Measuring systems for flow measurement

Abstract

A measuring system for measuring a flow rate at a load is known, comprising a supply unit, a measuring unit, an outlet pressure regulating unit, the measuring unit being connectable to the load via the outlet pressure regulating unit, the outlet pressure regulating unit having at least one outlet pressure sensor and at least one controllable valve, and a main line connected to a medium interface and through which the supply unit, the measuring unit, and the outlet pressure regulating unit are fluidically connected. In order to ensure reliable measurement results over a long period of time and under extreme conditions to which the load may be exposed, the present invention proposes that the supply unit and the measuring unit be arranged in a single housing, and that the outlet pressure regulating unit be arranged in a separate housing, wherein the measuring unit, the controllable valve of the outlet pressure regulating unit, and the outlet pressure sensor of the outlet pressure regulating unit are connected to the supply unit via a line.

Description

[0001] The present invention relates to a measuring system for measuring flow, which comprises a supply unit having a medium interface and a purge gas interface and / or an inert gas or pressurized air interface; a measuring unit having at least one flow meter and at least one controllable valve, the measuring unit being fluidly connected to the supply unit for selectively introducing a medium flow or a purge gas flow, and the flow being able to be measured by the measuring unit; an outlet pressure regulating unit having at least one outlet pressure sensor and at least one valve, the outlet pressure regulating unit being fluidly connected to the measuring unit, and the measuring unit being connected to a load via the outlet pressure regulating unit; and a main line, the main line being connected to the medium interface and the supply unit, the measuring unit and the outlet pressure regulating unit being fluidly connected via the main line.

[0002] Such measuring systems and the associated measuring methods are used in various applications where conclusions need to be drawn about the flow rate (either volumetric or mass) in the system. The measuring devices can be used to measure the flow of liquids and gases in corresponding lines. An example of flow measurement is the use of such devices to measure the consumption of fuel, such as diesel or gasoline, as well as hydrogen, in motor vehicles.

[0003] In known consumption measurement systems, Coriolis measuring devices are used because they offer high accuracy in single-phase flows and are also suitable for measuring flow velocities and volumes of gaseous media. However, these measuring devices can only achieve sufficiently accurate measurement results within a certain flow range. For this reason, measuring devices are known that combine several Coriolis measuring devices of different sizes.

[0004] Furthermore, it is known to combine a Coriolis measuring device with a pressure regulator in the measuring cell, and to switch back and forth between two Coriolis measuring devices of different sizes by bypassing at least one of the measuring devices with a valve. Such a measuring cell is known, for example, from WO 2016 / 206983 A1. The medium enters the measuring cell and the main line via an inlet connection. It is then temperature-controlled in a regulating device and expanded to the desired expansion pressure at a first pressure regulator. It then flows through the Coriolis measuring devices, which are used to measure the flow rate. A second pressure regulator is provided downstream of these measuring devices to set the outlet pressure. This is accomplished by providing an outlet pressure sensor at the outlet of the consumption measuring device. This sensor detects the outlet pressure and feeds it to a control unit that controls the outlet pressure regulator downstream of the Coriolis measuring device. The conditioned medium flows out through the outlet port and is supplied to the load. The measuring system also has an inert gas port through which inert gas can be introduced into the measuring system for purging.

[0005] However, a disadvantage of such systems is that measurement errors have been found to occur when the load is exposed to extreme pressure and temperature conditions, such as are simulated on a test bench (eg in a climate chamber).

[0006] The technical problem to be solved by the present invention is to provide a flow measurement system that can be used to obtain accurate measurement values ​​even when the load is exposed to extreme climatic conditions, while minimizing the equipment expenditure. Furthermore, the system should be as simple to use and maintain as possible and offer sufficient flexibility.

[0007] This object is achieved by a measuring system for measuring a flow rate having the features of claim 1 .

[0008] The measuring system of the present invention consists of three units: a supply unit, a measuring unit, and an outlet pressure regulation unit. The supply unit includes components for supply and control and has a medium interface and an inert gas interface. The measuring unit has at least one flow meter, such as a Coriolis measuring device, which measures the flow rate in a main line connected to the medium interface. The outlet pressure regulation unit has at least one outlet pressure sensor, which measures the outlet pressure of the measuring system. These units can be configured as separate modules. The measuring unit has at least one controllable valve for closing or opening the main line in the measuring unit and / or a pressure regulator for regulating the pressure in the main line. These valves can be pneumatically actuated, in particular. The measuring unit is fluidically connected to the supply unit for selectively introducing a flow of the measured medium or the inert gas. In addition to the outlet pressure sensor, the outlet pressure regulation unit also has a controllable valve for regulating the medium flow rate and is fluidically connected to the measuring unit. Furthermore, the outlet pressure regulation unit can be fluidically connected to a load, so that the measuring unit can be connected to the load via the outlet pressure regulation unit. This connection is made via a main line which extends from the medium inlet, which is connected to the source of the measured medium, to the supply unit and via the measuring cell and the outlet pressure regulating unit to the outlet.

[0009] According to the present invention, the supply unit and measuring unit are arranged in a single housing, while the outlet pressure regulating unit is housed in a separate housing, separate from the measuring unit's housing. In this case, the measuring unit, along with the controllable valve and pressure regulator, is connected to the supply unit via lines for controlling the valve and pressure regulator. These lines can be either pneumatic, hydraulic, or electrical. This design allows the outlet pressure regulating unit, and thus the outlet pressure sensor, to be positioned directly at the load without exposing the heat- or cold-sensitive components of the measuring unit to the corresponding conditions. Distances of up to approximately 10 meters are achievable. This allows highly accurate measurement results while ensuring a long service life for the measuring unit without increasing the complexity of the equipment. Conversely, the very small outlet pressure regulating unit can easily be accommodated in existing small climate chambers. This design offers a high degree of flexibility and allows for the measurement of diverse media.

[0010] The outlet pressure regulating unit is preferably spaced apart from the measuring unit and directly connected to the measuring unit only via a main line. This allows for a spatial distance between the measuring unit and its heat-sensitive components, allowing the outlet pressure regulating unit to be exposed to significant heat or cold. The outlet pressure sensor can then directly measure the load pressure under the same climatic conditions. The control unit uses the feedback signal from the outlet pressure sensor to control the outlet pressure regulator of the measuring unit.

[0011] Preferably, the outlet pressure regulator unit is also arranged remotely from the supply unit and is connected to the supply unit only via a main line, a pneumatic control line, and at least one electrical line, wherein the electrical line connects the outlet pressure sensor to the control unit of the supply unit. The entire electrical control and pneumatic supply of the outlet pressure regulator unit is correspondingly implemented via the remote supply unit.

[0012] The outlet pressure regulating unit can thus be placed inside the climate chamber together with the load, while the measuring unit and supply unit can be placed outside. This makes it easy to simulate various climate conditions in the laboratory without having to accept any resulting measurement errors.

[0013] Preferably, the supply unit includes a valve bank (or valve rail) with multiple solenoid valves. Each solenoid valve is connected to the controllable valve, the measuring unit, and the outlet pressure regulating unit of the supply unit via pneumatic control lines. These solenoid valves are also electrically connected to the control unit. By energizing the solenoid valves in the supply unit, the valve and pressure regulator of the measuring unit, the outlet pressure regulating unit, and the supply unit can be individually pneumatically actuated accordingly. This pneumatic actuation is not sensitive to temperature, so the supply unit, which only has sensitive electrical components, is not exposed to significant heat.

[0014] In a further embodiment, the inert gas or compressed air connection of the supply unit is connected to the valve bank via an inert gas or compressed air line, wherein an inert gas or air pressure regulator and an inlet pressure sensor are provided. Thus, the inert gas pressure regulator can be used to set the correct pressure for switching or controlling the valves based on feedback from the pressure sensor, ensuring that sufficient pressure is provided for switching by the solenoid valves.

[0015] Advantageously, the supply unit includes a damping element comprising a first switching valve in the main line and a bypass line that bypasses the first switching valve and contains a second switching valve and a throttle valve. This damping element prevents a sudden, sharp increase in pressure when the measuring system is switched on, which could damage downstream equipment, particularly downstream pressure regulators. To this end, when the measuring system is switched on, the main line is closed by a valve, and the medium is initially directed through the throttle valve. Consequently, the pressure gradually increases due to the throttle valve until the valve switches and flow through the main line resumes.

[0016] Advantageously, the supply unit includes an inlet pressure sensor arranged in the main line, based on which a first outlet pressure regulator (located in the main line before the flowmeter of the measuring unit) is regulated. This arrangement prevents pulsations downstream of the pressure regulator and at the flowmeter. For example, if the consumption suddenly jumps, the pressure at the pressure sensor may drop or rise by as much as 1 bar. Due to the hysteresis of the pump, an additional pressure difference of approximately 0.3 bar occurs, resulting in a pressure drop of approximately 1.3 bar at the inlet pressure sensor, which would lead to errors in the measured values. Therefore, the outlet pressure regulator upstream of the flowmeter is set to a pressure that is more than 1.3 bar below the supply pressure of the measuring system, for example 2 bar, which prevents pulsations from propagating further into the system. This arrangement thus eliminates the need to maintain a constant supply pressure in order to obtain reliable measurements, as a constant pressure condition can be established upstream of the Coriolis measuring device as long as the supply pressure does not drop below the outlet pressure of the measuring system.

[0017] Furthermore, the supply unit preferably has a purge gas supply line that leads from the purge gas connection to the main line, and in which a first purge gas valve, a first check valve, and a purge gas pressure sensor are arranged. This allows the measuring system to be purged in a simple manner, and the purge gas pressure sensor ensures that sufficient purge gas pressure is present. The purge gas valve serves to close and open the purge gas line, while the check valve ensures that no other media can flow from the main line into the purge gas line.

[0018] In a further development, the supply unit includes a supply unit purge gas discharge line that branches off from the main line upstream of the measuring cell and connects to the first purge gas outlet port. A second purge gas valve and a second check valve are provided in the supply unit purge gas discharge line. This allows for a separate purge of the area upstream of the measuring cell. The check valve prevents gas from flowing through the outlet port. In this case, the check valve or the supply unit purge gas discharge line is dimensioned so small that flow restriction is achieved through the existing throttling effect.

[0019] The supply unit also features a connection interface through which additional units can be connected to the main line. For example, this could be a preheater, which prevents the medium from cooling down during subsequent expansion through the first outlet pressure regulator of the measuring cell, which is outside the standard. However, the connection interface can also be used to connect mass flow calibration equipment or to extract samples. The permissible pressure range of the measuring system can also be extended by connecting an additional pressure regulator. However, this pressure regulator is not always connected, thus avoiding undesirable pressure losses within the normal pressure range.

[0020] Preferably, a second outlet pressure regulator, a first Coriolis measuring device, and a second Coriolis measuring device arranged downstream of the first Coriolis measuring device are arranged in the main line of the measuring cell. The second Coriolis measuring device can be bypassed by a bypass line in which a valve is arranged. Thus, the pressure downstream of the outlet pressure regulator can be set to any value, in particular, a constant value. Consequently, the subsequent line to the load can have virtually any length without causing errors in mass consumption measurement, allowing the outlet pressure regulator unit to be located relatively far from the measuring cell. In this design, only the line between the measuring cell and the second outlet pressure regulator has a non-constant pressure, resulting in a non-constant mass of the compressible medium in this section of the line. However, this makes it easy to minimize the length, resulting in highly accurate measurement results. Furthermore, it is possible to simulate conditions with varying pressure ratios, such as those that occur on vehicles when the pressure drops due to emptying of the fuel tank. Of course, for this purpose, the pressure in the main line between the supply unit and the measuring cell must be selected to be greater than the pressure at the outlet of the outlet pressure regulating unit, and therefore greater than the pressure at the load. Furthermore, the pressure regulator can also be used to limit the mass flow rate. Therefore, if the fuel cell exceeds the permissible mass flow rate limit, the permissible mass flow rate is restored by reducing the pressure. Therefore, the second outlet pressure regulator communicates with the outlet pressure sensor of the outlet pressure regulating unit via the control unit, so that the outlet pressure can be set and controlled very precisely.

[0021] The outlet pressure regulator is preferably located directly downstream of the measuring cell and can be controlled to a constant target value or to follow a target value characteristic curve. This minimizes the line length between the measuring cell and the outlet pressure regulator, and thus minimizes measurement errors due to non-constant mass in the line. Different characteristic curves can be used to simulate different load conditions.

[0022] Advantageously, the valve in the bypass line opens pressure-dependently, and the second Coriolis measuring device, which can be bypassed, is designed for a lower maximum flow rate than the first Coriolis measuring device. By using a pressure-dependent valve in the bypass, it is possible to use the measured values ​​of the Coriolis sensor, which measures with higher accuracy within the corresponding measuring range. A pressure-dependent valve is defined as a valve that, upon reaching a threshold pressure, releases an opening cross-section that increases with increasing pressure. This avoids pressure surges that can cause discontinuities in the measured flow rate, compared to switching valves.

[0023] In a preferred embodiment, the measuring cell pressure sensor is arranged between the first outlet pressure regulator and the first Coriolis measuring device, whereby the inlet pressure of the Coriolis measuring device is determined and correspondingly regulated by means of the first outlet pressure regulator of the measuring cell.

[0024] Furthermore, it is advantageous if a first measuring cell purge gas line branches off from the first outlet pressure regulator, and a second measuring cell purge gas line branches off from the second outlet pressure regulator, the second measuring cell purge gas line leading via a third check valve to the purge gas outlet connection. Thus, the measuring cell can be purged either completely or only in the inlet region of the measuring cell via these lines. The check valve prevents undesired gas flow in the opposite direction. The purge gas outlet connection of the supply unit can be used as an outlet. Here, throttling can also be achieved by means of check valves or correspondingly small lines.

[0025] Downstream of the second Coriolis measuring device and upstream of the second outlet pressure regulator, an additional connection port is formed through which the calibration unit can be connected to the main line. Connecting at this location allows the measuring unit to be fully calibrated without requiring further flow from the main line to the outlet pressure regulator. This eliminates the need to disconnect the fuel cell for calibration, saving time and eliminating the risk of leaks when reconnecting to the fuel cell.

[0026] In addition to the purge gas lines already described, it is advantageous to branch off a first purge gas line for the outlet pressure regulating unit from the main line of the outlet pressure regulating unit upstream of the outlet pressure sensor, and a second purge gas line for the outlet pressure regulating unit downstream or at the same level as the outlet pressure sensor. Switching valves are provided in each of the two lines, and these are guided to the second purge gas outlet connection via a check valve. Thus, the outlet pressure regulating unit can also be purged via these lines, or the valves can be switched so that the load is also purged. The outlet pressure regulator can also be used to control the pressure when purging the load and the outlet pressure regulating unit. Furthermore, the purge gas consumption can be determined using a flow meter.

[0027] In a further embodiment, a temperature sensor is arranged in the main circuit of the outlet pressure regulating unit, by means of which the temperature at the outlet and, correspondingly, the temperature at the inlet can be determined. This allows both temperature regulation using corresponding regulating devices and correction of the measured flow rate.

[0028] Furthermore, the outlet pressure regulating unit preferably has a connection interface via which a line volume simulation unit can be connected to the main line. This allows the simulation of a specific line volume from the tank to the load, which is particularly important during the fuel cell shutdown period, when hydrogen is still required.

[0029] Thus, a measuring system has been created that can very accurately measure the flow rates of gases and liquids over a wide flow range. Errors due to pressure fluctuations in the lines, and thus changes in volume in these lines, are largely avoided. Unexplained pressure variations between the measuring system and the load are also prevented, as the outlet pressure control unit can be positioned directly next to the load under the same climatic conditions. This also applies to larger distances between the load and the supply unit, as is often the case in climatic cabinet testing. Furthermore, this measuring system can be easily adapted to customer requirements for outlet pressure and temperature and achieves higher accuracy than known measuring devices.

[0030] An embodiment of the measuring system according to the present invention is shown in the drawings, and its function is also described below.

[0031] The drawing shows a schematic diagram of a measuring system according to the invention.

[0032] As shown in the figure, the measurement system according to the present invention can be used to measure the consumption or flow of a medium in a load 10, such as liquid fuel in an internal combustion engine and gaseous fuel such as hydrogen in a fuel cell. The measurement system includes three modules, namely a supply unit 12, a measuring unit 14 and an outlet pressure regulating unit 16.

[0033] The supply unit 12 serves for powering and controlling the measuring system, for which purpose a medium connection 18 , a purge gas connection 20 and an inert gas or compressed air connection 22 (for the pneumatic and, if necessary, hydraulic supply) as well as a control unit 24 for the electrical supply and regulation of the measuring system 12 are connected to the supply unit 12 .

[0034] The medium interface 18 leads to a main line 26 which extends from the supply unit 12 via the measuring unit 14 and the outlet pressure regulating unit 16 to a medium outlet 28 , via which the measuring system can be connected to the load 10 . During measurement, the medium flows through the main line and the mass flow of the medium is determined.

[0035] Immediately downstream of the media connection 18, an inlet pressure sensor 30 is located in the main line 26. This inlet pressure sensor checks whether sufficient pressure exists at the media connection 18. Next, a first pneumatic switching valve 32 is located, which interrupts the flow through the main line 26. This first pneumatic switching valve 32 can be bypassed by a bypass line 34, in which a second pneumatic switching valve 36 and a throttle valve 38 are arranged. Therefore, if the pressure applied when the measuring system is turned on is too high, the second switching valve 36 can be opened, while the first switching valve 32 initially remains closed. Consequently, the medium must flow through the throttle valve 38, and the pressure in the main line 26 gradually builds up. Once the required pressure is reached, the two switching valves 32 and 36 are switched over, eliminating the pressure loss through the throttle valve 38 and making the full pressure from the media connection 18 available to the measuring system. This prevents damage to downstream components during the start-up of the measuring system.

[0036] The main line 26 continues to a first connection port 40, to which, for example, an auxiliary heater or a calibration device can be connected, thereby providing access to the main line 26. Samples can also be drawn here, or an optional pressure regulator can be connected, which can be used to reduce the operating pressure from 250 bar to 25 bar. The advantage of this optional port is that it eliminates the pressure drop that occurs at the pressure regulator under normal operating pressure.

[0037] The main line 26 continues in the direction of the measuring cell 14 , whereby a spring-loaded safety valve 42 is provided on the main line 26 upstream of the measuring cell 14 , which opens at a pressure exceeding 30 bar to protect the components in the measuring cell 14 .

[0038] In order to be able to be independent of the constant supply pressure of the supply unit 12, a first outlet pressure regulator 44 is arranged in the main line 26 between the supply unit 12 and the measuring unit 14. In order to exclude a backflow through the measuring unit 14, the outlet pressure of the outlet pressure regulator 44 is set below the normal supply pressure of the supply unit 12, so that the outlet pressure at the outlet pressure regulator 44 and therefore in the measuring unit 14 can be maintained even if the pressure level of the supply unit 12 drops.

[0039] A switching valve 46 (for closing the main line 26 ) and a measuring unit pressure sensor 48 (for checking the pressure regulated by the outlet pressure regulator 44 ) are provided downstream of the first outlet pressure regulator 44 .

[0040] Downstream of the measuring cell pressure sensor 48, a flow meter 50 is provided. This includes a first Coriolis measuring device 52 designed for a maximum flow rate that is higher than the maximum flow rate expected in the measurement system. Such a Coriolis measuring device 52 is unable to provide accurate measurements at low flow rates due to zero drift, as a Coriolis measuring device requires a certain minimum flow rate for accurate measurement.

[0041] Downstream of the first Coriolis measuring device 52 , a second Coriolis measuring device 54 is arranged in the main line 26 , which has a lower maximum flow rate than the first Coriolis measuring device 52 but provides more accurate measurements at lower flow rates than the first Coriolis measuring device 52 due to its measuring range.

[0042] Because the second Coriolis measuring device 54 downstream will cause extremely high pressure loss in the upper measurement range above its maximum flow rate due to the orifice effect, the pressure loss will cause the flow rate to be measured on the sample to be erroneous or prevent flow due to insufficient minimum outlet pressure. Therefore, a bypass line 56 is branched from the main line 26 between the first Coriolis measuring device 52 and the second Coriolis measuring device 54. The bypass line 56 reconnects to the main line 26 downstream of the second Coriolis measuring device 54.

[0043] A pressure-dependent switching valve 58 (which is designed as a non-return valve) and a further switching valve 60 are arranged in the bypass line 56. The pressure-dependent switching valve 58 opens or closes the flow cross section of the bypass line 56 depending on the pressure difference acting on the valve 58. If a pressure difference exceeds a threshold pressure difference, the flow cross section is correspondingly released, and the medium can flow from the branch 62 of the bypass line 56 from the main line 26 through the bypass line 56 and back to the main line 26 through the connection opening 64 of the bypass line 56.

[0044] The flow meter 50 is connected to the control unit 24, transmits the measured values ​​of the Coriolis measuring devices 52, 54 to the control unit 24 and processes these measured values ​​in the control unit to generate a usable measurement result, wherein the measured value of the first Coriolis measuring device 52 or the second Coriolis measuring device 54 is used depending on the size of the flow, and the measured values ​​of both Coriolis measuring devices 52, 54 are used in the transition range.

[0045] This largely eliminates any negative effects on the output value of the measuring system due to the switching of the pressure-dependent valve 58, so that valve 58 opens further with increasing pressure, thereby gradually releasing an additional flow cross section and increasing the resistance at the second Coriolis measuring device 54. In this way, pressure jumps are reliably prevented.

[0046] Downstream of the connection 64 of the bypass line 56, a pressure gauge 66 is provided in the main line 26 for checking the pressure. The main line 26 is further connected to a further connection port 68, to which a calibration unit can be connected, by means of which the flow meter 50 can be calibrated without having to intervene in the further lines.

[0047] Connected to the other connecting valve 70, a second outlet pressure regulator 72 is arranged in the main line 26, by means of which the outlet pressure of the measuring system 10 at the load 10 is either kept constant or controlled according to a time-dependent characteristic curve. For example, a pressure characteristic curve can also be simulated when emptying a tank.

[0048] The supply unit 12 is arranged together with the measuring unit 14 in a common housing 74, which has an outlet interface 76, which is connected to the inlet interface 78 of the subsequent outlet pressure regulating unit 16. First, a switch valve 80 is provided in the main line 26 of the outlet pressure regulating unit 16, by which the main line 26 can be closed. Afterwards, the outlet pressure control unit 16 has another connection interface 82. In particular, a line volume simulation unit can be connected here. It simulates a specific line volume (or line volume) from the tank to the load 10. This may be necessary because the fuel cell system still needs hydrogen to be shut down. Ideally, the design of the entire system is such that the gas stored in the line is sufficient. In order to simulate this in the design, this connection interface 82 can be used.

[0049] In a subsequent extension, a temperature sensor 84 and an outlet pressure sensor 86 are arranged in the main line 26, which are arranged fluidically upstream of the medium outlet 28 and therefore upstream of the load 10, so that the inlet pressure and the inlet temperature at the load 10 are measured if the outlet pressure regulating unit 16 can be appropriately arranged near the load 10. The temperature sensor 84 and the outlet pressure sensor 86 are connected to the control unit 24 via electrical wires (not shown for clarity), which issues corresponding commands to the outlet pressure regulator 72 for regulation, so that the desired outlet pressure is measured at the outlet pressure sensor 86 and regulated by the outlet pressure regulator 72 according to its measured value.

[0050] In order to arrange the outlet pressure regulating unit 16 close enough to the load 10 , the outlet pressure regulating unit 16 can only be connected to the supply unit 12 via electrical lines and pneumatic control lines 88 , otherwise it can be set at a distance of up to 10 m from the supply unit 12 and the measuring unit 14 .

[0051] For this purpose, the outlet pressure regulating unit 16 is arranged in a separate housing 90, which can be arranged together with the load 10, for example in a climate chamber, so that the actual pressure value can be transmitted without having to worry about sensitive components of the measuring unit 14, such as the flow meter 50 or the outlet pressure regulator 44, 72, or sensitive elements of the supply unit 12, such as the control unit 24, being damaged.

[0052] The supply unit 12 can also be used to purge parts or the entire measuring system, for example with nitrogen, in order to enable a switchover to another medium. For this purpose, the purge gas connection 20 has a connection to a purge gas supply line 92, in which a gas pressure sensor 94, a first purge gas valve 96, and a first check valve 98 are arranged. This connection is connected to the main line 26 between the first switching valve 32 and the first connection connection 40. The purge gas is typically an inert gas, for example nitrogen.

[0053] The purge gas pressure sensor 94 is used to measure the pressure of the purge gas and is only used to detect a pressure that is too low, at which purge is no longer guaranteed. The purge gas valve 96 is opened to start the purge process and is otherwise in its closed position, while the non-return valve 98 is only used to prevent the measured medium from flowing into the purge gas supply line 92.

[0054] Downstream of the connection port and upstream of the safety valve 42, a supply unit purge gas discharge line 100 branches off from the main line 26. A second pneumatic purge gas valve 102 and a second check valve 104 are arranged therein. Supply unit purge gas discharge line 100 is designed so that the flow rate assumes a defined value. When purge gas valve 102 is open, the area of ​​the supply unit 12 upstream of the measuring cell 14 and, therefore, upstream of the outlet pressure regulator 44, is purged. Check valve 104 again prevents gas from flowing into the measuring system from a first purge gas outlet port 106 (where the first supply unit purge gas discharge line 100 is connected).

[0055] If measuring cell 14 or measuring cell 14 and outlet pressure regulating unit 16 are to be purged, on-off valves 32, 36 are first closed. A first measuring cell purge gas line 108 branches off from first outlet pressure regulator 44, and a second measuring cell purge gas line 110 branches off from second outlet pressure regulator 72; these lines merge upstream of third check valve 112. The common measuring cell purge gas line is connected to first purge gas outlet port 106. Furthermore, a thinner first purge gas line 114, again designed to reduce the flow rate, is provided at outlet pressure regulating unit 16. This line branches off from main line 26 and contains an on-off valve 116 and, for the reasons mentioned above, a check valve 118. Outlet pressure regulating unit purge gas line 114 terminates at a second purge gas outlet port 120, to which a thinner second outlet pressure regulating unit purge gas line 122 is also connected. This line branches off from main line 26 at outlet pressure sensor 86 and also contains an on-off valve 124 and a check valve 126. Depending on which of the on-off valves 102, 46, 70, 116, and 124 is open, different areas of the measurement system can be purged accordingly. By opening valves 46, 70, 96, and 124, the entire measurement system, including the outlet pressure regulating unit 16, is purged. If only the supply unit 12 and the measurement unit 14 are being purged, for example, valves 80 and 116 can be closed and valves 46, 70, and 96 can be opened. If the load 10 is also being purged, valve 80 is opened, while valves 116 and 124 are closed. When purging the load 10, a defined purge pressure, which can be customized by the customer, can be provided to the load via the remotely adjustable outlet pressure regulator 72.

[0056] Of course, if not only the supply unit 12 is purged, the purge gas flow rate can also be measured by the flow meter 50, thereby determining the purge gas consumption. Particularly efficient purging can be achieved by pulse operation. In this case, the switching valves 102, 46, 70, 116, 124 are only briefly opened to deliver pressurized gas to the purge gas lines 100, 108, 110, 114, 122. When the valves are closed, the purge gas can potentially mix with the main gas, thereby eliminating dead zones where the medium to be measured has collected by the mixture with the purge gas.

[0057] In addition to supplying inert gas to the measurement system, the supply unit 12 is designed to actuate the pneumatic valves 32, 36, 46, 60, 70, 80, 96, 102, 116, 124 and the outlet pressure regulators 44, 72. Pressurized air can also be supplied, hereinafter exemplarily based on inert gas. For this purpose, an inert gas line 128 leads from the inert gas connection 22 (where pressurized inert gas is present) via an inlet pressure sensor 130 and an inert gas pressure regulator 132 to a valve bank 134, where a plurality of solenoid valves 136 are arranged. The inlet pressure sensor 130 can be used to determine whether sufficient pressure exists, which can then be adjusted by the inert gas pressure regulator 132 to the pressure required to open and close the pneumatic valves 32, 36, 46, 60, 70, 80, 96, 102, 116, 124. Each solenoid valve 136 is assigned to one of the valves 32, 36, 46, 60, 70, 80, 96, 102, 116, 124 and is connected to the assigned valve 32, 36, 46, 60, 70, 80, 96, 102, 116, 124 via a corresponding pneumatic control line 88. When the solenoid valve 136 is switched on, the pressure controlled by the inert gas pressure regulator 132 or the pressure air regulator is supplied to the pressure chamber of the switching valve 32, 36, 46, 60, 70, 80, 96, 102, 116, 124, thereby setting the corresponding valve to its open state. When the solenoid valve is not switched on, the valve remains closed. The solenoid valve 136 is connected to the control unit 24 and is located in the same housing 74, so only short wires are required to switch the solenoid valve 136.

[0058] The pneumatically controllable outlet pressure regulators 44, 72 are switched on and off by electropneumatic transducers 138, 140, which adjust the flow cross section depending on the current applied to the coil. Consequently, an inert gas pressure dependent on the current intensity is supplied to the respective outlet pressure regulator 44, 72, via which the medium pressure can be regulated.

[0059] Measuring systems constructed in this way provide very precise measured values ​​over a wide range of pressures and flows. These values ​​are continuously available, even when the load must be tested under exceptional conditions, such as at very high or very low temperatures, which could damage the electronics of the measuring cell or supply unit. The measuring system is suitable for measuring gases and liquids and achieves high measuring accuracy even at very low flow rates. The modular design allows for very precise adaptation to customer requirements, as the cells can be positioned differently relative to each other and various additional units can be connected.

[0060] Of course, further design extensions not described in the embodiments are also conceivable. For example, a temperature control unit could still be installed, the valve could be designed as an electric or hydraulic valve, or other flow meters could be used. Those skilled in the art will readily appreciate further variations within the scope of the main claims.

Claims

1. A measuring system for measuring a flow rate at a load (10), said measuring system having a supply unit (12) having a medium connection (18) and a purge gas connection (20) and / or an inert gas or compressed air connection (22), a measuring unit (14) having at least one flow meter (50) and at least one controllable valve (46, 60, 70), the measuring unit (14) being fluidically connected to the supply unit (12) for selectively introducing a flow of a measuring medium or an inert gas and capable of measuring a flow rate via the measuring unit (14), An outlet pressure regulating unit (16), the measuring unit (14) can be connected to the load (10) via the outlet pressure regulating unit, and the outlet pressure regulating unit (16) has at least one outlet pressure sensor (86) and at least one controllable valve (80, 116, 124), a main line (26) which is connected to the medium interface (18) and through which the supply unit (12), the measuring unit (14) and the outlet pressure regulating unit (16) are fluidically connected, It is characterized by: The supply unit (12) and the measuring unit (14) are arranged in a housing (74), and the outlet pressure regulating unit (16) is arranged in a separate housing (90), wherein the controllable valves (46, 60, 70, 80, 116, 124) of the measuring unit (14) and the outlet pressure regulating unit (16) and the outlet pressure sensor (86) of the outlet pressure regulating unit (16) are connected to the supply unit (12) via a line (88).

2. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The outlet pressure regulating unit (16) is arranged at a distance from the measuring unit (14) and is directly connected to the measuring unit (14) only via a main line (26).

3. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The outlet pressure regulating unit (16) is arranged at a distance from the supply unit (12) and is connected to the supply unit (12) only via a main line (26), a pneumatic control line (88) and at least one electrical line, wherein the electrical line connects an outlet pressure sensor (86) to a control unit (24) of the supply unit (12).

4. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The outlet pressure regulating unit (16) is arranged together with the load (10) in the climate chamber, and the measuring unit (14) and the supply unit (12) are arranged outside the climate chamber.

5. A measuring system for measuring a flow at a load (10) according to claim 3 or 4, It is characterized by: The supply unit (12) has a valve row (134) equipped with a plurality of solenoid valves (136), which are respectively connected to the controllable valves (32, 36, 46, 60, 70, 80, 96, 102, 116, 124) of the supply unit (12), the measuring unit (14) and the outlet pressure regulating unit (16) via pneumatic control lines (88), and the solenoid valves are electrically connected to the control unit (24).

6. A measuring system for measuring a flow rate at a load (10) according to claim 5, It is characterized by: The inert gas or compressed air interface (22) of the supply unit (12) is connected to a valve bank (134) via an inert gas or compressed air line (128), in which an inert gas or air pressure regulator (132) and an inlet pressure sensor (130) are arranged.

7. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The supply unit (12) has a damping element having a controllable valve (32) configured as a first switching valve in a main line (26), and a bypass line (34) through which the controllable valve (32) configured as the first switching valve can be bypassed, and in which a controllable valve (36) configured as a second switching valve and a throttle valve (38) are arranged.

8. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The supply unit (12) has an inlet pressure sensor (30) arranged in the main line (26), as a function of which a first outlet pressure regulator (44) is regulated, the first outlet pressure regulator (44) being arranged in the main line (26) upstream of a flow meter (50) of the measuring unit (14).

9. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The supply unit (12) has a purge gas supply line (92) which leads from a purge gas interface (20) to a main line (26), and in which a controllable valve (96) serving as a first purge gas valve, a first check valve (98) and a purge gas pressure sensor (94) are arranged.

10. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The supply unit (12) has a supply unit purge gas discharge line (100), which branches off from the main line (26) upstream of the measuring unit (14) and is connected to a first purge gas outlet interface (106), wherein a controllable valve (102) serving as a second purge gas valve and a second check valve (104) are arranged in the supply unit purge gas discharge line (100).

11. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The supply unit (12) has a connection interface (40) via which the additional unit can be connected to the main line (26) upstream of the measuring unit (14).

12. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: A second outlet pressure regulator (72), a first Coriolis measuring device (52), and a second Coriolis measuring device (54) are arranged in the main line (26) of the measuring unit (14). The second Coriolis measuring device is arranged downstream of the first Coriolis measuring device (52) in the main line (26) and can be bypassed by a bypass line (56) in which a valve (58) is arranged.

13. A measuring system for measuring a flow rate at a load (10) according to claim 12, It is characterized by: The second outlet pressure regulator (72) is arranged downstream of the two Coriolis measuring devices (52, 54) and can be regulated to a constant setpoint value or according to a setpoint characteristic curve.

14. The measuring system for measuring a flow rate at a load (10) according to claim 12, It is characterized by: The valve (58) in the bypass line (56) opens in a pressure-dependent manner, and the second Coriolis measuring device (54) is designed for a lower maximum flow rate than the first Coriolis measuring device (52).

15. A measuring system for measuring a flow rate at a load (10) according to claim 13 or 14, It is characterized by: A measuring cell pressure sensor (48) is arranged between the first outlet pressure regulator (44) and the first Coriolis measuring device (52).

16. A measuring system for measuring a flow rate at a load (10) according to claim 15, It is characterized by: A first measuring unit purge gas line (108) branches off from the first outlet pressure regulator (44), and a second measuring unit purge gas line (110) branches off from the second outlet pressure regulator (72), the second measuring unit purge gas line (110) being guided to the purge gas outlet interface (106) via a third check valve (112).

17. The measuring system for measuring a flow rate at a load (10) according to claim 15, It is characterized by Downstream of the second Coriolis measuring device (54) and upstream of the second outlet pressure regulator (72), a connection interface (68) is formed, via which the calibration unit can be connected to the main line (26).

18. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: A first outlet pressure regulating unit purge gas line (114) branches off from a main line (26) of the outlet pressure regulating unit (16) upstream of an outlet pressure sensor (86), and a second outlet pressure regulating unit purge gas line (122) branches off downstream or at the same level as the outlet pressure sensor (86). Controllable valves (116, 124) configured as on / off valves are respectively provided in the first outlet pressure regulating unit purge gas line and the second outlet pressure regulating unit purge gas line and are guided to a second purge gas outlet interface (120) via check valves (118, 126).

19. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: A temperature sensor (84) is provided in the main line (26) of the outlet pressure regulating unit (16).

20. The measuring system for measuring a flow rate at a load (10) according to claim 1, It is characterized by: The outlet pressure regulating unit (16) has a connecting interface (82) through which the line volume simulation unit can be connected to the main line (26).

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