Method for validation of a fuse head in an electronic detonator

Abstract

A method for the validation of a fuse head in an electronic detonator is disclosed, the method including measuring at least once a first charge time; activating a switching means to a second position to replace a reference resistor in an RC circuit with the fuse head; measuring at least once a second charge time; and determining the deviation of the second charge time from the first charge time.

Claims

1. A method for the validation of a fuse head in an electronic detonator, said detonator comprising: a reference resistor, a fuse head, at least one capacitor, and switching means, wherein in a first position of the switching means, the reference resistor is connected to the at least one capacitor forming a first RC circuit, and in a second position of the switching means, the fuse head is connected to the at least one capacitor forming a second RC circuit; and wherein the method comprises the following steps: a) measuring at least once a first charge time t.sub.1, the first charge time being the time required for the at least one capacitor to reach a specified charge value in the first RC circuit, when the switching means is in the first position, b) activating the switching means to the second position, c) measuring at least once a second charge time t.sub.2, the second charge time being the time required for the at least one capacitor in the second RC circuit to reach the same specified charge value as specified in step a), and d) determining if the second charge time is within a range (t.sub.1.sub.1, t.sub.1+.sub.2), t.sub.1 being the first charge time, t.sub.1.sub.1 being a first validation threshold and t.sub.1+.sub.2 being a second validation threshold.

2. The method according to claim 1, wherein the method comprises an additional intermediate step between steps a) and c), which comprises: discharging the at least one capacitor, until the output voltage of the first RC circuit or the second RC circuit is lower than or equal to a charging threshold.

3. The method according to claim 2, wherein discharging the at least one capacitor comprises short-circuiting the at least one capacitor during a determined period of time.

4. The method according to claim 2, wherein the charging threshold is 0V.

5. The method according to claim 1, wherein the method comprises the further step of calculating the resistance of the fuse head.

6. The method according to claim 5, wherein calculating the resistance R.sub.fuse of the fuse head comprises applying the following expression: $R_{\mathrm{fuse}}=R_{\mathrm{ref}}*\frac{t_2}{t_1}$ wherein t.sub.2 is the second charge time measured in step c), t.sub.1 is the first charge time measured in step a) and R.sub.ref is the resistance of the reference resistor.

7. The method according to claim 1, wherein in step a) the measurement of the time required for the at least one capacitor to reach a specified charge value is taken at least twice and the first charge time t.sub.1 is obtained as the mean of the measurements taken.

8. The method according to claim 1, wherein in step c) the measurement of the time required for the at least one capacitor to reach a specified charge value is taken at least twice and the second charge time t.sub.2 is obtained as the mean of the measurements taken.

9. The method according to claim 1, wherein the reference resistor is a precision resistor with a resistance equal to the nominal resistance of the fuse head.

10. The method according to claim 1, wherein the method steps are performed by a microcontroller comprised in the electronic detonator.

11. The method according to claim 1, wherein the detonator comprises a second capacitor, the two capacitors being connected in parallel, and the first charge time t.sub.1 and the second charge time t.sub.2 being the time required for both capacitors to reach a specified charge value.

12. An electronic detonator comprising: a reference resistor, a fuse head, at least one capacitor, switching means, wherein in a first position of the switching means, the reference resistor is connected to the at least one capacitor forming a first RC circuit, and in a second position of the switching means, the fuse head is connected to the at least one capacitor forming a second RC circuit, and a microcontroller, wherein the microcontroller is configured to perform the method according to claim 1.

13. The electronic detonator according to claim 12, further comprising a second capacitor, the two capacitors being connected in parallel.

14. The electronic detonator according to claim 12, wherein the first and second validation thresholds (t.sub.1.sub.1, t.sub.1+.sub.2) are set in the firmware of the microcontroller.

Description

DESCRIPTION OF THE DRAWINGS

(1) These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.

(2) FIG. 1 This figure shows the fuse head and the connections points of an electronic circuit used in the method of the invention.

(3) FIG. 2 This figure shows the fuse head connected to an electronic circuit used in the method of the invention.

(4) FIG. 3 This figure shows the fuse head welded to an electronic circuit used in the method of the invention.

(5) FIG. 4 This figure shows an embodiment of an electronic circuit used in an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIGS. 1, 2 and 3 show the assembly process of a fuse head in an electronic circuit of an electronic detonator.

(7) FIG. 1 shows the fuse head (1) and a terminal (2) of the electronic circuit. This terminal (2) comprises two connection points (3) for the connection of the fuse head (1).

(8) FIG. 2 shows the fuse head (1) connected to the terminal (2) of the electronic circuit through the connection points (3).

(9) FIG. 3 shows the fuse head (1) welded to the terminal (2) of the electronic circuit through the connection points (3). This welding shown in FIG. 3 may be irregular due to the fact that the amount of tin used is not controlled. This may result in the creation of short circuits or open circuits in the electronic circuit of the detonator, thus compromising the quality of the detonators and implying economic costs and safety risks. Also, it is important to ensure prior to the use of the detonator if the welding of the fuse head (1) or the fuse head (1) itself have been damaged after the assembling of the detonator elements, e.g. during transportation or storage. Thus, in an embodiment of the invention the validation method is automatically performed during the programming of the electronic detonator.

(10) FIG. 4 shows an electronic circuit used in an embodiment of the invention, including the following elements: Connection points (3). A first input point (4), a second input point (5). An output point (6). Capacitors C1 and C2. The resistor R13 as reference resistor. The transistors T3 and T4, acting as switching means, in particular acting as a first switch and second switch, respectively. Resistors (R8, R12, R10, R15, R14). A discharge circuit (7).

(11) The connection points (3) are adapted for attachment and welding of the fuse head (1).

(12) The first input point (4) is adapted to send an instruction to the switching means to set it in a position adapted to measure the first charge time t.sub.1.

(13) The second input point (5) is adapted to send instruction to the switching means to set it in a position adapted to measure the second charge time t.sub.2.

(14) The output point (6) is adapted to transmit the first charge time t.sub.1 or/and the second charge t.sub.2 time to a microcontroller.

(15) The resistor (R13) is a precision resistor, i.e. its tolerance and variability of its properties along the time are very low. The resistor R12 is adapted to limit the current which flows through the precision resistor and the fuse head (1) in order to avoid an undesirable accidental initiation of the explosive charge attached to the fuse head (1). The resistors (R8, R10, R15, R14) are resistors adapted to polarise the transistors T4 and T3, which work as a first switch and a second switch and said switches are adapted to connect the resistor R13 and disconnect the fuse head (1) to measure the charge time of the capacitors, in the case of the first switch, and to connect the fuse head (1) and disconnect the resistor R13 to measure the charge time of the capacitors, in the case of the second switch.

(16) The capacitors C1 and C2 are connected in parallel to each other. In this way, the charge time is the same as for a capacitor with a capacitance C1+C2.

(17) In the embodiment shown in FIG. 4, the microcontroller M is adapted to be connected through the first input point (4), the second input point (5), the output point (6) and the discharge circuit (7). Through these input (4, 5) and output (6) points, the microcontroller M is able to communicate and send instructions to the circuit. The microcontroller M is adapted to perform the steps according to an embodiment of the invention: 1) Activating through the first input point (4) the first switch and thus setting the switching means in a first position.

(18) In this step the microcontroller activates the transistor T4. The current from the voltage source (8) flows through the resistor R12, the transistor T4 and the precision resistor R13 and loads the capacitors C1 and C2. 2) Measuring at least once a first charge time, the first charge time t.sub.1 being the time required for the capacitors to reach a specified charge value in the first RC circuit, when the switching means is in the first position.

(19) After performing the first measurement, the capacitors should be discharged until a certain level. To accelerate this process in this embodiment, the microcontroller activates the discharge circuit (7) through the transistor T2B. In this embodiment, the capacitors are short-circuited to ground through the transistor T2B, until the output voltage of the RC circuit is equal to 0V. 3) Activating through the second input point (5) the second switch and thus setting the switching means in the second position, to replace the reference resistor (R13) with the fuse head (1).

(20) In this step the microcontroller activates the transistor T3. The current from the voltage source (8) flows through the resistor R12, the transistor T3 and the parallel of the resistors R17 and the fuse head (1) connected to the connection points (3). Since the resistance of resistor R17 is much higher than the impedance of the fuse head (1), the current flows only through the fuse head (1) and loads the capacitors C1 and C2. 4) Measuring at least once a second charge time t.sub.2, the second charge time being the time required for the capacitors in the second RC circuit to reach the same specified charge value as specified in step 2. 5) Determining if the second charge time t.sub.2 is within a range (t.sub.1.sub.1, t.sub.1+.sub.2), t.sub.1 being the first charge time, t.sub.1.sub.1 being a first validation threshold and t.sub.1+.sub.2 being a second validation threshold. If the second charge time t.sub.2 falls within the specified range, the fuse head (1) is considered valid. On the contrary, if the second charge time t.sub.2 is lower than t.sub.1.sub.1 or greater than t.sub.1+.sub.2, the fuse head (1) is considered not valid.

(21) In one embodiment, .sub.1=.sub.2=10% t.sub.1. In this embodiment the range for validation would thus be (0.9 t.sub.1, 1.1 t.sub.1).

(22) In one embodiment, the detonator is adapted to store in a memory device the comparison performed and/or to send the results to an external entity and/or to display the results in a display.

(23) Preferably, the detonator is adapted to be connected to an external device, which can test the conditions of the detonator even when said detonator is placed in a localization to be used, for example in underground or open pit mining operations.

(24) Thanks to the method of the invention the validity of a detonator can be checked before its use. In the case of a controlled blast it is crucial that all the detonators work properly, therefore this method provides a solution to validate the fuse head (1) in order to guarantee the proper operation of the detonator.