14 dargestellt. Die Mediumstemperatur kann zur Berechnung der Dichte verwendet werden. Die Displayanzeige (V1) wird zur Ermittlung der Skalierung . des zweiten Sensorelements erfassten Mediumstemperatur ermittelt. The actual over-temperature is determined from the difference between the detected by. A thermal flow measurement device (1), especially for determining and / or monitoring the mass flow rate (Φ sen comparison of the temperatures (T11, T
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In addition, a statement on the state of at least one of the at least three sensor elements can be made. So the flowmeter has a diagnostic function. Thermal flowmeters are used in many mediumstemperaur in the field of process technology. Corresponding field devices by the applicant, for example, under the name t-switch made t-trend or t-mass and distributed.
The underlying measurement principles are known accordingly from a variety ermtitlung publications. Typically, a generic flow meter includes at least two sensor elements, each of which has a similarly configured possible temperature sensor, and at least one of the sensor elements is heatable. For this purpose within the respective sensor element either an additional resistance heater can be integrated.
Alternativ kann aber der Temperatursensor auch selbst als Widerstandselement, z. Alternatively, the temperature sensor can also itself as a resistance element such.
The resistance element, also referred to as a resistance thermometer, then the implementation of a supplied thereto electric power, z. As a result of an increased power supply, heated. Often, the temperature sensor is within wrmittlung cylindrical sleeve, especially a sleeve of a metal, in particular stainless steel or Hastelloy, arranged. The sleeve then mediumstemperatue the function of a housing which protects the temperature sensor, for example, against aggressive media.
Wherein each at least one heatable temperature sensor must also be ensured that there ermitlung a best possible ermittoung contact between the heatable temperature sensor and the sleeve. They can be to either introduced directly into the pipeline, or be integrated in a measuring tube which is installed in an existing pipeline. Both possibilities are the subject of the present invention, even if below always refers only to a pipeline will be.
In operation, at least one of the at least two temperature sensors is heated active temperature sensor while the second temperature sensor remains unheated passive temperature sensor.
The passive temperature sensor is used for detecting the temperature of the flowable medium. Is in the pipeline no flow exists, the dissipation of heat from the active temperature sensor via heat conduction, radiation and possibly also through free convection within the medium takes place. In order to maintain a specific temperature difference, a time-constant amount of heat is then required, for example.
In the presence of flow, however, there is an additional cooling of medoumstemperatur active temperature sensor by the passing colder medium. It takes an additional heat transport due to forced convection. Accordingly therefore a flow either an increased heating capacity must in consequence be fed in order to obtain a fixed temperature difference maintained, or the temperature difference between the active and passive temperature sensor decreases.
Daneben haben die thermophysikalischen Eigenschaften des Mediums sowie der in der Srmittlung herrschende Druck einen Einfluss auf den gemessenen Durchfluss. In addition, the thermo-physical properties of the medium and the pressure in the er,ittlung line pressure have an influence on the measured flow. In order to take account of the dependence of the flow on these variables, the thermophysical properties in the form mediumstemprratur characteristic curves or as constituents of functional conditional equations are, for example, stored in an electronic unit of the flowmeter.
By means of a thermal flow meter can not be readily between a forward and a backward flow differ. It should be mediumstempwratur the direction of flow again, macroscopic flow direction understood for which partially occurring vertebra or direction deviations are not considered.
DE102014119231A1 – Thermal flow meter with diagnostic function – Google Patents
To determine the direction of flow is often exploited for various types of local currents immediately surrounding the respective sensor element, leading to different cooling rates of the respective sensor element at each of the same supplied heating power.
Different local currents can be realized by a non-equivalent with respect to the airfoil assembly of the at least two sensor elements, or by different geometric configurations of the at least two sensor elements, for example by integrating a bluff body in the duct in the immediate vicinity medjumstemperatur at least one of the at least two sensor elements mediumstemperatug.
Based on the comparison of the so-called decision coefficients which result from the respective heating powers and temperatures of at least two heatable temperature sensor, the flow direction of the medium is then determined.
The third sensor element is also periodically briefly heated and disposed outside of the flow over the first two sensor elements. Other causes of an optionally considerable wrong reading consist for example in a change in the thermal resistance of at least one of the sensor elements used, which mediumstemperattur lead to a change of the heat transfer from the heating unit into the medium in an otherwise steady flow conditions.
Such a change of the thermal resistance is also referred to as sensor erkittlung. Otherwise, if necessary, the flow meter has to be at least partially replaced. Basically, an inner and an outer heat resistance can be distinguished in terms of the heat resistance.
The internal heat resistance depends inter alia on individual components within the sensor element, eg within the sleeves off. The exterior heat resistance on the other hand by the formation of deposits, mediumsteperatur of material or conversion material corrosion on the influence on the medium contacting surfaces of the respective sensor element.
Mediumstemperaturr the case of gaseous or vaporous media, the measurement of the mass flow rate or the flow speed of mediumstemperahur least one of the temperature sensors may be affected in addition by condensation ermittpung. From the prior art several flowmeters are known, by means of which can be make a diagnosis of at least one of the sensor elements used in each case.
In this way, plaque deposits and condensation can be detected. Der Massedurchfluss wird dann abwechselnd anhand des jeweils beheizten Sensorelements ermittelt, wobei das jeweils nicht beheizte Sensorelement zur Ermittlung der Mediumstemperatur herangezogen wird.
The mass flow is then determined alternately by means of the respective heated sensor element, wherein the respectively non-heated sensor element is used to determine the fluid temperature. Typically, the two heating powers are chosen so that the temperatures of the two different sensor elements.
Bei den jeweils angewendeten Messprinzipien werden die einzelnen Sensorelemente zeitweise beheizt, und dienen zeitweise der Erfassung der Mediumstemperatur. In the respectively applied measuring principles, the individual sensor elements are temporarily heated, and serve at times of detection of the medium temperature.
According to the temperature of the sensor elements to be until the next data acquisition waited so long for each change until the new temperature to each set stable. Accordingly, the respective employed methods employ at least over the period of time which is in each case up to the stable setting of a new temperature required by at least one of sensor elements, requires a nearly constant flow rate of the medium through the pipe.
However, it is in practice often the case that the flow rates vary at least slightly over time, which can then lead to a distorted measurement result. Dies ist insbesondere bei hohen Durchflussraten problematisch.
This is problematic especially at high flow rates. Thus, the electronic unit must be able, two at a time to heat each of the three sensor elements independently of one another and at least. Zumindest eines der Sensorelemente bleibt ferner unbeheizt und dient der Erfassung der Mediumstemperatur. At least one of the sensor elements further remains unheated and serves to detect the temperature of the medium. It is then the temperature differences between one of the heated sensor element and which detects that the medium temperature are compared, and the temperature differences between two heated to different temperatures sensor elements.
At the same time a diagnosis, that is a statement about the state of at least one of the at least three sensor elements is possible. Another advantage in terms of an inventive flowmeter is that not only predicted to be that at least one of the at least three sensor elements shows a sensor drift, but if possible, about which the at least three sensor elements is affected.
Dann kann im Falle von Sensordrift an einem der Sensorelemente der Durchfluss immer noch genau bestimmt werden kann. Then, in the case of sensor drift on one of the sensor elements can flow can still be accurately determined.
In a particularly preferred embodiment, the electronic unit is adapted to determine the flow direction of the flowable medium. A this configuration corresponding flowmeter then has therefore in addition to the additional functionality of being able to make a diagnosis, or a statement about the state be able to make at least one sensor element, a flow direction detection.
This increases the achievable measurement accuracy even further. Es ist von Vorteil, wenn zumindest eines der zumindest drei Sensorelemente eine erste Ausgestaltung bezogen auf die Geometrie, Aufbau und Material, aufweist, und zumindest ein zweites der zumindest drei Sensorelemente eine zweite von der ersten verschiedene Ausgestaltung aufweist.
It is advantageous if at least one of the at least three sensor elements, a first embodiment based on the geometry, structure and material, and in at least a second of the at least three sensor elements has a second different from the first embodiment.
It is also advantageous if at least two of the at least three sensor elements on which are arranged within the conduit to a relating respectively locally surrounding flow of the medium first equivalent position, and wherein at least one of the at least three sensor elements in a in respect of which it drmittlung surrounding flow of the medium second is arranged different from the first position within the pipeline.
This has a particularly advantageous with respect mediumtemperatur the recognition of the flow direction, but also to the diagnosis via sensor drift. The reason for this is that the characteristics or the functional dependencies between the temperatures of the heating powers supplied, and the thermophysical properties, and other parameters of the individual sensor elements for a forward and backward flow vary.
In a preferred embodiment, at least one of the at least three sensor elements with respect to the longitudinal axis through the pipeline in the immediate area in front of or behind a bluff body, or other flow-influencing module is disposed. By this measure, emdiumstemperatur local surrounding the respective sensor element airfoil is selectively changed as compared to a non-arranged behind a bluff body sensor element, or in comparison to a bluff body ermitrlung behind a different geometry sensor element.
The effect which is achieved by the integration of a bluff body thereby is greater than that which is obtained by different geometric configurations or arrangements, generally. According to a particularly preferred embodiment, the thermal flow meter includes exactly three sensor elements, wherein at least one of the three sensor elements in the immediate vicinity of a bluff body, or other flow-influencing module is arranged. It is advantageous if the first and the second sensor element are arranged symmetrically on opposite sides of an imaginary axis parallel to the pipeline, said third sensor element is arranged on the imaginary axis, and wherein between the imaginary connecting line through the first and the second sensor element and the third sensor element, a storage body is arranged, the distance is less for the third sensor element than the one to the imaginary connecting line.
The diagnosis is not limited ermittulng a statement that has changed for at least one of the sensor elements of the thermal resistance. The inventive method makes it possible in certain circumstances but rather to make a statement as to which of the three sensor elements, the thermal resistance has changed, and for which the thermal resistance has remained constant.
Es ist ferner von Vorteil, wenn vor dem gleichzeitigen Heizen von zumindest zwei der zumindest drei Sensorelemente mit jeweils einer einstellbaren Heizleistung ein Abgleich der gemessenen Mediumstemperaturen vorgenommen wird, und gegebenenfalls ein Temperaturkorrekturterm errechnet und auf alle folgenden Messungen angewendet wird.
It is also advantageous if a comparison of the measured medium temperature is carried out prior to the simultaneous heating of at least two of the at least three sensor elements each with an adjustable heat output, and, optionally, calculates a temperature correction term and is applied to all subsequent measurements.
The following cases are possible: When commissioning the flowmeter a first and a second sensor element to be heated.
DEB4 – Method and apparatus for measuring the mass flow of a medium – Google Patents
Before these sensor elements each have a heating temperature is applied, is determined by two, or even with all the sensor elements, the medium temperature. Somit lassen sich aufgrund nicht vermeidbarer Fertigungstoleranzen abweichende Messwerte und Unterschiede bei den jeweiligen Kalibrationen ausgleichen. Thus deviating measurements and differences in the respective calibrations can be compensated due to unavoidable manufacturing tolerances. Another case implies that if it is back and hergewechselt during operation between the respective sensor elements heated, a further temperature comparison is made.
This may be the medium temperature, either, or the temperatures at the same supplied heat output. A further preferred embodiment of the method is adapted for a thermal flow meter with exactly three sensor elements and comprises the following steps: It goes without saying that in the event that the thermal flow meter has at least three sensor elements, the diagnostic mode, optionally having more than three time intervals.
A comparison of the power coefficients of various sensor elements can for example be carried out on the basis of the above-mentioned earlier decision so-called coefficient DC. Depending on whether and if so to which of the at least three sensor elements there is a change in the thermal resistance, do not have to be optionally run through all three time intervals. Finally, according to the invention can also include a drift of the electrical resistance within at least one of the at least three sensor elements.
A sensor element may drift even without the occurrence of a change in the thermal resistance. This leads to a change in a characteristic of the electrical resistance as a function of temperature of the at least one sensor element, resulting in an erroneous temperature measurement results.
A change in electrical resistance within at least one sensor element can be detected from a pairwise comparison of power coefficient and determined now, namely in the unheated state of the at least one sensor element, for example on the basis of the phases in the determination of the temperature correction terms. If the currently measured temperature correction terms from those which are determined at the time of manufacturing of the respective sensor element and stored, for example in the electronics unit, differ, and the deviation exceeds a predetermined limit, can be closed to a change in the electrical resistance of the deviation.
In this way it can be distinguished between a change in the thermal resistance and a change in electrical resistance. Es zeigen Show it.
In den Figuren sind gleiche Merkmale mit gleichen Bezugszeichen gekennzeichnet. In the figures, like features are identified by like reference numerals. Strokes at a reference mark each have suggests different embodiments. Jedes der beiden Sensorelemente Each of the two sensor elements 4 4.
Insbesondere die beiden Temperatursensoren In particular, the two temperature sensors 5 5 .