GB2323165A

GB2323165A - Fluid sampling system

Info

Publication number: GB2323165A
Application number: GB9704966A
Authority: GB
Inventors: Robert R D Bradshaw
Original assignee: Graseby Dynamics Ltd
Current assignee: Smiths Detection Watford Ltd
Priority date: 1997-03-11
Filing date: 1997-03-11
Publication date: 1998-09-16
Anticipated expiration: 2017-03-11
Also published as: GB9704966D0; GB2323165B

Abstract

The system comprises a chamber intermediate a fluid to be sampled and an enclosure into which a fluid sample is to be introduced with means for introducing a volume of the fluid sampled into the chamber, and for introducing a sample of the fluid from the chamber into the enclosure. Typically the system has an enclosure (10) for a first fluid into which a sample of a second fluid is to be introduced; enclosure (10) has an orifice (12) through which the sample of second fluid is drawn by a by means (14); a chamber (16) is intermediate the orifice (12) and the outlet of a conduit (26), the inlet of which is surrounded a body of the second fluid, the internal volume of the chamber (16) being controlled by a piston (18, 20, 22) to draw in a volume of the second fluid from which a sample is taken into the enclosure (10) through through the orifice (12). System utility is in a vapour analyses or ion mobility spectrometer.

Description

Improvements in or relating to Fluid Sampling Systems The present invention relates to fluid sampling systems and more particularly to a method and means for enhancing the perfomance of fluid sampling systems for effecting the transfer of samples of a second fluid from a body of that fluid into a system incorporating an enclosed volume of a first fluid.

Such a fluid sampling system is described in the applicants' published PCT Application No WO 93/01845 (CP65), the contents of which are incorporated into this application by reference.

When the fluid sampling system of WO 93/01845 is used in a vapour-sensing instrument such as the ion mobility spectrometer described in relation to Figure 4 of WO 93/01845, in which an atmospheric sample, possibly containing vapours of interest, is drawn into the instrument through a small orifice, the sample may not be representative of the atmosphere in regions not immediately surrounding the instrument as the sample drawn in is of limited volume and is drawn only from a small approximately hemispherical volume close to the orifice. The sample may also not be representative of those further regions as it is drawn from a region close to a solid surface, whether of the nozzle or of the instrument case, or both, which close region may be within a boundary layer within which circulation may be inhibited, causing the concentration of any vapour(s) of interest to lag behind a changing concentration in the further regions. Additionally vapour(s) of interest may have been withdrawn from the close region by adsorption on to the nearby solid surface or surfaces.

In addition, constraints on the geometry of the inlet system of the fluid sampling system necessary to allow efficient transfer of the sample from the inlet orifice to the interior of the instrument may mean that the protrusion of the sampling nozzle of the instrument into the external atmosphere may be less than may be desirable for representative sample acquisition.

Both these problems may be mitigated by use of a rotating fan as a flow inducer, to draw in a substantial flow of atmospheric sample which may also irrigate the sampling orifice at the same time. Using a rotating fan can also allow a longer inlet nozzle to be used to draw in air from greater distances from the inlet nozzle of the instrument.

However such a system is relatively expensive to implement because of the cost of the motor required to drive the fan, and is disadvantageous in that it would deleteriously increase the weight and power consumption of the improved personal and portable vapour detector and analyser instruments made possible by the sampling system of WO 93/01485.

It is an object of the present invention to provide a fluid sampling system which enhances the performance of an instrument incorporating a fluid sampling system such as is described in WO 93/01845.

In accordance with one aspect the invention consists in a fluid sampling system comprising a chamber intermediate a fluid to be sampled and an enclosure into which a sample of said fluid is to be introduced, means being provided for introducing a volume of said fluid into the chamber, and for introducing a sample of said fluid into the enclosure from the chamber.

In accordance with a further aspect the invention consists in a fluid sampling system comprising a fluid enclosing means arranged to enclose a volume of a first fluid into which a sample of a second fluid is to be introduced, the fluid enclosing means having an orifice via which the sample of the second fluid may be drawn into the fluid enclosing means, and means arranged to draw in a sample of the second fluid into the fluid enclosing means through the orifice, and in which a chamber is arranged intermediate the orifice and the outlet of a conduit, the inlet of which is surrounded by the second fluid, the internal volume of the chamber being modifiable by volume controlling means whereby a volume of the second fluid may be drawn into the chamber, from which volume a sample of the second fluid may be drawn into the fluid enclosing means through the orifice.

The volume controlling means may be operated under the control of means which also control the operation of the means arranged to draw a sample into the orifice.

The control means may control the volume controlling means such as to apply a positive pressure to the interior of the chamber at substantially the same time as a sample from the chamber is drawn in through the orifice.

In a modification of the invention a sample may be caused to pass through the orifice from the chamber by means of the positive pressure applied by the volume controlling means, there being no means arranged to draw in the sample through the orifice.

The volume controlling means may comprise an aperture closed by a movable piston capable of movement such as to modify the internal volume of the chamber; the piston may be moved by a linearly acting device, for example a solenoid.

The invention may further comprise a vapour analyser or detector provided with a sampling system in accordance with the invention; the vapour analyser or detector may be an n ion mobility spectrometer vapour analyser or detector.

the invention may further consist in a method of introducing a sample of a second fluid from a volume of the second fluid into an enclosed volume of a first fluid comprising the steps of drawing a volume the second fluid into a chamber intermediate the second fluid volume and an orifice giving access to the enclosed volume, and of introducing a sample of the second fluid into the first fluid via the orifice from the chamber.

These and other aspects of the invention will be described by way of example in relation to a specific embodiment, with reference to the accompanying drawing.

Referring to the drawing, an instrument 10, representative of an instrument such as is described in WO 93/01845 in relation to Figure 4, is provided with an inlet orifice 12, through which a sample of external atmosphere may be drawn into the instrument 10, by means diagrammatically shown at 14, by which the internal volume of instrument 10 may be increased, thereby to draw in sample from the external atmosphere through orifice 12. The means 14 may be actuated repetitively, or periodically as required.

In the modified instrument here illustrated, orifice 10 is enclosed within a bulk-sampling chamber 16, part of the wall of which is provided by the inner face of a movable piston 18, moving in a cylinder 20 incorporated in the wall of chamber 16. The piston is linked to and driven by a linearly-acting solenoid 22, provided with a return spring 24.

The bulk-sampling chamber 16 further incorporates, or is formed to provide, an inlet pipe or nozzle 26 which gives access to the atmosphere surrounding the instrument 10 and sampling chamber 16. The pipe or nozzle 26 is arranged such that incoming sampled atmosphere is drawn into the region of or impinges upon the orifice 12 of instrument 10.

In operation solenoid 22 is operated to draw piston 18 outwardly in cylinder 20 (to the right in the drawing) against the force exerted by return spring 24, thereby increasing the inner vloume of chamber 16. Drawing the piston 18 outwardly causes a reduction of pressure within chamber 16 and an inward flow of external atmosphere into chamber 16, through pipe or nozzle 26.

With the sample of external atmosphere in chamber 16, instrument 10 under the control of means 14 is operated to draw in through orifice 12 some part of the external atmosphere sample held in bulk-sampling chamber 16.

Subsequently solenoid 22 is de-energised and piston 18 returned to its inner position by return spring 24, ready for the next sampling cycle.

Operation of solenoid 22 may conveniently be controlled and the operation of the bulk sampler sequenced in relation to the operating cycle of means 14 within the instrument 10, by means of the microprocessor controller conventionally present in the parent instrument 10.

It has been found that piston 18 does not need to be well-sealed into cylinder 20 as leakage will not be of importance so long as the leakage area around the piston 18 is small compared with the cross-sectional area of the nozzle 26.

In one modification of the composite system comprising a sampler in accordance with the invention and the instrument 10, by appropriate design the inward, postsampling, movement of piston 22 in cylinder 20 under the influence of return spring 24, can be arranged to impel a fraction of the bulk sample in chamber 16 through orifice 12 of instrument 10, thereby aiding the action of, or alternatively replacing, the instrument sampler means 14.

It will be apparent that other modifications may be made to the embodiment described herein without exceeding the scope of the invention.

For example, although reference is made to the use of the invention to introduce a sample of a second fluid into an enclosure containing a first fluid, the sampling system may equally well be employed for introducing a sample of a fluid from a volume of such fluid, via an intermediate chamber, into an analysing instrument not having an enclosure such as 10 containing another fluid.

Claims

1. A fluid sampling system comprising a chamber intermediate a fluid to be sampled and an enclosure into which a sample of said fluid is to be introduced, means being provided for introducing a volume of said fluid into the chamber, and for introducing a sample of said fluid into the enclosure from the chamber.

2. A fluid sampling system comprising: a fluid enclosing means arranged to enclose a volume of a first fluid into which a sample of a second fluid is to be introduced; the fluid enclosing means having an orifice via which the sample of the second fluid may be drawn into the fluid enclosing means; and means arranged to draw in a sample of the second fluid into the fluid enclosing means through the orifice; and in which a chamber is arranged intermediate the orifice and the outlet of a conduit, the inlet of which is surrounded by the second fluid; the internal volume of the chamber being modifiable by volume controlling means whereby a volume of the second fluid may be drawn into the chamber, from which volume a sample of the second fluid may be drawn into the fluid enclosing means through the orifice.

3. A fluid sampling system as claimed in Claim 2 in which the volume controlling means is operated under the control of means which also control the operation of the means arranged to draw a sample into the orifice.

4. A fluid sampling system as claimed in Claim 3 in which the control means controls the volume controlling means such as to apply a positive pressure to the interior of the chamber at substantially the same time as a sample from the chamber is drawn in through the orifice.

5. A fluid sampling systems as claimed in Claim 4 but having the modification that a sample is caused to pass through the orifice from the chamber by means of the positive pressure applied by the volume controlling means, there being no means arranged to draw in the sample through the orifice.

6. A fluid sampling system as claimed in any one of Claims 2 to 5, in which volume controlling means comprises an aperture closed by a movable piston capable of movement such as to modify the internal volume of the chamber.

7. A fluid sampling system as claimed in Claim 6 in which the piston is moved by a linearly acting device.

8. A fluid sampling system as claimed in Claim 7 in which the device is a solenoid.

9. A vapour analyser or detector provided with a sampling system in accordance with any preceding claim.

10. An ion mobility spectrometer vapour analyser or detector provided with a sampling system in accordance in accordance with any one of Claims 1 to 8.

11. A method of introducing a sample of a second fluid from a volume of the second fluid into an enclosed volume of a first fluid comprising the steps of drawing a volume the second fluid into a chamber intermediate the second fluid volume and an orifice giving access to the enclosed volume, and of introducing a sample of the second fluid into the first fluid via the orifice from the chamber.

12. A sampling system as described herein with reference to the accompanying drawing.

13. A method of sampling as described herein with reference to the accompanying drawing.