CA2177504C - Measurement of solid particle concentration in a fluid stream - Google Patents

Measurement of solid particle concentration in a fluid stream

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Publication number
CA2177504C
CA2177504C CA002177504A CA2177504A CA2177504C CA 2177504 C CA2177504 C CA 2177504C CA 002177504 A CA002177504 A CA 002177504A CA 2177504 A CA2177504 A CA 2177504A CA 2177504 C CA2177504 C CA 2177504C
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CA
Canada
Prior art keywords
signal
probe
providing
function
fluid stream
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA002177504A
Other languages
French (fr)
Other versions
CA2177504A1 (en
Inventor
Scott M. Hewelt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Venture Measurement Co LLC
Original Assignee
Bindicator Co LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bindicator Co LLC filed Critical Bindicator Co LLC
Publication of CA2177504A1 publication Critical patent/CA2177504A1/en
Application granted granted Critical
Publication of CA2177504C publication Critical patent/CA2177504C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/60Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrostatic variables, e.g. electrographic flaw testing
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/06Investigating concentration of particle suspensions
    • G01N15/0656Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00Sampling; Preparing specimens for investigation
    • G01N1/02Devices for withdrawing samples
    • G01N1/22Devices for withdrawing samples in the gaseous state
    • G01N1/2202Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G01N2001/222Other features
    • G01N2001/2223Other features aerosol sampling devices

Abstract

Apparatus for measuring concentration of solid particles in a fluid stream that includes a probe for disposition in the fluid stream to provide an electrical probe signal as a triboelectric function of concentration of solid particles in the fluid stream. A first circuit is coupled to the probe for providing a first electrical signal as a proportional function of the probe signal. A second circuit is coupled to the probe for providing a second electrical signal as a function of rate of change of the probe signal. Differential amplifiers received the first and second signals, and provide a third signal as a function of a difference therebetween. An apparatus output signal is provided when such difference exceeds a preselected threshold.

Description

2~ 77504 MEASUREMENT OF SOLID PARTICLE CONCENTRATION IN A FL~ID
STREAM
The present invention is directed to a method and apparatus for measuring ollC~ILIdLi~l~ of solid particles in a fluid stream such as air employing the so-called , il.o~ . ;. effect.
and Summar~ of the Invention It has heretofore been proposed to measure lU~ IdLiUII of solid materials, such as dust, powder or granular products, flowing in a pneumatic conveyor line. One typical installation would be d~J..IIaLltdlll of a dust collector, with the device being configured to sense material in suspension and thus indicating failure at the dust collector.
Another applicdtion is as a flow sensor to monitor continuous flow of material in a pneumatic conveyor, and to provide an indicati`on of flow t~ ", ~ due, for example, to a plugged conveyor or loss of material feed. It is a general object of the present invention to provide a method and apparatus for measuring ~IJllC~ dLi~Jll of solid particles in a fluid strearn employing the 1~ effect tnat are of simple and ill."~ .laiv~ design, that do not require ~ rl;~l during operation, thdt ~.. I.. ~l;.-lly adjust for voltage and dLulc drift during operation, that have operator selectable sensitiviy, and that rnay be readily employed with minimum operatom~ as either a flow sensor or flow-interruption sensor.
Bnefly stated, . ,..,. ~ ..11,.~;,... of solid particles in a fluid stream is monitored in accordance with a presently preferred ;...~ i.... of the invention by p~ a sensor or probe in the fluid stream so as to provide a sensor output signal that varies as a function of triboelectric effect of solid particles in the stream on the probe, and thus as a 2 ~ 77504 unction of ::ollC~ dLioll of the particles in the fluid stream. In æcordance with a g feature of the present invention, both change and rate of change of the sensor signal are monitored, and an output signal is provided when both change and rate of change of the sensor signal exceed a preselected threshold. By monitoring both change and rate of change of the sensor signal, gradual changes due to voltage and ~~ dlUlt: drift are ignored. This technique eliminates any l~uluil~ ,lll for a dead band to ~(~cnmmn~' voltage drift, or for additional circuitry to adjust for Lt;~ ,ld~u~ nmr~nC~i~inn Following selection of desired sensitivity and installation of the apparatus, no further calibration is necessary. Ill~ ive off-the-shelf electronic c.l."~ can be utilized without batch testing for low offset voltage or Lt:lll,u.,ldLul~ drift.
Apparatus for measuring concentration of solid particles in a fluid stream in accordance with the present invention thus includes a probe for disposition in the fluid stream to provide an electrical probe signal as a ~libocl~ LIic function of ~ollc~ ldLiull of solid particles in the fluid stream. A first circuit is coupled to the probe for providing a first electrical signal as a proportional function of the probe signal. A second circuit is coupled to the probe for providing a second electrical signal as a function of rate of change of the probe signal. Differential amplifiers received the first and second signals, and provide a third signal as a function of a difference LII~ An apparatus output signal is provided when such difference exceeds a preselected threshold. The first circuit in the preferred ~ ù~ of the invention includes facility for adjusting sensitivity of the apparatus by selectively IJlU,UUlLiUI~Iy scaling the first signal to the probe signal. This sensitivity adjustment circuit comprises a switchselectable voltage divider. The differential -2,--2 ~ 77504 amplifler provides the third signal when either of the first and second signals exceeds the other by more than the preselected threshold. In this way, the apparatus is responsive to both positive and negative changes in concentration of solid particles in the fluid stream, and thus may be employed as either a flow sensor or a flow~ r~llu,uLio-- sensor. In this respect, the apparatus circuitry also includes facility for selectively delaying provision of the apparatus output signal, and fail-safe facility for providing the apparatus output signal l. L~ of particle flow in the event of circuit or power failure.
Brief Description of the Drawin~s The invention, together with additional objects, features and advantages thereof, will be best understood from the following ~ rirtit)n, the appended claims and the a~,-,ulll,uallyillg drawings in which:
FIG. 1 is a schematic diagram of a dust collection system equipped with a flow sensor in æcordance with the present invention;
FIG. 2 is a functional block diagram of the flow sensor illustrated in FIG.
I; and FIG. 3 is an electrical schematic diagram of the flow sensor illustrated functionally in FIG. 2.
Detailed Description of Preferred ~ ` ' FIG. 1 illustraoes a dust collector system 10 equipped with a flow sensor 12 in accordance with the present invention. In system 10, an input pneumatic conveyor 14 feeds material 16 such as grain to a hopper 18. Grain 16 collects in the lower portion of hopper 18 for output to a railway car, for example. Filter bags 20 are disposed at the upper 2 ~ 775~4 portion of hopper 18, and air is drawn through filter bags 20 to a pneumatic conveyor output 22. The purpose of sensor 12 in this application is to detect presence of dust or other particles in pneumatic output line 12, and thus to detect rupture or failure at one or both of the filter bags 20. Flow sensor 12 includes a triboelectric probe or sensor 24 disposed within pneumatic line 22. Probe 24 provides an electrical probe or sensor signal to a detector circuit 26 that varies, according to the so-called triboelectric effect, with cùrlc~ dLiull of particles in the fluid stream passing the probe. That is, electric charge carried by particles in the air stream transfer to the probe, and the amplitude of the probe output signal is thus a direct function of ~UIII_~IILId~iUII of particles in the air stream.
Detector circuit 26 is responsive to such probe signal to provide an output signal to an alarm 28 when l .."~ ." of particles in the air stream exceeds a preselected threshold, thus indicating failure at one or more of the filter bags 20.
Sensor circuit 12 is illustrated in greater detail in FIG. 2 as including a high-gain highimpedance input amplifier 30 that receives the signal from probe 24. The output of amplifier 30 is fed to an adjustable voltage divider circuit 32 for selecting sensitivity of the overall detector circuit 26. The output of amplifier 30 is also fed to a delay circuit 34 that includes a resistor 36 connected in series with a capacitor C1. The voltage across capacitor Cl thus varies as a function of rate of change of the signal from probe 24 and amplifier 30. The voltage across capacitor Cl is connected through a unity gain amplifier 38 to one input of a differential amplifler circuit 40. The other input to differential amplifier circuit 40 is received from sensitivity adjustment circuit 32 across a capacitor C2, and through a second unity gain amplifier 42. The output of differential amplifier circuit 40, which varies as a function of the voltage vcl across capacitor Cl minus the voltage Vc2 across capacitor C2, is fed to an inverting differential amplifier circuit 44, which provides an output that varies as a function of the quantity (2V~-vcl) A first comparator amplifier 46 receives a signal input from capacitor Cl and a reference input from capacitor C2, and thus provides an output that switches high and low as a function of a ~nmr~rjSnn between the voltages Vcl and Vc2. A second .UllI,Udld~UI 48 receives a reference input from capacitor C2 and a signal input from inverting differential amplifier 44. Amplifier 48 thus provides an output that switches high and low as a function of a Cull~,u~i~ull between the quantity (2Vcz~Vcl) and voltage ~ . The output of comparator 46 thus responds to an increase in output voltage from amplifier 30, while the output of 48 responds to a decrease in such output voltage. At the same time, both 46, 48 are responsive to the rate of change of the output of amplifier 30 by means of the delay circuit consisting of resistor 36 and capacitor C1. Thus, when both the change and rate of change of the probe signal arnplifier output exceed the threshold settings of one of the LUlll,U~lG~UI~ 46, 48 in CUU,U~ld~iull with sensitivity adjustment circuit 32, the output of one of the CUlllu~.d~ul~ 46, 48 switches low, illllmin:lrin~ an LED 50 and providing an input alarrn signal to a Illi-,lU,UlUl,c;l:~UI 52. Miu-u,uluc~ol 52 also receives inputs from delay and fail safe selection circuits 54, 56, and provides a detector circuit output to alarm 28 (FIG. 1) through an output transistor 58 and an output relay 60.
FIG. 3 illustrates detector circuit 26 in greater detail. Sensitivity selection circuit 32 includes a BCD switch 62 for selectively ~onfi~lrin2 the voltage divider that consists of the resistor Rl coupled to probe amplifier 30, and the resistors R, 2R, 4R and 21 7750~
8R. Thus, the voltage appearing across capacitor C2 is proportionately related to the voltage output of amplifier 30 as a function of operator setting of switch 62. Fail safe selection circuit 56 comprises a switch 64 that provides either a high or low voltage input to a co~ uollvill~ port of ~ lu,uluCC~ul 52. The setting of switch 64 is selected as a function of the output desired at relay 60 in the event of circuit or power failure. For example, when detector circuit 26 is configured to provide an alarm output upon detection of dust in what should otherwise be a clear fluid stream, as in broken bag detection configuration 10 illustrated in FIG. 1, switch 64 may be configured to connect the cullt~uondillg Illi~lUulU~t~Ul port to electrical ground as illustrated in FIG. 3.
Mi~luu~u~ 52 is suitably l~lu~ æd to respond to this input signal so that transistor 58 and relay 60 are normally energized, and become vc~ i~l in the event of detection of material at probe 24. Thus, in the event of either circuit or power failure, relay 26 becomes dc~ ,l, and thus provides the desired alarm signal i"~ of actual conditions at probe 24.
A further input port of III;~,IU,UIU~ VI 52 is connected to electrical ground through a removable jumper or switch 66, and to the voltage supply through a pull-up resistor 68. Jumper 66 is provided to configure detector circuit 26 to be responsive either to presence of particles in a normally clear fluid stream (FIG. I) with jumper 66 ;n place, or for detection of di~a,u,u~ of particulate matter from an otherwise continuous flow with jumper 66 removed. Delay selection circuit 54 comprises a pair of switches 68, 70 and associated series resistors 69, 71 connected to cullt~,uù~ldillg Illi~lU~UlUCt~VI input ports for selecting one of four delay settings by which activation or deactivation of relay 60 is 21 775~4 delayed as cornpared with the outputs of ~,UIIIIJdlOLUl~ 46, 48 tû ~rC()m--- ' transient changes in material flow. Also connected tû (.UII~.,UOI~dill~ output ports of Illi~,lU,UlU~ UI
52 are a pair of LED's 72, 74. LED 72 is green, and indicates applicatiûn of electrical power to the apparatus. LED 74 is red, and indicates an alarm status when illllmin:~tPrl Both LED's are visible through the unit hûusing. See U.S. Patent No. 5,æ3,819, assigned tû the assignee hereof. A reed switch 76 is connected acrûss capacitor Cl, and is responsive to imposition of a magnetic field from outside ûf the apparatus hûusing for selectively testing circuit operation. Such external test feature is described in greater detail in U.S. Patent Nû. 5,048,335.
In operation, Illil,lU~lUC.,~UI 52 cûntains internal ~/IU~,Ii~'lllll;'l~, to respûnd to a low input from CùllllJ~laLul:~ 46, 48, after a delay set by switches 54, to change the status of transistor 58 and relay 60. In the example discussed above in which transistor 58 and output relay 60 are normally energized, a low output at Culll~ d~ul 46, indicating detection of dust at sensûr 24, turns transistor 58 and relay 60 off after the delay set by switches 54. Of course, if the output of UUII~lOld~UI 48 is only transient and disappears during the delay time, transistor 58 and relay 60 remain energized.
There is thus provided in accordance with the present invention a method and apparatus for measuring CUll~ dLiull ûf solid particles in a fluid stream that satisfy all of the objects and aims previûusly set fûrth. By monitoring both change and rate of change of the sensor output, there is no need fûr either continuous calibration or a voltage dead band tû ~ c~ ^ ' either voltage or L~ ldLUlC drift. Nor is there any need for continuous circuit calibration. The method and apparatus of the present invention are ~ I ~7~Q4 simple and inexpensive to implement, and ~ JIy adjust for voltage and L~ U~,ldLulc:
drift. The disclosed Pmhr~riimPnlc provide for operator selection of circuit sensitivity, to be set for example upon initial installation in a fluid flow system. Ful~ .lllolt:, the disclosed circuit rl,~ i."~ may be employed either as a flow sensor for detecting presence of particles in a normally clear air stream, or as a flow i~ ,llululi~ll serlsor for detecting absence of particles in a particulate conveyor ~ ilUlllll~llL.

Claims (12)

1.
Apparatus for measuring concentration of solid particles in a fluid stream that comprises:
triboelectric probe means for disposition in the fluid stream to provide an electrical probe signal as a function of concentration of solid particles in the fluid stream, first circuit means coupled to said probe means for providing a first electrical signal as a proportionate function of said probe signal, second circuit means for providing a second electrical signal as a function of rate of change of said probe signal, third circuit means for receiving said first and second signals, and providing a third signal as a function of a difference therebetween, and means for providing an output signal when said difference exceeds a preselected threshold.
2.
The apparatus set forth in claim 1 wherein said first circuit means includes means for adjusting sensitivity of said apparatus by selectively proportionately scaling said first signal to said probe signal.
3.
The apparatus set forth in claim 2 wherein said sensitivity adjusting means comprises voltage divider means and switch means for selectively connecting said voltage divider means to said first circuit means.
4.
The apparatus set forth in claim 1 wherein said third circuit means includes means providing said third signal when either of said first and second signals exceeds the other by said preselected threshold, such that said apparatus is responsive to both positive and negative changes in concentration of solid particles in the fluid stream.
5.
The apparatus set forth in claim 4 further comprising means for selectively delaying said output signal to accommodate transient changes in particle concentration at said probe means.
6.
The apparatus set forth in claim 1 wherein said means for providing said output signal includes fail-safe circuit means for providing said output signal independent of said first and second signals in the event of circuit as power failure at said apparatus.
7.
A method of monitoring concentration of solid particles in a fluid stream that comprises the steps of:
(a) positioning a sensor in the fluid stream so as to provide a sensor signal as a function of triboelectric effect of particles in the stream, (b) monitoring both change and rate of change of such sensor signal, and (c) providing an output signal when both change and rate of change of said sensor signal exceed a preselected threshold.
8.
Apparatus for measuring a condition of materials that comprises:
probe means for providing an electrical probe signal as a function of material condition, first circuit means coupled to said probe means for providing a first electrical signal as a proportionate function of said probe signal, second circuit means for providing a second electrical signal as a function of rate of change of said probe signal, third circuit means for receiving said first and second signals, and providing a third signal as a function of a difference therebetween, and means for providing an output signal when said difference exceeds a preselected threshold.
9.
The apparatus set forth in claim 8 wherein said first circuit means includes means for adjusting sensitivity of said apparatus by selectively proportionately scaling said first signal to said probe signal.
10.
The apparatus set forth in claim 9 wherein said sensitivity adjusting means comprises voltage divider means and switch means for selectively connecting said voltage divider means to said first circuit means.
11.
The apparatus set forth in claim 8 wherein said third circuit means includes means providing said third signal when either of said first and second signals exceeds the other by said preselected threshold, such that said apparatus is responsive to both positive and negative changes in material condition.
12.
The apparatus as set forth in claim 11 wherein said probe means comprises a triboelectric probe for providing said probe signal as a function of concentration of solid particles in a fluid stream.
CA002177504A 1995-09-25 1996-05-28 Measurement of solid particle concentration in a fluid stream Expired - Fee Related CA2177504C (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/533,438 US5644241A (en) 1995-09-25 1995-09-25 Measurement of solid particle concentration in a fluid stream responsive to magnitude and rate of change of a triboelectric probe output signal
US08/533,438 1995-09-25

Publications (2)

Publication Number Publication Date
CA2177504A1 CA2177504A1 (en) 1997-03-26
CA2177504C true CA2177504C (en) 1998-09-29

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CA002177504A Expired - Fee Related CA2177504C (en) 1995-09-25 1996-05-28 Measurement of solid particle concentration in a fluid stream

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Families Citing this family (10)

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DE19729144C2 (en) * 1997-07-08 2001-02-22 Foedisch Umweltmestechnik Gmbh Process and device system for the continuous determination of the dust concentration in flowing gases
GB2335745B (en) * 1998-03-27 2003-04-09 Pcme Ltd Improvements in and relating to particle detectors
DE19900484A1 (en) * 1999-01-08 2000-08-10 Wap Reinigungssysteme Measuring system for residual dust monitoring for safety vacuums
AUPP883399A0 (en) * 1999-02-24 1999-03-25 Commonwealth Scientific And Industrial Research Organisation A filter bag monitoring system
AUPQ685900A0 (en) 2000-04-12 2000-05-11 Goyen Controls Co Pty Limited Method and apparatus for detecting particles in a gas flow
GB0019132D0 (en) * 2000-08-04 2000-09-27 Aurora Technical Trading Ltd A solution monitor
US9261037B2 (en) * 2011-09-16 2016-02-16 Cummins Emission Solutions, Inc. Particulate matter sensor and systems
WO2018122416A1 (en) * 2016-12-30 2018-07-05 Televic Healthcare Nv Connection unit for connecting a plurality of medical devices and system comprising same
GB2578084B (en) 2018-08-10 2021-11-10 Pcme Ltd A particle concentration sensor
DE102018133546A1 (en) * 2018-12-21 2020-06-25 Minebea Mitsumi Inc. Combined Hall sensor / coding interface with integrated protection function

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Publication number Publication date
US5644241A (en) 1997-07-01
CA2177504A1 (en) 1997-03-26

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