Patent Application
20070220947
This application claims priority from German Application Nos. DE 10 2005 062 105.8 filed on Dec. 23, 2005 and DE 10 2006 006 152.7 filed on Feb. 10, 2006 the contents of which are relied upon and incorporated herein by reference in their entirety, and the benefit of priority under 35 U.S.C. 119 is hereby claimed.
The invention relates to a method for regulating and monitoring a measuring system, in particular a flow measuring device, and the flow measuring device itself.
The method for operating an inductive flow measuring instrument with a magnet system, which is excited by a sinusoidal AC voltage, is a method in which the measuring system is monitored.
The equivalent circuit diagram of the signal-generating magnet system of a magnetically inductive flow meter (IFM) is represented below.
In order to minimize the power losses, reactive current compensation is carried out by means of a capacitor.
Mathematical observation:
{square root over (E)}={square root over (v)}×{square root over (B)} Initial equation:
Equation after simplification: Uo=kvBD
It is therefore an object of the invention to develop a method and a measuring system so that it is proof from external interfering effects.
The Figure shows an equivalent circuit diagram of a measuring system.
For a method of the species, said object is achieved according to the invention in that besides measuring the terminal voltage Uk and the terminal current Ik, in addition the ohmic impedance, the inductance, the value of the reference resistor and the magnetization current are measured at cyclically recurring intervals, compared with reference values from a previous calibration measurement and stored.
In this context, it is of considerable practical use for the data to be recorded as historical data and for an evaluation of the expectable operating failures or maintenance to be calculated from the development trends of the respectively said values as a whole.
In respect of a measuring system, said object is achieved according to the invention in that the sensors provided for measuring the terminal voltage Uk, the terminal current Ik, the ohmic impedance Rcu, the magnetization current Iu, the inductance Lsp and the reference resistance Rfe are measurable, as well as a timer which writes the respective currently measured values into a data storage device at cyclic intervals.
Here as well it is possible to be able to predetermine failure times of the system.
In order to develop a stable measuring system which is proof against environmental effects, it is necessary to keep the magnetization current and therefore the field strength B constant (at the optimal working point of the magnet system).
For direct determination of the field strength B, which is a factor influencing the measurement voltage Uo, it is possible to use an additional copper winding on the field-forming magnetic circuit.
Most currently used measuring systems deduce the field strength B by measuring the current Ik (voltage drop across a reference resistor).
However at the terminals it is only possible to measure the current Ik, phase-shifted relative to the magnetization current, and the terminal voltage Uk.
The phase shift between and the ratio of Ik and Iu can change because of environmental influences.
The functional essence of the invention is that not only the terminal voltage Uk and the terminal current Ik are used for regulating and monitoring the measuring system. In order to identify changes in the system, the elements represented in the equivalent circuit diagram are determined cyclically so as to react accordingly where appropriate. It is therefore possible to keep the magnetization current Iu constant by regulating the value of Ik. The characteristic data of the individual values of the elements are stored as reference values during the calibration.
By comparing the measured values of the individual elements with the associated stored reference values and reference limits, the functional capability of the system can be determined and failures in the future can be inferred by trends.
The principle employed here is that Faraday's law of induction is used for measuring flow rates. If an electrically conductive substance to be measured is passed through a magnetic field B, then an electric field E is set up in the substance to be measured perpendicularly to the flow direction V and to the magnetic field direction E=V×B.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE 102005062105.8 | Dec 2005 | DE | national |
| DE 102006006152.7 | Feb 2006 | DE | national |
