Particle monitoring system, portable microorganism air sampler, method for monitoring particles in a sample fluid, and method for calibrating / adjusting a particle monitoring system

Abstract

The present application relates to a particle monitoring system, a portable microbial air sampler, a method for monitoring particles in a sample fluid, such as a gas (especially a compressed gas), and a method for calibrating / adjusting a particle monitoring system.

Description

[Technical field]

[0001] Technical Field The present application relates to a particle monitoring system, a portable microbial air sampler, a method for monitoring particles in a sample fluid, such as a gas (especially a compressed gas), and a method for calibrating / adjusting a particle monitoring system. [Background technology]

[0002] background Monitoring of sample fluids, either liquids or more commonly gases such as air including compressed gas / air (as used herein the term "compressed" is used to denote a pressure of at least 1.1 bar, preferably at least 1.2 bar) is frequently performed to assess contaminants for classification and monitoring purposes in a range of cleanroom and manufacturing environments requiring low levels of particles, such as cleanroom environments for electronics manufacturing and sterile environments for manufacturing pharmaceutical and biological products such as sterile pharmaceutical products. For the purposes of monitoring the air in this context, particle monitoring systems are known and include microbial or active air samplers and particle counters. Microbiological or active air samplers and airborne particle counters are beneficial as they allow a user to sample a quantitative amount of air and determine the risk to contamination (microflora) of sterile products in the surrounding environment.

[0003] For example, an example of a microbial air sampler and method for sampling, detecting and / or characterizing particles through collection, growth and analysis of viable biological particles such as microorganisms is disclosed in EP 0 964 240 A1. The device includes an integral sampler and an impaction surface, such as a receiving surface for growth media, for collecting biological particles. The collected particles are then typically incubated to grow live particles, which are then analyzed by a variety of techniques including visual inspection, microscopy, fluorescence or autofluorescence, ATP detection or others.

[0004] Particle counters, as other types of particle monitoring devices, typically pump the gas to be monitored through a measurement system. A laser beam is directed at the gas stream, and particles that cross the laser beam generate a signal that is detected by a photomultiplier tube. The output of the photomultiplier tube has several amplifiers with different gain stages that allow for the identification of particle number and particle size based on the evaluation of the signal, and more specifically, the amplitude of the signal.

[0005] The present invention relates to a particle monitoring system, in which a sampling section for performing a sampling process on a sample fluid, preferably a gas or compressed gas such as air or compressed air, comprises either a particle collector or a particle counter, or the sampling section comprises a combination of a particle collector and a particle counter. The monitoring procedure of the particle monitoring system will not be described in detail as it is not affected by the present invention.

[0006] In microbial air samplers using the Anderson impact principle, the airflow is accelerated through a lid with numerous tiny nozzles towards a collection plate, allowing efficient separation of airborne microorganisms for downstream analysis. To achieve optimal sampling efficiency without damaging the microorganisms, a precisely set flow rate needs to be maintained during the sampling process. Similarly, determining the number of microorganisms per volume of air requires the highest throughput control. Hence, only microbial air samplers with built-in flow sensors reach optimal capture efficiency with the highest process control.

[0007] Both portable and permanently installed stationary microbial air samplers are available. Portable devices are used to sample at multiple locations and can be carried by the operator, while stationary devices are often employed with isolator units, for example in pharmaceutical companies to maintain a sterile environment during drug packaging. In addition, since monitoring of microbial contamination in process gases is important for many industrial applications, namely in medicine or in the food and beverage industry, there are also dedicated devices that allow sampling of compressed gases. Various types of sensors have been commercially employed as flow sensors in such devices. These are often thermoanemometers that measure the change in temperature gradient between a heater and a sensor module due to the airflow along these elements. These sensors are highly sensitive to airflow conditions and are housed in bulky housings to control the flowpath geometry and guide the airflow along the sensor elements. This poses several constraints on the design of microbial air samplers. In addition, these sensors are relatively expensive and the measurement uncertainty over various flow rate ranges is typically around ±4% mean variation (mv).

[0008] Furthermore, many microbial air samplers that employ flow sensing technology are quite bulky and have limited accuracy, especially when a wide range of different flow rates needs to be accurately qualified. Thus, to date, most microbial air samplers have the ability to operate only at one fixed flow rate, typically 100 LPM or 1.0 CFM (28.3 LPM) or 0.1 CFM (2.83 LPM) ("CFM" stands for "cubic feet per minute" and "LPM" stands for "liters per minute"). As cleanliness requirements for drug or food production become increasingly high, this has led to a situation where sampling times are often 10 minutes or more to collect the desired amount of liquid. Portable devices are required to be small and easy to use. Therefore, bulky and heavy flow sensors that require long flow paths for accurate measurements are not optimal for such types of portable devices.

[0009] Another difficult area to solve is the calibration / adjustment of such microbial air samplers. Currently, compressed gas / air samplers are not calibrated / adjusted at all or need to be sent to a manufacturing or service location. In this case, they need to be connected to a large pressurized tank that can supply the full pressure range to the instrument via a pressure regulator. An alternative is to use pressurized bottles, but this requires and consumes expensive gas just for adjustment / calibration purposes. Flow rates may be calibrated / adjusted at, for example, 100LPM and 50LPM using a reference flow meter.

[0010] Additionally, flowmeter designers often need to test new flowmeter designs for accuracy, quality, and the like. Most design companies can perform in-house testing of flowmeters with liquids because liquid testing equipment can be installed without excessive cost or time. In contrast, gas testing equipment is less common in-house. Thus, those wanting to use such equipment must usually travel there and pay a fee to use it. This can be costly and time consuming, and also has the disadvantage that designers do not have the benefit of immediate feedback on design changes. Frequently, designers must wait weeks or months before they can test new designs and obtain test results on the new designs. Thus, designers and users would generally benefit from gas testing equipment that is small and cost-effective enough to be installed in-house.

[0011] There are two main types of test equipment for gas. One type is the blowdown system. In a blowdown system, a compressor takes in air from the atmosphere and compresses it into a tank. When the pressure in the tank is at the desired pressure for testing, the air is released from the tank and passes through a reference meter and a unit under test (UUT). The air is then returned to the atmosphere. The reference meter and UUT measure the flow rate of the gas as it returns from the tank to the atmosphere. The measurements from the reference meter are used to calibrate / adjust the UUT. Unfortunately, blowdown systems have a short runtime, are costly and inefficient, and are extremely noisy.

[0012] Another type of test facility is a recirculating gas loop. An example of such a test facility is the Metrology Research Facility operated by Southwest Research Institute in San Antonio, Texas, USA. The facility uses a recirculating gas loop and includes a compressor, chiller, sonic nozzle, and a station for units under test (UUT). The compressor circulates gas around the gas loop at a desired flow rate. The compressor adds heat to the gas in the gas loop as it circulates the gas. The chiller cools the gas in the gas loop to a desired temperature. The UUT and one or more sonic nozzles measure the flow rate of the gas. The sonic nozzle is a reference meter for the UUT. Measurements from the UUT are compared to measurements from the sonic nozzle to verify the accuracy of the meter under test or to calibrate / adjust the UUT. Recirculating gas loops such as the Metrology Research Facility are very large in size, costly, and power-intensive to operate, and cannot be effectively built and operated in many companies due to size, cost, and power requirements.

[0013] An example of a prior art gas testing system is disclosed in US 2007 / 0043976 A1. The gas testing system is composed of a flow loop, a blower system, a temperature control system, a reference meter system, and a unit under test (UUT) system. The UUT system is configured to connect the unit under test (UUT) to the flow loop. With the flow loop pressurized with gas, the blower system receives gas under pressure at an inlet. From the pressurized gas at the inlet, the blower system generates a large flow rate of gas out an outlet, circulating the gas through the flow loop. When generating the large flow rate, the blower system generates a weak pressure rise from the inlet to the outlet. The temperature control system receives the gas flow from the blower system and controls the temperature of the gas. The reference meter system measures the properties of the gas circulating through the flow loop. If the UUT in the UUT system also measures the properties of the gas circulating through the flow loop, the measurements of the reference meter system can be compared to the measurements of the UUT to calibrate / adjust the UUT.

[0014] The present invention aims to provide a particle monitoring system and method for monitoring particles in a sample fluid (preferably a gas such as air, most preferably a compressed gas), which can be easily integrated or implemented into a microbial air sampler for compressed gas (preferably air), employs flow sensing technology, provides lower measurement uncertainty, reduces device size, inter alia to provide a portable device, and has low cost compared to existing concepts. It is also an object of the present invention to provide a portable microbial air sampler that is small, easy to use, and provides lower measurement uncertainty at reduced cost. Finally, the present invention also aims to provide a method for calibrating / adjusting a portable particle monitoring system, preferably for compressed gases such as air, that can be performed relatively easily in the field, reducing maintenance calibration / adjustment turnaround time for the user while maintaining the highest measurement quality. Summary of the Invention

[0015] overview In order to solve the above mentioned problems and to achieve the indicated objects singly or in any combination, there is provided a particle monitoring system as defined by claim 1, a portable microbial air sampler as defined by claim 18, a method for monitoring particles in a sample fluid as defined by claim 12, and a method for calibrating / adjusting a particle monitoring system as defined by claim 16. Preferred aspects of the systems and methods are defined in the respective dependent claims. In particular, the present invention provides a particle monitoring system comprising a sampling section for performing a sampling process on a sample fluid flowing through the sampling section, and a sensor arrangement for determining a volumetric flow rate of the sample fluid flowing through the sampling section, the sensor arrangement being associated with a flow path downstream of the sampling section through which the sample fluid flows in operation after passing through the sampling section, wherein the sensor arrangement includes a flow sensor for determining a mass flow rate of the sample fluid flowing through the flow path downstream of the sampling section.

[0016] Preferably, the sensor arrangement includes an absolute pressure sensor for determining absolute fluid pressure in the flow path, and the flow sensor is disposed in a section of the flow path downstream of the sampling section and downstream of the absolute pressure sensor, in a flow direction away from the sampling section. Preferably, the sensor arrangement includes a flow regulating component disposed in the flow path between the absolute pressure sensor and the flow sensor. Preferably, the particle monitoring system further includes a control section configured to calculate a volumetric flow rate of the sample fluid flowing through the sampling section based on the mass flow rate determined by the flow sensor and the absolute fluid pressure determined by the absolute pressure sensor. Preferably the sensor arrangement (preferably the flow sensor) includes a temperature sensor for measuring the temperature of the fluid within the flow sensor. Preferably, the flow sensor includes a differential pressure gauge for determining the pressure difference of the sample fluid across a predetermined geometric flow restriction (preferably a nozzle) through which the sample fluid flows, and a temperature sensor for measuring the temperature of the fluid preferably within the differential pressure gauge.

[0017] Preferably, the control section regulates the volumetric flow rate through the sampling section according to the following formula:

number

[0018] Preferably, the control section is configured to be able to switch between the types of fluid / gas being sampled by selecting a fluid correction factor specific to each type of fluid / gas. Preferably, the control section is configured to be calibrated or adjusted with respect to fluid flow rate as determined by the flow sensor, and / or absolute fluid pressure as determined by the absolute pressure sensor. Preferably, the control section is configured to control the degree of restriction of the flow regulating component based on the calculated volumetric flow rate to set the flow rate to a predetermined value. Preferably, the particle monitoring system further includes a particle filter, preferably a HEPA filter, disposed in the flow path between the sampling section and the flow sensor.

[0019] In particular the present invention provides a method for monitoring particles in a sample fluid, the method comprising: Sampling particles in the sample fluid flowing through the sampling section; and The volumetric flow rate of the sample fluid flowing through the sampling section is defined as: determining a mass flow rate of the sample fluid flowing through the flow path downstream of the sampling section; determining an absolute pressure in the flow path upstream of the location where the mass flow rate is determined and downstream of the sampling section; and calculating a volumetric flow rate of the sample fluid flowing through the sampling section based on the determined mass flow rate and the determined absolute pressure; To be determined by Includes. Preferably, the mass flow rate of the sample fluid flowing through the flow channel is determined by measuring the pressure difference of the sample fluid upstream and downstream of a restriction (preferably a nozzle) through which the sample fluid flows.

[0020] Preferably, the volumetric flow rate through the sampling section (2) is determined according to the following formula:

number

[0021] Preferably, the method for monitoring particles in a sample fluid includes controlling the opening of a flow control component located in a flow path between a position where the absolute pressure in the flow path is determined and a position where the pressure difference is measured based on the calculated volumetric flow rate, to set the flow rate to a predetermined value.

[0022] The present invention also provides a method of calibrating / adjusting a particle monitoring system according to the present invention, comprising: closing the flow regulating component to block a flow path between the absolute pressure sensor and the flow sensor; connecting an external test fluid source to the inlet of the sampling section of the particle monitoring system and to the flow sensor; Supplying test fluid from an external test fluid source to a sampling section of the particle monitoring system in a stepped sequence of increasing and / or decreasing pressure or in a continuous increase and / or decrease in pressure; supplying a test fluid from an external test fluid source to the flow sensor in a stepped sequence of increasing and / or decreasing flow values ​​or at a continuously increasing and / or decreasing flow rate; Simultaneously determining pressure and / or volumetric flow values ​​at the external test fluid source and the particle monitoring system; selecting correction values ​​for the discrete selected pressure / volume flow levels by curve fitting (preferably a polynomial curve fit) or by an interpolated look-up table, preferably by interpolating between the discrete levels; and inputting the correction values ​​into a control section of the particle monitoring system; The steps include: Preferably, the pressure and flow corrections are applied independently and either sequentially or simultaneously.

[0023] The present invention also provides, inter alia, a portable microbial air sampler, preferably for compressed gases, which comprises a particle monitoring system according to the present invention. [Brief description of the drawings]

[0024] BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in detail based on preferred embodiments with reference to the accompanying schematic exemplary drawings. [Figure 1] FIG. 1 is a schematic illustrative schematic diagram of a first preferred embodiment of the present particle monitoring system in a microbial air sampler for sampling compressed gas; [Diagram 2] FIG. 2 is a schematic exemplary conceptual diagram of a setup for calibrating / adjusting a microbial air sampler described herein for sampling compressed gas; [Figure 3a] Figure 3a shows an example of a stepwise sequence of increasing (left) and decreasing (right) pressure / flow rates in the present calibration / adjustment method using the setup of Figure 2; and [Figure 3b] FIG. 3b shows an example of a continuous sequence of increasing (left) and decreasing (right) pressure / flow rates in the present calibration / adjustment method using the setup of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Detailed explanation The particle monitoring system of the present invention will be described as an example using a variation of the microbial air sampler 1 for sampling compressed gas shown in Figure 1. Since the monitoring procedure of the particle monitoring system is not affected by the present invention, the sampling section 2 of the particle monitoring system for performing a sampling process on a sample fluid (preferably a gas, more preferably a compressed gas) is configured as known in the art, and the sampling section may include one or both of a particle collector and a particle counter, as described above (the sampling section 2 in the exemplary embodiment of Figure 1 is a particle collector). The particle monitoring system 1 functionally comprises a sampling section 2 for performing a sampling process on a sample fluid flowing through the sampling section 2, and a sensor arrangement 3 for determining the volumetric flow rate of the sample fluid flowing through the sampling section 2.

[0026] In operation, the microbial air sampler incorporating the particle monitoring system is connected through tubing or piping 11 to a gas source 12, from which pressurized gas passes through tubing 11 to the sampling section 2. The sampling section 2 contains a perforated lid 10 which accelerates the gas and causes particles contained in the gas to impinge on the culture media plate 9 below. The gas then passes through a particle filter 8, preferably a HEPA filter, which is positioned in the flow path 7 between the sampling section 2 and the sensor placement section 3, i.e. downstream of the culture media plate 9, to remove any remaining particles or oily residue from the gas.

[0027] The sensor arrangement 3 is associated with a flow path 7 through which a sample fluid flows in operation after a sampling operation has been performed. The sensor arrangement 3 is positioned on the flow path downstream of the sampling section 2 and downstream of a particle filter 8. The sensor arrangement 3 includes an absolute pressure sensor 5 for determining the absolute fluid pressure in the flow path 7 in the flow direction from the sampling section 2 to the outlet 13, and a flow sensor 4 arranged in a section of the flow path 7 downstream of the absolute pressure sensor 5 in the flow direction away from the sampling section 2 for determining the mass flow rate of the sample fluid flowing through the flow path 7 downstream of the sampling section 2.

[0028] The pressure sensor 5 is configured to determine the absolute gas pressure in the section of the fluid flow path up to the regulating valve 6a. The flow sensor 4 is located downstream of the regulating valve 6a and further downstream communicates with an outlet 13 that is exposed to ambient pressure conditions. The flow regulating components or valves 6, 6a thus separate the pressurized zone of the particle monitoring system from the zone of ambient pressure, such that the flow sensor is in the zone of ambient pressure.

[0029] The regulator valve 6a is one example of a flow regulation component 6, which is disposed in the flow path 7 between the absolute pressure sensor 5 and the flow sensor 4 to restrict the flow rate through the flow path towards the flow sensor 4. In a preferred embodiment configured for the calibration / adjustment method described below, the flow regulation component 6 is capable of selectively blocking the flow path 7 between the absolute pressure sensor 5 and the flow sensor 4. In this variation shown in FIG. 2, the particle monitoring system 1 may be provided with a further port or inlet 14 configured to be connected to an external test fluid source 15 for introducing test fluid into the flow path section downstream of the flow regulation component 6 at a defined flow rate and directed towards the flow sensor 4.

[0030] The flow sensor 4 in the preferred embodiment includes a differential pressure gauge for determining the pressure difference of the sample fluid across (upstream and downstream of) a given geometric flow restriction 4a (preferably a nozzle as shown diagrammatically in the example) through which the sample fluid flows. A differential pressure gauge, as known, works on the principle of partially obstructing the flow in a pipe. This creates a static pressure difference between the upstream and downstream sides of the device. Since the pressure difference created is proportional to the square of the mass flow rate, this difference in static pressure (called the differential pressure or pressure drop) is measured and used to determine the mass flow rate using Bernoulli's equation and the law of conservation of mass. A Venturi nozzle type differential pressure gauge is preferred in certain applications of portable or mobile microbial air samplers for reasons indicated below, although other types of differential pressure gauges selected from the group consisting of orifice plates, Venturi tubes, cone meters (e.g., V-cones or segmented wedge elements), other nozzles, low loss meters (e.g., Dole tubes), variable area flow meters, inlet flow meters, Venturi cones, drag plates, elbow flow elements, Pitot tubes, and averaging Pitot tubes may also be used.

[0031] In further options, flow sensors operating on various physical principles may be employed, including contact flow sensors such as vortex flow sensors, and mechanical or mechatronic flow sensors, or non-contact flow sensors such as ultrasonic flow sensors, magnetic induction flow sensors, or thermal flow sensors, or Coriolis flow sensors. On the other hand, due to the inherent design configurability of the Venturi nozzle type differential pressure gauge, i.e., by changing the size and shape of the Venturi nozzle, and the wide range of applicable flow rates, it is possible to separate the gas flow control (using the flow regulation component 6) at the time of microbial sampling from the gas volume measurement (i.e., integration of the gas flow rate to determine the volume of the sampled gas). This is beneficial because the flow sensor 4 is downstream of the sampling section 2 and downstream of the flow regulation component 6, which places the flow sensor 4 outside the pressure path, which is downstream of the sampling section 2 and upstream of the flow regulation component 6, thereby lowering the design requirements for pressure and leak tightness of the flow sensor 4.

[0032] The sensor arrangement 3 preferably also includes a temperature sensor (not shown) for measuring the temperature of the fluid in the flow sensor 4. However, alternatively, it is possible to omit the temperature sensor, in which case the temperature is measured at a standard temperature T N The sensor may be implemented in the form of a MEMS (micro-electro-mechanical system) differential pressure sensor that measures differential pressure and temperature and integrates a PCB (printed circuit board) that contains all the electronics required for temperature compensated flow measurement. Such a sensor configuration provides high measurement accuracy over a wide range of applicable flow rates.

[0033] A well-known drawback of differential pressure sensors is the effect that small particle contamination has on the sensor's response. This can be problematic and can adversely affect long-term stability. In the present invention, a particle filter 8 integrated into the particle monitoring system 1 addresses this type of problem. The particle monitoring system 1 further includes a control section 20 configured to calculate the volumetric flow rate of the sample fluid flowing through the sampling section 2 based on the mass flow rate determined by the flow sensor 4 and the absolute fluid pressure determined by the absolute pressure sensor 5.

[0034] The control section 20 determines the volumetric flow rate through the sampling section 2 according to the following formula:

number

[0035] The control section 20 is configured to be able to switch between different types of fluid / gas to be sampled by selecting a fluid correction factor specific to each type of fluid / gas (for air, the factor is 1). The correction factors available for different gas types can be predefined and stored in the software or memory and selected through a switch arrangement or configuration software. As described in more detail below, the control section 20 is configured to be calibrated / adjusted for fluid flow rate as determined by the flow sensor 4 and / or absolute fluid pressure as determined by the absolute pressure sensor 5 .

[0036] Furthermore, the control section is configured to control the opening of the flow regulating components 6, 6a based on the calculated volumetric flow rate to set the flow rate to a predetermined value. In sensor arrangement 3 described above in connection with the exemplary embodiment, the flow sensor has two tasks to fulfill: i) measuring the mass flow rate of the sampled gas; and ii) feeding the measured mass flow rate to the control section 20, which, together with the measurement from the pressure sensor 5 and the above formula, can determine the total amount of sampled gas (by integrating over time) and control the opening of the flow regulation component 6 (regulating valve 6a). More specifically, based on the measured flow rate through the flow sensor 4 (i.e. in the peripheral path communicating with the outlet 13) and the measured absolute pressure (i.e. in the pressure path upstream of the flow sensor and upstream of the flow regulation component 6), the flow rate through the sampling section 2 (i.e. in the pressure path) is calculated. This calculated flow rate is then compared to a target flow rate. As a result of this comparison, the restriction of the flow regulation component 6 is increased or decreased to adjust the flow rate through the flow path 7 reaching the flow sensor 4.

[0037] This construction allows for the sampling of microorganisms under pressure, which means that the gas being sampled is not subjected to sudden pressure or temperature changes prior to sampling for flow rate determination purposes, so that microorganisms carried by the gas are not damaged by the suddenly changing conditions. Given the relatively small dimensions of the components of the particle monitoring system, the present invention may provide a portable or mobile microbial air sampler, preferably for compressed gases such as air, that includes a particle monitoring system according to the present invention provided within a housing.

[0038] Based on the principles discussed above in connection with the exemplary particle monitoring system, the present invention also provides, independent of the particular device structure, a method for monitoring particles in a sample fluid, comprising the steps of: Sampling particles in the sample fluid flowing through the sampling section 2; and The volumetric flow rate of the sample fluid flowing through the sampling section 2 is defined as follows: determining a mass flow rate of the sample fluid flowing through the flow path downstream of the sampling section 2; determining the absolute pressure in the flow path upstream of the location at which the mass flow rate is determined and downstream of the sampling section 2; Optionally, determining the temperature within the flow sensor / differential pressure gauge 4; and Determined mass flow rate and determined absolute pressure and temperature (if the temperature is not specifically determined, the temperature is the standard temperature T N calculating a volumetric flow rate of the sample fluid flowing through the sampling section 2 based on To be determined by.

[0039] The mass flow rate of the sample fluid flowing through the flow path is determined by measuring the pressure difference of the sample fluid upstream and downstream of a restriction (preferably a nozzle) through which the sample fluid flows. The volumetric flow rate through the sampling section 2 can be calculated based on the formula described above.

[0040] The method for monitoring particles in a sample fluid may also include controlling the opening of a flow control component 6 located in the flow path between the position where the absolute pressure in the flow path is determined and the position where the pressure difference is measured based on the calculated volumetric flow rate, to set the flow rate to a predetermined value. Based on a particle monitoring system including a flow regulating component 6 in a flow path between a position where the absolute pressure in the flow path is determined and a position where the pressure difference is measured, with a configuration allowing substantially complete selective blocking of the flow path by closing the flow regulating component 6;6a (or by a dedicated further valve specifically adapted for blocking the flow path) to block the flow path 7 between the absolute pressure sensor 5 and the flow sensor 4, the present invention provides a method for calibrating / adjusting a particle monitoring system 1 based on a test setup shown in the schematic conceptual diagram of Figure 2 for calibrating / adjusting an air sampler, preferably in a mobile microbial air sampler for sampling compressed gases.

[0041] Thus, the present invention provides a solution to the originally described problems with existing large-scale gas testing systems, making it possible to calibrate / adjust a compressed gas air sampler (unit under test--UUT), such as the one described above in connection with Figure 1, for sampling air under pressure in the field using only a portable instrument (external test fluid source 15) capable of delivering the appropriate pressure range and flow rate after pressure reduction to 1 atm. The calibration / adjustment method decouples pressure from flow rate calibration / adjustment, thus removing the constraint of high flow rates occurring at high pressure.

[0042] This method involves the following: completely closing the flow regulating component 6;6a, or a further valve specifically adapted for blocking the flow path, in order to block the flow path 7 between the absolute pressure sensor 5 and the flow sensor 4; connecting an external test fluid source 15 to the inlet of the sampling section 2 of the particle monitoring system 1 and to the flow sensor 4 (e.g., via separate ports 14); supplying test fluid from an external test fluid source 15 to the sampling section 2 of the particle monitoring system 1 in a stepped sequence of increasing and / or decreasing pressures or at continuous increasing and / or decreasing pressures; supplying test fluid from an external test fluid source 15 to the flow sensor 4 only, in a stepped sequence of increasing and / or decreasing flow values ​​or at a continuously increasing and / or decreasing flow rate; simultaneously determining pressure and / or volumetric flow values ​​at the external test fluid source and at the particle monitoring system 1; selecting correction values ​​for the discrete selected pressure / volume flow levels by an appropriate (e.g., polynomial) curve fit or by an interpolated look-up table, preferably by interpolating between the discrete levels; and inputting the correction values ​​into a control section of the particle monitoring system 1; The steps include:

[0043] Any one or more of the corrections for temperature, pressure, and flow rate may be applied independently, sequentially, or simultaneously. In this test setup, unlike prior art techniques, the gas (here ambient air) does not need to be temperature controlled because warming does not affect the calibration / adjustment of the pressure sensor, and compressed air is not used to calibrate / adjust the flow sensor. Indeed, advantageously, the calibration / adjustment of the flow rate of the flow sensor 4 bypasses the flow regulation components of the UUT and uses ambient air. Therefore, both flow sensors (one from the external test fluid source 15 and one from the UUT) see the same air flow (since there is no flow restriction between the two) and at the same temperature (since there is no reduced pressure of gas / air).

[0044] In comparison to large volume dedicated gas test systems or equipment, the calibration / adjustment method of the present invention offers the advantages of being a portable solution, offering the possibility of fully automated calibration / adjustment which reduces maintenance time and costs, ensures good metrology practices and eliminates or significantly reduces the risk of human error, being applicable to calibration / adjustment over the full pressure and flow ranges, being able to be configured as a "plug and play" concept with respect to a compressed gas air sampler as the UUT, reducing the risks inherently associated with the use of high pressure and large volumes of gas associated with the use of pressure tanks in some existing test gas systems, and avoiding the need for the user to provide and stock compressed gas containers (bottles) for calibration purposes. The external test fluid source 15 for performing the calibration / adjustment method of the present invention using ambient air includes, as shown in FIG. 2, a flow generator 15a (e.g., an axial or centrifugal fan or blower) and a flow sensor 15c capable of generating and measuring the total flow rate (e.g., 50 SLPM to 700 SLPM, where "SLPM" stands for "standard liters per minute") of each compressed gas air sampler (UUT) to be tested after reducing the pressure of the gas to 1 atm, a pressure generator 15b and a pressure sensor 15d (e.g., a mechanical compressor) capable of generating and measuring the total pressure range (e.g., a range of absolute pressures of 1.1, preferably 1.2 to 7 bar) of each compressed gas air sampler (UUT) to be tested, and a controller 15e for receiving the measurement results and communicating with the UUT.

[0045] The pressure and flow sensors of the external test fluid source 15 mirror those of the UUT. The external test fluid source 15 itself (and its sensors) are calibrated / tuned by the sensor provider or at the manufacturing site to provide a high quality calibration / tune.

[0046] First, the flow regulation components 6 (valves) of the UUT or a dedicated further valve specifically adapted to block the flow path are closed so that the pressure generator 15b of the external test fluid source 15 can pressurize both pressure sensors of the external test fluid source 15 and the UUT (i.e. the pressure sensor 15d and the absolute pressure sensor 5) with the same pressure. This sequence can consist of steps by switching the pressure generator 15b on and off. The result is a sequence with a plateau such that the acquisition of both sensors is performed under steady state conditions. At each step, the pressure is monitored on both sensors 5, 15d. Optionally, after pressurizing the pressure path, the flow regulation components 6 (valves) of the UUT can be repeatedly opened and closed to proceed through a stepwise descending sequence (see FIG. 3a). Alternatively, the flow regulating component 6 (valve) of the UUT may be opened slightly so that air is slowly evacuated resulting in a continuous ramp down sequence (see FIG. 3b).

[0047] An up sequence may be followed by a down sequence to collect more data sets for calibration / adjustment, but this is not required. However, it may be useful to collect more data sets in this manner to determine whether hysteresis effects are present and, if so, to assess their impact. Collecting more data sets in this manner may also be used to determine a "mean" or "average" data set that may then be used in the calibration / adjustment. A stepwise sequence may follow a continuous sequence or vice versa. The UUT's absolute pressure sensor 5 is then recalibrated based on an appropriate (e.g.: polynomial) curve fit or an interpolated look-up table (LUT), thus obtaining the adjusted pressure of the UUT from a discrete number of data sets acquired during the calibration sequence. If a curve fit method is used to calibrate / adjust the UUT absolute pressure sensor 5, the UTT value is calculated using the inverse function UUT pressure = f -1 It is derived from (X). When a LUT is used, the UUT values ​​are derived by interpolation (if the inputs do not match the index values ​​of the breakpoint data set).

[0048] Interpolation may involve all common interpolation methods known in the art, including (but not limited to) flat (disables interpolation), nearest (disables interpolation and returns the table value corresponding to the breakpoint closest to the input), linear point-slope (fits a line between adjacent breakpoints and returns the point on that line that corresponds to the input), cubic spline (fits a cubic spline to adjacent breakpoints and returns the point on that spline that corresponds to the input), linear Lagrange (fits a line between adjacent breakpoints using first order Lagrange interpolation), and Akima spline (fits an akima spline to adjacent breakpoints and returns the point on that spline that corresponds to the input). The same type of methodology as described above for calibrating / adjusting the UUT's absolute pressure sensor 5 also applies to calibrating / adjusting the flow sensor 4 (hence the diagram in FIG. 3 indicates both pressure and flow as labels on the vertical axis).

[0049] To calibrate / adjust the flow sensor 4, the flow generator 15a (blower / fan) is activated, blowing air through the mass flow sensor 15d of the external test fluid source 15 and the flow sensor 4 of the UUT. The flow sensor 4 of the UUT is located downstream of the (closed) flow regulation component 6 (valve), and air is introduced into the flow path 7 between the regulation component 6 and the flow sensor 4, so that the air coming from the external test fluid source 15 can bypass the flow regulation component 6 and is subject to a lower or no flow restriction. The flow rate generated by the flow generator 15a is increased stepwise or continuously (e.g., by increasing the rotational speed of the blower / fan) as described above in connection with the calibration / adjustment of the pressure sensor. The mass flow rate is measured simultaneously in each step or continuous manner by the mass flow sensor 15c of the external test fluid source 15 and the flow sensor 4 of the UUT.

[0050] The flow rate may also be decreased in steps or continuously, combining ascending and descending sequences to increase the data set. These values ​​are used to re-adjust / re-calibrate the UUT's flow sensor 4 based on a polynomial curve fit or an interpolated look-up table (LUT), for example, by inputting correction values ​​into the control section of the UUT's particle monitoring system 1, just as described above in connection with pressure calibration / adjustment. Finally, the flow regulation component 6 (valve) of the UUT or (if provided) a dedicated shut-off valve (i.e. a dedicated further valve specifically adapted to block the flow path) is reopened, the external test fluid source 15 is disconnected from the UUT, and the port 14 for introducing air flow between the flow regulation component 6 (or the dedicated shut-off valve, if provided) and the flow sensor 4 is closed.

[0051] The calibration / adjustment sequence may use 1) increasing pressure and flow rate, or 2) decreasing pressure and flow rate, or 3) a combination of both. Pressure and flow adjustment / calibration can be performed in sequence or simultaneously, with the advantage of reducing calibration and adjustment times. In this latter case, the flow regulation component 6 (or a dedicated shut-off valve, if supplied) must remain closed to avoid pressure application affecting the flow measurement. The calibration / adjustment method of the present invention has been described using a compressed gas air sampler with the particle monitoring system 1 of the present invention as an example UUT, however, the calibration / adjustment method of the present invention may also be applied to other types of air samplers, including fixed or stationary air samplers, and may also be applied to existing air samplers with flow regulating components (valves) between the absolute pressure sensor and the flow sensor.

[0052] The particle monitoring system of the present invention differs from the known prior art, especially with regard to the placement of the flow sensor, which is of particular interest in the monitoring of compressed gases. The flow sensor of the present system is no longer installed in the pressurized zone, but is located in the ambient pressure zone, and preferably the pressurized zone and the ambient pressure zone are separated from each other by a valve (e.g., a flow regulating component, i.e., valve 6, 6a). This particular difference provides significant advantages over known designs, for example, by allowing easier and simplified assembly, increased flow sensor life, and / or improved flow sensor reliability. Furthermore, because the flow sensors no longer need to be designed to withstand increasing pressures, broader range suitable and potentially more accurate and reliable flow sensors become available, thereby allowing for improved overall accuracy of the particle monitoring system of the present invention as well as improved suitability to specific requirements. As an additional benefit, broader range suitable flow sensors allow for improved security of supply, which has recently been a cause of concern for manufacturers due to the COVID pandemic and the resulting supply chain disruptions.

[0053] Furthermore, by locating the flow sensor outside of the pressurized zone of the particle monitoring system, flow and pressure are separated, thereby eliminating the effect or cross-sensitivity of pressure on the flow sensor, resulting in accurate flow measurements. This increased accuracy of the present particle monitoring system is particularly beneficial and serves to effectively enable calibration of flow in the present particle monitoring system at ambient pressure. This, in turn, allows for simultaneous (i.e., not sequential, as in conventional particle monitoring systems) pressure and flow calibration.

[0054] The specific arrangement of the components of the particle monitoring system as defined herein also allows for a portable calibration system, thereby providing the opportunity for on-site calibration. This also eliminates the need to either maintain an in-house calibration laboratory or benchtop calibration equipment, which involves significant effort and cost to maintain and operate, or to send the particle monitoring system to a specialized calibration service. Not having to send the particle monitoring system avoids the risk of the equipment being damaged during transport, and also avoids the inconvenience of the user having to own or rent a back-up particle monitoring system while the equipment to be calibrated is away from the site.

Claims

1. A particle monitoring system (1), comprising: A sampling section (2) for performing a sampling process on a sample fluid flowing through the sampling section (2); and a sensor arrangement (3) for determining a volumetric flow rate of a sample fluid flowing through the sampling section (2), said sensor arrangement (3) being associated with a flow path (7) downstream of the sampling section (2) through which the sample fluid flows in operation after having passed through the sampling section (2); wherein the sensor arrangement (3) comprises a flow sensor (4) for determining a mass flow rate of a sample fluid flowing through a flow path (7) downstream of the sampling section (2), The particle monitoring system (1).

2. 2. A particle monitoring system (1) as described in claim 1, wherein the sensor arrangement (3) includes an absolute pressure sensor (5) for determining an absolute fluid pressure in the flow path (7), and the flow sensor (4) is disposed in a section of the flow path (7) downstream of the sampling section (2) and downstream of the absolute pressure sensor (5), in a flow direction away from the sampling section (2).

3. 3. A particle monitoring system (1) as claimed in claim 2, wherein the sensor arrangement (3) includes a flow regulation component (6; 6a) arranged in the flow path (7) between the absolute pressure sensor (5) and the flow sensor (4).

4. 4. The particle monitoring system (1) of claim 3, further comprising a control section (20) configured to calculate a volumetric flow rate of the sample fluid flowing through the sampling section (2) based on a mass flow rate determined by the flow sensor (4) and an absolute fluid pressure determined by the absolute pressure sensor (5).

5. A particle monitoring system (1) according to any one of the preceding claims, wherein the sensor arrangement (3), preferably the flow sensor (4), comprises a temperature sensor for measuring the temperature of the fluid in the flow sensor (4).

6. A particle monitoring system (1) according to any one of claims 1 to 5, wherein the flow sensor (4) comprises a differential pressure gauge for determining the pressure difference of the sample fluid across a predetermined geometric flow restriction, preferably a nozzle, through which the sample fluid flows, and a temperature sensor, preferably for measuring the temperature of the fluid within the differential pressure gauge.

7. The control section (20) regulates the volumetric flow rate through the sampling section (2) according to the following formula: [0010] The particle monitoring system (1) according to claim 6 in combination with claim 4, configured to calculate based on:

8. 8. A particle monitoring system (1) as described in claim 7, wherein the control section (20) is configured to be able to switch between types of sampled fluid / gas by selecting a fluid correction factor specific to each type of fluid / gas.

9. A particle monitoring system (1) as claimed in claim 4, or as claimed in claim 5 or claim 6 in combination with claim 4, or as claimed in claim 7 or claim 8, wherein the control section (20) is configured to be calibrated or adjusted with respect to a fluid flow rate determined by the flow sensor (4) and / or an absolute fluid pressure determined by the absolute pressure sensor (5).

10. A particle monitoring system (1) according to any one of claims 4 to 9 in combination with claim 3, wherein the control section (20) is configured to control the degree of restriction of the flow regulating components (6, 6a) based on the calculated volumetric flow rate to set the flow rate to a predetermined value.

11. A particle monitoring system (1) according to any one of claims 1 to 10, further comprising a particle filter (8), preferably a HEPA filter, arranged in the flow path (7) between the sampling section (2) and the flow sensor (4).

12. 1. A method for monitoring particles in a sample fluid, comprising: Sampling particles in a sample fluid flowing through the sampling section (2); and The volumetric flow rate of the sample fluid flowing through the sampling section (2) is defined as follows: determining a mass flow rate of the sample fluid flowing through the flow path downstream of the sampling section (2); Determining the absolute pressure in the flow path upstream of the location where the mass flow rate is determined and downstream of the sampling section (2); and Calculating a volumetric flow rate of the sample fluid flowing through the sampling section (2) based on the determined mass flow rate and the determined absolute pressure; To be determined by 20. A method for monitoring particles in said sample fluid comprising:

13. A method for monitoring particles in a sample fluid as described in claim 12, wherein the mass flow rate of the sample fluid flowing through the flow path is determined by measuring the pressure difference of the sample fluid upstream and downstream of a restriction (preferably a nozzle) through which the sample fluid flows.

14. The volumetric flow rate through the sampling section (2) is calculated according to the following formula: [0025] is calculated based on, and Preferably, the method comprises controlling the opening of a flow regulating component (6; 6a) arranged in the flow path between the position where the absolute pressure in the flow path is determined and the position where the pressure difference is measured, based on the calculated volumetric flow rate, to set the flow rate to a predetermined value. A method for monitoring particles in a sample fluid according to claim 13.

15. 10. A method for calibrating / adjusting a particle monitoring system (1) according to claim 9, comprising the steps of: closing the volume control component (6; 6a) to block the flow path (7) between the absolute pressure sensor (5) and the flow sensor (4); connecting an external test fluid source (15) to the inlet of the sampling section (2) of the particle monitoring system (1) and to the flow sensor (4); supplying a test fluid from an external test fluid source (15) to the sampling section (2) of the particle monitoring system (1) in a stepped sequence of increasing and / or decreasing pressures or at continuously increasing and / or decreasing pressures; supplying a test fluid from an external test fluid source (15) to the flow sensor (4) in a stepped sequence of increasing and / or decreasing flow values ​​or at a continuously increasing and / or decreasing flow rate; Simultaneously determining pressure and / or volumetric flow values ​​at the external test fluid source and the particle monitoring system (1); selecting correction values ​​for the discrete selected pressure / volume flow levels by curve fitting (preferably a polynomial curve fit) or by an interpolated look-up table, preferably by interpolating between the discrete levels; and inputting correction values ​​into a control section (20) of the particle monitoring system (1); Preferably, the pressure and flow corrections are applied independently and either sequentially or simultaneously. The method comprising the steps of:

16. A portable microbial air sampler, preferably for compressed gases, comprising a particle monitoring system according to any one of claims 1 to 11.

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