Particle sensor and sensing method

Patent metadata

Field	Value
Publication number	US-10859485-B2
Application number	US-201615578759-A
Country	US
Kind code	B2
Filing date	May 31, 2016
Priority date	Jun 5, 2015
Publication date	Dec 8, 2020
Grant date	Dec 8, 2020

Abstract

A particle sensor includes an aperture for receiving a gas flow with entrained particles, an electrostatic particle charging section, a parallel-plate particle precipitation section; and a sensor for detecting precipitated particles to produce a sensor signal. The sensor signal I sensor is related to an apparent particle number concentration of the particles in the gas flow entering the charging section by a calibration constant S 1 , such that I sensor =f(N app , S 1 ), the calibration constant being dependent on a count mean diameter of the particles in the gas flow entering the charging section according to a first relationship. The particle sensor includes a pre-filter positioned upstream from the charging section, the pre-filter filtering a part of the particles from the gas flow entering the pre-filter, a fractional degree of particle filtering depending on the count mean particle diameter of the particles entering the pre-filter according to a second relationship.

First claim

The invention claimed is:

1. A particle sensor, comprising: an input aperture for receiving a gas flow with entrained particles; an electrostatic particle charging section; a parallel-plate particle precipitation section, wherein the parallel-plate particle precipitation section has a plate aperture; and a sensor, wherein the sensor is arranged to detect precipitated particles to produce a sensor signal, wherein the sensor signal Isensor is related to an apparent particle number concentration N app of the particles in the gas flow entering the charging section by a calibration constant S1, such that Isensor=f(Na pp , S1), wherein the calibration constant S1 is dependent on a count mean diameter d p,av(cs) of the particles in the gas flow entering the charging section according to a first relationship:
S 1 =f 1 ( d p,av(cs) )
wherein the particle sensor comprises a pre-filter positioned upstream from the charging section, wherein the pre-filter removes a portion of the particles from the gas flow entering the pre-filter, wherein a fractional degree η of particle filtering depends on the count mean particle diameter d p,av of the particles entering the pre-filter according to a second relationship:
η= f 2 ( d p,av )

wherein characteristics of the pre-filter are such that the produced sensor signal is in response to entrained particles which are not filtered out by the pre-filter relates to the apparent particle number concentration N app of the particles entering the pre-filter by a calibration constant S, wherein the calibration constant S is dependent on the count mean diameter d p,av of the particles entering the pre-filter according to a third relationship:
S=f 3 ( d p,av )

wherein the third relationship is less dependent on the respective count mean diameter than the first relationship for a range of count mean diameters 25 nm to 100 nm, such that the dependency of the sensor signal obtained from the parallel-plate precipitation section on a particle size distribution at the plate aperture is at least partly compensated for, such that the sensor signal is less dependent on the particle size distribution at the input aperture of the particle sensor.

2. The particle sensor as claimed in claim 1 , wherein the first relationship is approximated by a linear relationship:
S 1 =A 1 ·d p,av(cs) +B 1
wherein A 1 and B 1 are positive constants,
wherein A 1 and B 1 depend on a gas flow rate, an applied particle precipitation voltage, and a design of the parallel-plate particle precipitation section.

3. The particle sensor as claimed in claim 2 , wherein the second relationship is approximated according to a power relationship:

η
=

A
2

(

d

p
,
av

)

B
2

wherein A 2 and B 2 are positive constants,
wherein A 2 and B 2 depend on the characteristics of the pre-filter and a gas flow speed through the pre-filter.

4. The particle sensor as claimed in claim 3 , wherein the pre-filter and the operating gas flow speed are arranged such that the calibration constant S given by the third relationship according to an approximate function

S
=

A
1

⁢

d

p
,
av

+

B
1

1
-

A
2

(

d

p
,
av

)

B
2

reaches a minimum value within a range of 25 nm≤d p,av ≤50 nm.

5. The particle sensor as claimed in claim 1 , wherein the pre-filter comprises an activated carbon filter.

6. The particle sensor as claimed in claim 5 , wherein the pre-filter has a volume of at least 1 ml per 0.1 liter/min of the sampled gas flow.

7. A method of designing a particle sensor, comprising: designing an electrostatic particle charging section and a parallel-plate particle precipitation section, wherein the parallel-plate particle precipitation section has a plate aperture; selecting a sensor for detecting the precipitated particles to produce a sensor signal, wherein the sensor signal is related to an apparent particle number concentration N app of the particles entering the electrostatic charging section by a calibration constant S 1 , such that Isensor=f(Napp, S1), wherein the calibration constant S1 is dependent on a count mean diameter d p,av (cs) of the particles in a gas flow entering the charging section according to a first relationship:
S 1 =f 1 ( d p,av(cs) ), and
designing a pre-filter for positioning upstream from the charging section, wherein the pre-filter has a second relationship between a fractional degree of particle deposition η within the pre-filter and the count mean diameter d p,av of the particles in the gas flow entering the pre-filter:
η= f 2 ( d p,av )

selecting characteristics of the pre-filter such that the sensor signal in response to entrained particles which are not filtered out by the pre-filter relates to the apparent particle number concentration N app of the particles entering the pre-filter by a calibration constant S, wherein the calibration constant S is dependent on the count mean diameter d p,av of the particles entering the pre-filter according to a third relationship:
S=f 3 ( d p,av )

wherein the third relationship is less dependent on the respective count mean diameter than the first relationship for a range of count mean diameters 25 nm to 100 nm, such that the dependency of the sensor signal obtained from the parallel-plate precipitation section on a particle size distribution at the plate aperture is at least partly compensated for, such that the sensor signal is less dependent on the particle size distribution at an input aperture of the particle sensor.

8. The method as claimed in claim 7 , wherein the first relationship is approximated by a linear relationship:
S 1 =A 1 ·d p,av(cs) +B 1
wherein A 1 and B 1 are positive constants,
wherein A 1 and B 1 depend on a flow rate, a precipitation voltage, and a design of the p

Assignees

• Koninklijke Philips Nv

Inventors

• Marra Johan

Classifications

• B03C3/155

  Filtration · CPC title

• B03C2201/06

  Ionising electrode being a needle · CPC title

• B03C3/49

  tubular · CPC title

• B03C3/368

  by other than static mechanical means, e.g. internal ventilator or recycler · CPC title

• B03C3/12

  characterised by separation of ionising and collecting stations · CPC title