GB2144850A

GB2144850A - Air samplers

Info

Publication number: GB2144850A
Application number: GB08321798A
Authority: GB
Inventors: Geoffrey Malcolm Wili
Original assignee: BURKARD MANUFACTURING Co
Current assignee: BURKARD MANUFACTURING Co
Priority date: 1983-08-12
Filing date: 1983-08-12
Publication date: 1985-03-13
Also published as: IT1174645B; IT8422308A0; GB2144850B; GB8321798D0

Abstract

A motor-driven turbine (7) draws air into a housing (3, 4) through an inlet (50) and slit orifice (15. Fig. 5 not shown) to impinge as a ribbon jet against a slowly- moving adhesive-coated substrate (31). The inlet (50) forms a vertical passage so as to be insensitive to the direction of the wind or draughts and includes a diffusor (56, Fig. 3) defining a large number of parallel vertical passages. The slit orifice is formed in the bottom of a well the upper and lower longitudinal edges of which are respectively convex and concave with regard to the inside of the well (Fig. 4 not shown). <IMAGE>

Description

SPECIFICATION Air samplers The present invention relates to air samplers of the kind in which a narrow stream of air is continuously directed at a surface of a slowing moving substrate carrying an adhesive substance for retaining from the air stream a substantial proportion of dust, pollen or spores which may be present in the air stream. Typically, the substrate may be a microscope slide or a flexible transparent plastics film and the deposit which is formed along its length provides an indication of the variation in the intensity of contamination of the air over the period taken by the substrate to travel from one end to the other, typically 24 hours or seven days. Analysis of the deposit is normally performed under the microscope.

In one known form of air sampler which is in general use, the substrate and its clockwork driving mechanism are located in a rotatable housing and the air stream is formed by drawing in air through a slit formed in a side wall of the housing, the housing carrying a wind vane which serves to hold the slot always pointing into the wind.

An object of the present invention is to provide an air sampler which does not require a rotatable housing and wind vane and which will provide a consistent and high yield regardless of the direction of any wind.

According to the present invention there is provided an air sampler comprising a housing, means for drawing air into the housing through an inlet orifice, and means within the housing for moving a substrate past the orifice, wherein the orifice is formed in a horizontal wall of the housing with its axis vertical and comprises, in the direction leading into the housing, a well extending over the width of the substrate, the two edges of the entry to the well which are transversed to the direction of the movement of the substrate being convexly curved, and the exit from the well is formed by a slit extending over the width of the substrate, the exit wall surfaces at each long side of the slit being concavly curved.

With this arrangement, then sunction is applied to the interior of the housing, air can be drawn into the well from all directions without experiencing sudden changes of direction which would result in the contamination of the air being no longer representive of that of the surrounding atmosphere. Preferably, the outlet end of the slit opens directly into an end face adjacent the substrate, without any rounding of edges of the outlet end of the slit.

According to another aspect of the invention there is provided as sampling apparatus comprising a housing, means for continuously drawing air from the housing, an air inlet slit for admitting air in a vertical direction into the housing and means within the housing for moving a collecting substrate past the delivery end of the slit, wherein air is supplied vertically to the inlet slit from a substantially vertical passage offering negligible resistence to the flow of air being drawn into the housing and the passage includes a diffusor extending across the passage, the diffusor being preferrably adjacent the inlet to the passage and defining an array of parallel ducts of length greater than their width. The effect of the diffusor is to align the incoming air flow so as to be parallel to the access of the passage. At the same time it discourages insects from entering the passage.Preferably the slit is preceded by the well formation in accordance with the first aspect of the invention.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a vertical sectional view of an air sampler device according to the invention, Figure 2 is a view of part of the housing of the device of Fig. 1 taken in axial section at right angles to Fig. 1, Figure 3 shows the air intake portion of Fig.

1 on an enlarged scale, Figure 4 is a vertical cross section through the air intake nozzle of Fig. 1, Figure 5 is a view taken in the direction of the arrows v-v of Fig. 4, and Figure 6 is a section on the line vi-vi of Fig. 4.

The air sampling apparatus shown in the drawings has a base casting 1 supported by means of three legs 2. Supported on the casting 1 is an inverted bell shaped casting 3 the upper end of which is closed by a cover casting 4. The casting 1, 3 and 4 are preferrably of aluminium.

An O-ring 5 is located in a groove around the rim of the bell shaped casting 3 to form a seal between the castings 3 and 4 which together form a housing defining a chamber 6. Air is continuously drawn from the chamber 6 by a motor-driven turbine 7 which conviently consists of upper and lower discs 8 and 9 which are spaced apart by wires 10, the discs 8 and 9 being secured to a hub 11 which is mounted on the shaft 1 2 of an electric motor (not shown). The hub 11 is hollow and communicates both with the space between the discs 8 and 9 and with the lower end a tubular passage 1 3 which leads from the chamber 6 to the hub 11 past an adjustable throttle screw 1 4.

Air enters the chamber 6 through an orifice 1 5 (to be described in more detail later) in the form of a ribbon jet which is directed at a surface of a substrate in the form of a microscope slide 16.

A downwardly extending bracket 1 7 is cast intergrally with the cover 4 and on one face has a T-shaped slot 1 8 in which a complementarily shaped block 19, secured to the housing casting 3, is a close sliding fit. A plunger 21 mounted on the rod 22 in a sleeve 23 secured to the casting 3 is urged by a spring 24 to engage in a hold 25 in the bracket 1 7 to hold the cover 4 firmly in place.

The cover can however be released by pulling on a knob 26 on the rod 22.

The bracket 1 7 carries a plate 27 on the upper end of which are mounted two horizontal arms 28 which are interconnected by two guide rods 29 on which a carrier 30 for the microscope slide 1 6 is slidable. The carrier 30 is driven slowly from one end of the guide rods 29 to the other by a drive tape 31 which is fixed to the carrier 30 and extends over rollers 32 to pass downwards and engage a clockwork-driven drum 33, the two ends of the tape being attached to the drum 33.

Preferrably the attachment of one end of the tape to the drum includes a tensioning spring for the tape. The drum 33 is connected to its clockwork movement through a friction clutch, thereby enabling the angular position of the drum 33 and thus the position of the microscope slide carrier 30 to be adjusted when the cover 4 is removed from the chamber 6.

As can be seen in Figs. 4 to 6, the orifice slit 1 5 extends over the full width of the microscope slide 1 6 and is formed at the bottom of a well 37 also extending over the full width of the slide. Whilst the intermediate portion of the well 37 is parallel sighted, its upper edges, along its longer sides, are rounded at 39 so as to be convexly curved, conveniently of circular radius. Also, the bottom of the well at 41 is concavely curved, conveniently in the form of a half cylinder from which the narrow outlet slit 15, also parallel-sided, leads into a lower end face 42 without any rounding of the edges.

With this construction, air can be drawn into the well 37 from any direction without any sharp changes of direction which would lead to turbulence. Further, any flying insect which is drawn into the well 37 can escape without being caught in and partially blocking the slit 15.

Typically, the slit 1 5 has a width of 2mm and a length of 14mm. The slide, which is coated with a layer of appropriate adhesive such as that available under the trade mark Gelvatol is advanced, past the end of the slit, at about 2mm per hour.

Fig. 1 also shows an air intake which may be used when the sampler is in use outside.

When used inside a building, the air intake 1 5 may not be required.

As shown in Fig. 1 and, on a larger scale, in Fig. 3, the air intake 1 5 comprises a tube 51 of large horizontal area, on the upper end of which is supported a dished cover 52 to protect the inlet from rain. The cover 52 is spaced above the upper end of the inlet 51 by spacer rods 53 of sufficient length to provide unrestricted access for incoming air. Conveniently, the rods 53 are secured to a disc 54 to which the cover 52 is secured by a screw 55.

Mounted in the upper end of the tube 51 is a disc 56 of an open honeycomb material which is conveniently of the kind manufactured for use in aircraft flooring by Ciba-Geigy under the trade mark AEROWEB. A suitable material is designated "8.1-1/8-20(5052)T'. Such material is about 15.88mm thick and provides a large number of axially extending passages about 3mm in diameter. The wall thickness of aluminium between adjacent passages is about 0.6mm.

The effect of the disc 56 is to prevent turbulence in the air flow within the tube 51

Claims

1. An air sampler comprising a housing, means for drawing air into the housing through an inlet orifice, and means within the housing for moving a substrate past the orifice, characterised in that the orifice (15) is formed in a horizontal wall (4) of the housing with its axis vertical and comprises, in the direction leading into the housing, a well (37) extending over the width of the substrate (31), the two edges (39) of the entry to the well which are transverse to the direction of the movement of the substrate (31) are convexly curved, and the exit from the well is formed by a slit (15) extending over the width of the substrate (31), the exit wall surfaces (41) of the well at each long side of the slit being concavely curved.

2. An air sampler comprising a housing, means for continuously drawing air from the housing, an air inlet slit for admitting air in a vertical direction into the housing and means within the housing for moving a collecting substrate past the delivery end of the slit, characterised in that air is supplied vertically to the inlet slit (1 5) from a substantially vertical passage (51) offering negligible resistance to air drawn into the housing and the passage includes a diffusor (56) extending across the passage, the diffusor (56) defining an array o-F parallel ducts of length greater than their width.

3. An air sampler according to claim 2, characterised in that the diffuser (56) is adjacent the inlet to the vertical passage (51).

4. An air sampler according to claim 2 or 3, characterised in that the orifice is formed in a horizontal wall (4) of the housing with its axis vertical and comprises, in the direction leading into the housing, a well (37) extending over the width of the substrate, the two edges 39 of the entyr to the well which are transverse to the direction of the movement of the substrate (31) are convexly curved, and the exit from the well is formed by a slit (15) extending over the width of the substrate (31), the exit wall surfaces (41) of the well at each long side of the slit being concavely curved.

5. An air sampler according to any of the preceding claims characterised in that the outlet end of the slit opens directly into an end face (42) adjacent the substrate (31), without any rounding of edges of the outlet end of the slit.