WO1984004967A1

WO1984004967A1 - Gas detecting system and method of making such gas detecting system

Info

Publication number: WO1984004967A1
Application number: PCT/DK1984/000053
Authority: WO
Inventors: Hans Henrik Haraldsted
Original assignee: Hans Henrik Haraldsted
Priority date: 1983-06-10
Filing date: 1984-06-12
Publication date: 1984-12-20
Also published as: DK265183A; EP0148212A1; DK265183D0

Abstract

A readily demountable and in terms of manufacture favourable gas detecting system made of a plastic material, e.g. nylon, which, as a precaution is provided with a flame proof enclosure (1) involving an increased safety and a special protection against acetylene and ambient temperatures of 100o Centigrade, and the design of which utilizes the self-sealing properties of the plastic material, the system including an electrode lead-in which is in an increased safety and which maintains the flame proof enclosure, and which permits during operational conditions the mounting of a forced gas supply equipment.

Description

GAS DETECTING SYSTEM AND METHOD OF MAKING SUCH GAS DETECTING SYSTEM.

The object of the present invention is to indicate a method and give an example of an embodiment of an inexpensive and readily demountable gas detecting system which is made of a plastics material, e.g. nylon, which in accordance with international as well as national heavy-cur¬ rent regulations for "Electrical equipment for potentially explosive atmospheres" can be made as an "EEx"-type device, having a "d"-type flame proof enclosure, an "e"-type increased safety together with an "s"-type special protection.

It is previously known to provide gas detecting systems for an "i"-type intrinsic safety circuit, as indicated in for instance the German pa- tent specification No. 2625891, and the British patent specification No. 2068561. Those systems implies that the employed electronic con¬ trols become very expensive since they have to be secured as an "EEx"- type equipment. Or popularly speaking, then the "i"-type embodiment will delimit the power in the conductors in the dangerous area by means of an electronic unit, whereas the "e"-, "d"- and "s"-type embodiments permit the power to exist in det dangerous area.

An "i"-type embodiment with an "EEx"-type gas detecting equipment may involve a multiplication of the expenditure on the electronic measuring apparatus. Thus, an EX-type embodiment of the gas detector enclosure plus a "d"- and "e"-type sensor results in a low-cost electronic device. However, it has hitherto involved the Ex-protected gas detecting equipment being of a very complex design and very expensive.

In German patent specification No. 2625891, in which an "i"-type in¬ trinsic safety current circuit is disclosed, the possibility of having a forced gas supply, e.g. via a pump, during the operation of l e diffusion measuring head is also indicated. Hitherto, this has b t*n arduous and expensive in connection with other EEX-type embodiment*?. Further, the embodiment disclosed in said German specification is complex too.

OMPI In said British patent specification No. 2068561 there is disclosed, in connection with a single gas sensor having a filter, an embodiment which can only operate in an "i"-type intrinsic safety circuit. Fur¬ thermore, it is suggested therein that the sensor socket of the house- iήg itself being made of a plastics material.

The embodiment indicated therein can only be used together with elec¬ tronic devices the circuits of which are of the "i"-type intrinsic safety type, but it will not have a "d"-type flame proof enclosure or an "e"-type increased safety enclosure, and it will not as indicated in the German specification be readily demountable or permit a forced gas supply during operational conditions.

The present invention represents a substantial improvement of previous¬ ly known embodiments, since the safety has moved up from an "EEx"-type protection within an "i"-type intrinsic safety circuit to a "d"-type flame proof enclosure involving an "e"-type increased,security; addi¬ tionally, flash-overs are eliminated through the choice of material, which at the same time is made More corrosion-resistant and much more favourable having regard to production costs. Further, in the chosen design the capability of the plastics material to be gas-proof is utilized. The design is furthermore so good that the unit during ope¬ ration may be readily connected to a forced gas supply unit.

Fig. 1 shows in a sectional view an example of a gas detecting system which complies with international as well as national heavy-current re¬ gulations for electrical equipment for potentially explosive atmos¬ pheres under the "EEx"-type of protection which is provided with a "d"-type flame proof enclosure, involving an "e"-type increased safety and an "s"-type special protection for gas detection within the "II C"- group of materials, in which 1 designates an "EEx"-type terminal box of a plastics material provided with an "e"-type increased safety for the mounting thereon of a gas detector housing of a plastics material and having a "d"-type flame proof enclosure comprising of a readily de¬ mountable top part 3 and a bottom part 2 in which the removable gas sensor 4 with its six electrode legs 7 is placed and plugged into a protrusion 5 which, in connection with the flat connection 6 and the gas-proof property of the plastics material together with said "EEx"- type tolerances, makes an "EEx"-type gas-proof and "d"-type flame proof enclosure. The sensor head 4 is kept in place against the socket member 5 by being plugged into six separate socket holes 7 for the electrode legs. Additionally, the inside top section of the flame arresting filter 8 prevents the sensor 4 from dropping out owing to e.g. vibrations.

The bottom and top parts 2 and 3 of the "EEx"-type gas sensor housing are here kept together by means of two steel bolts 10 thus providing a "d"-type flame proof assembly. Between the outer atmosphere and the gas sensor 4 there is placed a flame arresting member 8 which permits a through-flow of gas and which for instance may be made of vitrified stainless steel. It is shaped and dimensioned with tolerances accord- ing to Fig. 1 which renders the gas sensor housing 2, 3 a "d"-type flame proof enclosure and, if made of nylon »6.6, strong enough to en¬ dure a small gas explosion within the sensor compartment 4, and this applies to a temperature of the outer atmosphere or an ambient tempe¬ rature of approximately 100° Centigrade as well as e.g. a gas like acetylene or a gas chosen from the "EEx"-safety group II C.

The current and voltage supplied from the terminal box 1 to the gas sensor compartment 4 is provided as an "EEx"-type safety facility and a "d"-type flame proof facility by means of, in the present case, six specially designed single electrodes 9 which, due to their larger dia¬ meter thread towards the flame chamber 4 and smaller diameter thread towards the inside of the terminal box 1 and due to two holes in each end of each separate electrode, makes an assembly or joint which, when seen from the sensor compartment 4, is "d"-type flame proof and, when seen from the terminal box compartment 1, represents an "e"-type in¬ creased safety facility, through which current and voltage can be ;ujμ- plied and delivered. Embedding a standard socket for the sensor Irijy in the nylon material 2, 3 by means of e.g. epoxy bodies will not b»^« possible because no glue or cement of known types will be able to .nl- here to nylon or teflon in a "d"-type flame proof manner so that neither the "e"-type nor "d"-type safety facility will be available. During operational conditions, for example, the gas sensor housing 3 may be readily mounted with, as an auxiliary device, a closed cover 11 in front of the entrance 8 to the sensor 4, and the cover 11 may then by means of two pipe stubs 13 be used to conduct a predetermined amount of gas or gasflow 14 across the sensor head 2, 3 and 4.

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OMPI

Claims

P A T E N T C L A I M S.

1. A method of making an explosion proof "EEx"-type gas de¬ tecting system including a mechanical readily demountable gas sensing unit which, with reference to international as well as national heavy-current regulations for "Electrical Equipment for Potentially Explosive Atmospheres", is provided with an "e"-type increased safety, a "d"-type flame proof enclosure and an "s"-type special protection and within the "II C"-group of materials and the "T5"-range of tempera- tures, c h a r a c t e r i z e d by the use of a self-sealing pla¬ stics material such as nylon or teflon, and by utilizing the self-locking and self-sealing properties of the plastics material during the design.

2. A gas detecting system according to claim 1, c h a r a c ¬ t e r i z e d by having a readily demountable gas sensor surrounded by a readily mechanically demountable "d"-type flame proof enclosure, the sensor housing being in two parts, said enclosure having a cover which is- provided with a gas opening towards the open air, and by a tight explosion proof fit to the internal flame arresting cup.

3. A gas detecting system according to claim 1 and 2, c h a - r a c t e r i z e d by its capability of being connected during opera¬ tional conditions to a forced gas sypply unit like a blind cover having hose unions.

4. A gas detecting system according to claim 1 and 2, c h a - r a c t e r i z e d by said gas sensing unit being so mounted on a terminal box of a plastics material that an "EEx"-type safety is ob- tained with respect to said box and an "e"-type increased safety for the entire system.

5. A gas detecting system according to claim 1 and 4, mrlij- ding an electrical lead-in through the "d"-type flame proof eπclo;.urt* to the inside of the terminal box, the safety of which is of the "e"- type increased safety where said safety areas are maintained, and made of the enclosure material itself, c h a r a c t e r i z e d by an electrode and a conductor retainer which is designed with larger dimen¬ sions towards the sensor side and with a self-locking facility against said sensor side.

6. A gas detecting system according to claim 1 and 2 and in¬ cluding a flame arresting cup around said sensor, c h a r a c t e ¬ r i z e d in that it is shaped like a cup, in which the flame arresting capability is provided by a vitrified stainless steel material, and in that its dimensions and tolerances relative to the dimensions and tolerances of the outer housing of plastics material ensure a "d"-type flame proof enclosure.

7. A gas detecting system according to claim 1, 2 and 3 and including an enclosure, in which an "EEx"-type and "d"-type flame proof enclosure among the "II C"-group of materials is provided by means of a labyrinth!form sealing, c h a r a c t e r i z e d by a cylindrical vertical fitting member combined with a horizontal binding surface, in which the tolerances of the gaps provide the "d"-type flame pioof en- closure.