Method for controlling fluid flow and biological analysis device

Abstract

The invention relates to a method for controlling a mass flow of a fluid in a biological analysis device (1) and a biological analysis device (1), the biological analysis device (1) comprising a control unit (2) and a fluid flow generating device (3) for generating a fluid flow (F) of the fluid, the method comprising the following steps: inputting a desired volumetric flow setpoint of the fluid flow into the control unit (2); automatically calculating a mass flow setpoint of the fluid flow (F) corresponding to the volumetric flow setpoint by means of the control unit (2); measuring an actual mass flow of the fluid flow (F) by means of a mass flow sensor (4) of the bioanalysis device (1); and regulating the flow generation device (3) by the control unit (2) to bring the actual mass flow close to the mass flow setpoint.

Description

Technical Field

[0001] The present invention relates to a method for controlling the mass flow of a fluid in a bioanalytical device, and to a bioanalytical device for carrying out the method according to the invention. The invention can be used in the field of particle collection and sampling and all kinds of particle analysis. In particular, the invention relates to bioanalytical devices, such as instruments for characterizing the gas or air quality required in the food and beverage industry or in clean environments such as clean rooms and manufacturing environments. An example of such a clean environment is a production line in the pharmaceutical industry, where the air quality must be constantly monitored and tested. Background Art

[0002] A bioanalytical device in the form of a microbial air sampler is a specialized type of air monitoring device that focuses on the collection of particles on a microbial growth medium (usually in the form of a petri dish filled with agar medium or similar.) After the particles are collected from the gas / air on such a plate of media, the plate is incubated for several hours or even days to allow the collected live microorganisms to grow into visible colonies for subsequent counting and analysis.

[0003] Often, regulations limit the number and types of microorganisms that can be tolerated in a particular environment, and if these limits are exceeded, drug production batches are discarded. Therefore, air quality analysis with a focus on microbial contamination is a key quality indicator for product release in several large industries.

[0004] High measurement accuracy can only be achieved when high system performance (stable air flow during measurement and accurate quantification of sampled gas volume) is combined with well-trained personnel and appropriate cleaning and handling procedures.

[0005] Air sampling devices are often combined with miniature sensors for gas flow. These sensors usually measure mass flow rather than volume flow, and depending on environmental conditions (absolute pressure, temperature, humidity level), the ratio between air / gas mass and volume can vary significantly. Therefore, when it is necessary to determine the exact gas volume flow rate, it is necessary to combine one or more of the above parameters to obtain high accuracy.

[0006] Any particle collector and / or counter for gaseous media relies on two key functions, quantifying the particulate matter and quantifying the sampled gas volume in which the particulate matter is present.

[0007] US2015355000A1 discloses a method for controlling the volumetric flow rate of a fluid flow through a particle impactor system, the method comprising the following steps: passing the fluid flow through a plurality of air inlet holes of a sampling head of the particle impactor system; determining the flow rate of the fluid; determining the ambient pressure; determining the volumetric flow rate as a function of the flow rate of the fluid and the ambient pressure; and using the volumetric flow rate to control the fluid flow in the particle impactor system.

[0008] However, controlling the volume flow usually requires a continuous calculation of this quantity from, for example, the mass flow, which can result in a disadvantageous constant load on the computing unit of the device. Summary of the invention

[0009] Therefore, based on the above, the problem to be solved by the present invention is to provide a method for controlling fluid flow in a biological analysis device, especially in a microbial air sampler, which method has improved the above difficulties.

[0010] This problem is solved by a method having the features of claim 1 and a bioanalysis device having the features of claim 15 .

[0011] Preferred embodiments of these aspects of the invention are set out in the respective dependent claims and are also described below.

[0012] According to claim 1, a method for controlling a mass flow of a fluid in a bioanalysis device is disclosed, the bioanalysis device comprising a control unit and a fluid flow generating device for generating a fluid flow of the fluid, wherein the method comprises the following steps:

[0013] a) inputting a desired volume flow set point for the fluid flow into the control unit (and in particular generating the fluid flow by means of the fluid flow generating device),

[0014] b) automatically calculating, by means of a control unit, a mass flow set point for the fluid flow, which mass flow set point corresponds to said volume flow set point,

[0015] c) measuring the actual mass flow of the fluid flow using a mass flow sensor of the bioanalyzer, and

[0016] d) The flow generating device is adjusted by the control unit so that the actual mass flow approaches the mass flow set point.

[0017] In particular, sensors for mass flow of fluids, in particular gases, either directly or in a bypass configuration to measure the pressure difference across the bypass, are also available in miniaturized form, allowing even cost-critical applications. In particular, the mass flow sensor is a thermal mass flow sensor.

[0018] The present invention allows the mass flow sampled by the bioanalysis device to be accurately controlled using at least one mass flow sensor and in particular one or more sensors for at least two parameters of temperature, pressure and relative humidity of the sampled fluid. Preferably, the sampled fluid is air which may be contaminated with pollutants / impurities such as particulate matter, bacteria etc.

[0019] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0020] e) Repeating steps c) and / or d).

[0021] According to a preferred embodiment, step d) may be performed at longer intervals (ie at a slower rate) than the intervals at which step c) is performed.

[0022] Furthermore, according to a preferred embodiment of the method, step b) is performed only once before starting the fluid flow using the fluid flow generating device.

[0023] According to another embodiment, step d) further comprises automatically recalculating the mass flow setpoint of the fluid flow corresponding to the volume flow setpoint at predetermined intervals. In a preferred embodiment, the predetermined interval is longer than the interval at which step c) is performed, ie the interval at which the control of the fluid flow generating means takes place.

[0024] According to another embodiment, step b) also includes: measuring the pressure of the fluid and / or the temperature of the fluid and / or the relative humidity of the fluid, and using the measured pressure of the fluid and / or the measured temperature of the fluid and / or the measured relative humidity of the fluid to automatically determine the mass flow set point of the fluid flow corresponding to the volume flow set point.

[0025] According to another preferred embodiment, step b) further comprises measuring the pressure, temperature and relative humidity of the fluid (e.g. by using the sensors or a single sensor arrangement described further below), and determining the relative humidity of the fluid p fluid The actual density, and the volume flow set point based on and the actual density, in particular to determine the mass flow set point of the fluid flow according to the formula

[0026]

[0027] In another preferred embodiment, automatic recalculation of the mass flow set point is performed only if the temperature has changed by at least a predetermined amount and / or if the pressure has changed by at least a predetermined amount and / or if the relative humidity has changed by at least a predetermined amount.

[0028] In this way, the corresponding embodiments of the invention allow to reduce the computational load on the control unit in an advantageous manner, i.e., for example, by assuming that the temperature, pressure and / or relative humidity vary rather slowly, so that the recalculation of the mass flow set point can be performed at longer intervals than the loop controlling the fluid flow. Alternatively, the recalculation of the mass flow set point can be performed only when the temperature, pressure and / or relative humidity vary, which is considered to be important. Furthermore, if the variation of the ambient conditions is considered to be negligible or unimportant, taking into account the duration of the flow and the required accuracy, the mass flow set point can even be initially calculated only once, which further reduces the computational load.

[0029] Furthermore, according to a preferred embodiment, the pressure is measured using a pressure sensor arranged in a flow channel of the bio-analysis device. Alternatively, the pressure sensor may be arranged to measure the pressure of the surrounding environment of the bio-analysis device.

[0030] Likewise, in a preferred embodiment, the temperature is measured using a temperature sensor arranged in a flow channel of the bio-analysis device.Alternatively, the temperature sensor may be arranged to measure the temperature of the surrounding environment of the bio-analysis device.

[0031] Furthermore, in a preferred embodiment, the relative humidity is measured using a relative humidity sensor arranged in the flow channel of the bioanalysis device. Alternatively, in a preferred alternative embodiment, the relative humidity sensor may also be arranged to measure the relative humidity of the surrounding environment of the bioanalysis device.

[0032] Regarding the corresponding sensors, several or all of the pressure sensor, temperature sensor, and relative humidity sensor can be integrated into a single sensor device according to a preferred embodiment of the present invention. Then, the single sensor device is configured to measure the corresponding quantities, i.e., several or all of the pressure, temperature, and relative humidity.

[0033] In particular, according to an embodiment, the flow channel may include a constriction for generating a pressure drop in the flow channel, ie across the constriction.

[0034] According to a further embodiment of the method according to the invention, a (eg thermal) mass flow sensor comprises a conduit for passing a partial flow of the fluid flow through the conduit of the mass flow sensor, the conduit extending between a first port and a second port.

[0035] According to a preferred embodiment, the first port is in flow connection with the flow channel.

[0036] According to a preferred embodiment, the second port is in flow connection with the flow channel.Alternatively, in a preferred embodiment, the second port preferably opens the flow channel of the bio-analysis device outwardly to the surroundings of the bio-analysis device.

[0037] Furthermore, according to a preferred embodiment, the first port is flow-connected to a location upstream of said constriction of the flow channel.Furthermore, according to a preferred embodiment, the second port is flow-connected to a location at or downstream of the constriction.

[0038] In a preferred alternative embodiment, the mass flow sensor is a thermal mass flow sensor which is not placed in the bypass. Here, in particular, this also means that no constriction is required when the fluid (e.g. air) passes through the mass flow sensor anyway and thereby generates a temperature offset between the temperature sensing elements of the flow sensor, which are located upstream and downstream of the heating element of the thermal mass flow sensor. Alternatively, the heating element of the thermal mass flow sensor is kept at a desired temperature and the current required to keep the heating element at the desired temperature is determined. The greater the flow, the more heat is transferred from the heating element and the more current is needed to heat it to keep the temperature constant.

[0039] Furthermore, according to a preferred embodiment of the method, the fluid flow is passed through a filter of the bioanalysis device.

[0040] Furthermore, in a preferred embodiment of the method, it is automatically detected whether a filter is already arranged in the bioanalytical device. This can be achieved by exploiting the fact that the filter will form a flow resistance to the fluid flow, which can be detected by a pressure reduction of the fluid downstream of the filter and / or an increase in the pressure of the fluid upstream of the filter compared to a reference value of the pressure. Therefore, in particular, in an embodiment, the method comprises the further step of detecting whether a filter (through which the fluid flow will pass) is present in the bioanalytical device, which further step is performed by measuring the pressure at least upstream or downstream of the position of the filter in the fluid flow and comparing the measured pressure with at least one reference value of the pressure.

[0041] According to a further preferred embodiment, a state of a filter is detected, said state being indicative of the loading of said filter with respect to impurities present in said fluid flow.

[0042] According to another embodiment, it is automatically detected whether the filter is loaded with impurities to a certain extent, so that it is necessary or beneficial to replace the filter in particular. This can also be detected by measuring the pressure, which will change due to the filter forming a greater flow resistance when loaded with impurities.

[0043] According to another embodiment, the user will be automatically notified by the bioanalysis device in the event that it is determined that the filter is loaded to a certain extent with impurities and therefore requires replacement or cleaning.

[0044] Furthermore, according to yet another embodiment, when the filter needs to be replaced, the user is advised to order a replacement filter through the bioanalysis device.

[0045] Furthermore, according to a preferred embodiment, the bioanalysis device is configured to provide a link to a URL of a provider of replacement filters for ordering them.

[0046] Furthermore, according to yet another embodiment, an increase in flow resistance in the flow channel upstream of the location where the pressure is measured is detected. Preferably, in an embodiment, a user is alerted that the inlet may be blocked (e.g. by a lid placed on a lid of the bioanalysis device, the lid comprising the inlet).

[0047] According to another aspect of the present invention, a bioanalytical device (in particular a microbial air sampler) is disclosed, in particular for carrying out the method according to the present invention, the bioanalytical device comprising:

[0048] - a housing which surrounds the flow channel,

[0049] - a fluid flow generating device for generating a fluid flow in the flow channel,

[0050] - a control unit for controlling the fluid flow generating device,

[0051] - a mass flow sensor configured to measure the actual mass flow of the fluid flow

[0052] The control unit is configured to receive as input a desired volume flow set point of the fluid flow, calculate a mass flow set point of the fluid flow corresponding to the volume flow set point, and adjust the flow generating device to make the actual mass flow close to the mass flow set point.

[0053] According to a preferred embodiment of the bio-analysis device, the bio-analysis device comprises a pressure sensor configured to measure the pressure of the fluid.

[0054] Furthermore, according to a preferred embodiment of the bio-analysis device, the bio-analysis device comprises a temperature sensor configured to measure the temperature of the fluid.

[0055] Furthermore, according to a preferred embodiment of the bio-analysis device, the bio-analysis device comprises a relative humidity sensor configured to measure the relative humidity of the fluid.

[0056] According to a preferred embodiment, a pressure sensor is arranged in the flow channel or outside the flow channel to measure said pressure in the surroundings of the housing of the bioanalysis device.

[0057] Furthermore, according to a preferred embodiment, a temperature sensor is arranged in the flow channel or outside the flow channel to measure said temperature in the surroundings of the housing of the bioanalysis device.

[0058] Furthermore, according to a preferred embodiment, a relative humidity sensor is arranged in the flow channel or outside the flow channel to measure the relative humidity in the surrounding environment of the housing of the bioanalysis device.

[0059] In a preferred embodiment of the bioanalysis device, several or all of the pressure sensors, temperature sensors, and relative humidity sensors are integrated into a single sensor device, which is configured to measure the corresponding quantities, namely several or all of the pressure, temperature, and relative humidity.

[0060] Furthermore, in a preferred embodiment, the flow channel comprises a constriction to generate a pressure drop across the constriction.

[0061] Furthermore, in a preferred embodiment of the bioanalytical device, the mass flow sensor comprises a conduit for passing a partial flow of the fluid flow through the conduit of the mass flow sensor, the conduit having a first port (e.g. an inlet) in flow connection with the flow channel of the bioanalytical device and a second port (e.g. an outlet), wherein the second port is in flow connection with the flow channel (particularly near a constriction or downstream of said constriction) or opens outside the flow channel to the surroundings of the bioanalytical device. In an alternative embodiment, the mass flow sensor is a thermal mass flow sensor, which is in thermal contact with the fluid flow in the flow channel to measure the mass flow of the latter, as described above.

[0062] Furthermore, in a preferred embodiment of the bioanalysis device the control unit is configured to use the measured pressure of the fluid and / or the measured temperature of the fluid and / or the measured relative humidity of the fluid to determine a mass flow set point of the fluid flow corresponding to said volume flow set point.

[0063] According to a preferred embodiment, the control unit is configured to determine the actual density of the fluid (e.g. air) using the measured pressure, the measured temperature and the measured relative humidity of the fluid and to set the volume flow setpoint based on said volume flow setpoint. and the actual density ρ fluid , in particular to determine the mass flow set point of a fluid flow according to the formula

[0064]

[0065] Furthermore, according to an embodiment of the bioanalysis device, the housing is configured to accommodate a carrier carrying the wet medium in an internal space of the housing such that the flow channel extends along the wet medium.

[0066] In a preferred embodiment of the bioanalytical device, the moist medium is a moist growth medium for promoting the growth of microorganisms, wherein the bioanalytical device is a microbial air sampler.

[0067] Furthermore, in a preferred embodiment, the flow channel of the bioanalysis device extends from an inlet of the housing to an outlet of the housing.

[0068] In a preferred embodiment of the bioanalytical device, the fluid flow generating device is also configured to provide a fluid flow through the flow channel so that when the carrier is arranged in the internal space, the fluid flow passes through the wet medium carried by the carrier, wherein the bioanalytical device is configured to allow the fluid flow to pass along the wet medium when the carrier is arranged in the internal space, so that the particulate matter contained in the fluid flow settles on the wet medium (e.g., the growth medium).

[0069] According to a further preferred embodiment of the bio-analysis device, the fluid flow generating means for generating said fluid flow is a fan comprising a rotating arrangement of blades, wherein adjusting the fluid flow generating means comprises adjusting a rotational speed of the arrangement of blades.

[0070] Furthermore, according to a preferred embodiment of the bioanalysis device, the housing comprises an openable lid to allow access to the interior space, such that a moist medium can be accommodated in the interior space when the lid is open and is enclosed by the housing when the lid is closed, wherein the inlet is particularly formed in the lid.

[0071] Furthermore, in a preferred embodiment, the bioanalytical device (e.g., a microbial air sampler) comprises a filter, which is arranged upstream of said outlet of the housing, in particular downstream of the mass flow sensor and the sensor for measuring temperature and / or pressure and / or relative humidity. As described above, the presence and / or loading of the filter can be detected by the bioanalytical device.

[0072] In particular, the bioanalysis device according to the present invention can, in a preferred embodiment, be further characterized by the features and embodiments described above in conjunction with the method according to the present invention. In particular, the bioanalysis device is configured to perform the method according to the present invention.

[0073] The invention proves to be advantageous because the calculation of the desired mass flow set point can be based on absolute pressure and temperature and optionally relative humidity. Furthermore, the method according to the invention, i.e. achieving a desired volume flow by adjusting its corresponding target mass flow, significantly reduces the computational effort.

[0074] Additionally, while fluid flow is ongoing, the pressure is compared to a threshold value (eg, a characteristic value for the instrument type or the pressure present during instrument calibration) to allow one to make predictions about the status of the instrument.

[0075] Furthermore, advantageously, since the fluid flow in the bioanalysis device can be effectively controlled, increased or decreased aerodynamic resistance in the system (eg caused by aging and partial clogging of the integrated filter) can be compensated.

[0076] Furthermore, the invention in principle allows controlling mass and volume flows of a bioanalytical device.

[0077] Furthermore, the invention allows achieving higher accuracy over a wide temperature and / or humidity range without significantly increasing the cost and compactness of the solution (temperature and humidity sensors are affordable and require only a small space on a printed circuit board).

[0078] The invention also allows a simplified implementation of the control logic (compared to a continuous conversion of mass flow into volume flow). Regardless of whether mass flow or volume flow is operated, in both cases the control loop controls the mass flow.

[0079] According to yet another aspect of the present invention, a method for detecting a filter and / or the state of a filter in a bioanalysis device is disclosed, the bioanalysis device comprising a flow generation device for generating a fluid flow in a flow channel comprised by the bioanalysis device, the method comprising the following steps: generating a fluid flow in the flow channel, and automatically detecting the presence or absence of the filter of the bioanalysis device in the flow channel and / or automatically detecting the state of the filter, the state indicating the load of the filter on impurities present in the fluid flow.

[0080] According to another aspect of the present invention, a bioanalysis device is disclosed, in particular for performing the method for detecting the filter and / or state, the bioanalysis device comprising:

[0081] - a housing which surrounds the flow channel,

[0082] - a fluid flow generating device for generating a fluid flow in the flow channel,

[0083] a filter configured to be positioned in the flow channel (in particular such that a fluid flow can pass through the filter),

[0084] Therein, the bioanalysis device is configured to automatically detect the presence or absence of a filter in the flow channel and / or automatically detect a status of the filter, the status being indicative of the loading of the filter with respect to impurities present in the fluid flow.

[0085] Preferably, the bioanalysis device comprises at least one pressure sensor located upstream or downstream in the flow channel, configured to receive the filter, to detect said presence / absence and / or state (see also above). BRIEF DESCRIPTION OF THE DRAWINGS

[0086] In the following, embodiments of the present invention and other features, advantages and other aspects of the present invention will be described with reference to the accompanying drawings, in which

[0087] Figure 1 A control loop according to an embodiment of the method / bioanalysis device according to the present invention is shown,

[0088] Figure 2 A perspective view showing an embodiment of a biological analysis device in the form of a microbial air sampler,

[0089] Figure 3 Shows Figure 2 A schematic cross-sectional view of a microbial air sampler, and

[0090] Figure 4 Different embodiments of the bioanalysis device are shown with respect to the configuration of the flow channel and mass flow sensors as well as temperature, pressure and relative humidity sensors. DETAILED DESCRIPTION

[0091] for Figure 1 A block diagram of a preferred control loop 100 that can be used in a method / bioanalytical device 1 according to the present invention is shown. Importantly, the present invention is not intended to directly control the volume flow through the bioanalytical device 1 (using the current temperature, pressure and humidity sensor readings to convert the mass flow into a volume flow and adjust the fan to achieve a target volume flow rate), but rather to calculate a target mass flow (called the mass flow set point) that matches the volume flow set point under the current temperature T, pressure P and relative humidity RH conditions. The advantage of this approach is that the same process can always be used, whether adjusting to achieve a constant mass flow or volume flow, and only the mass flow set point needs to be recalculated according to the environmental conditions.

[0092] Preferably, the present invention uses a thermal mass flow sensor 4 as well as a sensor 5 to measure the temperature T, the absolute pressure P and optionally the relative humidity RH of the sampled air. Since all these sensors 5 are available in miniaturized form, the method can be implemented not only in large-scale equipment, but is also suitable for portable applications ( Figure 1 ).

[0093] like Figure 2 and Figure 3As shown, the bioanalysis device 1 can be, for example, a portable microbial air sampler (as an example of a particle monitoring system), which draws a fluid (here a gas, such as air) through an inlet 16 formed by a perforated cover 14 at the top of the housing 13 of the bioanalysis device 1. The fluid flow F flows through the integrated fluid flow generating device 3 (such as a fan), the flow channel 10 forming the sensing path, and is finally released via an outlet 17 (here on the bottom side of the sampling head). In particular, a replaceable filter 12 can be placed upstream of the outlet 17, wherein the bioanalysis device 1 can be configured to automatically detect the presence or absence of the filter 12 and / or automatically detect the state of the filter 12, which indicates the load of the filter 12 to impurities present in the fluid flow F. In particular, the bioanalysis device 1 can prompt the user to arrange the filter 12 in the flow channel 10, or to replace / clean the filter when necessary.

[0094] In particular, the housing 13 is configured to accommodate a carrier 15 carrying a wet medium so that the flow channel 10 extends along the wet medium. In particular, the wet medium is a wet growth medium for promoting the growth of microorganisms. The fluid flow generating device 3 is configured to pass the fluid flow F through the flow channel 10 so that the fluid flow F passes through the wet medium carried by the carrier 15 so that the particulate matter contained in the fluid flow F settles on the wet medium (e.g., the growth medium).

[0095] The flow channel / sensing path 10 preferably includes a thermal flow sensor 4 for measuring the pressure drop along a specific portion of the flow channel 10 (such portions may include constrictions 11, venturi structures, orifices, etc.), or the pressure drop between a specific point of the flow channel 10 and the surrounding environment P ambient The pressure drop between , and the sensor 5 for measuring the parameters: temperature T, absolute pressure P and relative humidity RH. The latter parameter can be measured by a single sensor device 5 in which the function of measuring said parameter is integrated.

[0096] Sensors 5 for P, T, RH allow the current air density to be determined. The mass flow sensor 4 determines the actual mass flow in the bioanalysis device 1. The requested volume flow (i.e., volume flow set point) and the actual fluid (e.g., air) density can be used to calculate the volume flow equivalent mass flow set point. The fluid flow generating device (e.g., fan) 3 is then controlled so that the mass flow sensor signal matches the desired mass flow set point.

[0097] also, Figure 4Possible embodiments of mass flow control with different sensor configurations (ac) and exemplary measurement workflows (d) are shown. Note that the absence of one or more sensor elements in the P, T, RH sensor 5 is feasible. In this case, a simplified equation for the relationship between mass flow and volume flow can be used (see below), or a predefined approximation of the missing sensor value can be used (e.g., a fixed value of 40% RH is substituted for the actual humidity from the RH sensor).

[0098] according to Figure 4 a. The thermal mass flow sensor 4 is used in a bypass configuration to measure the pressure drop along the flow channel 10. Here, the mass flow sensor 4 includes a conduit 40 having a first port 41 (e.g., an inlet) that is flow-connected to the flow channel 10 and a second port 42 (e.g., an outlet) that is also flow-connected to the flow channel 10. The pressure drop can be artificially enlarged using a flow constriction 11, wherein the inlet 41 of the conduit 40 can be arranged upstream of the constriction 11, and the outlet 42 of the conduit 40 of the mass flow sensor can be positioned near the constriction 11 or downstream of the conduit 40. The measurement points of temperature T, pressure P, and relative humidity RH are preferably located directly before, after, or in the flow channel 10 parallel to the mass flow sensor 4. As Figure 4 As shown in FIG. 1 , the sensor 5 can also be configured to measure T, P, and RH in the surrounding environment of the bioanalysis device 1. This also applies to Figure 4 The configuration shown in bc. In particular, with Figure 4 On the contrary, Figure 4 c shows a configuration in which the thermal mass flow sensor 4 is not placed in a bypass configuration, but is in thermal contact with the fluid in the flow channel 10, wherein the fluid in the flow channel 10 (e.g. air) passes through the mass flow sensor 4, thereby generating a temperature change between the temperature sensing elements (not shown) of the flow sensor 4, which are located above and downstream of the heating element (not shown) of the thermal mass flow sensor 4 (see also above). In addition, Figure 4 On the contrary, Figure 4 b shows a configuration in which the outlet 42 of the conduit 42 of the mass flow sensor is directed toward the surrounding environment P of the bioanalysis device 1 ambient open.

[0099] In the following, the physical background of the invention is described, which allows the control unit to estimate the mass flow set point based on a given volume flow set point. It should be noted that different theories and corresponding equations can be used to calculate the quantities discussed below. In particular, other equations can be used instead of the Magnus equation. The constants used in the corresponding equations can have a precision suitable for the desired level of accuracy.

[0100] When regulating to a fixed mass flow, the thermal mass flow sensor is used alone. When regulating to a volumetric flow rate set point, the corresponding mass flow rate set point is determined by using the parameters temperature, pressure and humidity in order to calculate the density of the fluid (in the following, air as an example) under these conditions:

[0101]

[0102] where ρ air is the density of the air, P is the absolute pressure, T is the temperature in Kelvin, and R f is the gas constant. The gas constant itself depends on the ambient conditions and can be calculated using the following equation:

[0103]

[0104] Here, R s is the gas constant for dry air, And R d is the gas constant for water vapor, Humidity sensor determines relative humidity Absolute ambient pressure P and saturated vapor pressure P sat This should also be taken into consideration.

[0105] Using the Magnus equation for the horizontal plane as an approximation, the current temperature T act The saturated vapor pressure can be calculated using the following equation:

[0106]

[0107] Taking all of this into account, the density of air depends only on the temperature, absolute pressure, and relative humidity of the sampled air and follows the following equation:

[0108]

[0109] When the volume flow rate of a fluid (such as air) can be easily converted to the mass flow rate of fluid / air when given

[0110]

[0111] However, it is common to refer to the normalized or standardized volume flow Rather than mass flow To convert between these units, information on standard conditions (T, P, relH) and the corresponding normative or standard density ρ for conversion is required. air,norm :

[0112]

[0113] When measuring gases other than air, the mass flow rate is calculated using the gas-dependent factor The gas correlation factor itself can be a function of the current sensor signal:

[0114]

[0115] When air is the fluid / gas of interest and lower accuracy is required, the relative humidity of air can be assumed to be 0%. The gas constant is then equal to the ideal gas constant:

[0116] R f =R s

[0117] In this case, the volume flow is related to the mass flow (normalized volume flow) The relationship between them is:

[0118]

[0119] which can be rearranged, for example, to calculate a mass flow target based on a desired volume flow:

[0120]

Claims

1. A method for controlling the mass flow of a fluid in a bioanalytical device (1), the bioanalytical device comprising a control unit (2) and a fluid flow generating device (3) for generating a fluid flow (F) of the fluid, the method comprising the following steps: a) inputting a desired volume flow set point for the fluid flow into the control unit (2), b) automatically calculating, by means of the control unit (2), a mass flow set point of the fluid flow (F) corresponding to the volume flow set point, c) measuring the actual mass flow of the fluid flow (F) using a mass flow sensor (4) of the bioanalysis device (1), and d) regulating the flow generating device (3) by the control unit (2) so that the actual mass flow approaches the mass flow set point.

2. The method according to claim 1, wherein: The method further comprises the following steps: e) Repeating steps c) and / or d).

3. The method according to claim 1 or 2, wherein: Step b) is performed only once, before starting the fluid flow (F) using the fluid flow generating device (3).

4. A method according to any one of the preceding claims, wherein: Step d) further comprises automatically recalculating at predetermined intervals a mass flow set point of said fluid flow (F) corresponding to said volume flow set point.

5. The method according to claim 4, wherein: The predetermined interval is longer than the interval for performing steps c) and / or d).

6. A method according to any one of the preceding claims, wherein: Step b) also includes: measuring the pressure (P) of the fluid and / or the temperature (T) of the fluid and / or the relative humidity (RH) of the fluid, and using the measured pressure (P) of the fluid and / or the measured temperature (T) of the fluid and / or the measured relative humidity (RH) of the fluid to automatically determine the mass flow set point of the fluid flow corresponding to the volume flow set point.

7. The method according to claims 4 and 6, wherein: Automatic recalculation of the mass flow set point is performed only if the temperature (T) has changed by at least a predetermined amount and / or if the pressure (P) has changed by at least a predetermined amount and / or if the relative humidity (RH) has changed by at least a predetermined amount.

8. The method according to claim 6 or 7, wherein the pressure (P) is measured by a pressure sensor (5) arranged in the flow channel (10) of the bioanalysis device (1), or by a pressure sensor (5) arranged in the surrounding environment (P ambient ) in a flow-connected position, or with a pressure sensor (5) located in the surrounding environment (P ambient ) is measured by the pressure sensor (5).

9. The method according to any one of claims 6 to 8, wherein the temperature (T) is measured by a temperature sensor (5) arranged in the flow channel (10) of the bioanalysis device (1), or by a temperature sensor (5) arranged in an environment (P ambient ) in the flow connection, or with a temperature sensor (5) in the surrounding environment (P ambient ) is measured by the temperature sensor (5) in ).

10. The method according to any one of claims 6 to 9, wherein: The relative humidity (RH) is measured by a relative humidity sensor (5) arranged in a flow channel (10) of the bioanalysis device (1), or by a relative humidity sensor (5) arranged in an environment (P ambient ) fluid connection position, or using the surrounding environment (P ambient ) is measured by the relative humidity sensor (5).

11. The method according to any one of claims 8 to 10, wherein: Several or all of the pressure sensor, the temperature sensor, and the relative humidity sensor are integrated into a single sensor device (5).

12. A method according to any one of the preceding claims, wherein: The mass flow sensor (5) comprises a conduit (40) for passing a portion of the fluid flow (F) through the conduit (40) of the mass flow sensor (4), the conduit (40) having a first port (41) and a second port (42) connected in flow connection with the flow channel (10) of the bioanalytical device (1), wherein the second port (42) is connected in flow connection with the flow channel (10) or opens the flow channel (10) outwardly to the surrounding environment (P) of the bioanalytical device (1). ambient ).

13. A method according to any one of the preceding claims, wherein: The mass flow sensor (4) is a thermal mass flow sensor, comprising at least two temperature sensing elements and a heating element located between the at least two temperature sensing elements, wherein the temperature sensing elements and the heating element are configured to be in thermal contact with the fluid flow (F) in the flow channel (10).

14. Method according to any of the preceding claims, wherein the presence or absence of a filter (12) of the bioanalysis device (1) is detected automatically and / or wherein the state of the filter (12) is detected automatically, the state being indicative of the load of the filter (12) on impurities present in the fluid flow (F).

15. A bioanalytical device, in particular for carrying out the method according to any one of the preceding claims, comprising: - a housing (13) which surrounds the flow channel (10), - a fluid flow generating device (3) for generating a fluid flow (F) in said flow channel (10), - a control unit (2) for controlling the fluid flow generating device (3), a mass flow sensor (4) configured to measure the actual mass flow of said fluid flow (F), The control unit (2) is configured to receive a desired volume flow set point of the fluid flow as input, calculate a mass flow set point of the fluid flow (F) corresponding to the volume flow set point, and adjust the flow generating device (3) so that the actual mass flow approaches the mass flow set point.

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