Measuring systems for measuring mass flow, density, temperature and / or flow velocity

Abstract

The invention relates to a measuring system for measuring mass flow, density, temperature and / or flow velocity, the measuring system comprising: a main line (10), the main line leading from a supply unit (36) to a load (40); a measuring unit (34), the measuring unit consisting of a first Coriolis flowmeter (12) arranged in the main line (10), a second Coriolis flowmeter (14) arranged in series with the first Coriolis flowmeter (12) in the main line (10) and designed for a smaller maximum flow than the first Coriolis flowmeter (12), a bypass line (16) bypassing the second Coriolis flowmeter (14) and a valve (18) arranged in the bypass line (16); and a calculation unit (32), the calculation unit being connected to the first Coriolis flowmeter (12) and the second Coriolis flowmeter (14), wherein the valve (18) opens in a pressure-dependent manner and an outlet pressure regulator (38) is arranged in the main line (10) downstream of the measuring unit (34).

Description

Technical Field

[0001] The present invention relates to a measuring system for measuring mass flow, density, temperature and / or flow velocity, the measuring system comprising: a main line, the main line leading from a supply unit to a load; a measuring unit, the measuring unit consisting of a first Coriolis flowmeter arranged in the main line, a second Coriolis flowmeter arranged in the main line and connected in series with the first Coriolis flowmeter and designed for a smaller maximum flow than the first Coriolis flowmeter, a bypass line capable of bypassing the second Coriolis flowmeter and a valve arranged in the bypass line; and a calculation unit, the calculation unit being connected to the first Coriolis flowmeter and the second Coriolis flowmeter.

[0002] Such measuring systems and the associated measuring methods are used in a large number of devices in which the flow, density or velocity present has to be determined. With the aid of the measuring devices used, the flow of liquids as well as gases in the corresponding pipelines can be measured. An example of flow measurement is the use of such devices for measuring the consumption of fuel in motor vehicles, which can be present in gaseous or liquid form. Background Art

[0003] In known consumption measurement systems, Coriolis flowmeters are used, since they have a high accuracy in the case of single-phase flows and are also suitable for measuring flow velocities and flow rates of gaseous media. Coriolis flowmeters are measuring devices for which pressure must be built up in order to display correct measurement results. Furthermore, the measuring devices can only always obtain sufficiently accurate measurement results within one and a specific flow range. Therefore, measuring devices are known which are composed of a plurality of Coriolis flowmeters of different sizes combined with one another.

[0004] An example for this is the system for supplying gaseous fuel to a gas turbine described in EP 2 660 570 A2. Here, for the purpose of consumption measurement, it is proposed to connect two flow meters in parallel and to connect a third flow meter in series. In this case, all three flow meters can be bypassed by a bypass line in which a switching valve is arranged. For this purpose, two smaller flow meters are connected in parallel before the larger flow meter, wherein the maximum flow of the smaller flow meters corresponds in sum to the maximum flow of the larger flow meter. In this case, all three flow meters are always flowing, unless one of the flow meters is removed for calibration. The result of the sum of the two smaller flow meters is compared with the measurement result of the larger flow meter. In the case of large deviations, either the measured values ​​are weighted or only one of the measured values ​​is used as the result.

[0005] However, when using flowmeters of different sizes connected in series or in parallel, the problem arises that sufficient accuracy cannot be continuously provided for the different required pressures within a large flow measurement range. In addition, in the known embodiments, when the switching valve is switched, a pressure surge occurs, which affects the entire system and thus not only causes measurement errors, but may also damage the connected device to be measured.

[0006] Furthermore, from the hitherto unpublished A51099 / 2018 a measuring system is known in which, instead of a switching valve in a bypass line, a valve is used which opens depending on pressure, in particular a non-return valve, by which the relatively small Coriolis sensor is bypassed above a certain pressure. The measuring errors can then only be caused by the mass stored in the connecting line between the measuring cell and the load, since with increasing flow an increasing pressure loss is generated by the measuring cell at the sensor and in the subsequent line. Therefore, the measuring cell is placed as close as possible to the load in order to obtain sufficiently accurate measurement results. Summary of the invention

[0007] Therefore, the technical problem to be solved by the present invention is to provide a measuring system and a measuring method for measuring mass flow, density, temperature and / or flow velocity, by means of which high-precision measurements can be carried out when the measuring unit is arranged at a large distance relative to the load, such as in the case of air conditioning cabinet testing, because there are no sensors specifically designed for such environmental conditions in such tests. In addition, it should also be possible to simulate the actual pressure conditions of the load.

[0008] This object is achieved by a measuring system and a measuring method for measuring mass flow, density, temperature and / or flow velocity having the features of claim 1 .

[0009] Since the opening of the valve depends on the pressure and the outlet pressure regulator is arranged downstream of the measuring cell in the main line, the pressure downstream of the outlet pressure regulator can be set to any value, in particular a constant value. Correspondingly, the subsequent line to the load can have almost any length without any mass consumption measurement errors. However, in order to keep the pressure stable, it is recommended to keep the line between the outlet pressure regulator and the load as short as possible. Only the line between the measuring cell and the outlet pressure regulator has a non-constant pressure, which can cause a non-constant mass in the line section in the case of compressible media. However, the length of the line section can also be minimized without any doubt, so that very precise measurement results can be obtained. In addition, it is possible to simulate situations in which the pressure ratio changes, such as in a vehicle when the tank is empty, as the pressure drops. Of course, for this purpose, the pressure in the main line between the load and the measuring cell must be selected so that it is greater than the pressure between the pressure regulator and the load. By using a valve that is opened depending on the pressure in the bypass line, the measured values ​​of the Coriolis sensor measured with higher accuracy in the corresponding measuring range can be used respectively. Thus, a pressure-dependent opening valve is to be understood as a valve which begins to open an opening cross section when a critical pressure is reached, wherein the opening cross section increases with increasing pressure. In this way, compared to a switching valve, pressure surges which lead to instabilities in the measured flow can be avoided.

[0010] Preferably, the outlet pressure regulator is arranged directly downstream of the measuring cell so that the line length between the measuring cell and the outlet pressure regulator is minimized and thereby also measurement errors caused by non-constant masses present in the line are minimized.

[0011] In another embodiment, a second outlet pressure regulator is arranged in the main line upstream of the measuring cell. This arrangement makes it possible to dispense with the requirement that the supply pressure must be kept constant in order to obtain reliable measured values. This is because as long as the supply pressure does not drop below the outlet pressure of the second outlet pressure regulator, constant pressure conditions are established before the Coriolis measuring device and thus a return flow through the pressure regulator can be eliminated and, accordingly, the line between the load and the pressure regulator will no longer cause errors when taking into account a non-constant pressure in the line and thus a non-constant mass.

[0012] Furthermore, it is advantageous if the outlet pressure of the outlet pressure regulator and / or the second outlet pressure regulator is adjustable, since in this way a desired pressure or a variable inlet pressure can be set at the load, thereby being able to simulate, for example, an emptying tank with a resulting pressure drop.

[0013] In this regard, in an alternative embodiment, a controllable compressor is arranged upstream of the measuring cell in the main line. This should be controlled in a highly dynamic manner so that a stable equalization pressure can be generated at its outlet, whereby in this embodiment the supply pressure no longer has to remain constant. Furthermore, the pressure in the line after the supply device no longer has to be greater than the pressure in the line before the load, since the pressure can be increased to the desired pressure level by the compressor.

[0014] In another embodiment, the compressor is pulsation-free, thereby avoiding pressure surges in the downstream line without having to use a buffer store or a pressure reducer to compensate for such pressure surges.

[0015] It is particularly advantageous here if the compressor is designed as a Tesla compressor, since it can be operated without pulsation and does not require any additional lubrication.

[0016] In another embodiment of the present invention, in the main line, a temperature regulating unit is arranged between the measuring unit and the outlet pressure regulator, which can keep the gas temperature between the outlet of the measuring unit and the inlet in the load constant, or be used to simulate temperature fluctuations of the load in order to study the impact on the load.

[0017] It is therefore most advantageous if the temperature control unit has a control line in which a second compressor and a heat exchanger operating without pulsation are arranged and which also has a return line which branches off from the control line downstream of the heat exchanger and the second compressor and leads back to the control line upstream of the heat exchanger and the second compressor. By means of the circulation path of the measuring medium in the temperature control unit, a thermal short circuit can be established between the outlet of the measuring unit and the inlet of the pressure regulator, whereby the temperature can be kept constant or adjustable completely independently of the flow rate. The sensitive temperature unit can also be arranged at a distance from the outlet pressure regulator and the outlet pressure regulator is directly adjacent to the load to ensure that the desired outlet pressure is established at the load.

[0018] In another embodiment of the present invention, in the main line, pressure sensors are arranged between the measuring unit and the temperature regulating unit and between the temperature regulating unit and the outlet pressure regulator, respectively, and the pressure sensors are connected to the control unit of the second compressor operated without pulsation, and the second compressor operated without pulsation is regulated so that a constant pressure loss is generated between the pressure sensors in the main line. In this way, the pressure gradient of the temperature regulating unit is set to a desired constant value, thereby reliably avoiding measurement errors caused by a sudden pressure increase generated by the temperature regulating unit.

[0019] Accordingly, a measuring system and a measuring method are created, with which the resulting flow can be measured very accurately over a wide flow range, even in the case of gases, since errors due to pressure fluctuations in the lines and to changing volumes in these lines can be avoided or minimized to the greatest extent possible. In another embodiment, this also applies in the case of large distances between the load and the supply unit, as is often the case, for example, in the testing of air-conditioning cabinets. In addition, such a measuring system meets the customer's expectations regarding outlet pressure and temperature in a simple manner and achieves significantly higher accuracy than known measuring devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Four exemplary embodiments of the measuring system according to the invention are shown in the drawings and their function is also described below with reference to the drawings.

[0021] Figure 1 A schematic diagram of a first embodiment of a measuring system according to the invention is shown.

[0022] Figure 2 A schematic diagram of a second embodiment of a measuring system according to the invention is shown.

[0023] Figure 3 A schematic diagram showing a third embodiment of a measuring system according to the present invention is shown.

[0024] Figure 4 A schematic diagram showing a fourth embodiment of a measuring system according to the invention is shown. DETAILED DESCRIPTION

[0025] Figure 1 The illustrated measuring system according to the invention consists of a first main line 10 , through which flows a gaseous or liquid medium, for example a gaseous fuel, whose mass flow is to be determined.

[0026] A first Coriolis flowmeter 12 is arranged in the main line 10, which has a maximum flow rate that is higher than the expected maximum flow rate into the measuring system. Due to the resulting zero drift, such a Coriolis flowmeter 12 cannot provide accurate measured values ​​at low flows, because a certain minimum flow rate is required for accurate measurement in a Coriolis flowmeter.

[0027] In the main line 10, a second Coriolis flowmeter 14 is arranged downstream of the first Coriolis flowmeter 12. The maximum flow rate of the second Coriolis flowmeter 14 is smaller than the maximum flow rate of the first Coriolis flowmeter 12. However, at a smaller flow rate, due to its measuring range, the second Coriolis flowmeter 14 provides a more accurate measurement value than the first Coriolis flowmeter 12.

[0028] However, since the second Coriolis flowmeter 14 downstream may be located in the upper part of the measurement range above its maximum flow rate and thus cause extremely high pressure loss due to the resulting throttling orifice effect, which will distort the flow rate to be measured on the test piece, or fail to handle the flow rate to be measured on the test piece due to insufficient minimum outlet pressure, a bypass line 16 is branched from the main line 10 between the first Coriolis flowmeter 12 and the second Coriolis flowmeter 14. In the present embodiment, this bypass line 16 leads to the main line 10 again downstream of the second Coriolis flowmeter.

[0029] A valve 18 which opens in a pressure-dependent manner and can be designed as a nonreturn valve or as a pressure regulator is arranged in the bypass line 16 .

[0030] The pressure-dependent opening valve 18 opens or closes the flow cross section of the bypass line 16 depending on the pressure difference acting on the valve 18. If a pressure difference is present that exceeds a critical pressure difference, the flow cross section is correspondingly released and the medium can flow from the branch 28 of the bypass line 16 through the bypass line 16 out of the main line 10 and into the main line 10 via the inlet 30 of the bypass line 16.

[0031] The two Coriolis flowmeters 12, 14 together with the pressure-dependently switched valve 18 and the bypass line 16 form a measuring unit 34 and are connected to a computing unit 32. The measured values ​​of the Coriolis flowmeters 12, 14 are transmitted to this computing unit and processed therein to generate a usable measurement result.

[0032] If the medium enters the main line 10 via the supply unit 36, the medium first flows through the first Coriolis flowmeter 12 and builds up pressure. The medium also flows through the second Coriolis flowmeter 14, where pressure is also built up. The smaller second Coriolis flowmeter 14 has already reached its measuring range at relatively small flow rates, within which it obtains accurate measured values. At this point in time, in the Coriolis flowmeter 12 with a higher maximum flow rate, a sufficient flow rate for obtaining accurate measured values ​​has not yet been reached. Correspondingly, in the first measuring range, the calculation unit 32 uses the measured value of the second Coriolis flowmeter 14 as an output value.

[0033] As the flow rate in the measuring system increases, the accuracy of the first Coriolis flowmeter 12 increases and the pressure drop across the second Coriolis flowmeter 14 increases. Correspondingly, a second measuring range is selected, in which both the measured values ​​of the first Coriolis flowmeter 12 and the measured values ​​of the second Coriolis flowmeter 14 are taken into account by the calculation unit 32 and processed by weighting and interpolating these measured values ​​according to the pressure difference of the second Coriolis flowmeter 14. In both the first measuring range and the second measuring range, the valve 18 closes the bypass line 16.

[0034] In the subsequent region, the flow volume in this region is so large that precise measured values ​​are output by the first Coriolis flow meter 12 , which are also used as output values ​​by the calculation unit 32 .

[0035] This area is divided into two parts, more precisely, into a third measuring area, in which the valve 18 depending on the pressure switch is opened due to the applied pressure, and a fourth measuring area, which is located between the second measuring area and the third measuring area, although the measured value of the first Coriolis flowmeter 12 is used as the output value, the valve 18 that is opened depending on the pressure remains closed.

[0036] This means that the switching point of the pressure-dependent valve 18 is spaced apart from the region in which the smaller measured values ​​of the second Coriolis flowmeter 14 are used, so that distortions of the output value can be eliminated by a shift in the opening pressure of the pressure-dependent valve 18. Thus, erroneous output values ​​caused by distorted measurement results of the second Coriolis flowmeter 14 due to premature opening of the pressure-dependent valve 18, for example due to a shift caused by hysteresis or aging of the valve, are reliably eliminated.

[0037] When the resistance at the second Coriolis flowmeter 14 increases, the valve 18 continues to open with increasing pressure and thereby gradually releases an additional flow cross section, so that the adverse effects on the output value of the measuring system due to the switching of the pressure-dependent valve 18 are largely eliminated. In this way, sudden pressure changes are reliably prevented.

[0038] According to the present invention, according to Figure 1In the embodiment of the present invention, an outlet pressure regulator 38 is arranged in the main line 10 after the measuring unit 34, that is, downstream of the measuring unit 34 and before the load 40 whose fuel consumption is measured, by which the inlet pressure at the load 40 is kept constant. This results in that the length of the main line 10 between the outlet pressure regulator 38 and the load 40 no longer has any influence on the measuring accuracy of the measuring system, because the change of the fuel volume caused by the pressure change in this area has been eliminated. Therefore, the main line 10 between the outlet pressure regulator 38 and the load 40 can be selected to be any length. In order to also minimize the influence of the pipeline section between the outlet pressure regulator 38 and the measuring unit 34, the outlet pressure regulator 38 is arranged directly adjacent to the measuring unit 34. As a result, under the premise of providing a constant supply pressure by the supply unit 36, the measurement result will no longer be adversely affected by the fuel mass present in the main line. In addition, an arbitrary pressure can be set by the adjustable outlet pressure regulator 38 or a variable pressure can be generated according to a stored characteristic curve, which can be used to simulate certain situations, such as simulating an empty tank.

[0039] In order to additionally achieve independence of the constant supply pressure of the supply unit 36, in accordance with Figure 2 In the embodiment of the present invention, a second outlet pressure regulator 42 is additionally arranged between the supply unit 36 ​​and the measuring unit 34 in the main line 10, so that the supply unit 36 ​​can also be arranged at a certain distance from the measuring unit 34 and a non-constant pressure can be delivered, because the measurement error caused by the volume change of the fuel in the main line 10 between the second outlet pressure regulator 42 and the measuring unit 34 is eliminated and the pipeline section of the main line 10 between the outlet pressure regulator 42 and the supply unit 36 ​​no longer causes a measurement error due to the elimination of the backflow through the outlet pressure regulator 42. For this purpose, the outlet pressure of the outlet pressure regulator 42 is set to be lower than the normal supply pressure of the supply unit 36, so that the outlet pressure at the outlet pressure regulator 42 and the outlet pressure of the measuring unit 34 can be maintained when the pressure level of the supply unit 36 ​​is reduced.

[0040] exist Figure 3 In the alternative embodiment shown, the second outlet pressure regulator 42 is replaced by a pulsation-free and adjustable compressor 44, which is preferably designed as a Tesla compressor. Figure 2The second outlet pressure regulator 42 in the compressor 44 can ensure, on the one hand, that the pipeline section upstream of the compressor 44 no longer generates measurement errors, because when the pressure suddenly increases here, the backflow in the pipeline section is prevented by the compressor 44; on the other hand, the pressure provided by the supply unit 36 ​​can be made smaller, because the pulsation-free compressor 44 can provide a constant outlet pressure without having to select a pressure at the load 40 that is significantly greater than the inlet pressure.

[0041] exist Figure 4 The measurement system shown in provides another optimized solution. Figure 3 In contrast, here, in the main line 10, the temperature control unit 46 is arranged between the measuring unit 34 and the outlet pressure regulator 38. Correspondingly, the main line 10 leads to the control line 48, in which the second compressor 50, which is preferably designed as a Tesla compressor and operates without pulsation, and the heat exchanger 52 for generating the desired temperature are arranged. In addition, the temperature control unit 46 also has a return line 54, through which the fuel branches off from the heat exchanger 52 and the second compressor 50 downstream of the control line 48, and enters the control line 48 again from the upstream of the heat exchanger 52 and the second compressor 50.

[0042] The temperature control unit 46 can be installed downstream of the measuring unit 34 without difficulty, since it can reliably set the fuel delivered to the load 40 to a desired constant temperature even at minimum flow rates, since the fuel can be delivered to the control circuit via the second compressor 50, which operates without pulsation, at a constant pressure drop and at a constant temperature, so that even at very small flows to the load 40, no temperature changes occur. The constant pressure drop can be achieved by corresponding control of the compressor 50, wherein the compressor has a control unit 53, which is electrically connected to a first pressure sensor 56, which is arranged in the main line 10 directly upstream of the temperature control unit 46, and a second pressure sensor 58, which is arranged in the main line 10 downstream of the temperature control unit 46, and by means of which the second compressor 50 is controlled as a function of the measured pressure difference between the first pressure sensor 56 and the second pressure sensor 58.

[0043] The measuring system described provides continuously available, very precise measured values ​​over a wide pressure and flow range. When the pressure changes, no transient oscillation of the system is required. The measuring system is also particularly suitable for measuring gas flows and a high measuring accuracy is achieved even with very small flows, since any changes in the fuel volume are limited to a very small line section and, in addition, a constant pressure is generated in the line, thereby, on the one hand, eliminating volume changes caused by changing pressure and, on the other hand, avoiding backflows in other line sections.

[0044] Of course, additional extensions can also be considered. Thus, more than two different Coriolis flowmeters with reduced maximum flow can be connected in series with each other, wherein, in addition to the largest Coriolis flowmeter, a bypass should be provided respectively. In this case, the measured value of the Coriolis flowmeter with the smallest maximum flow will be obtained in the lowest measurement area. Then, before the corresponding valve in the bypass line is opened, the measured value of each larger Coriolis flowmeter is used to determine the output value, wherein an interpolation area is interpolated respectively. Then, the opening point of the valve changes in accordance with the pressure difference generated on the valve, which is formed by the pressure loss in the Coriolis flowmeters connected in parallel respectively. Different valves that depend on pressure opening and different pressure regulators can also be used. They can be driven, for example, electrically or electromagnetically and adjusted according to the value of the pressure sensor. Within the scope of protection of the independent claims, other variants can also be given to those skilled in the art.

Claims

1. A measurement system for measuring mass flow, density, temperature and / or flow velocity, the measurement system comprising: a main line (10), the main line leading from the supply unit (36) to the load (40); A measuring unit (34), the measuring unit comprising a first Coriolis flowmeter (12) arranged in the main pipe (10), a second Coriolis flowmeter (14) arranged in series with the first Coriolis flowmeter (12) in the main pipe (10) and designed for a smaller maximum flow rate than the first Coriolis flowmeter (12), a bypass line (16) capable of bypassing the second Coriolis flowmeter (14), and a valve (18) arranged in the bypass line (16); and a calculation unit (32) connected to the first Coriolis flowmeter (12) and the second Coriolis flowmeter (14), It is characterized in that An outlet pressure regulator (38) is arranged in the main line (10) downstream of the measuring unit (34), and The valve (18) opens in a pressure-dependent manner and begins to open an opening cross section when a critical pressure is reached, wherein the opening cross section increases with increasing pressure, wherein: A controllable compressor (44) is arranged in the main line (10) upstream of the measuring unit (34), the compressor (44) being pulsation-free or being operable in a pulsation-free manner.

2. The measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 1, characterized in that: The outlet pressure regulator (38) is arranged directly downstream of the measuring cell (34).

3. A measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 1 or 2, characterized in that: The outlet pressure of the outlet pressure regulator (38) is adjustable.

4. The measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 1, characterized in that: The compressor (44) is a Tesla compressor.

5. The measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 1, characterized in that: In the main line (10), a temperature regulating unit (46) is arranged between the measuring unit (34) and the outlet pressure regulator (38).

6. The measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 5, characterized in that The temperature control unit (46) comprises a control line (48) and a return line (54), in which a second compressor (50) and a heat exchanger (52) operating without pulsation are arranged, and the return line branches off from the control line (48) downstream of the heat exchanger (52) and the second compressor (50) and leads back to the control line (48) upstream of the heat exchanger (52) and the second compressor (50).

7. The measuring system for measuring mass flow, density, temperature and / or flow velocity according to claim 6, characterized in that In the main line (10), pressure sensors (56, 58) are arranged between the measuring unit (34) and the temperature regulating unit (46) and between the temperature regulating unit (46) and the outlet pressure regulator (38), respectively. The pressure sensors are connected to a control unit (53) of a second compressor (50) in non-pulsation operation, and the second compressor (50) in non-pulsation operation is regulated so that a constant pressure loss is generated between the pressure sensors (56, 58) in the main line (10).

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