring element, ie without noticeable heat input, is switched. It can also be briefly interrupted during the heating phase for the purpose of measuring the heating phase, if this is metrologically or device technology cheaper. Alternatively, however, in addition to the heating element, a separate sensor for detecting the temperature profile may be provided preferably in the region of the surface of the heating element.

The arrangement of the heating element or sensor is expediently carried out where the dry run occurs first, so for example when the shaft is stationary in the region of the upper bearing, but can also be provided at any other suitable location, where appropriate. The heating element can also be mounted on remote from the pump unit body, for example, if the absence of fluid to be determined before the pump unit has run dry. In such a case, the heating element is expediently designed in the manner of a cartridge or a module and connected to the pump unit via a hermetically sealed line connection. In this case, the evaluation electronics can be provided either in the terminal box of the pump unit or as a separate module for attachment to the pump unit. For evaluation and control of the electrical resistance is advantageously associated with an analog temperature measuring device whose signal output is fed via an analog-to-digital converter to a microprocessor which controls a power pulse generator for heating the resistor and the associated control electronics. At the same time, the microprocessor controls the motor of the pump so that the necessary circuitry measures in the case of dry running can be made on the pump side.

Fig. 1

zeitliche Temperaturverläufe eines Heizelements eines Pumpen- aggregats bei unterschiedlichen Umgebungsmedien,

Fig. 2

den zeitlichen Temperaturverlauf eines Heizelements und die rech- nerisch bei zwei unterschiedlichen Medien ermittelten Kurven ohne Beheizung,

Fig. 3

den Temperaturverlauf gemäß Fig. 2 bei einem anderen Medium und die rechnerisch bei zwei unterschiedlichen Medien ermittelten Kurven ohne Beheizung,

Fig. 4

zwei Temperaturverläufe des Heizelements bei einem vierstufigen Verfahren und

Fig. 5

in schematischer Darstellung einen Längsschnitt durch ein Pumpen- aggregat mit Heizelement und Auswertelektronik im Klemmenkas- ten.

The invention is explained below with reference to exemplary embodiments illustrated in the drawing. Show it:

Fig. 1

temporal temperature profiles of a heating element of a pump unit with different ambient media,

Fig. 2

the temporal temperature profile of a heating element and the calculated curves for two different media without heating,

Fig. 3

according to the temperature profile Fig. 2 for another medium and the curves computationally determined for two different media without heating,

Fig. 4

two temperature curves of the heating element in a four-stage process and

Fig. 5

in a schematic representation of a longitudinal section through a pump unit with heating element and evaluation electronics in the terminal box th.

In Fig. 1 two curves are shown, wherein the upper curve 1 represents the temperature profile of a heating element in a pump unit in air and the lower curve 2 represents the temperature profile of such a heating element first in water, then in air and then back into water. In both cases, the heating element is heated periodically and then cooled by the surrounding medium. In each case, electrical heating of the heating element at constant power takes place for four seconds, followed by a phase of four seconds, in which no heating takes place, that is, only cooling by the surrounding medium. As can be seen from the temperature profile of curve 1, the heating element requires approximately six heating cycles in the presence of air until a stationary state occurs, ie at the beginning and at the end of each interval a constant temperature is established - a constant ambient temperature of the surrounding medium provided. Before that occurs, at least for the surrounding medium air, a certain thermal inertia effect that this gradual increase in the Temperatures at the end of each heating period and at the end of each cooling phase compared to the corresponding previous value.

If the ambient medium is water as at the beginning and end of curve 2, this thermal inertia effect can be practically neglected, as can be seen from the first five cycles of the lower curve 2. The two curves 1 and 2 illustrate that the differences in the curves in the environment of the heating element of air on the one hand and water on the other hand already during the first heating period (first cycle) are so large that the ambient medium can be determined based on the temperature profile.

In addition, in the lower curve 2, a medium change from water to air is shown in a medium time range, namely the region marked in the diagram in FIG. 3, as occurs, for example, during the sudden dry running of a pump. As the sixth to tenth period of the curve 2 in the area 3 illustrate, the curve 2 has the same course there as the curve 1 in the periods 1 to 5, whereas the curve 2 immediately after the area 3 very quickly again the typical for ambient medium water Course takes. It thus becomes clear that the pump running dry can be detected sufficiently quickly, especially by continuous signal analysis, by signal evaluation, whereby a temperature change of the medium can be automatically taken into account even within limits.

In the simplest evaluation, it is therefore sufficient to measure the initial temperature 4a and the final temperature 4b (as exemplified by curve 4 on the basis of the third heating period) in order to be able to reliably determine whether the heating element is in air or in water.

Fig. 2 shows the temperature profile of a periodically heated heating element, which is heated for 4 sec. At a constant power, after which a 4-second cooling takes place. The determined temperature profile is in two different Model calculations entered, which determine the temperature of the heating element for the state in which no heating takes place, that is, the heating element should behave in temperature terms as the surrounding medium. While the curve 5 of the upper diagram represents the actual temperature curve at the heating element, the lower curve shows the calculated temperature curve, in curve 6 for water and in curve 7 for air. It is clear that the curve 6 is completely smooth, whereas the curve 7 represents the curve 5 approximately out of phase. Since the model calculation should detect the determination of the temperature profile without heating the heating element, therefore, the curve 6 represents the medium in which the heating element is located, namely water.

In Fig. 3 is analogous to in the upper diagram Fig. 2 a curve 8 is shown, which represents the temperature profile of a periodically heated heating element in air. Corresponding arithmetically determined curves 9 and 10 are shown in the lower diagram, wherein the curve 9 is outflow of the calculation model for ambient air and the curve 10 outflow of the computing model for ambient water. In this case, the smoother curve is the curve 9 and thus air is determined as the surrounding medium.

Based on Fig. 4 is a four-stage process is shown, in the upper diagram with unchanged medium temperature and in the lower diagram with increasing medium temperature. The steps are marked with I to IV. The first stage begins with a heating phase at a predetermined temperature difference of 3.5 ° C. relative to the starting temperature (at the beginning of stage I). After completion of stage I, heating of the heating element with constant power takes place in stage II, the power being selected is that it is smaller than the one at the end of stage I, so that a uniform temperature course of the second stage arises.

In the third stage, the heating element is not heated. At the end of the third stage, the temperature difference is determined at the end of the first stage, and then in the fourth stage to heat the heating element so that a constant temperature difference to the temperature profile of stage II arises. The heating power is determined, which represents a characteristic value for whether the ambient medium is air or water. If the surrounding medium is water, a significantly higher heat output is required than, for example, with air. This refined method according to Fig. 4 compensates temperature changes of the medium itself, which do not go back to the heating of the heating element. Such a case is in the lower diagram in Fig. 4 represented there, the medium temperature rises during the measurement method according to stages I to IV by about 3 ° C. As a comparison of the curves in the range of stages II and IV between the upper and lower diagram shows, regardless of the temperature of the medium, the temperature difference and thus the heating power to be introduced is always the same if the same ambient medium is present. Thus, this method can be used to compensate for a changing temperature of the medium without influencing the reliability of the method for determining the medium itself or a substance property.

The methods described above by way of example only represent a section of numerous possible methods operating according to the inventive principle. They are described above for determining whether the heating element is in air or in water, ie. H. to determine the medium itself. This method can be used by usually a few empirical experiments for the determination of other media or material properties, but this is not to be described in detail here.

The basis of Fig. 5 schematically illustrated pump assembly 11 has a motor housing 12 in which a wet-running motor is arranged, the shaft of which carries a centrifugal gear 13 which is located within an inline pump housing 14 with a suction-side port 15a and a pressure-side port 15b. When viewed in the direction of flow, immediately downstream of the suction-side connection 15a, a dry running sensor 16 is provided, which is constructed according to the method described above operates and is formed by a heating element 17 in the form of a PTC resistor, which is arranged in a thin-walled stainless steel cylinder 18 which is formed like a cartridge and projects into the flow path of the suction port 15 a. Between the serving as a heating element and sensor PTC resistor 17 and the thin-walled housing 18, a thermal paste is provided to ensure the best possible heat conduction between the resistor and the outside of the housing 18. The housing 18 is soldered end, the electrical connections are led out to a line 19, which opens in the terminal box 20, which is mounted on the motor housing 12 and next to the motor controlling the frequency converter and the connection wiring and the control and evaluation electronics for the PTC resistor 17 includes. In the present embodiment, this electronics is integrated into the terminal box 20, but it can also be provided as a separate module or as a plug-on module, so that the pump unit can be optionally equipped with dry-running sensor or without.

In the illustrated embodiment, the dry running sensor 16 is on the input side, so that during normal flow operation, a dry run of the pump can be detected before the liquid in the can is escaped and the pump runs dry with increased bearing wear. The electronic evaluation system can therefore switch off the engine in good time or switch it on again as soon as the pumping medium is present on the suction side.

With the illustrated dry-running sensor 16, not only the surrounding medium can be detected, but also the temperature of the pumped medium. The arrangement of the actual sensor 16 can also take place at another suitable location, since this can be formed like a cartridge and can be arranged after attachment of a housing bore at virtually any point. It is understood that depending on the arrangement and design of the pump unit, the sensor 16 may also be provided directly in the can or at another suitable location.

The provided within the terminal box 20 evaluation electronics consists of an analog temperature measuring device, as it is known per se for connecting a PTC resistor. The signal of this device is fed to an analog-to-digital converter, the digital output of which is then supplied to a microprocessor which controls a power pulse generator for the resistor 17. The microprocessor is part of the frequency converter electronics, which controls the electric motor. The operation / programming of the microprocessor, which contains and monitors the central control of the entire pump set, takes place via a digital interface.

Claims (13)

1. A method for determining at least one characteristic of a medium located in the delivery path of a pump assembly (1), or the medium, with which a heating element (17) located in the medium is heated with a predefined power over a predefined time, and the temperature course of the heating element (17) during or after the heating procedure is evaluated by way of comparison with previously determined values, for determining a substance characteristic of the medium or the medium, characterised in that the temperature course of media of different characteristics or different media without the supply of heat of the heating element (17) is computed by way of the determined temperature course of the heating element (17), and that the characteristic of the medium, which is to be determined or the medium to be determined, is determined by the computed temperature course of the medium, which has the smoothest running curve (6, 9).
2. A method according to claim 1, characterised in that the heating element (17) is heated with a constant power.
3. A method according to one of the preceding claims, characterised in that the temperature course is determined during the heating phase.
4. A method according to one of the preceding claims, characterised by the following steps:

   a) heating up the heating element

   b) detecting the temperature course of the heating element during a predefined time after the heating-up phase, and determining the characteristic of the medium or the medium.
5. A method according to claim 2 or 3, characterised in that the temperature course of media of different characteristics or different media without the supply of heat of the heating element is computed by way of the determined temperature course of the heating element, and that the characteristic of the medium, which is to be determined or the medium to be determined, is determined by way of the computed temperature course of the medium, which has the smoothest running curve.
6. A method according to claim 1, characterised by the following steps:

   a) heating up the heating element by a predefined temperature difference

   b) detecting the temperature course of the heating element during a predefined time after the heating phase

   c) heating the heating element over a predefined time, such that a constant temperature difference results between the achieved value directly after the completion of the heating phase a

   d) determining the characteristic of the medium or medium by way of the supplied power in step c.
7. A method according to claim 6, characterised in that after heating up the heating element according to step a, the heating element is heated over a predefined time with a constant heating power (constant heating phase), wherein the constant power is smaller than that of the heating phase according to step a, and that the temperature course of the heating element during this constant heating phase is determined, and a deviation from a constant value is taken as an expression for a change of the media temperature and that a change of the medium temperature which thereby results as the case may be, is taken into account with the evaluation according to step d, so that influences of a change of the medium temperature during the method are ruled out.
8. A pump assembly with a device for determining at least one characteristic of the delivery medium or the delivery medium, characterised in that a heating element and means for detecting the temperature of the heating element are provided, that the heating element may be heated temporarily, and that evaluation electronics are provided, which determine at least one characteristic of the delivery medium or the delivery medium, by way of the electrical power introduced into the heating element and the temperature course of the heating element.
9. A pump assembly according to claim 8, characterised in that the heating element is an electrical resistance, preferably a PTC-resistance and that the temperature detection of the heating element is effected by way of evaluation of the electrical variables at the heating element.
10. A pump assembly according to one of the preceding claims, characterised in that additionally to the heating element, a sensor for detecting the temperature course at the heating element is provided.
11. A pump assembly according to one of the preceding claims, characterised in that a sensor for detecting the temperature of the delivery medium is provided.
12. A pump assembly according to one of the preceding claims, characterised in that an analog temperature measurement device is assigned to the electrical resistance, whose signal output is supplied via an analog/digital converter to a microprocessor, which controls a power pulse generator for the resistance, wherein an operating unit is assigned to the microprocessor.
13. A pump assembly according to one of the preceding claims, characterised in that the control and evaluation electronics for the electrical resistance are provided in the terminal box or as a separate module on the pump assembly.

Images