Electronic control module for detonator
Electronic control module for a detonator comprising a printed circuit board (1) equipped with components of the circuit, enclosed in a tubular casing (12) embedded in a blocking resin (15) of the board in the casing, wherein a shielding screen (3) is interposed between the board (1) and the tubular casing (12), which screen has an insulating face turned towards the casing (12) and a conductive face (6) turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board (1).
The present invention relates to an electronic control module for a detonator, used in mines and quarries and forming the priming system of explosives.
A detonator module generally comprises a printed circuit board carrying the electronic components of the circuit, which board has the shape of an elongated card accommodated in a section of tubing and embedded in this section or tubular casing by a blocking resin. From one of the ends of the casing extend conductors for connecting the module to a firing line, which in turn is connected to a central programming and control unit, whereas at its other end the casing and the printed circuit board that it contains has means for connecting it to the pyrotechnical primer that is added to it.
These electronic detonators are used in a hostile environment. It is necessary, therefore, to protect the components of the electronic module as much as possible on the one hand against mechanical stresses resulting from the shock waves coming from the explosions of preceding charges in a programmed firing plan and from electromagnetic stresses that can perturb the communications between the module and the central programming and firing control unit.
To withstand mechanical stresses, generally a strong metal casing of steel is chosen. However, this has drawbacks: on the one hand inopportune electrical contacts may occur between the electronic components of the module and the casing, and on the other hand this casing transmits and concentrates all the electromagnetic perturbations that may come from the outside environment onto the electronic circuits.
To remedy these drawbacks, it is the object of the invention to provide an electronic module for a detonator comprising a printed circuit board equipped with components of the circuit, which is enclosed in a tubular casing and is embedded in a blocking resin of the board in the casing, wherein a shielding screen is interposed between the board and the tubular casing, which screen has an insulating face turned towards the casing and a conductive face turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board.
This screen thus ensures a double function, i.e. an insulation against inopportune electrical contacts that may occur between the components of the electronic circuit of the module and the outside casing and a screen for electromagnetic perturbations coming from the outside environment and transmitted or concentrated by the ferromagnetic metal casing.
In an advantageous embodiment of this screen, the screen is formed by a sheet of flexible and elastic plastic material, the conductive face of which is covered with a conductive ink, except for a peripheral margin. This sheet can thus be easily connected electrically to the printed circuit board and be wound around this board with a large overlap, the elasticity of the sheet making it possible to easily insert it into the metal casing by rolling it up with a diameter smaller than the inside diameter of this casing and, once inserted in the casing, the sheet tends to unroll elastically and comes to rest against the inside surface of the tubular casing, thus forming a provisional holding means of the electronic board before it is cast with the blocking resin.
Other characteristics and advantages of the invention will become apparent from the description given below of an exemplified embodiment.
Reference will be made to the attached drawings, wherein:
From
During the mechanical electrical assembly of the screen 3 and printed circuit board 1, the sheet 3 is rolled up enclosing the printed circuit board 1, as illustrated in
Having taking the trouble to roll up the screen to form a tube with a diameter smaller than the inside diameter of a metal casing tube 12, it is easy to insert the board 1 and rolled up screen 3 into the inside of the metal tube 12, and when one lets go off the screen 3 after inserting it, the screen tends to unroll and flattens itself against the inside surface of the metal tube 12. The printed circuit board 1 is then provisionally held in place inside the metal tube by the friction between the screen 3 and this tube. It will have been noted that the margin 7 ensures that the conductive ink will not come into contact with the metal tube 12.
This metal tube will preferably be a seamless steel tube.
Finally, it will have been noted that
It will furthermore be understood that the casting of the polyurethane resin can take place easily since the tube is held vertically, which position is made possible by the holding in position without sliding of the printed circuit board inside the tube 12 by means of the elastic screen.
Claims
1. Electronic control module for a detonator comprising a printed circuit board (1) equipped with components of the circuit, which is enclosed in a tubular casing (12) and is embedded in a blocking resin (15) held inside the casing, wherein it comprises a shielding screen (3) interposed between the board (1) and the tubular casing (12), provided with an insulating face turned towards the casing (12) and a conductive face (6) turned towards the board, the conductive face being electrically connected to the earth wire of the printed circuit board (1).
2. Module according to claim 1, wherein the shielding screen (3) is formed by a sheet of flexible and elastic plastic material (5), the conductive face of which is covered with a conductive ink (6) except for a peripheral margin (7).
3. Module according to claim 2, wherein the layer of conductive ink (6) is covered by an insulating protection film (8).
4. Module according to claim 1, wherein the tubular casing (12) is formed by a section of seamless steel tubing and in that the blocking resin (15) is a polyurethane resin.
5. Module according to claim 1, comprising in the known manner an electrochemnical capacitive component (2), wherein this component (2) has an outside shock absorption casing (16).
Type: Application
Filed: Nov 14, 2002
Publication Date: Mar 31, 2005
Inventor: Guy Mausy (Colomars)
Application Number: 10/495,849