The invention relates to an electronic device for use in explosion endangered areas. The electronic device has a superordinated electronic unit and a plurality of electronic components connected to the superordinated unit and supplied with energy by such. The invention relates further to a protective element, with which, in the case of a malfunction of a component, power provided by the superordinated unit is safely transformable into heat.
A large number of electronic devices, especially measuring devices, such as e.g. pressure-, temperature-, flow or fill level measuring devices, are applied in industrial measurements technology. These have, as a rule, an energy supplied, superordinated electronic unit, to which are connected a number of electronic components supplied with energy via the superordinated unit, e.g. electronic components, such as sensors, measuring-, control- and/or evaluation circuits or signal processors.
In fields of use in which danger of explosion is present, strict safety specifications are applied. In such case, especially spark formation is to be prevented, since such could, in given cases, trigger an explosion. Correspondingly, the power available to the superordinated unit is today regularly limited by corresponding electrical current and voltage limiting, protective circuits to a predetermined maximum power, e.g. to 1 Watt. Moreover, it must be assured in the device that the power provided to the components by the superordinated unit can also not cause a spark in the case of a malfunction. This is accomplished today usually by a safe conversion of the power into heat. This safe conversion of the electrical power provided to the respective component by the superordinated electronic unit in the case of a malfunction of the component into heat is accomplished in such a manner that explosive media located in the environment, such as e.g. gases or dusts, cannot be ignited.
This requirement is today usually fulfilled in the manner shown in
This leads due to the required size of the explosion protection resistors REx, especially in the case of devices with many subordinated components 3, to a considerable space requirement and conflicts with miniaturization and cost optimization.
It is an object of the invention to provide a protective element and a device of the initially stated type equipped with such a protective element, with which, in the case of malfunction of a component, in place saving manner, a safe conversion of the power available from the superordinated unit into heat is assured.
For this, the invention resides in an electronic device for use in explosion endangered areas, comprising
In a preferred embodiment, the base body comprises a ceramic, especially aluminum nitride (AlN).
In an additional embodiment, the resistors are thin film resistors, especially thin film resistors of TaNi or NiCr.
In a first further development, there is applied on a side of the base body lying opposite that bearing the resistors a heat conducting layer, especially a metal coating.
In an additional further development of the first further development
In a second further development
In a further development of the second further development, an electrically insulating heat conducting element is arranged between the circuit board and the protective element.
In a further development of the second further development, the spacers are the connections of the resistors and protrude out from a plane of the resistors on the side of the base body bearing the resistors in a direction facing away from the base body.
In a third further development, a side of the protective element bearing the resistors is coated with an electrically insulating, heat conducting layer, especially a lacquer or a potting compound.
Moreover, the invention resides in a protective element for electrically connecting a superordinated electronic unit to a number of electronic components supplied with energy via the superordinated unit, comprising
The invention and other advantages will now be explained in greater detail based on the figures of the drawing, in which two examples of embodiments are presented; equal elements are provided in the figures with equal reference characters. The figures of the drawing show as follows:
According to the invention, a protective element 7 is provided inserted in a number of connection lines 5 connecting respective ones of the components 3 with the superordinated unit 1. In the illustrated example of an embodiment, all components 3 are connected with the superordinated unit 1 via the shown protective element 7. Alternatively, however, also a number of groups of components can, in each case, be connected to the superordinated unit 1 via an individual protective element inserted into the connection lines of all components of the respective group.
Applied on the base body 9 are a number of resistors R corresponding to the number of connection lines 5 leading across the protective element 7. The resistors R are preferably thin film resistors, especially thin film resistors of TaNi or NiCr.
Each resistor R is provided input and output side with a connection 11 for one of the connection lines 5. In the variant illustrated in
In the case of malfunction of one or more components 3 connected via the protective element 7 to the superordinated unit 1, the energy available via the superordinated unit 1 is to be converted safely into heat. Since only one superordinated unit 1 is present, this energy also is present only once, independently of how many components 3 are connected to the superordinated unit 1 via the protective element 7. Other than in the case of the initially described state of the art, in the case of which each individual protective resistor REx must be able to convert the energy available from the superordinated unit 1 in the case of malfunction safely into heat, here the one-time conversion by the protective element 7 suffices, independently of the number of components 3 connected thereacross.
A malfunction of one of the components 3 leads to an increased electrical current through that resistor R of the protective element 7 located in the connection line 5 of such component 3. The heat released in such case is absorbed by the base body 9 and removed via the base body 9. In such case, the preferably high thermal conductivity of the base body 9 effects an approximately equally distributed warming of the base body 9 and therewith an effective, large surface, heat removal. Due to the only once present energy to be converted into heat, a simultaneously occurring malfunctioning of two or more components 3 does not lead to a higher heat development on the protective element 7. Thus, even in the case of simultaneous malfunctioning of a plurality of components 3, a single base body 9 suffices for safe heat conversion. According to the invention, consequently, only a single, centrally arranged, base body 9 is required for the connection of a number of components 3 to a superordinated unit 1. In this way, considerable space is saved, which is then available for miniaturization of the device, for other components or for other uses.
For improving the heat removal, a heat conducting layer 13, especially a metal coating, can be applied on a side of the base body 9 lying opposite the resistors R. As shown in
The protective element 7 is, for example, such as shown in
For additionally improving the heat removal in the case of a malfunction, circuit board 15 has in its region covered by the protective element 7 a cavity 19, via which heat is removed through the circuit board 15. This measure leads to a very effective heat removal, especially in combination with a heat conducting layer 13 provided on the side of the base body 9 facing the circuit board 15. Alternatively, the heat conducting layer 13 can, however, also be applied, respectively soldered, to a cooling surface (not shown) provided on the circuit board 15.
Spacers 21 are preferably formed by the connections 11′ of the resistors R, which, for this, protrude out on the side of the base body 9 bearing the resistors R from a plane of the resistors R in a direction facing away from the base body 9. The connections 11′ are also here preferably connected via soldered connections 17′ to the connection lines 5 extending on the circuit board 15 to the protective element 7′.
Exactly as in the case of the example of an embodiment illustrated in
Alternatively, an electrically insulating, heat conducting element 23 can be arranged between the circuit board 15 and the protective element 7′ for improving the heat removal.
Moreover, preferably at least the side of the protective element 7, respectively 7′, bearing the resistors R is coated with an electrically insulating, heat conducting layer, especially a lacquer or a potting compound. This heat conducting layer offers, on the one hand, the advantage that it promotes and accelerates the uniform distribution of the local heat evolution in the region of individual resistors R over the base body 9. On the other hand, it improves the insulation of the individual resistors R from one another given by the separation between the individual resistors R, and contributes therewith to increasing the breakdown voltage.
1 superordinated unit
3 component
5 connection line
7 protective element
7′ protective element
9 base body
11 connection
11′ connection
13 heat conducting layer
15 circuit board
17 soldered connection
19 cavity in the circuit board
21 spacers
23 heat conducting element
Number | Date | Country | Kind |
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10 2011 004 061.7 | Feb 2011 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/052298 | 2/10/2012 | WO | 00 | 8/13/2013 |