EP-4739994-A1 - METHOD AND APPARATUS FOR MEASURING CHARACTERISTICS OF A PARTICLE FLOW

Abstract

In the presented solution characteristics of a particle flow is measured. A sample flow (Q) comprising electrically charged particles is guided through a passage (2). A mobility analyser (8) having a particle cut-off size is provided. An electrical current carried by the charged particles penetrated through the mobility analyser (8) is measured. The cut-off size of the mobility analyser (8) is alternated. A dynamic model provides a simulated signal (Si m) describing the behaviour of the electrical current during the state of change as a response to alternating the cut-off size of the mobility analyser (8). Similarity between the simulated signal (Si m ) and measured electrical current (I em ) is optimized. A value of a particle size parameter (pS) is updated. Concentration quantities (C1-Cn) of the particle flow are determined using the updated parameter value (pS) and the measured electrical current (I em ).

Inventors

• JANKA, KAUKO
• SAUKKO, ERKKA

Assignees

• Pegasor Oy

Dates

Publication Date

20260513

Application Date

20240704

Claims (17)

1. 1. A method of measuring characteristics of a particle flow, the method comprising guiding a sample flow comprising electrically charged particles through a passage; providing a mobility analyser having a particle cut-off size, the mobility analyser allowing particles having a size larger than the cut-off size to penetrate through the mobility analyser; measuring an electrical current carried by the charged particles penetrated through the mobility analyser; alternating the cut-off size of the mobility analyser thereby forming a state of change for the resulting electrical current; providing a dynamic model providing a simulated signal describing the behaviour of the electrical current during the state of change, the model comprising as input parameters a variable alternating the cut-off size of the mobility analyser, and a particle-size parameter of the sample flow; optimizing similarity between the simulated signal and measured electrical current; updating a value of the particle-size parameter based on adequate similarity between the simulated signal and measured electrical current; and determining, already during the state of change, concentration quantities of the particle flow using the updated parameter value and the measured electrical current.
2. 2. A method as claimed in claim 1, wherein the model comprises as an input parameter also a flow-rate parameter of the sample flow and also a value of the flow-rate parameter is updated based on adequate similarity between the simulated signal and the measured electrical current.
3. 3. A method as claimed in claim 1 or 2, wherein the concentration quantities of the particle flow are determined using the updated parameter value, the measured electrical current, and the simulated signal.
4. 4. A method as claimed in claim 3, comprising eliminating an effect of alternating the cut-off size of the mobility analyser to the measured electrical current by dividing the measured electrical current or its derivative by the simulated signal or its derivative, thereby forming a reformed signal.
5. 5. A method as claimed in claim 4, wherein similarity between the simulated signal and measured electrical current is optimized by minimizing the influence of cut-off size modulation on the reformed signal.
6. 6. A method as claimed in any one of the preceding claims, comprising controlling alternating the cut-off size of the mobility analyser such that a resulting modulation ratio is kept essentially constant, the resulting modulation ratio being a ratio between the measured electrical current on a higher cut-off size and the measured electrical current on a lower cut-off size.
7. 7. A method as claimed in any one of the preceding claims, wherein the dynamic model comprises differential equations or difference equations as a function of time.
8. 8. A method as claimed in claim 7, wherein the simulated signal of the dynamic model is achieved by computing the results of the equations over time.
9. 9. A method as claimed in any one of the preceding claims, wherein similarity between the simulated signal and measured electrical current is optimized by performing similarity calculations between the measured current and the simulated signal.
10. 10. A method as claimed in claim 9, wherein the similarity calculations utilize covariance, correlation, or essentially same kind of statistical measure between the measured electrical current and the simulated signal.
11. 11. A method as claimed in claim 9 or 10, wherein the similarity calculations comprise interpolation.
12. 12. A method as claimed in any one of the preceding claims, wherein a zeroth-order mobility analyser is used as the mobility analyser.
13. 13. An apparatus for measuring characteristics of a particle flow, the apparatus comprising a passage guiding a sample flow comprising electrically charged particles; a mobility analyser having a particle cut-off size, the mobility analyser allowing particles having a size larger than the cut-off size to penetrate through the mobility analyser; a measuring device measuring an electrical current carried by the charged particles penetrated through the mobility analyser; and a control unit, the control unit being arranged to alternate the cut-off size of the mobility analyser thereby forming a state of change for the resulting electrical current; comprising a dynamic model providing a simulated signal describing the behaviour of the electrical current during the state of change, the model comprising as input parameters a variable alternating the cut-off size of the mobility analyser, and a particle-size parameter of the sample flow ; being arranged to optimize similarity between the simulated signal and measured electrical current; being arranged to update a value of the particle-size parameter based on adequate similarity between the simulated signal and measured electrical current; and being arranged to determine, already during the state of change, concentration quantities of the particle flow using the updated parameter value and the measured electrical current.
14. 14. An apparatus as claimed in claim 13, wherein the control unit being arranged to determine the characteristics of the particle flow using the determined parameter value, the measured electrical current, and the simulated signal.
15. 15. An apparatus as claimed in claim 13 or 14, wherein the dynamic model comprises differential equations or difference equations as a function of time.
16. 16. An apparatus as claimed in claim 15, wherein the control unit is arranged to compute the results of the equations over time to achieve the simulated signal of the dynamic model.
17. 17. An apparatus as claimed in any one of the claims 13 to 16, wherein the mobility analyser is a zeroth-order mobility analyser.

Description

METHOD AND APPARATUS FOR MEASURING CHARACTERISTICS OF A PARTICLE FLOW FIELD OF THE INVENTION The invention relates to a method of measuring characteristics of a particle flow and to an apparatus for measuring characteristics of a particle flow. BACKGROUND OF THE INVENTION Particles suspended in gaseous carrier i.e. aerosols play a significant role in ambient and indoor air quality and in many technical processes. An important task lies in detecting the concentration of the particles by way of measurement technology. Particles in the size range of smaller than 10 micrometers diameter may be breathed in by humans and may have a detrimental effect on health. The most recent research results indicate that the usual protective functions of humans are no longer effective for nanoparticles <100 nm in diameter. Nanoparticles arise mainly in combustion processes such as in motor vehicles, coal-fired power stations, wood heating installations, etc. The increased awareness of the adverse health effect of the air pollutants has led to a growing need for up-to-date information on the air quality. Thus, there is an increased need for improved solutions for measuring characteristics of a particle flow. Previous state of the art includes detection methods where the detection instrument changes state of the response between two states to gain advanced information about the particle flow, such as particle size. The problem with this approach is that as the instrument state is changed, the response has a time period where it is transient between these two states and a period of measurement signal is lost. When reaching for faster response time of the device, by increasing the frequency of state changes, an increasing amount of measurement time is lost to settling time between these different states. At the limit, no measurement time is used when the half cycle is as long as the response time of the instrument. BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a new method and apparatus. The invention is characterized by what is stated in the independent claims. Some embodiments of the invention are disclosed in the dependent claims. In the presented solution characteristics of a particle flow is measured. A sample flow comprising electrically charged particles is guided through a passage. A mobility analyser having a particle cut-off size is provided. The mobility analyser allows particles having a size larger than the cut-off size to penetrate through the mobility analyser. An electrical current carried by the charged particles penetrated through the mobility analyser is measured. The cut-off size of the mobility analyser is alternated. Alternating the cut-off size of the mobility analyser forms a state of change for the resulting measured electrical current. A dynamic model provides a simulated signal describing the behaviour of the electrical current during the state of change. The model comprises as input parameters a variable alternating the cut-off size of the mobility analyser, and a particle-size parameter of the sample flow. Similarity between the simulated signal and measured electrical current is optimized. A value of the particle-size parameter is updated based on adequate similarity between the simulated signal and measured electrical current. Concentration quantities of the particle flow are determined already during the state of change using the updated parameter value and the measured electrical current. Similarity between the simulated signal and measured electrical current may be optimized by performing similarity calculations between the measured current and the simulated signal. The definition that the model is dynamic means that the model comprises a at least one time dependent factor. Alternating and controlling the cut-off size is continuous and dependent on measurement result such as measured particle size, flow rate, and/or other factors, and thereby regenerative. The alternating and controlling is so fast that an automatic control device is required. The length of measurement cycle of repeating instrument state is according to an embodiment smaller that 5 seconds and according to another embodiment smaller than 1 second. According to another embodiment the length of the measurement cycle is less than five times and according to another embodiment two times a response time of the device for the change in the cut-off size. The response time is the time duration in which the change in the measured electrical current to 90 % of the final change takes as a result of cut-off size change. In the presented solution in parallel with the measured signal a comparison or simulated signal corresponding to the size factor(s) of the particles is simulated. The idea is that the comparison or simulated signal is as similar as possible with the measured signal when the same particle size is used in the measurement and in the simulation. In the presented solution the similarity betwe