Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
1999-03-16
2002-04-02
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
C439S709000, C073S035170, C073S035140
Reexamination Certificate
active
06366436
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electronic device for use in regions subject to explosion hazards.
BACKGROUND AND SUMMARY OF THE INVENTION
Electronic devices, in particular measuring instruments, are used regularly in industrial measuring techniques at places where there is a risk of an explosion. Flour silos, filling stations and chemical plants at which explosive gases can occur may be named here as examples.
Special safety requirements are placed on devices which can be used in regions subject to explosion hazards. These have the aim of avoiding sparking which could, possibly, trigger an explosion, or of preventing a spark produced in the interior of a closed space from affecting the surroundings. This aim can be achieved in various ways, which are laid down in appropriate European standards as types of protection.
Thus, for example, in accordance with European standard EN 50 020 of 1994, there is explosion protection when devices are designed in accordance with the defined safety class therein, bearing the name of “intrinsic safety” (Ex-i). In accordance with this safety class, the values for the electric labels of current, voltage and power each have to be below a prescribed limiting value at any time in a device. The three limiting values are selected such that in the event of a fault, for example owing to a short circuit, the maximum heat produced is insufficient to generate an igniting spark. The current is held, for example, by resistors, the voltage by, for example, zener diodes, and the power by an appropriate combination of current- and voltage-limiting components below the prescribed limiting values.
A further safety class, bearing the name of “Increased safety” (Ex-e) is specified in European standard EN 50 019 of 1994. In the case of devices which are designed in accordance with said safety class, the explosion protection is achieved by virtue of the fact that the spatial distances between two different electric potentials are so large that because of the distance sparking cannot occur even in the event of a fault. However, in some circumstances this can lead to the need for circuit arrangements to have very large dimensions in order to satisfy these requirements.
A further safety class conducted under the designation of “Explosion-proof enclosure” (Ex-d) is described in European standard EN 50 018 of 1994. Devices which are designed in accordance with said safety class have a pressure-proof housing which ensures that an explosion occurring in the interior of the housing cannot be transferred to the outside. In order for them to have adequate mechanical strength, pressure-proof housings are thick-walled and thus heavy and expensive.
The USA, Canada, Japan and other countries have standards comparable to said European standards. A device is to be connected as a rule to an electric power supply, and/or means are to be provided for transmitting signals. Provided in many cases for this purpose are standardized lines which are laid up to the measurement instrument in accordance with the safety class Ex-d or Ex-e. For example, when there is an explosion hazard on site and it is necessary to provide various measuring instruments of which individual ones require so much power that they cannot be fed by an intrinsically safe supply, it is frequent to provide lines in accordance with the safety class Ex-d or Ex-e for all devices. There are also locations at which intrinsically safe supply is not available for other reasons.
Designing a measuring instrument in accordance with safety class Ex-d requires a closed pressure-proof, and thus heavy and expensive housing. Designing a measuring instrument in accordance with safety class Ex-e requires observance of the minimum spacings described above, and this can lead to large dimensions of the individual components.
It is an object of the invention to specify a device for use in regions subject to explosion hazards which does not have these disadvantages, can be produced cost-effectively and, in addition, offers a high degree of flexibility.
Pursuant to an embodiment of the present invention, there is provided an electronic device for use in regions subject to explosion hazards. The electronic device includes a measurement instrument, a connecting chamber, a connecting element, a limiting circuit, an electronics chamber, and an electronic system. The measurement instrument of the electronic device is operable to generate measurement signals, and the connecting chamber of the electronic device includes walls designed to contain an explosion within the connecting chamber. The connecting element of the electronic device is arranged in the connecting chamber of the electronic device and is operable to receive electric lines supplying a current, a voltage, and a power. The limiting circuit of the electronic device is arranged in the connecting chamber and is operable to receive the current, the voltage and the power from the connecting element. The limiting circuit is further operable to provide a limited current, a limited voltage and a limited power that are below prescribed limiting values selected to ensure that if a fault occurs insufficient heat is produced to generate an igniting spark. The electronics chamber is separate from the connecting chamber and includes an opening and a cover that is operable to close the opening. The electronic system is arranged in the electronics chamber and is powered by the limited current, the limited voltage and the limited power of the limiting circuit. The electronic system is operably coupled to the measurement instrument to receive measurement signals and is designed to ensure if a fault occurs insufficient heat is produced to generate an igniting spark.
In accordance with a further development of the invention, space is provided in the electronics chamber for accommodating a display and/or operating element.
In accordance with a preferred embodiment, the display and/or operating element can be removed with the electronics chamber open.
In accordance with a preferred embodiment, the electronic system is designed as a replaceable plug-in module.
In accordance with a further preferred embodiment, the display and/or operating element can be mounted on the plug-in module by means of a detachable mechanical plug-in connection.
In accordance with a preferred embodiment, the display and/or operating element is connected via a line to the electronic system, and a device for holding the line is provided in the electronics chamber.
In accordance with a further preferred embodiment, the electronics chamber can be closed by a cover having a window, and the display and/or operating element is visible from outside through the window with the cover closed.
An advantage of the invention consists in that the housing in the region of the electronics chamber can have very thin walls by comparison with a chamber designed in accordance with safety class Ex-d. It is therefore lighter and more cost-effective.
Because of the intrinsically safe design of the electronic system, the latter has smaller dimensions than a corresponding electronic system designed in accordance with safety class Ex-e.
The increased space requirement caused by safety class Ex-e, or the requisite pressure resistance stipulated by safety class Ex-d is limited exclusively to the connecting chamber. All succeeding constituents have lesser dimensions, and the associated housing sections have thinner walls and are thus lighter and more cost-effective.
A further advantage consists in that the electronics chamber can be opened during operation without needing to fear an explosion. There is consequently a substantial increase in flexibility with reference to the possibilities of using the device, and to its operability. Here, flexibility is understood, for example as the possibility of accessing the electronic system on site without the need for special precautions, for example switching off a system and/or parts thereof. A defective electronic system can be replaced, and it is possible to realize operation in situ in a simple wa
Cudini Roberto
Güthner Hartmut
Maier Winfried
Bose McKinney & Evans LLP
Endress + Hauser GmbH + Co.
Huynh Kim
LandOfFree
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