FLOW MONITORED PARTICLE SENSOR

• US 20120222495A1
• Filed: 08/24/2010
• Published: 09/06/2012
• Est. Priority Date: 08/24/2009
• Status: Active Grant

• Current Assignee: Particle Measuring Systems Incorporated (Spectris PLC)
• Original Assignee: Particle Measuring Systems Incorporated (Spectris PLC)
• Inventors: Bates, Thomas
• Granted Patent: US 8,800,383 B2
• Time in Patent Office: Days
• US Class Current: 73/861.61
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G01N 1/2273 Atmospheric sampling
• CPC Class Codes: G01N 1/24 Suction devices G01N1/22 - G01N1/2294 take precedence
• CPC Class Codes: G01N 15/06 Investigating concentration of particle suspensions by weighing G01N5/00; investigating sedimentation of particle suspensions G01N15/04; investigating individual particles G01N15/10
• CPC Class Codes: G01N 2001/2223 aerosol sampling devices
• CPC Class Codes: G01N 2001/244 using critical flow orifices
• CPC Class Codes: G01N 2001/245 Fans

Abstract

Provided are devices and methods for monitoring flow rate in aerosol particle counters. The particle sensor has a particle counter, a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure (DP) across the flow measurement orifice during particle sensor operation and a critical flow orifice. A vacuum source pulls ambient gas through each of the particle counter, flow measurement orifice and critical flow orifice. An atmospheric pressure sensor measures atmospheric pressure (AP) and a bench pressure sensor measures pressure in the particle sensor (BP). The output from the sensors is used to identify a flow condition, such as by a monitor operably connected to each of the differential pressure sensor, atmospheric pressure sensor and bench pressure sensor. In this manner, deviation in flow rate from a target flow rate is readily monitored without the need for expensive sensors or other flow-controlling components.

Claims

1. A method of monitoring flow rate of a gas in a particle sensor, said method comprising the steps of:

providing a particle sensor comprising;

a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure across said flow measurement orifice;

a critical orifice;

a vacuum system for generating gas flow across said flow measurement orifice and said critical orifice;

generating a flow of gas through said particle sensor by establishing a vacuum pressure at a position downstream of said critical orifice;

determining a pressure drop (DPI) across said flow measurement orifice;

determining atmospheric pressure (API);

determining a pressure in said particle sensor (BPI) at a position that is upstream of said critical orifice; and

identifying a flow condition from said DPI, API and BPI values;

thereby monitoring said flow rate in said particle counter.

2. The method of claim 1, wherein said flow condition is selected from the group consisting of:

a satisfactory flow rate; and

a flow rate error condition.

3. The method of claim 1, wherein said flow condition is a flow rate error condition.

4. The method of claim 3, further comprising identifying said flow rate error condition as a vacuum-induced flow loss or an inlet-induced flow loss.

5. The method of claim 4, wherein said vacuum-induced flow loss is identified for:

DPI_corr<

(1−

TOLERANCE)²*DPI_target;

or

DPI_corr>

(1+TOLERANCE)₂*DPI_target;

wherein;

DPI_corr is the differential pressure sensor current reading across said now measurement orifice during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

DPI_target is a differential pressure sensor target value calculated as;

DPC_corr*(BPI_corr/BPC_cor), wherein;

DPC_corr is the differential pressure sensor value during system calibration;

BPI_corr is the bench pressure value during particle sensor operation; and

BPC_corr is the bench pressure value during system calibration.

6. The method of claim 5, wherein the TOLERANCE value is selected from a range that is greater than or equal to 5% and less than or equal to 15%.

7. The method of claim 6, wherein the TOLERANCE value is 10%.

8. The method of claim 4, wherein said inlet-induced flow loss is identified for:

APR_insitu<

(1−

TOLERANCE)*APR_calibration;

or

APR_insitu>

(1+TOLERANCE)*APR_calibration;

wherein;

APR_insitu is the pressure ratio of API_corr and BPI_corr during particle sensor operation;

(BPI_corr/API_corr), wherein;

API_corr is the atmospheric pressure value during particle sensor operation;

BPI_corr is the bench pressure value during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

APR_calibration is the pressure ratio of APC_corr and BPC_corr;

(BPC_corr/APC_corr), wherein;

BPC_corr is the bench pressure value at calibration; and

APC_corr is the atmospheric pressure at calibration.

9. The method of claim 8, wherein the TOLERANCE value is selected from a range that is greater than or equal to 5% and less than or equal to 15%.

10. The method of claim 9, wherein the TOLERANCE value is 10%.

11. The method of claim 1, wherein BPI is measured within an optical block of said particle sensor.

12. The method of claim 1, wherein said flow measurement orifice is positioned upstream of said critical orifice.

13. The method of claim 1, wherein the vacuum source is a house vacuum.

14. The method of claim 1, wherein the gas is air.

15. The method of claim 1, further comprising identifying a flow condition that deviates by 10% or more from a target flow rate.

16. The method of claim 15, wherein the target flow rate is 1 CFM.

17. The method of claim 15 further comprising identifying a source of said flow condition deviation, wherein said source is a vacuum-induced loss or an inlet-induced flow loss.

18. A method of monitoring volumetric flow rate of a gas in a particle sensor, said method comprising the steps of:

providing a particle sensor comprising;

a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure across said flow measurement orifice, a critical orifice;

a vacuum system for generating gas flow across said flow measurement orifice and said critical orifice;

generating a flow of gas through said particle sensor by establishing a vacuum pressure at a position downstream of said critical orifice;

determining a pressure drop (DPI) across said flow measurement orifice;

determining atmospheric pressure (API); and

determining a pressure in said particle sensor (BPI) at a position that is upstream of said critical orifice; and

identifying a flow condition from said DP, AP and BP values, wherein said flow condition is identified as;

a vacuum-induced flow loss for;

DPI_corr<

(1−

TOLERANCE)²*DPI_target;

or

DPI_corr>

(1+TOLERANCE)₂*DPI_target;

wherein;

DPI_corr is the differential pressure sensor current reading across said flow measurement orifice during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

DPI_target is a differential pressure sensor target value calculated as;

DPC_corr*(BPI_corr/BPC_cor), wherein;

DPC_corr is the differential pressure sensor value during system calibration;

BPI_corr is the bench pressure value during particle sensor operation; and

BPC_corr is the bench pressure value during system calibration;

or;

an inlet-induced flow loss for;

APR_insitu<

(1−

TOLERANCE)*APR_calibration;

or

APR_insitu>

(1+TOLERANCE)*APR_calibration;

wherein;

APR_insitu is the pressure ratio of API_corr, and BPI_corr during particle sensor operation;

(BPI_corr/API_corr);

API_corr is the atmospheric pressure value during particle sensor operation;

BPI_corr is the bench pressure value during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

APR_calibration is the pressure ratio of APC_corr and BPC_corr;

(BPC_corr APC_corr), wherein;

BPC_corr is the bench pressure value at calibration; and

APC_corr is the atmospheric pressure at calibration.

thereby monitoring said volumetric flow rate in said particle counter.

19. A particle sensor comprising:

a particle counter;

a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure across said flow measurement orifice (DPI) during particle sensor operation;

a critical flow orifice;

a vacuum source for pulling ambient gas through each of said particle counter, flow measurement orifice and critical flow orifice;

an atmospheric pressure sensor for measuring atmospheric pressure (API);

a bench pressure sensor for measuring pressure in said particle sensor (BPI);

a monitor operably connected to each of said differential pressure sensor, atmospheric pressure sensor and bench pressure sensor, wherein said monitor identifies a flow condition from said DPI, API and BPI.

20. The particle sensor of claim 19, wherein said monitor is an alarm that indicates when said flow condition is a flow-rate error.

21. The particle sensor of claim 20, wherein said flow-rate error is a 10% or greater deviation from a target flow rate of gas through said particle sensor.

22. The particle sensor of claim 20, wherein said flow rate error is for one or more conditions defined by:

DPI_corr<

(1−

TOLERANCE)²*DPI_target;

DPI_corr>

(1+TOLERANCE)^2*DPI_target;

APR_insitu<

(1−

TOLERANCE)*APR_calibration; and

APR_insitu>

(1+TOLERANCE)*APR_calibration;

wherein;

DPI_corr is the differential pressure sensor current reading across said flow measurement orifice during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

DPI_target is a differential pressure sensor target value calculated as;

DPC_corr*(BPI_corr/BPC_cor) wherein;

DPC_corr is the differential pressure sensor value during system calibration;

BPI_corr is the bench pressure value during particle sensor operation; and

BPC_corr is the bench pressure value during system calibration;

APR_insitu is the pressure ratio of API_corr and BPI_corr during particle sensor operation;

(BPI_corr/API_corr), wherein;

API_corr is the atmospheric pressure value during particle sensor operation;

BPI_corr is the bench pressure value during particle sensor operation;

APR_calibration is the pressure ratio of APC_corr and BPC_corr;

(BPC_corr/APC_corr), wherein;

APC_corr is the atmospheric pressure at calibration.

23. The particle sensor of claim 19, wherein said flow condition is a satisfactory flow condition, wherein said satisfactory flow condition is a flow-rate that is less than or equal to 10% deviation from a target flow-rate.

24. The particle sensor of claim 19 wherein the flow measurement orifice is positioned between said particle counter and critical flow orifice.

25. The particle sensor of claim 19, wherein the bench pressure sensor measures pressure within an optical block of said particle counter.

26. A particle sensor comprising:

a particle counter;

a flow measurement orifice comprising a differential pressure sensor for measuring differential pressure across said flow measurement orifice (DPI) during particle sensor operation;

a critical flow orifice;

a vacuum source for pulling ambient gas through each of said particle counter, flow measurement orifice and critical flow orifice;

an atmospheric pressure sensor for measuring atmospheric pressure (API);

a bench pressure sensor for measuring pressure in said particle sensor (BPI);

a monitor operably connected to each of said differential pressure sensor, atmospheric pressure sensor and bench pressure sensor, wherein said monitor identifies a flow condition from said DPI, API and BPI, and said flow condition is a flow rate error for one or more of;

DPI_corr<

(1−

TOLERANCE)²*DPI_target;

DPI_corr >

(1+TOLERANCE)²*DPI_target;

APR_insitu<

(1−

TOLERANCE)*APR_calibration; and

APR_insitu>

(1+TOLERANCE)*APR_calibration;

wherein;

DPI_corr is the differential pressure sensor current reading across said flow measurement orifice during particle sensor operation;

TOLERANCE is a user-selected flow rate tolerance level;

DPI_target is a differential pressure sensor target value calculated as;

DPC_corr*(BPI_corr/BPC_cor), wherein;

DPC_corr is the differential pressure sensor value during system calibration;

BPI_corr is the bench pressure value during particle sensor operation; and

BPC_corr is the bench pressure value during system calibration.

APR_insitu is the pressure ratio of API_corr and BPI_corr during particle sensor operation;

(BPI_corr/API_corr), wherein;

API_corr is the atmospheric pressure value during particle sensor operation;

BPI_corr is the bench pressure value during particle sensor operation;

APR_calibration is the pressure ratio of APC_corr and BPC_corr;

(BPC_corr/APC_corr), wherein;

APC_corr is the atmospheric pressure at calibration.