Patent Application
20240210225
The present application is related to and claims the priority benefit of German Patent Application No. 20 2022 107 233.7, filed Dec. 23, 2022, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a thermal flow meter with automatic gas detection, in particular, for detecting the composition of gas mixtures, in particular binary gas mixtures, and/or pure gases.
Thermal flow meters are usually adjusted to a particular medium or gas because the ascertained measurement value is influenced by the thermal conductivity and heat capacity of the gas. Thus, a specially calibrated sensor is required for each gas, or correction factors for various gases are specifically stored in the sensor by the manufacturer. Consequently, which gas is currently being measured must always first be communicated to the sensor. However, if the gas composition changes during a measurement, the current sensors are not able to ascertain the flow correctly.
The object of the present disclosure is, therefore, to find a remedy here. The object is achieved according to a flow meter according to the present disclosure.
A thermal flow meter according to the present disclosure for measuring a flow rate of a gas comprises: a measurement channel for guiding the gas between a channel inlet and a channel outlet; a thermal flow sensor which is arranged in the measurement channel; a density sensor which has an oscillator which can be acted upon by the gas, wherein a natural frequency of an oscillation mode of the oscillator depends upon the density of the gas; a temperature sensor element for ascertaining a gas temperature; and a pressure sensor element for ascertaining a gas pressure of the gas; and a measuring and operating circuit for operating the thermal flow sensor and the density sensor, wherein the measuring and operating circuit is configured to determine a density measurement value of the gas on the basis of the natural frequency of the oscillator and to identify the composition of the gas on the basis of the density measurement value, the gas pressure, and the gas temperature, and, as a function of the composition on the basis of flow-dependent signals of the thermal flow sensor, to output a flow measurement value corrected with respect to a cross-sensitivity to the composition of the gas.
In an embodiment according to the present disclosure, the measuring and operating circuit is configured to identify the composition of the gas, assuming a binary gas mixture of known components and/or a pure gas.
In an embodiment according to the present disclosure, the oscillator comprises a quartz tuning fork or a cantilever oscillator.
In an embodiment according to the present disclosure, the thermal flow sensor and/or the density sensor have a MEMS sensor element.
In an embodiment according to the present disclosure, the thermal flow sensor and the density sensor have a respective MEMS sensor element, wherein the two MEMS sensor elements are arranged on a common measuring board.
In an embodiment according to the present disclosure, the pressure sensor element and/or the temperature sensor element each comprise a MEMS sensor element.
In an embodiment according to the present disclosure, the measurement channel extends through a measurement chamber in which the density sensor, the temperature sensor element, and the pressure sensor element are arranged and can be acted upon by the gas.
In an embodiment according to the present disclosure, the thermal flow meter furthermore comprises a housing body through which the measurement channel extends, wherein the housing body has a mounting surface, wherein the mounting surface has openings which communicate with the measurement channel, wherein the sensor elements which can be acted upon by the gas are arranged, supported by the measuring board, in the openings.
In an embodiment according to the present disclosure, the measuring board seals the openings in a gas-tight manner.
In an embodiment according to the present disclosure, the thermal flow sensor comprises the temperature sensor element which is used to sense the gas temperature.
In an embodiment according to the present disclosure, the thermal flow meter furthermore comprises at least one further sensor element for sensing a measured variable of the gas, which is selected from a list comprising: moisture, viscosity, thermal conductivity, heat capacity. With each of the further sensor elements, a further property of the gas can be ascertained so that, with one further sensor, ternary gas mixtures and, with two further sensors, quaternary gas mixtures can thus also be characterized with regard to their composition in order to correct corresponding cross-sensitivities in the flow measurement.
The present disclosure will now be explained in more detail on the basis of the exemplary embodiments shown in the figures. In the figures:
The operating principle of the flow meter according to the present disclosure is explained with reference to the graph in
In order to be able to compensate for this cross-sensitivity, the flow meter according to the present disclosure includes a density sensor, the measurement data of which make it possible to ascertain the composition of a binary gas mixture of known components, wherein the result of this ascertainment is shown in curve (c). With knowledge of the actually current gas composition, the cross-sensitivity of the thermal flow sensor to the composition of the gas can be compensated for, which ultimately results in the measurement data shown in curve (d), which match the actual flow rate of 100 (sccm) very well. In the case of changes in the gas composition, a delay of a few seconds is given until the correct composition is detected. During this time, there are slight deviations of the measured flow rates from the actual flow rate, as can be seen in curve (d).
In comparison to the data according to the conventional thermal flow sensor in curve (b), the measurement data sensed by the flow meter according to the present disclosure demonstrate a considerable improvement. If various pure gases are present in a process plant, which are used alternately, they can likewise be identified by means of the density sensor in order to correct the flow rate with respect to the cross-sensitivity of the thermal flow measurement to the gas composition. The corresponding compensation functions with gas-dependent parameters are stored in a working memory of the measuring and operating circuit.
The exemplary embodiment shown in
A thermal flow sensor 11, which comprises a heating element and two temperature sensor elements, is positioned in the opening 5 to the measurement channel 3, wherein the heating element is arranged between the temperature sensor elements in the flow direction. The thermal flow sensor 11 is in particular designed as a micro-electromechanical systems (MEMS) sensor element. A density sensor 12, an absolute pressure sensor 14, and a temperature sensor 16 are furthermore arranged on the measuring board 10, wherein these three sensors are designed as MEMS sensor elements. The density sensor 12 comprises an oscillator, which may comprise a quartz tuning fork.
The flow meter 1 according to the present disclosure furthermore comprises a measuring and operating circuit 18 which, in particular, comprises a microcontroller, which is configured to operate the sensor elements and to evaluate the measurement signals thereof. The algorithms and parameters for identifying a gas composition on the basis of the signals of the density sensor 12 and of the pressure sensor 14 and the temperature sensor 16 are stored in a (program) memory of the microcontroller 18, as are the algorithms and gas-specific parameters for compensating for the cross-sensitivity of the thermal flow measurement with respect to the gas composition.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20 2022 107 233.7 | Dec 2022 | DE | national |
