System for extracting samples from a stream

Abstract

A system for extracting samples from a stream in a conduit utilizing a probe, placed in the stream and having a channel for passing samples from the conduit stream. First and second pressure taps measure the pressure inside and outside the probe. A feedback signal, based on a pressure differential relative to the probe, is generated and controls a valve regulating sample velocity flow through the probe channel, that bears a fixed proportion to the velocity of flow in the conduit. The constant of proportionality between flow velocities in the conduit and the probe may be 1.0, resulting in an isokinetic sampling condition.

1 . A system for extracting samples from a stream flowing in a conduit, comprising: 
 a. a probe located in said conduit, said probe including a channel for passing a sample flow from the conduit for analysis;    b. regulating means for controlling the velocity of the sample flow through said probe channel to correspond to the velocity of the stream flowing in the conduit, said regulating means comprising means for generating a feedback signal representing the relative velocities of the stream flowing in the conduit and the sample flow through said probe channel; and    c. a filter for capturing particulate matter, said filter communicating with said probe channel,    wherein said means for generating a feedback signal includes a conduit static pressure measuring means formed in an enclosed path located closely adjacent an external surface of said probe.    
   
   
       2 . The system of  claim 1  which additionally comprises a pump, said regulating means feedback signal controlling the pump flow rate of said pump to isokinetically deliver sample from said probe channel to said filter.  
   
   
       3 . The system of  claim 1  in which said means for generating a feedback signal further comprises first pressure measuring means for determining the pressure within said probe channel, and a comparator means for measuring the pressure differential between pressure determined by said first pressure measuring means and the conduit static pressure measuring means and for generating a signal representative of said pressure differential.  
   
   
       4 . The system of  claim 1  which additionally comprises a condenser communicating with the pump to generate liquid matter from said sample flowing from said probe channel and a dry gas meter communicating with said pump for measuring the volume of gas in said sample flowing from said probe channel.  
   
   
       5 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, the probe having an interior and an external surface;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) an external pressure port that is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe, said external pressure port being formed into an enclosed path located closely adjacent to the external surface of said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe; and    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure ports, to maintain at least substantially equal static pressures internally of and externally to said probe.    
   
   
       6 . The sampling system as recited in  claim 5 , wherein said external pressure port is formed in a tube located on an external surface of said probe.  
   
   
       7 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, said probe having an interior and an external surface;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) an external pressure port that is located externally of the external surface of said probe and that is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe;    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure taps, to maintain at least substantially equal static pressures internally of and externally to said probe; and    F) at least one additional external pressure port configured to provide an indication of a static pressure in said portion of the fluid stream.    
   
   
       8 . The sampling system as recited in  claim 7 , wherein said external pressure ports are arranged relative to one another so as to substantially cancel the effects of any misalignment between the direction of flow in the stream and the orientation of the pressure ports.  
   
   
       9 . The sampling system of  claim 7 , further comprising a differential pressure sensor that is coupled to said external pressure port, said internal pressure port, and said controller, said differential pressure sensor generating a signal indicative of a pressure differential between the interior of said probe and the exterior of said probe and transmitting said signal to said controller.  
   
   
       10 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, said probe having an interior and an external surface;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) an external pressure port that is located externally of the external surface of said probe and that is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe;    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure taps, to maintain at least substantially equal static pressures internally of and externally to said probe; and    F) a dilution tunnel and an exhaust line having an inlet connected to said probe and an outlet opening into said dilution tunnel, wherein said flow control device comprises a damper that controls an ambient fluid flow rate though said dilution tunnel.    
   
   
       11 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, said probe having an interior and an external surface;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) an external pressure port that is located externally of the external surface of said probe and that is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe; and    (D) a flow control device that is configured to adjust a fluid flow rate through said probe; and    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure taps, to maintain at least substantially equal static pressures internally of and externally to said probe, wherein said flow control device comprises a variable speed pump that is coupled to said probe.    
   
   
       12 . The sampling system as recited in  claim 5 , wherein said controller is a closed-loop feedback controller.  
   
   
       13 . The sampling system as recited in  claim 6 , wherein said internal pressure port is located adjacent a tip of said probe.  
   
   
       14 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, said probe having an interior and an external surface;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) an external pressure port that opens into a conduit located on the external surface of said probe, the external pressure port configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe; and    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure taps, to maintain at least substantially equal static pressures internally of and externally to said probe.    
   
   
       15 . An isokinetic sampling system comprising: 
 (A) a probe that is configured for insertion into a fluid stream, said probe having an interior, an external surface, and a tip;    (B) an internal pressure port that opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe at a location adjacent said tip of said probe;    (C) an external pressure port that is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe at said location adjacent said tip of said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe; and    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure ports, to maintain at least substantially equal static pressures internally of and externally to said probe.    
   
   
       16 . A sampling method comprising: 
 (A) inducting a fluid sample into an interior of a probe disposed in a fluid stream, said probe also having an external surface;    (B) measuring a static pressure of fluid flowing through the interior of said probe;    (C) measuring a static pressure of a portion of the fluid stream surrounding at a location closely adjacent the external surface of said probe; and    (D) based on the static pressure measurements, adjusting a fluid flow rate through said probe to at least substantially eliminate a static pressure differential between the interior and the external surface of said probe.    
   
   
       17 . The method as recited in  claim 16 , further comprising determining, based on the measuring steps, a pressure differential between the interior of said probe and the external surface of said probe.  
   
   
       18 . The method as recited in  claim 17 , wherein the adjusting step comprises adjusting operation of a flow control device using a closed-loop feedback control scheme.  
   
   
       19 . The method as recited in  claim 18 , wherein the adjusting step comprises decreasing a fluid flow rate through said probe if the determined pressure differential is positive, increasing the fluid flow rate through said probe if the determined pressure differential is negative, and maintaining the fluid flow rate through the probe at least substantially constant if the determined pressure differential is substantially zero.  
   
   
       20 . The method as recited in  claim 16 , further comprising directing fluid from said probe, through an exhaust conduit located at least in substantial part external to said fluid stream, and into a sampling device.  
   
   
       21 . An isokinetic sampling system, comprising: 
 (A) a probe that is configured for insertion into a fluid stream, the probe having an interior and an external surface;    (B) an first internal pressure port and a second internal pressure port that each opens into the interior of said probe and that is configured to provide an indication of a static pressure within said probe;    (C) a first external pressure port and a second external pressure port that each is configured to provide an indication of a static pressure in a portion of the fluid stream that surrounds said probe, said external pressure port being formed into an enclosed path located closely adjacent to the external surface of said probe;    (D) a flow control device that is configured to adjust a fluid flow rate through said probe; and    (E) a controller that is operable to control said flow control device, in response to pressure measurements obtained from said external and internal pressure ports, to maintain at least substantially equal static pressures internally of and externally to said probe, wherein the first internal pressure port is located closely adjacent the first external pressure port and located generally diametrically opposed at the probe relative to the second internal pressure port located closely adjacent the second external pressure port at the external surface of the port, and    wherein the first and second internal pressure ports combine to a first single tube and wherein the first and second external pressure ports combine to a second single tube.