GB1585631A - Gas-measuring apparatus - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO GAS-MEASURING APPARATUS (71) We, AUERGESELLSCHAFT GMBH, a German Body Corporate, of 24 Friedrich Krause-Ufer, 1000 BERLIN 65 (West), Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to gas-measuring apparatus of the kind having a measuring head with catalytically active and inactive gas detecting elements.

Gas measuring apparatus is used to monitor toxic or explosive gas/air or vapour/air mixtures.

Gas measuring apparatus is known in which the atmosphere to be monitored is drawn in via ducts by means of a pump for the gas to be measured. The measuring chamber and the gas detecting elements in this case are generally situated in or directly adjacent the measuring apparatus.

Gas-measuring apparatus is also known which operates with a pure diffusion-type measuring head. In such heads the atmosphere to be monitored reaches the gas detecting elements by diffusion. The measuring head can easily be installed in the space to be monitored by using electrical cables and it is a simple matter to design the measuring head to be explosion-proof and to set it up in the atmosphere which presents the risk of explosion so that it is separated from the measuring apparatus.

In portable apparatus also it is generally necessary for both the diffusion-type measuring head and the measuring apparatus to be of explosion-proof design.

When the gas-detecting elements have aged, which becomes apparent by a fall-off in sensitivity and which, in the case of certain gases, may occur within a short period, often after only a few hours of operation, the measuring apparatus has in every case to be switched off and the measuring head and the gas-detecting elements exchanged. In the case of portable apparatus it is necessary for this purpose to remove the apparatus from the danger area which is being monitored. To allow a gas sample to be taken from a remote and not easily accessible point for a portable apparatus having a built-in diffusion-type measuring head, an attachment is known which is provided with gas pipes. This component is composed of an elastic material such as rubber and can be used when required. The sample of gas to be measured is drawn up with a rubber bulb or a pump.

Such an arrangement has the disadvantage however that if there is the slightest leakage ambient air may be drawn in along with the air to be examined.

In German Offenlegungschrift 2426773 there are disclosed gas-detecting elements which have a low current requirement of less than 100 mA and can be used in so-called intrinsically safe circuits. An intrinsically safe circuit is one in which a break or short-circuit in the circuit does not produce sparks capable of causing ignition. If gas-detecting elements or measuring heads can be operated in intrinsically safe circuits this allows the elements or heads to be replaced quickly and directly in areas where there is a risk of explosion, without the need for the apparatus itself to be switched off. So far however no gas-detecting apparatus has been disclosed which has gas-detecting element inserts which can easily and safely be replaced during operation.

It is an object of the invention to provide a gas-detecting element arrangement which can easily be replaced even during operation and which can be used both as a pure diffusion-type measuring head and as a pump-assisted measuring head.

Accordingly, the invention consists in gasmeasuring apparatus having a measuring head with catalytically active and inactive gasdetecting elements located in a gas-detecting element insert, and a holder for reception of the gas-detecting element insert, said holder having a bore for introducing gas, wherein said gasdetecting element insert is insertable between a holder cover plate provided with a gaspermeable sintered metal disc and a holder bottom plate which is removably held to the cover plate by means of fastening devices, and wherein a capping part is provided which can be plugged into the cover plate when required, said capping part containing a recess which is arranged above the sintered metal disc.

In one embodiment, the capping part also has a bore, and the bore for introducing gas to the measuring head is of greater cross-sectional area than said bore in the capping part for the outflow of gas, so that a certain back pressure can be created over the sintered disc to prevent the infiltration of ambient air.

The advantages which are achieved by means of the invention lie in particular in that fact that the whole measuring head is fittable into an intrinsically safe circuit due to the low current requirement of the head, can easily be removed from the gas-measuring apparatus during operation without the need for the apparatus to be switched off, and the gas-detecting element insert can be exchanged as a throw-away part, so that in the event of a defect in the gasdetecting elements measurement can continue after a brief interruption.

In a preferred embodiment, a gas sample is conducted through the measuring chamber at a certain super-atmospheric pressure and in this way any falsification of the results of measurement as a result of the infiltration of outside or ambient air is prevented.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show one embodiment thereof by way of example and in which: Figure 1 is a sectional view of the apparatus and, Figure 2 is an exploded view of a measuring head.

Referring now to the drawings, a measuring head 1 of a gas-detecting apparatus consists of a gas-detecting element insert 2, which is mounted between two fastening parts, namely a cover plate 4 and a bottom plate 6. These parts are connected by four screws 17 so that the gas-detecting element insert is easy to exchange.

The gas-detecting elements 3 are fitted into bores in the gas-detecting element insert 2 with, for example, one of these elements operating as an active element and another as an inactive element. To obtain a gas-tight seal with the seating in the parts 4 and 6, the insert 2 is surrounded by an O-ring 13 which occupies a position on the joint plane of parts 4 and 6. By means of bores 16 and internally threaded bores in the cover plate 4, screws 17 connect the parts 2, 4 and 6. The cover plate 4 is provided with a gaspermeable sintered metal disc 5. The terminal ends 12 of the gas-detecting elements 3 are electrically connected to a plug which is not shown.

The parts 4 and 6 are held together by screws which are arranged in bores 18.

If gas to be measured is to be fed to the apparatus from a remotely situated point by means of a pump then a capping part 7, which is provided with holding grooves 11 for easier handling, is plugged into the cover plate 4 by inserting spring clips 15 into bores 14 provided for the purpose in the plate. The gas to be measured then passes to the capping part 7 through a pipe 21 and through a gas-infeed stubtube 19 arranged in the front plate 20 of the apparatus which projects into the gas infecd opening 9 in the measuring head. A recess 8 arranged in the capping part conducts the gas to be measured to the gas-detecting elements 3 via the sintered disc 5. The gas to be measured is able to make its way out again through an opening 10 which is of smaller cross-section than that of the stub-tube 19 and bore 9.The dimensions of this opening 10 are therefore such that a certain back pressure is created over the sintered disc so that even if there are slight leaks no ambient air, which might falsify the results of measurement, can make its way in.

WHAT WE CLAIM IS: 1. Gas measuring apparatus having a measul- ing head with catalytically active and inactive gas-detecting elements located in a gas-detecting element insert, and a holder for reception of the gas-detecting element insert, said holder having a bore for introducing gas, wherein said gasdetecting element insert is insertable between a holder cover plate provided with a gaspermeable sintered metal disc and a holder bottom plate which is removably held to the cover plate by means of fastening devices. and wherein a capping part is provided which can be plugged into the covcr plate when required, said capping part containing a recess which is arranged above the sintered metal disc.

2. Gas-measuring apparatus as claimed in Claim 1, wherein the capping part also has a bore, and the bore for introducing gas to the measuring head is of greater cross-sectional area than said bore in the capping part for the outflow of gas, so that a certaill hack pressure can be created over the sintered disc to prevent the infiltration of ambient air.

3. Gas-measunog apparatus subslanrially as hereinbefore described with reference to the accompanying drawings.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. In one embodiment, the capping part also has a bore, and the bore for introducing gas to the measuring head is of greater cross-sectional area than said bore in the capping part for the outflow of gas, so that a certain back pressure can be created over the sintered disc to prevent the infiltration of ambient air. The advantages which are achieved by means of the invention lie in particular in that fact that the whole measuring head is fittable into an intrinsically safe circuit due to the low current requirement of the head, can easily be removed from the gas-measuring apparatus during operation without the need for the apparatus to be switched off, and the gas-detecting element insert can be exchanged as a throw-away part, so that in the event of a defect in the gasdetecting elements measurement can continue after a brief interruption. In a preferred embodiment, a gas sample is conducted through the measuring chamber at a certain super-atmospheric pressure and in this way any falsification of the results of measurement as a result of the infiltration of outside or ambient air is prevented. In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show one embodiment thereof by way of example and in which: Figure 1 is a sectional view of the apparatus and, Figure 2 is an exploded view of a measuring head. Referring now to the drawings, a measuring head 1 of a gas-detecting apparatus consists of a gas-detecting element insert 2, which is mounted between two fastening parts, namely a cover plate 4 and a bottom plate 6. These parts are connected by four screws 17 so that the gas-detecting element insert is easy to exchange. The gas-detecting elements 3 are fitted into bores in the gas-detecting element insert 2 with, for example, one of these elements operating as an active element and another as an inactive element. To obtain a gas-tight seal with the seating in the parts 4 and 6, the insert 2 is surrounded by an O-ring 13 which occupies a position on the joint plane of parts 4 and 6. By means of bores 16 and internally threaded bores in the cover plate 4, screws 17 connect the parts 2, 4 and 6. The cover plate 4 is provided with a gaspermeable sintered metal disc 5. The terminal ends 12 of the gas-detecting elements 3 are electrically connected to a plug which is not shown. The parts 4 and 6 are held together by screws which are arranged in bores 18. If gas to be measured is to be fed to the apparatus from a remotely situated point by means of a pump then a capping part 7, which is provided with holding grooves 11 for easier handling, is plugged into the cover plate 4 by inserting spring clips 15 into bores 14 provided for the purpose in the plate. The gas to be measured then passes to the capping part 7 through a pipe 21 and through a gas-infeed stubtube 19 arranged in the front plate 20 of the apparatus which projects into the gas infecd opening 9 in the measuring head. A recess 8 arranged in the capping part conducts the gas to be measured to the gas-detecting elements 3 via the sintered disc 5. The gas to be measured is able to make its way out again through an opening 10 which is of smaller cross-section than that of the stub-tube 19 and bore 9.The dimensions of this opening 10 are therefore such that a certain back pressure is created over the sintered disc so that even if there are slight leaks no ambient air, which might falsify the results of measurement, can make its way in. WHAT WE CLAIM IS:

1. Gas measuring apparatus having a measul- ing head with catalytically active and inactive gas-detecting elements located in a gas-detecting element insert, and a holder for reception of the gas-detecting element insert, said holder having a bore for introducing gas, wherein said gasdetecting element insert is insertable between a holder cover plate provided with a gaspermeable sintered metal disc and a holder bottom plate which is removably held to the cover plate by means of fastening devices. and wherein a capping part is provided which can be plugged into the covcr plate when required, said capping part containing a recess which is arranged above the sintered metal disc.

2. Gas-measuring apparatus as claimed in Claim 1, wherein the capping part also has a bore, and the bore for introducing gas to the measuring head is of greater cross-sectional area than said bore in the capping part for the outflow of gas, so that a certaill hack pressure can be created over the sintered disc to prevent the infiltration of ambient air.

3. Gas-measunog apparatus subslanrially as hereinbefore described with reference to the accompanying drawings.