METHOD AND DEVICE FOR ASCERTAINING A FLOW PARAMETER USING A CORIOLIS FLOW METER

Abstract

The invention relates to a method for ascertaining a flow parameter of a medium, in particular the mass flow rate, using a Coriolis flow meter of a specified measurement device type and to a device which is suitable for said method. According to the method, the medium, which has a medium viscosity, flows through at least one measurement tube piece that is mechanically vibrated by a respective excitation signal, at least one measurement signal dependent on the flow parameter, in particular a phase shift, is ascertained in the vibration behavior of the respective measurement tube piece, and the flow parameter is determined from the at least one measurement signal while taking into consideration the dependency of the flow parameter on the medium viscosity, wherein a data field which is ascertained using an interpolation method, in particular a kriging method, and which indicates the dependency of the flow parameter on the medium viscosity is used in order to determine the flow parameter.

Claims

1. A method for determining a flow parameter of a medium, in particular a mass flow, by means of a Coriolis flowmeter of a certain type of measuring device, in which the medium having a medium viscosity flows through at least one measuring tube piece that is excited to mechanical vibrations by means of an excitation signal, at least one measurement signal that is dependent on the flow parameter, in particular a phase shift, is determined in the vibration behavior of the respective measuring tube piece, and the flow parameter is determined from the at least one measurement signal, taking into account the dependence of the flow parameter on the medium viscosity, a data field determined by means of an interpolation method and showing the dependence of the flow parameter on the medium viscosity being used to determine the flow parameter.

2. The method according to claim 1, characterized in that the interpolation method for determining a data field is applied to a basic data set determined experimentally and/or by simulation.

3. The method according to claim 1, characterized in that the interpolation method is used when calibrating the device type.

4. The method according to claim 12, characterized in that the interpolation method is used for an evaluation during or after the determination of the at least one measurement signal.

5. The method according to claim 1, characterized in that at least kriging is also used as the interpolation method.

6. A device for determining a flow parameter of a medium, in particular a mass flow, by means of a Coriolis flowmeter, comprising a) a transducer, the transducer having a measuring tube intended for the flow of a fluid, a vibration exciter for generating measurement signals in the form of mechanical vibrations on the measuring tube and vibration sensors for detecting the vibrations of the measuring tube, and b) a measuring device electronics unit, the measuring device electronics unit being set up to determine a measured value for the desired flow parameter from measurement signals transmitted from the transducer to the measuring device electronics unit, characterized in that c) the measuring device electronics unit is set up to carry out the method according to claim 1.

7. The device according to claim 6, characterized in that the measuring device electronics unit has a data memory having a data field which shows the dependence of the flow parameter on the medium viscosity, wherein the data field is generated using an interpolation method.

8. The device according to claim 6, characterized in that the interpolation method is a kriging method.

Description

[0036] An embodiment of the method according to the invention is presented below with the aid of figures.

[0037] FIG. 1 shows again the table already set out in the introduction to the description having percentage deviations of the measured uncorrected mass flow values, that is, those based on a calibration of the measuring device with water, in kg/h from actual mass flow values, determined experimentally by measurements and/or simulation methods, which mass flow values result when taking into account the medium viscosity (here in mPas) of the medium flowing through a Coriolis flowmeter of the calibrated measuring device type. The table thus shows a basic data set having a data volume for which measurements or simulation calculations still represent an acceptable expense.

[0038] A kriging method is now used as the interpolation method on the basic data set of the table according to FIG. 1. The data field is thus completed starting from the relatively small number of output values, so that a data field having a significantly increased resolution is achieved, as is exemplified, for example, from excerpts from the table in FIG. 2. There are several possibilities for the concrete application of kriging to a basic data set, as is depicted in the table according to FIG. 1. In principle, the kriging method can be programmed by the user himself. However, suitable kriging software can be purchased or is even available free of charge, including the source code. In particular, there is the option of integrating suitable additional functions in spreadsheet programs such as Microsoft Excel®, such as the XonGrid add-in, which was available at http://xongrid.sourceforge.net/ at the time this application was submitted and offers kriging in addition to other interpolation methods.

[0039] Finally, reference is also made to the comments on kriging in the publication “Optimale Methoden zur Interpolation von Umweltvariablen in Geographischen Informationssystemen” (Optimal methods for the interpolation of environmental variables in geographic information systems) by P.A. Burrough in Geographica Helvetica 1990 no. 4, p. 159-160.

[0040] The refined table according to FIG. 2 obtained by means of kriging also shows, in the first column, the mass flow in kWh that would be measured using a Coriolis flowmeter calibrated with water without taking into account the medium viscosity. This mass flow is referred to below as the calibration medium mass flow. The media viscosity is set out in the first line in mPas.

[0041] The following can be read from the data field as an example: If a calibration medium mass flow of 110,000 kg/h, that is, 110 tons per hour, were measured without taking the medium viscosity into account, this would mean an error of −0.6% with an actual medium viscosity of 600 mPas. This means that the actual measuring medium mass flow is 0.6% higher than the calibration medium mass flow, namely 110,000 kg/h*1.006=110,660 kg/h.

[0042] If necessary, the data field can be further refined as required, for example, by further application of the kriging method or preferably by less complex interpolation methods, such as linear interpolation or higher-grade polynomials.

[0043] FIG. 3 shows a characteristic diagram developed from the table according to FIG. 2, as it can be used for a measurement that takes the medium viscosity into account.

[0044] The characteristic diagram according to FIG. 3 or the table according to FIG. 2 can be stored in advance in a memory of a measuring device electronics of the Coriolis flowmeter for further processing or for consideration in the evaluation. Alternatively, it is also possible to store the basic data set or a relatively coarse data field in the measuring device electronics and to use the kriging method or other interpolation methods, optionally also in combination, in the evaluation software during or after the measurement,