Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-01-21
2001-10-02
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S29000R, C073S861250
Reexamination Certificate
active
06295874
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for determining a physical process variable of a medium. In connection with the present invention, the concept “physical process variable” is to be understood in particular to mean the filling level of a medium in a container or the flow of a medium through a line. However, the apparatus according to invention can not only be used for these explicitly mentioned process variables but can be extended to any desired process variables determined by means of a delay-time method.
BACKGROUND OF THE INVENTION
Both in the case of the “genuine radar method” and in the case of the Time Domain Reflectometry (TDR) method, measuring signals are transmitted in the direction of the surface of a medium and at least partially reflected at the surface of the medium as so-called echo signals. The reflected echo signals are detected and evaluated by means of a delay-time method. The main difference between the genuine radar method and the TDR method is that in the first case the electromagnetic waves, or the sound or ultrasound waves are freely emitted, while in the case of the TDR method the electromagnetic or acoustic measuring signals propagate in a directed manner along an element guiding the measuring signals. By evaluation of the amplitude values and possibly the phase values of the echo signals, the filling level in the container is determined by means of a delay-time method. Both the pulsed radar method, in which the echo signals are emitted in a pulsed manner, and the FMCW method, in which continuous waves arc frequency-modulated in a periodically linear manner, for example with a sawtooth voltage, may be used. In the case of the TDR method, usually steep-edged delta pulses are sent to the conductive element.
Delay-time methods use the physical law according to which the transit distance is equal to the product of the delay time and the propagation velocity. In the case of filling level measurement, the transit distance corresponds to twice the distance between the antenna and the surface of the filled product. The actual useful echo signal and its delay time arc usually determined on the basis of the so-called echo function or the digital envelope curve, the envelope curve reproducing the amplitudes of the echo signals as a function of the “antenna - surface of the filled product” distance. The filling level itself is then obtained from the difference between the known distance of the antenna from the bottom of the container and the measured distance of the surface of the filled product from the antenna. Analogous considerations apply to the determination of the mass how through a line.
Instruments of the type referred to above are manufactured and sold by Endress+Hauser in the area of filling level measurement and flow measurement. For instance, the product designation “Mikropilot” stands for a sensor which freely emits microwaves; “Prosonic” or “Prosonic Flow” identify sensors which operate on the basis of ultrasound waves, and “Levelflex” designates a TDR sensor.
SUMMARY OF THE INVENTION
The object of the invention is to provide an apparatus which can be used in conjunction with various sensors, the sensors having in common that they determine a process variable by means of a delay-time method.
The object is achieved by the apparatus being made up of the following component parts: a sensor, a sensor-specific application unit, and an evaluation unit which is essentially independent of the sensor type used. The sensor being assigned a transmitting/receiving unit, the transmitting unit transmitting measuring signals in the direction of the medium and the receiving unit receiving the measuring signals influenced by the interaction with the medium. The application unit being designed in such a way that it processes the measuring signals and provides measurement data which is independent of the sensor type used. The evaluation unit processes the measurement data and determines the physical process variable using a delay-time method by means of a uniform evaluation algorithm. By dividing up of the individual components of the sensor, one effect that is consequently achieved according to invention is, for example, that now just one evaluation unit can be used universally for any desired sensor type based on the delay-time method. The application unit is also designed such that it can largely be used universally and likewise exhibits only slight deviations, dependent on the sensor type used.
According to an advantageous embodiment of the apparatus according to the invention, it is provided that a communication unit, which is independent of the sensor type used, is provided for the data exchange with a remote process control station. In addition to the application and evaluation unit, which is essentially the same for all common sensor types in the area of no-contact filling level or flow measurement, this embodiment also standardizes the area concerning the communication between the sensor and a remote process control station.
According to a preferred embodiment of the apparatus according to the invention, the communication unit and the process control station are preferably connected via a serial bus, the communication unit having interfaces which are configured for data exchange by means of different transmission standards. As examples of such transmission standards, the Profibus PA, the Fieldbus Foundation Protocol or the HART Protocol may be mentioned.
As mentioned previously, an advantageous development of the apparatus according to the invention concerns a sensor which freely emits electromagnetic waves or acoustic waves in the direction of the medium or guides them in the direction of the medium via a conducting element.
In the case of a microwave sensor, it is provided according to a preferred embodiment that the application unit is assigned a high-frequency module, which generates the high-frequency measuring signals and subsequently transforms them into the low-frequency measuring range. In particular, it is proposed that the high-frequency module is part of the sensor-specific application unit. A preferred embodiment of the apparatus according to the invention providing that the high-frequency module and the application unit are integrated into the sensor.
An advantage of the transformation of the high-frequency measuring signals into the low-frequency range is that relatively slow and consequently low-cost electronic components can be used for the signal acquisition and/or signal evaluation. An essential prerequisite for time dilation or time delay by means of sequential sampling is a constant time difference between two successive sampling points. Known methods which satisfy this prerequisite are based on the mixer principle and the ramp principle.
It is possible within the scope of the apparatus according to the invention for the application unit also to be of a standard design for all types of sensor. It is preferred, however, to dispense with this, since in the case of ultrasound sensors the high-frequency module represents a superfluous and relatively expensive additional assembly. Consequently, if it is already known at the time of production that the application unit and the evaluation unit will be assigned exclusively to an ultrasound sensor, the high-frequency module is not integrated into the application unit for reasons of reducing cost.
As mentioned previously, the process variable to be measured is preferably the filling level of a medium in a container or the flow of a medium through a line.
According to an advantageous and cost-saving development of the apparatus according to the invention, at the sensor-specific application unit there is respectively provided an interface via which, in the case of an ultrasound sensor, the transmit frequency and the transmit pulse duration are transferred to the transmitting unit; in the case of a microwave sensor or a sensor which guides the microwaves in the direction of the medium by means of a conducting element, the high-frequency module is activated via the int
Michalski Bernhard
Strutt Bernd
Bose McKinney & Evans LLP
Endress + Hauser GmbH & Co.
Moller Richard A.
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