US3866475A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Stack sampling method and apparatus
Assignee: Individual
•
Filing: 1973-11-19
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Granted: 1975-02-18
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Expires: 1993-11-19
Abstract
Abstract A method and apparatus for achieving isokinetic sampling of a gas stream passing through a conduit, which method is independent of the local gas density. Side-by-side reference and sampling ducts are disposed within the conduit. The reference duct is open at both ends while the sampling duct is coupled with vacuum pumping apparatus and qualitative analysis instruments. Appropriate differential pressure sensing circuitry is coupled with each of the ducts to monitor the static pressure drop resulting from the flow of gas between two points in each duct. The differential pressure value is converted into an electrical signal and the signal originating from the reference duct circuitry is scaled by a factor of (1/k)2. This scaled reference duct signal is then compared with the signal originating from the sampling duct circuitry to provide an electrical difference signal that is utilized to drive the vacuum pumping means. This assures that the velocity of gas entering into the sampling duct will always equal the velocity of the gas passing through the conduit and isokinetic sampling will therefore be achieved.
Inventors
- 👤 Stanley P Thompson
- 👤 Thomas B Swearingen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 21:34
CPC Classifications
G; G01; G01N; G01N1/00; G01N1/02; G01N1/22; G01N1/2247; G01N1/24; G01N2001/225
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
207 words
Apparatus for achieving isokinetic sampling of a gas passing through a conduit, said apparatus comprising: a reference duct positioned in said conduit, said reference duct being open at opposite ends for the unimpeded flow of gas therethrough; a sampling duct disposed adjacent Said reference duct within said conduit, said reference and sampling ducts having like flow constants (c) and a velocity coefficient (k); vacuum pumping means coupled with said sampling duct for causing the flow of gas therethrough; first pressure sensitive means for monitoring the pressure drop between two points in said reference duct and converting the pressure drop value into a first electrical signal; second pressure sensitive means for monitoring the pressure drop between two points in said sampling duct and converting the pressure drop value into a second electrical signal; means for scaling the first electrical signal by a factor directly proportional to (1/k)2 to provide an electrical output signal; and means for comparing the second electrical signal with the electrical output signal to provide an electrical difference signal; said vacuum pumping means being operable in response to said electrical difference signal to cause the velocity of the gas passing through the sampling duct to equal the velocity of the gas passing through the conduit.
Claim 2
Dependent Claim
207 words
Apparatus for achieving isokinetic sampling of a gas passing through a conduit, said apparatus comprising: a reference duct positioned in said conduit, said reference duct being open at opposite ends for the unimpeded flow of gas therethrough; a sampling duct disposed adjacent Said reference duct within said conduit, said reference and sampling ducts having like flow constants (c) and a velocity coefficient (k); vacuum pumping means coupled with said sampling duct for causing the flow of gas therethrough; first pressure sensitive means for monitoring the pressure drop between two points in said reference duct and converting the pressure drop value into a first electrical signal; second pressure sensitive means for monitoring the pressure drop between two points in said sampling duct and converting the pressure drop value into a second electrical signal; means for scaling the first electrical signal by a factor directly proportional to (1/k)2 to provide an electrical output signal; and means for comparing the second electrical signal with the electrical output signal to provide an electrical difference signal; said vacuum pumping means being operable in response to said electrical difference signal to cause the velocity of the gas passing through the sampling duct to equal the velocity of the gas passing through the conduit.
Claim 3
Dependent Claim
33 words
The invention of claim 1, wherein each of said reference and sampling ducts includes a venturi section, said two points in each duct being located on opposite ends of the venturi entrance cone.
Claim 4
Dependent Claim
28 words
The invention of claim 2, wherein said two points in each of said ducts are located, respectively, ahead of the venturi entrance cone and at the venturi throat.
Claim 5
Dependent Claim
20 words
The invention of claim 1, wherein said reference and sampling ducts are disposed within said conduit in aligned side-by-side relationship.
Claim 6
Dependent Claim
16 words
The invention of claim 1, wherein said reference and sampling ducts are of identical geometric configuration.
Claim 7
Independent Claim
210 words
A method of isokinetically sampling a gas passing through a conduit having adjacent sampling and reference ducts, said ducts characterized by like flow constants (c) and a velocity coefficient (k), said reference duct being open at opposite ends for the unimpeded flow of gas therethrough and said sampling duct being coupled with vacuum pumping apparatus, said method comprising the steps of: moving a first quantity of said gas through said sampling duct; moving a second quantity of said gas through said reference duct by operation of said vacuum pumping apparatus; monitoring the static pressure drop attributable to the flow of gas between two points in said reference duct and converting the pressure drop value into a first electrical signal; monitoring the static pressure drop attributable to the flow of gas between two points in said sampling duct and converting the pressure drop value into a second electrical signal; scaling the first electrical signal by a factor directly proportional to (1/k)2 to provide an electrical output signal; comparing the value of the second electrical signal with the value of the output signal to provide an electrical difference signal; and driving said vacuum pumping apparatus with said difference signal to cause the second electrical signal to equal the scaled first electrical signal.
Claim 8
Independent Claim
210 words
A method of isokinetically sampling a gas passing through a conduit having adjacent sampling and reference ducts, said ducts characterized by like flow constants (c) and a velocity coefficient (k), said reference duct being open at opposite ends for the unimpeded flow of gas therethrough and said sampling duct being coupled with vacuum pumping apparatus, said method comprising the steps of: moving a first quantity of said gas through said sampling duct; moving a second quantity of said gas through said reference duct by operation of said vacuum pumping apparatus; monitoring the static pressure drop attributable to the flow of gas between two points in said reference duct and converting the pressure drop value into a first electrical signal; monitoring the static pressure drop attributable to the flow of gas between two points in said sampling duct and converting the pressure drop value into a second electrical signal; scaling the first electrical signal by a factor directly proportional to (1/k)2 to provide an electrical output signal; comparing the value of the second electrical signal with the value of the output signal to provide an electrical difference signal; and driving said vacuum pumping apparatus with said difference signal to cause the second electrical signal to equal the scaled first electrical signal.
Claim 9
Dependent Claim
53 words
A method as set forth in claim 6, wherein each of said reference and sampling ducts includes a venturi section, and each of the two monitoring steps comprises monitoring the pressure drop in the respective ducts between a first point ahead of the venturi cone and a second point at the venturi throat.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-02-17 | 1978-08-19 | 1979-02-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-02-17 | 1982-08-19 | 1983-02-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-02-17 | 1986-08-19 | 1987-02-18 | $7700.00 | Window Closed / Lapsed |