EP0148212A1

EP0148212A1 - Gas detecting system and method of making such gas detecting system

Info

Publication number: EP0148212A1
Application number: EP19840902338
Authority: EP
Inventors: Hans H. Haraldsted
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-06-10
Filing date: 1984-06-12
Publication date: 1985-07-17
Also published as: DK265183D0; WO1984004967A1; DK265183A

Abstract

Système de détection de gaz aisément démontable et de fabrication avantageuse, composé d'un matériau plastique, par exemple du nylon, pourvu par précaution d'une enceinte résistant au flammes (1), permettant d'obtenir une sécurité accrue et une protection spéciale contre l'acétylène et des températures ambiantes de 100oC, et ayant recours aux propriétés d'auto-étanchéification du matériau plastique. Le système comprend un passage de traversée d'électrodes comportant une sécurité accrue, qui maintient l'enceinte étanche aux flammes et qui permet le montage d'un équipement d'alimentation forcée en gaz pendant le fonctionnement.Easily removable and advantageously manufactured gas detection system, composed of a plastic material, for example nylon, provided with a flame resistant enclosure (1) as a precaution, making it possible to obtain increased security and special protection against acetylene and ambient temperatures of 100oC, and using the self-sealing properties of plastic material. The system includes an electrode crossing passage with increased security, which keeps the enclosure flameproof and which allows the mounting of equipment for forced gas supply during operation.

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.

^"BUR£

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.