WO2024068678A1 - Procédé et dispositif bioanalytique pour réguler un débit de fluide - Google Patents

Procédé et dispositif bioanalytique pour réguler un débit de fluide Download PDF

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Publication number
WO2024068678A1
WO2024068678A1 PCT/EP2023/076617 EP2023076617W WO2024068678A1 WO 2024068678 A1 WO2024068678 A1 WO 2024068678A1 EP 2023076617 W EP2023076617 W EP 2023076617W WO 2024068678 A1 WO2024068678 A1 WO 2024068678A1
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WO
WIPO (PCT)
Prior art keywords
flow
fluid
sensor
mass flow
set point
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PCT/EP2023/076617
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English (en)
Inventor
Lucas ARMBRECHT
Markus Wiget
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Mbv Ag
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Filing date
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Publication of WO2024068678A1 publication Critical patent/WO2024068678A1/fr

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Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D7/00—Control of flow
    • G05D7/06—Control of flow characterised by the use of electric means
    • G05D7/0617—Control of flow characterised by the use of electric means specially adapted for fluid materials
    • G05D7/0629—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means
    • G05D7/0676—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means by action on flow sources
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G01N1/2205—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling with filters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2273—Atmospheric sampling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/24—Suction devices

Definitions

  • the present invention relates to a method for controlling a mass flow of a fluid in a bioanalytical device as well as to a bioanalytical device for conducting the method according to the present invention.
  • the present invention can be used in the field of particle collection and sampling as well as analysis of particles of all kinds. Especially, it is related to bioanalytical devices such as e.g. instruments for characterization of gas or air quality as necessary in food and beverage industries or clean environments such as cleanrooms and manufacturing environments. Examples for such clean environments are production lines in the pharmaceutical industries, where air quality has to be constantly monitored and tested.
  • bioanalytical devices such as e.g. instruments for characterization of gas or air quality as necessary in food and beverage industries or clean environments such as cleanrooms and manufacturing environments. Examples for such clean environments are production lines in the pharmaceutical industries, where air quality has to be constantly monitored and tested.
  • Bioanalytical devices in form of microbial air samplers are a specific type of air monitoring devices that focus on the collection of particles on a microbial growth medium - usually in form of a petri dish filled with agar media or similar. After collection of particles from the gas/air on such a medium plate, the plate is incubated for several hours or even days in order to let collected living microorganisms grow into visible colonies for subsequent counting and analysis.
  • High measurement precision can only be achieved when high system performance (stable air flow during the measurement and accurate quantification of the sampled gas volume) come together with well-trained personnel as well as appropriate cleaning and handling procedures.
  • Air sampling devices often incorporate miniature sensors for gas flow. These sensors typically measure mass flow but not volumetric flow and depend on ambient conditions (absolute pressure, temperature, humidity level), the ratio between air/gas mass and volume can change significantly. Hence, when the determination of accurate gas volume flow rates is required one or more of the afore-mentioned parameters need to be incorporated for high accuracy.
  • Any particle collector and/or counter for gaseous media relies on two critical functions, namely quantifying the particulate matter, and quantifying the sampled gas volume in which the particulate matter has been present.
  • US2015355000A1 discloses a method of controlling a volumetric flow rate of a fluid flow through a particle impactor system, the method comprising the steps of: letting said fluid flow through a plurality of intake apertures of a sampling head of said particle impactor system; determining a flow rate of said fluid; determining ambient pressure; determining said volumetric flow rate as a function of said flow rate of said fluid and said ambient pressure; and controlling the fluid flow in said particle impactor system using said volumetric flow rate.
  • controlling the volume flow usually requires to continuously compute this quantity from, e.g., a mass flow, thus creating a disadvantageous constant load onto the computing unit of the device.
  • the problem to be solved by the present invention is to provide a method for controlling a fluid flow in a bioanalytical device, particularly in a microbial air sampler, that is improved regarding the above-stated difficulty.
  • a method for controlling a mass flow of a fluid in a bioanalytical device comprising a control unit and a fluid flow generating device for generating a fluid flow of the fluid, wherein the method comprising the steps of: a) inputting a desired volume flow set point of the fluid flow into the control unit (and particularly generating the fluid flow by means of the fluid flow generating device), b) automatically calculating a mass flow set point of the fluid flow with the control unit, the mass flow set point corresponding to said volume flow set point, c) measuring an actual mass flow of the fluid flow with a mass flow sensor of the bioanalytical device, and d) adjusting the flow generating device by the control unit to let the actual mass flow approach the mass flow set point.
  • sensors for mass flow of fluids are available also in miniaturized form even allowing cost-critical applications.
  • the mass flow sensor is a thermal mass flow sensor.
  • the invention allows to accurately control the mass flow sampled by a bioanalytical device using at least one mass flow sensor and particularly one or several sensors for at least two parameters out of temperature, pressure and relative humidity of the sampled fluid.
  • said sampled fluid is air that may be contaminated with contaminants/impurities such as particulate matter, bacteria etc.
  • the method further comprises the step of e) repeating steps c) and/or d).
  • step d) can be conducted at a longer interval (i.e. with slower rate) than the interval at which step c) is conducted.
  • step b) is conducted only once before starting the fluid flow using the fluid flow generating device.
  • step d) further comprises automatically recalculating the mass flow set point of the fluid flow corresponding to said volume flow set point at a pre-defined interval.
  • said pre-determined interval is longer than an interval at which step c) is conducted, i.e., the interval at which controlling of the fluid flow generating device takes place.
  • step b) further comprises measuring a pressure of the fluid and/or a temperature of the fluid and/or a 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 for automatically determining the mass flow set point of the fluid flow corresponding to said volume flow set point.
  • step b) further comprises measuring the pressure, the temperature and the relative humidity of the fluid (e.g. by using said sensors or single sensor device described further below) and determining an actual density of the fluid P fluid , and determining the mass flow set point M set of the fluid flow based on said volume flow set point V set and said actual density, particularly according to the formula
  • automatically recalculating the mass flow set point is conducted only in case the temperature has changed at least by a pre-defined amount and/or in case the pressure has changed at least by a pre-defined amount and/or the relative humidity has changed at least by a predefined amount.
  • the respective embodiments of the present invention allow to reduce computational load on the controlling unit in an advantageous manner, namely e.g., by assuming that temperature, pressure and/or relative humidity change rather slowly, so that recalculation of the mass flow set point can be performed at a longer interval than the loop controlling the fluid flow.
  • a recalculation of the mass flow set point may be conducted.
  • the mass flow set point may even be calculated only once initially, which further reduces computational load.
  • the pressure is measured with a pressure sensor arranged in a flow channel of the bioanalytical device.
  • the pressure sensor can be arranged to measure the pressure of an ambient environment of the bioanalytical device.
  • the temperature is measured with a temperature sensor arranged in the flow channel of the bioanalytical device.
  • the temperature sensor can be arranged to measure the temperature of an ambient environment of the bioanalytical device.
  • the relative humidity is measured with a relative humidity sensor arranged in the flow channel of the bioanalytical device.
  • the relative humidity sensor can be arranged to measure the relative humidity of an ambient environment of the bioanalytical device in a preferred alternative embodiment.
  • the pressure sensor can be integrated into a single sensor device according to a preferred embodiment of the present invention.
  • This single sensor device is then configured to measure the respective quantity, i.e., several or all of said pressure, temperature, relative humidity.
  • the flow channel can comprise a constriction for generating a pressure drop in the flow channel (i.e., across the constriction).
  • the (e.g. thermal) mass flow sensor comprises a conduit for passage of a partial flow of the fluid flow through the conduit of the mass flow sensor, the conduit extending between a first and a second port.
  • the first port is in flow connection with the flow channel.
  • the second port is in flow connection with the flow channel.
  • the second port preferably opens outside the flow channel of the bioanalytical device to an ambient environment of the bioanalytical device.
  • the first port is in flow connection with a location upstream said constriction of the flow channel.
  • the second port is in flow connection with a location at the constriction or downstream the constriction.
  • the mass flow sensor is a thermal mass flow sensor not placed in a bypass.
  • this also means that there is no need for a constriction as the fluid (e.g. air) passes by the mass flow sensor anyway and thereby creates a temperature shift between temperature sensing elements of the flow sensor that are located up- and downstream of a heating element of the thermal mass flow sensor.
  • a heating element of the thermal mass flow sensor is kept at a desired temperature and the electrical current necessary to keep the heating element on the desired temperature is determined. The more flow, the more heat is transported from the heating element and the more current is needed to heat it up to keep the temperature constant.
  • the fluid flow is passed through a filter of the bioanalytical device.
  • the method comprises the further step of detecting if a filter, through which the fluid flow is to be passed, is present in the bioanalytical device, by measuring at least the pressure upstream or downstream of a position of the filter in the fluid flow and comparing the measured pressure to at least one reference value of the pressure.
  • a state of the filter is detected, the state being indicative of a loading of the filter with impurities present in the fluid flow.
  • the filter is loaded with impurities to a certain degree so that particularly a replacement of the filter is required or beneficial.
  • This can also be detected by measuring the pressure which will change due to the filter forming a larger flow resistance when being loaded with impurities.
  • the user will be automatically notified by the bioanalytical device in case it is determined that the filter is loaded with impurities to a certain degree and therefore requires replacement or cleaning.
  • the user is proposed to order a replacement filter by the bioanalytical device when the filter requires replacement.
  • the bioanalytical device is configured to provide a link to a URL of a provider of a replacement filter for ordering thereof.
  • an increase in flow resistance in the flow channel upstream a location where the pressure is measured is detected.
  • the user is alerted that said inlet might be blocked (e.g., by a cover placed on a lid of the bioanalytical device, the lid comprising said inlet).
  • a bioanalytical device (particularly a microbial air sampler) is disclosed particularly for conducting the method according to the present invention, the bioanalytical device comprising:
  • control unit for controlling the fluid flow generating device
  • control unit configured to receive a desired volume flow set point of the fluid flow as an input, to calculate a mass flow set point of the fluid flow corresponding to said volume flow set point, and to adjust the flow generating device to let the actual mass flow approach the mass flow set point.
  • the bioanalytical device comprises a pressure sensor configured to measure a pressure of the fluid.
  • the bioanalytical device comprises a temperature sensor configured to measure a temperature of the fluid.
  • the bioanalytical device comprises a relative humidity sensor configured to measure a relative humidity of the fluid.
  • the pressure sensor is arranged in the flow channel or is arranged outside the flow channel to measure said pressure in an ambient environment of the housing of the bioanalytical device.
  • the temperature sensor is arranged in the flow channel or is arranged outside the flow channel to measure said temperature in an ambient environment of the housing of the bioanalytical device.
  • the relative humidity sensor is arranged in the flow channel or is arranged outside the flow channel to measure said relative humidity in an ambient environment of the housing of the bioanalytical device.
  • the bioanalytical device several or all of: the pressure sensor, the temperature sensor, the relative humidity sensor is integrated into a single sensor device configured to measure the respective quantity, i.e., several or all of said pressure, temperature, relative humidity.
  • the flow channel comprises a constriction to generate a pressure drop across the constriction.
  • the mass flow sensor comprises a conduit for passage of a partial flow of the fluid flow through the conduit of the mass flow sensor, the conduit having a first port (e.g. 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 in the vicinity of the constriction or downstream said constriction) or opens outside the flow channel to an ambient environment of the bioanalytical device.
  • the mass flow sensor is a thermal mass flow sensor being in thermal contact with the fluid flow in the flow channel to measure a mass flow of the latter as e.g. described above.
  • 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 for determining the mass flow set point of the fluid flow corresponding to said volume flow set point.
  • control unit is configured to determine the actual density of the fluid (e.g., air) using the measured pressure, measured temperature and measured relative humidity of the fluid and to determine the mass flow set point M set of the fluid flow based on said volume flow set point V set and said actual density Pfizid , particularly according to the formula
  • the housing is configured to accommodate a carrier carrying a moist medium in the internal space of the housing so that the flow channel extends along the moist medium.
  • the moist medium is a moist growth medium for promoting microbial growth, wherein here the bioanalytical device is a microbial air sampler.
  • the flow channel of the bioanalytical device extends from an inlet of the housing to an outlet of the housing.
  • the fluid flow generating device is further configured to provide the fluid flow through the flow channel so that the fluid flow passes the moist medium carried by the carrier when the carrier is arranged in the internal space, wherein the bioanalytical device is configured to pass the fluid flow along the moist medium when the carrier is arranged in the internal space such that particulate matter contained in said fluid flow settles on the moist medium (e.g. said growth medium).
  • the fluid flow generating device for generating said fluid flow is a fan comprising a rotating arrangement of blades, wherein adjusting the fluid flow generating device comprises to adjusting a rotation speed of the arrangement of blades.
  • the housing comprises an openable lid to allow access to said internal space, so that the moist medium can be accommodated in said internal space in an open state of the lid and is enclosed by the housing in a closed state of the lid, wherein said inlet is formed in the lid in particular.
  • the bioanalytical device e.g., microbial air sampler
  • the bioanalytical device comprises a filter arranged upstream said outlet of the housing and particularly downstream the mass flow sensor and sensor(s) for measuring temperature and/or pressure and/or relative humidity. Presence and/or Loading of the filter can be detected by the bioanalytical device as described above.
  • the bioanalytical device according to the present invention can be further characterized in preferred embodiments by the features and embodiments described above in conjunction with the method according to the present invention.
  • the bioanalytical device is configured to conduct the method according to the present invention.
  • the present invention proves to be advantageous in that calculation of the desired mass flow set point can be based on absolute pressure and temperature as well as optionally relative humidity. Furthermore, the approach according to the present invention, namely achieving a desired volumetric flow by regulating for its corresponding target mass flow, significantly reduces computational effort.
  • comparing pressure with threshold values allows one to make predictions about the state of the instrument.
  • an increased or decreased pneumatic resistance in the system - such as caused by aging and partial blockage of an integrated filter- can be compensated.
  • the invention in principle allows controlling the bioanalytical device for both mass flow and volume flow.
  • the invention allows to achieve a higher precision over a wide temperature and/or humidity range without significantly increasing cost and compactness of the solution (temperature and humidity sensors are affordable and require only small footprint on a printed circuit board).
  • the invention further allows simplifying the implementation of a control logic (compared to continuously converting a mass flow to a volume flow). Regardless of running mass flow or volumetric flow, in both cases the control loop is controlling mass flow.
  • a method for detecting a filter and/or a state of a filter in a bioanalytical device comprising a flow generating device for generating a fluid flow in a flow channel comprised by the bioanalytical device, the method comprising the steps of: generating a fluid flow in the flow channel and automatically detecting the presence or absence of a filter of the bioanalytical device in the flow channel and/or automatically detecting a state of the filter, the state being indicative of a loading of the filter with impurities present in the fluid flow.
  • a bioanalytical device particularly for conducting said method for detecting said filter and/or state is disclosed, comprising:
  • a filter configured to be positioned in the flow channel (particularly such that the fluid flow can be passed through the filter), wherein the bioanalytical device is configured to automatically detect the presence or absence of the filter in the flow channel and/or to automatically detect a state of the filter, the state being indicative of a loading of the filter with impurities present in the fluid flow.
  • the bioanalytical device comprises at least one pressure sensor upstream or downstream a location in the flow channel configured to receive the filter to detect said presence/absence and/or state (see also above).
  • at least one pressure sensor upstream or downstream a location in the flow channel configured to receive the filter to detect said presence/absence and/or state (see also above).
  • Fig. 1 shows a control loop of an embodiment of the method I bioanalytical device according to the present invention
  • Fig. 2 shows a perspective view of an embodiment of a bioanalytical device in form of a microbial air sampler
  • Fig. 3 shows a schematic cross-sectional view of the microbial air sampler of Fig. 2
  • Fig. 4 shows different embodiments of a bioanalytical device regarding a configuration of the flow channel and mass flow sensor as well as temperature, pressure and relative humidity sensor(s).
  • Fig. 1 shows a block diagram of a preferred control loop 100 that can be used in the method / bioanalytical device 1 according to the present invention.
  • the invention does not aim to control the volume flow through the bioanalytical device 1 directly (convert mass flow to volume flow with current sensor readings for temperature, pressure, and humidity and adjust fan to reach a target volume flow rate), but to calculate a target mass flow (termed mass flow set point) that matches the volume flow set point at the current conditions of temperature T, pressure P and relative humidity RH.
  • T temperature
  • P and relative humidity RH relative humidity
  • this invention uses a thermal mass flow sensor 4 together with sensors 5 to measure the temperature T, absolute pressure P, and optionally relative humidity RH of the sampled air.
  • sensors 5 are available in miniaturized formats, this method can be implemented not only in large devices, but is also suited for portable applications (Fig. 1).
  • the bioanalytical device 1 can be an e.g., portable microbial air sampler (as an example of a particle monitoring system) that draws a fluid (here a gas such as air) through an inlet 16 formed by a perforated lid 14 at a top of a housing 13 of the bioanalytical device 1 .
  • the fluid flow F flows through an integrated fluid flow generating device 3 such as a fan, a flow channel 10 forming a sensing path, and is eventually released via an outlet 17 (here on the bottom side of the sampling head).
  • a replaceable filter 12 can be placed upstream said outlet 17, wherein the bioanalytical device 1 can be configured to automatically detect the presence or absence of the filter 12 and/or to automatically detect a state of the filter 12, the state being indicative of a loading of the filter 12 with impurities present in the fluid flow F.
  • the bioanalytical device 1 can prompt the user to arrange a filter 12 in the flow channel 10 or to replace/clean the filter if necessary.
  • the housing 13 is configured to accommodate a carrier 15 carrying a moist medium so that the flow channel 10 extends along the moist medium.
  • the moist medium is a moist growth medium for promoting microbial growth.
  • the fluid flow generating device 3 is configured to let the fluid flow F pass through the flow channel 10 so that the fluid flow F passes the moist medium carried by the carrier 15 such that particulate matter contained in said fluid flow F settles on the moist medium (e.g. said growth medium).
  • the flow channel / sensing path 10 preferably comprises a thermal flow sensor 4 measuring the pressure drop along a specific portion of the flow channel 10 (this section may include elements such as a constriction 11 , a venturi configuration, an orifice, or similar) or between a specific point in the flow channel 10 and the ambient environment Pambient and sensors 5 for the parameters: temperature T, absolute pressure P and relative humidity RH.
  • the latter parameters may be measured by a single sensor device 5 having integrated therein the functionalities to measure said parameters.
  • the sensor(s) 5 for P, T, RH allow determination of the current air density.
  • the mass flow sensor(s) 4 determine the actual mass flow in the bioanalytical device 1. Requested volume flow (i.e., the 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 such that the mass flow sensor signal matches the desired mass flow set point.
  • Fig. 4 shows possible embodiments of the mass flow control with different sensor configurations (a-c) and exemplary measurement workflow (d). Note that absence of one or more sensor elements in the P, T, RH sensor 5 is possible. In such a case, either simplified equations for the relationship between mass flow and volume flow can be used (see below) or pre-defined approximate values for missing sensor-values can be used (like substituting the actual humidity from a RH sensor with a fixed value of 40%RH).
  • a thermal mass flow sensor 4 is used in a bypass configuration to measure the pressure drop along the flow channel 10.
  • the mass flow sensor 4 comprises a conduit 40 having a first port 41 (e.g. inlet) in flow connection to the flow channel 10 and a second port 42 (e.g. an outlet) being in flow connection with the flow channel 10, too.
  • the pressure drop can be artificially enlarged using a flow constriction 11 , wherein the inlet 41 of the conduit 40 can be arranged upstream the constriction 11 , whereas the outlet 42 of the mass flow sensor’s conduit 40 can be positioned in the vicinity of the constriction 11 or downstream the constriction 11.
  • the measuring points for temperature T, pressure P, and relative humidity RH are preferably located directly in the flow channel 10 before, after, or in parallel to the mass flow sensor 4.
  • the sensor(s) 5 can alternatively also be configured to measure T, P, RH in an ambient environment of the bioanalytical device 1 .
  • This also applies to the configurations shown in Figs. 4 b-c.
  • Fig. 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 (e.g.
  • Fig. 4 b shows a configuration in which the outlet 42 of the mass flow sensor’s conduit 42 opens to the ambient environment Pambient of the bioanalytical device 1.
  • the thermal mass flow sensor When regulating to a fix mass flow, the thermal mass flow sensor is used alone.
  • 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) at these conditions:
  • R s is the gas constant for dry air with and R d the gas constant of water vapor with 461.523
  • the relative humidity as determined by humidity sensors p, the absolute ambient pressure P, and the saturation vapor pressure P sat are also to be taken into account.
  • the saturation vapor pressure at the current temperature T act can be calculated with the following equation: Taking all this together, the density of air is only dependent on temperature, absolute pressure and relative humidity of the sampled air and follows this equation:
  • V air When the volume flow rate of the fluid (e.g. air) V air is given, one can then easily convert to mass flow rate of the fluid/air M air '.
  • the fluid e.g. air
  • volume flow and mass flow (normalized volume flow) iorm IS. which may be rearranged to e.g., calculate a mass flow target based on a desired volumetric flow:

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  • General Physics & Mathematics (AREA)
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  • Analytical Chemistry (AREA)
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Abstract

La présente invention concerne un procédé et un dispositif bioanalytique (1) pour réguler un débit massique d'un fluide dans un dispositif bioanalytique (1) comprenant une unité de régulation (2) et un dispositif de génération d'écoulement de fluide (3) pour générer un écoulement de fluide (F) du fluide, le procédé comprenant les étapes consistant à : entrer un point de consigne de débit volumique souhaité de l'écoulement de fluide dans l'unité de régulation (2), calculer automatiquement avec l'unité de régulation (2) un point de consigne de débit massique de l'écoulement de fluide (F) correspondant audit point de consigne de débit volumique, mesurer un débit massique réel de l'écoulement de fluide (F) avec un capteur de débit massique (4) du dispositif bioanalytique (1), et régler le dispositif de génération d'écoulement (3) par l'unité de commande (2) pour laisser le débit massique réel s'approcher du point de consigne de débit massique.
PCT/EP2023/076617 2022-09-26 2023-09-26 Procédé et dispositif bioanalytique pour réguler un débit de fluide WO2024068678A1 (fr)

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EP22197883 2022-09-26

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5927321A (en) * 1995-10-30 1999-07-27 Nuovo Pignone, S.P.A. System for measuring and controlling gas mass flow
US20150355000A1 (en) 2014-03-14 2015-12-10 Particle Measuring Systems, Inc Pressure-Based Airflow Sensing in Particle Impactor Systems

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5927321A (en) * 1995-10-30 1999-07-27 Nuovo Pignone, S.P.A. System for measuring and controlling gas mass flow
US20150355000A1 (en) 2014-03-14 2015-12-10 Particle Measuring Systems, Inc Pressure-Based Airflow Sensing in Particle Impactor Systems

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