GB2101310A

GB2101310A - Gas detection apparatus

Info

Publication number: GB2101310A
Application number: GB08119082A
Authority: GB
Inventors: Colin A F Rattray
Original assignee: GAS MEASUREMENT INSTR Ltd
Current assignee: GAS MEASUREMENT INSTR Ltd
Priority date: 1981-06-20
Filing date: 1981-06-20
Publication date: 1983-01-12
Also published as: GB2101310B

Abstract

Gas detection apparatus comprises a probe 12 for gathering a gaseous sample and connected by conduit 11 to a detector head 13, the sample being transported by the effect of aspirator 10 connected to conduit 11. The conduit 11 end the aspirator 10 are dimensioned to provide a transport rate of not greater than 2 litres/minute and prior to detector head 13 there is a hydrophobic membrane filter 15 in conduit 11. Filter 15 has a pore size of about 1 micron and is mounted on a holder which is releasable from conduit 11 for replacement purposes. The membrane may be made of PTFE. <IMAGE>

Description

SPECIFICATION Gas detection apparatus This invention relates to gas detection apparatus.

Gas detection apparatus which is currently available on the commercial market comprises a detection head to which is transported a gaseous sample in order for the head to detect the presence and quantity of a specific constituent or group of constituents in the sample. The gaseous sample is taken from an area which could contain water and in order to prevent this water contaminating the detection head the apparatus comprises a water trap in the transport path prior to the detection head. This trap is relatively massive and of uncertain efficiency when the gaseous sample is transported at a rate compatible with efficient operation of the detector head.

According to the present invention there is provided gas detection apparatus comprising a detection head and means for transporting a gaseous sample from a sample source to said detection head, wherein prior to the detection head there is located a hydrophobic membrane filter having a pore size of about 1 micron and the transport means is arranged to provide a differential pressure across the membrane filter such that the transport rate for the gaseous sample is not greater than 2 litres per minute.

We have discovered that with our invention efficiency of operation of the detector head can be maintained at or about an optimum level with the hydrophobic membrane filter effectively protecting the detector head from contamination whilst maintaining the efficiency of the detection system due to the selected pore size of about 1 micron.

The transport means is conveniently in the form of a hand-operated aspirator or mechanical pump the pressure of which together with the bore of the associated conduits are specified to limit the differential pressure across the membrane filter and to limit the flow rate of transported sample to the range 0--2 litres/minute.

The hydrophobic membrane filter is preferably a thin polymeric disc mounted on a holder, being made by the Millipore Corporation of the U.S.A.

and conveniently is replaceably mounted in the transport path. The membrane filter is preferably made of PTFE and performs its filter function due to the surface tension of the water on the membrane. We have found that if the membrane filter has a pore size substantially larger than 1 micron (by greater than 20%) or if the differential pressure is substantially greater than 36 inches water (gauge) giving a flow rate greater than 2 litres/minute the membrane filter no longer functions in the desired manner and we believe this to be due to the reduction in the surface tension effect referred to above. We have also found that a significant reduction in the pore size restricts the sample transport rate to such an extent that the detector head is rendered inefficient.

The detector head may incorporate a detector element of the pellistor or semicondutor type both of which are known per se and we have found that these detector elements function most efficiently at sample transport rates within the limited range of 1-2 litres/minute which is compatible with a filter of 1 micron pore size.

By way of example the accompanying schematic drawing illustrates apparatus according to the present invention. In the drawing an aspirator 10 is connected to conduit 11 which at its remote end 12 functions as a probe for gathering a gaseous sample. The conduit 11 transports the sample to a detector head 13 which has associated electrical circuitry including a readout device 1 4 whereat the result of the test is displayed. The filter 1 5 transverses the conduit 11 upstream of the detector head 1 3 and may be located inside a housing 1 6 containing components 13, 14 or secured to the outside of the housing 1 6 to facilitate replacement when the filter becomes clogged.

1. Gas detection apparatus comprising a detection head and means for transporting a gaseous sample from a sample source to said detection head, wherein prior to the detection head there is located a hydrophobic membrane filter having a pore size of about 1 micron and the transport means is arranged to provide a differential pressure across the membrane filter such that the transport rate of the gaseous sample is not greater than 2 litres per minute.

2. Apparatus as claimed in claim 1 , wherein the membrane filter comprises a thin polymeric disc mounted on a holder.

3. Apparatus as claimed in claim 2, wherein the thin polymeric disc is made of PTFE.

4. Apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Gas detection apparatus This invention relates to gas detection apparatus. Gas detection apparatus which is currently available on the commercial market comprises a detection head to which is transported a gaseous sample in order for the head to detect the presence and quantity of a specific constituent or group of constituents in the sample. The gaseous sample is taken from an area which could contain water and in order to prevent this water contaminating the detection head the apparatus comprises a water trap in the transport path prior to the detection head. This trap is relatively massive and of uncertain efficiency when the gaseous sample is transported at a rate compatible with efficient operation of the detector head. According to the present invention there is provided gas detection apparatus comprising a detection head and means for transporting a gaseous sample from a sample source to said detection head, wherein prior to the detection head there is located a hydrophobic membrane filter having a pore size of about 1 micron and the transport means is arranged to provide a differential pressure across the membrane filter such that the transport rate for the gaseous sample is not greater than 2 litres per minute. We have discovered that with our invention efficiency of operation of the detector head can be maintained at or about an optimum level with the hydrophobic membrane filter effectively protecting the detector head from contamination whilst maintaining the efficiency of the detection system due to the selected pore size of about 1 micron. The transport means is conveniently in the form of a hand-operated aspirator or mechanical pump the pressure of which together with the bore of the associated conduits are specified to limit the differential pressure across the membrane filter and to limit the flow rate of transported sample to the range 0--2 litres/minute. The hydrophobic membrane filter is preferably a thin polymeric disc mounted on a holder, being made by the Millipore Corporation of the U.S.A. and conveniently is replaceably mounted in the transport path. The membrane filter is preferably made of PTFE and performs its filter function due to the surface tension of the water on the membrane. We have found that if the membrane filter has a pore size substantially larger than 1 micron (by greater than 20%) or if the differential pressure is substantially greater than 36 inches water (gauge) giving a flow rate greater than 2 litres/minute the membrane filter no longer functions in the desired manner and we believe this to be due to the reduction in the surface tension effect referred to above. We have also found that a significant reduction in the pore size restricts the sample transport rate to such an extent that the detector head is rendered inefficient. The detector head may incorporate a detector element of the pellistor or semicondutor type both of which are known per se and we have found that these detector elements function most efficiently at sample transport rates within the limited range of 1-2 litres/minute which is compatible with a filter of 1 micron pore size. By way of example the accompanying schematic drawing illustrates apparatus according to the present invention. In the drawing an aspirator 10 is connected to conduit 11 which at its remote end 12 functions as a probe for gathering a gaseous sample. The conduit 11 transports the sample to a detector head 13 which has associated electrical circuitry including a readout device 1 4 whereat the result of the test is displayed. The filter 1 5 transverses the conduit 11 upstream of the detector head 1 3 and may be located inside a housing 1 6 containing components 13, 14 or secured to the outside of the housing 1 6 to facilitate replacement when the filter becomes clogged. CLAIMS