Velocity of detonation measurement
A method of obtaining velocity of detonation (VOD) information from a borehole wherein an explosive in the borehole is ignited by initiation of a detonator, the method including the steps of using a control circuit which obtains a measurement of the VOD and which is subsequently destroyed by ignition of the explosive, and of transmitting from the borehole a wireless signal which contains the VOD measurement and data which identifies the borehole before the control circuit is destroyed.
1 . A blasting system comprising: a plurality of detonator assemblies, a blast controller and at least one receiver, wherein each detonator assembly includes a detonator which, in use, is positioned inside a borehole which is charged with an explosive, a communication module and conductors which connect the detonator to the communication module, wherein the detonator in response to a fire command signal from the blast controller received by the detonator at a time A is initiated at a time B to cause ignition of the explosive in the borehole, and wherein the communication module includes a control circuit which is configured to obtain a measurement of the velocity of detonation (VOD) of the explosive which is based on a resistance value which is presented by the conductors to the control circuit, and which is indicative of a predetermined length of the conductors consumed by the ignited explosive and a transmitter for transmitting to the receiver a wireless signal which commences at the time B and is maintained for a time period until the predetermined length of the conductors is consumed by the ignited explosive, and wherein the time period for which the wireless signal is transmitted is indicative of the VOD measurement and is reduced to a minimum to assist in discriminating between the wireless signal and respective wireless signals transmitted from other detonator assemblies of the plurality of detonator assemblies, and wherein the wireless signal contains identification information which identifies the detonator assembly from which the wireless signal was transmitted before the transmitter is destroyed by the ignited explosive.
2 . A blasting system according to claim 1 wherein the control circuit, in response to receipt of the fire command signal from the blast controller, transmits the fire command signal at the time A to the detonator.
3 . A blasting system according to claim 1 wherein the fire command signal is transmitted to the detonator from the blast controller using a through-the-earth signal.
4 . A blasting system according to claim 1 wherein the identification information comprises at least one of: a modulation technique, on the wireless signal, which is uniquely related to the detonator assembly; a data packet which contains the wireless signal and which is uniquely linked to the detonator assembly; and
a unique identifier, in the wireless signal, of the detonator assembly.
5 . A blasting system according to claim 1 wherein said respective wireless signals are transmitted simultaneously or in a first time slot by said transmitters from said plurality of detonator assemblies and are multiplexed to enable the respective wireless signals to be distinguished from one another.
6 . A blasting system according to claim 5 wherein the respective wireless signals which are transmitted in a second time slot, which is different from the first time slot, are modulated so that the frequency spectrums of the respective wireless signals transmitted in the second time slot are the same as the frequency spectrums of the respective wireless signals transmitted in the first time slot.
7 . A blasting system according to claim 1 wherein the communication module is configured to change the nature of another wireless signal which is sent from the communication module and which is indicative of the detonator assembly being in an effective working order from the nature of the wireless signal which contains the VOD measurement.
8 . A blasting system according to claim 1 wherein the conductors are separated into a succession of the predetermined lengths to allow determination of respective VOD measurements which are associated with the predetermined lengths, and wherein the communication module is configured such that an amplitude of the wireless signal during respective time periods which are associated with the predetermined lengths is gated on and off successively.
9 . A blasting system according to claim 1 wherein the borehole is uniquely distinguishable from other boreholes which, together with the identification information allows the VOD measurement to be associated with the borehole from which the VOD measurement was taken.
10 . A method of obtaining velocity of detonation (VOD) information from each of a plurality of boreholes in a blasting system which comprises a plurality of detonator assemblies, a blast controller and at least one receiver, wherein each detonator assembly includes a detonator which, in use, is positioned inside a respective borehole of the plurality of boreholes, a communication module and conductors which connect the detonator to the communication module which includes a control circuit, wherein each borehole is respectively charged with an explosive which is ignited by initiation of the respective detonator in the borehole at a time B in response to a fire command signal from the blast controller received by the detonator at a time A, the method comprising the steps, at each borehole, of: using the respective control circuit which is associated with the respective detonator to obtain a measurement of the VOD of the explosive which is based on a resistance value which is presented by the conductors to the control circuit, and which is indicative of a predetermined length of the conductors consumed by the ignited explosive; and transmitting from the borehole to the receiver a respective wireless signal which commences at the time B and is maintained for a time period until the predetermined length of the conductors is consumed by the ignited explosive, and wherein the time period for which the wireless signal is transmitted is indicative of the VOD measurement and is reduced to a minimum to assist in discriminating between the wireless signal and respective wireless signals transmitted from other detonator assemblies of the plurality of detonator assemblies and wherein the wireless signal contains data which identifies the borehole.
11 . A method according to claim 10 wherein said wireless signal is modulated to enable the wireless signal to be distinguished from any other wireless signal which contains a VOD measurement and which is simultaneously transmitted.