logo RFID Technologies CC

color line

5,406,890

Text of Timing Apparatus patent as granted in the US. and recorded in the US Patent Office.

Patent Number:     5,406,890

Date of Patent:    Apr. 18,1995 

Title: Timing Apparatus 

Inventors:      Marsh; Michael J. C.,ZAX;
                Atkins; Raymond C.,ZAX;
                Hodson; Trevor M.,ZAX

Assignee:       CSIR
                Pretoria,ZAX

Appl No:    993,824

Filed:      Jul. 30, 1993 

Related U.S. Application Data
Application Number 921,147 filed Jul 28, 1992  Pat. No. 5,282,421  
Application Number 587,914 filed Sep 25, 1990  Pat. No. 5,189,246

Foreign Application Priority Data
Sep 28,1989    South Africa 	   89/7389


Int Cl.:    F23Q 2100 
U.S. Cl.:   102/217 

Field of Search: 102/217;206


References Cited
     US Patent Documents
     Re32888  3/1989   Kirby et al.    102/217
     2546686  3/1951   Bickel et al.
     3312869  4/1967   Werner
     4489379  12/1984  Lanier et al.   364/200 
     4496010  1/1985   Chapman, III    102/217
     4527636  7/1985   Bordon          102/217
     4610203  9/1986   Bock            102/217
     4646640  3/1987   Florin et al.   102/217
     4674047  6/1987   Tyler et al.    102/206
     4869171  9/1989   Abouav          102/206
     4976199  12/1990  Beukes et al.   102/217 
     5014622  5/1991   Jullian         102/217  
     5117756  6/1992   Goffin, II      102/217   
     5189246  2/1993   Marsh et al.    102/217  

     Foreign Patent Documents
     0003412  8/1979   European Patent Office
     136919   4/1985   European Patent Office   102/217   
     2352273  1/1978   France
     72/8367  11/1973  South Africa
     72/8368  11/1973  South Africa
     79/0355  4/1980   South Africa

Primary Examiner: Johnson, Stephen M.
Agent: Lowe, Price, Leblanc & Becker


Abstract

The invention relates to a blasting apparatus for activating a plurality of 
electrical detonators after predetermined time delays. The blasting 
apparatus includes a plurality of remote electrical delay devices. Each 
device is linked to a detonator, and is arranged to be serially programmed 
with a timing signal, which originates from the central control unit and 
which determines the time delay. A bidirectional signal harness, having 
ends which terminate at I/O ports in the control unit, serially links the 
delay devices to the control unit. In the event of a fault of discontinuity 
occurring in the harness prior to programming of the delay devices, the 
discontinuity is detected and the direction of programming along the 
bidirectional harness is reversed so that those delay devices which, due to 
the break, cannot be programmed in the initial direction, are programmed 
with timing signals travelling along the signal line in the opposite 
direction. The invention extends to a method of activating a plurality of 
electrical detonators, as well as to the individual delay devices forming 
part of the blasting apparatus.

Parent Case Text

     This application is a division of application Ser. No. 07/921,147 filed
Jul. 28, 1992, now U.S. Pat. No. 5,282,421, which is a division of
application Ser. No. 07/587,914 filed Sep. 25, 1990, which is now U.S.
Pat. No. 5,189,246.

Brief Summary

                        BACKGROUND OF THE INVENTION

     This invention relates to a timing apparatus, and in particular to a 
timing apparatus for activating a plurality of electrical loads at 
predetermined time intervals in blasting operations.

     During mining and quarrying operations, it is necessary to detonate a
series of explosive charges in an accurately timed sequence to achieve the
correct blast pattern. In the past, the most common way of achieving this
has been to use a train of pyrotechnic delay fuses and ignitor cord to
link up detonators. In recent years however, systems for generating a
controlled sequence of electrical timing signals have been introduced
(see, for instance, U.S. Pat. Nos. 2,546,686 and 3,212,869, and South
African Patent No. 79/0355).

     In South African Patent No. 79/0355, a system is described in which a
central control unit programmes a plurality of remote delay devices with
corresponding reference timing signals via an electrical cable line and
subsequently activates the detonators to which the delay devices are
attached.

     Rockfalls and explosions elsewhere in the mine can damage both the 
remote delay devices and the electrical harness line interlinking these 
devices and the control unit. If this occurs before or during programming, 
then it becomes necessary to abort the blasting operation, as some of the 
delay devices have not been provided with their reference timing signals, 
and cannot be subsequently triggered.

     Electrical failure or malfunctions in the central control unit or in 
the remote delay devices may also lead to serious accidents.

     As a mine is generally evacuated during blasting, the down-time wasted 
as a result of such malfunctions occuring is extremely costly.

                          SUMMARY OF THE INVENTION

     According to the first aspect of the invention, there is provided 
apparatus for activating a plurality of electrical loads after 
predetermined time delays comprising:

     The apparatus includes a central control unit for generating timing 
signals and a plurality of remote electrical delay devices, each device 
being associated with a corresponding electrical load. The remote 
electrical delay devices are arranged to be serially programmed by a timing 
signal originating from the central control unit. The timing signal 
determines the time delay. At least one bidirectional timing signal line 
allows the timing signals to be transmitted in series from the central 
control unit to each remote electrical delay device in either of two 
preselected directions.

     In a preferred form of the invention, the apparatus further comprises
sensing means for sensing a fault in the timing signal line, and direction
selection means for selecting the direction of transmission of the timing
signals from either the first or the second ports. The direction selection
means select a direction of transmission opposite to the initial direction
of transmission of the timing signals from the control unit in the event
of a fault sensed in the timing signal path, for programming those delay
devices which cannot be programmed in the initial direction.

     Conveniently, the apparatus further includes monitoring means for
monitoring the number of electrical delay devices which have been
correctly programmed, and deactivation means for deactivating the delay
devices and aborting the blasting procedure in the event of a
predetermined number of the delay devices not having been programmed
correctly or at all.

     Preferably, the monitoring means includes fault location means for 
locating the position of a fault in relation to the delay devices, and 
counting means for counting the number of delay devices on opposite sides 
of the fault, for establishing the correct timing signal pattern to ensure 
that each delay device is programmed with its corresponding timing signal.

     The control unit preferably has first and second signal I/O ports to 
which opposite ends of the timing signal line are connectable, the second 
signal I/O port in use receiving a signal transmitted from the first signal 
I/O port, and vice versa, in the event of no fault existing in the timing 
signal line.

     In a preferred form of the invention, the control unit includes both 
timing and triggering signal generating means, and each electrical delay 
device is configured to activate its associated electrical load a 
predetermined time delay after receipt of a triggering signal, and may 
further include power signal generating means for generating power signals 
for powering up each delay device.

     Conveniently, the timing, triggering and power signals are transmissible
along separate respective bidirectional timing, triggering and power
signal lines which together constitute a harness. The ends of the harness
are connectable to ports at the control unit, which include the first and
second respective signal output ports.

     The harness preferably includes a ground line. Each delay device is
connectable to the control unit in parallel between the triggering and
power signal lines and the ground line, so as to receive power and
triggering signals simultaneously from the control unit.

     The sensing means may comprise microprocessor-controlled signal 
generating means for generating a test signal and for transmitting the test 
signal from one of the ports of the control unit to another along one of 
the signal lines, and test signal receipt means for detecting the presence 
or otherwise of the test signal at the opposite port from which it was 
transmitted.

     The direction selection means is preferably responsive to the sensing
means, and forms part of a microprocessor-based routine at the control
unit.

     The monitoring means may be in the form of a counter for counting the
number of timing signals received at one of the ports of the control unit
along one of the signal lines. A memory module stores the number of delay
devices utilized for a particular blasting operation. A comparator
compares the number of signals received with the number of delay devices
stored in the memory module.

     Safety control means are preferably provided for ensuring that the 
delay devices are not programmed or triggered by spurious signals. The 
safety control means include switching means for disconnecting the signal 
lines from the control unit and for shorting them to the ground line.

     The switching means are preferably operable by a motor-powered slug 
from a safe position, in which the signal lines are isolated from the 
control unit and shorted to earth, to an enabled position in which the 
signal lines are connected to the ports of the controller.

     Microcomputer monitoring means may be provided to monitor a 
microcomputer which controls the operation of the control unit, and power 
supply means for powering the power and trigger signal lines. The 
microcomputer monitoring means only activates the power supply means in the 
event of the microcomputer operating normally.

     In one form of the invention, the central control unit includes a 
precise timing pulse generator, measuring means for measuring pulse 
duration and computation means for computing a correction factor. Each 
delay device includes an imprecise timing pulse generator, and each delay 
device is responsive to a signal from the control unit to transmit at least 
one imprecise timing pulse to the control unit for measurement of the 
duration thereof using the measuring means. The computation means compute a 
correction factor on the basis of the ratio between the duration of the 
imprecise timing pulse and a precise timing pulse from the precise timing 
pulse generator. This correction factor is applied to a timing signal for 
receipt by a delay device.

     The imprecise and precise pulse generators may be in the form of 
respective local and precision oscillators, and the timing signal may be in 
the form of a digital word.

     According to a second aspect of the invention, there is provided a 
method of activating a plurality of electrical loads after predetermined 
time delays comprising the steps of:

 a) providing a central control unit for generating timing signals which
  determine the time delays;

 b) providing a plurality of remote electrical delay devices, each delay
  device being associated with a corresponding electrical load;

 c) providing a bidirectional timing signal line for connecting the delay
  devices in series with the central control unit;

 d) transmitting the timing signals in series from the central control unit
  along the bidirectional timing signal line to each remote electrical delay
  device for programming thereof;

 e) selecting the direction of transmission of the timing signals along the
  bidirectional timing signal line.

     Preferably, the method includes the steps of detecting a fault in the
bidirectional signal line and selecting the direction of transmission of
the timing signals along the bidirectional timing signal line in
accordance with the location of the fault.

     Conveniently, the method includes the further steps of monitoring the
number of electrical delay devices which have been programmed with timing
signals and deactivating the control unit and the delay devices and
aborting the blasting procedure in the event of at least one of the delay
devices not having been programmed correctly or at all.

     The further steps of locating the position of a fault in relation to the
delay devices, and counting the number of delay devices on opposite sides
of the fault between the fault and the control unit for establishing the
correct timing signal pattern to ensure that each delay device is
programmed with its correct corresponding timing signal may preferably be
followed.

     In a preferred form of the invention, there are provided the further 
steps of generating a triggering signal at the central control unit 
subsequent to programming of the delay devices, and transmitting the 
triggering signal simultaneously to all of the delay devices for activating 
the electrical loads after the predetermined time delays in respect of each 
delay device have lapsed.

     Power signals are preferably also transmitted from the central control 
unit for powering up each delay device.

     Preferably, the timing, triggering and power signals are transmitted 
along separate respective bidirectional timing, triggering and power signal 
lines, the lines together constituting a harness which is connectable to 
separate I/O ports at the control unit.

     The method preferably includes the step of providing a ground line in 
the harness, connecting each delay device in parallel between the 
triggering and power signal lines and the ground line and in series with 
the timing signal line, and receiving at each delay device power and 
triggering signals simultaneously and timing signals serially from the 
control unit.

     In a preferred form of the invention, there are included the steps of
transmitting timing signals in series from first or second signal I/O
ports at the control unit, and monitoring the progress of programming of
the delay devices by receiving the timing signals at a signal input port,
non-receipt of the timing signals at the signal input port being
indicative of a fault in the timing signal line.

     Conveniently, the method includes the preliminary steps of isolating the
signal lines from the controller and shorting them to earth, selecting at
the central control unit the timing pattern for blasting in respect of
each delay device, connecting the signal lines to the control unit after
the elapsing of a stand-off time, and programming the delay devices with
timing signals from the central control unit.

     The subsequent steps of charging the energy storage means in the delay
devices with a charge signal from the control unit along one of the signal
lines, triggering the delay devices with the trigger signal from the
control unit via the trigger signal line, and directly thereafter
disconnecting the signal lines from the controller and shorting them to
the ground line.

     The further step of monitoring the functioning of a microcomputer which
controls the control unit, and only allowing triggering and powering
signals to be transmitted along the signal lines in the event of the
microcomputer functioning normally is preferably included in the
invention.

     In one form of the invention, the method includes the further steps of
transmitting at least one imprecise timing pulse from a delay device to
the control unit, generating at least one precise timing pulse at the
control unit, measuring the duration of the imprecise timing pulse,
computing a correction factor on the basis of the ratio between the
duration of the imprecise and precise timing pulses, and applying this
correction factor to a timing signal for receipt by the delay device.

     According to a third aspect of the invention, there is provided an
electrical delay device for activating an electrical load associated
therewith after a predetermined time delay, the electrical delay device
being serially connectable to a bidirectional timing signal path, and
being arranged to receive a timing signal, which is a function of the
predetermined time delay, from a central control unit, the electrical
delay device comprising:

 a) first timing signal steering means for steering a timing signal arriving
  at the delay device in a first direction along the bidirectional timing
  signal path;

 b) second timing signal steering means for steering a timing signal
  arriving at the delay device in a second direction along the bidirectional
  timing signal path;

the first and second timing signal steering means being operable to
function in a signal storage mode for allowing storage of a timing signal
in the delay device, and a signal bypass mode, in which a timing signal is
permitted to bypass the delay device.

     Preferably, the first and second timing signal steering means are further
operable to function in a timing signal blockage mode, for preventing the
passage of timing signals through or into the delay device.

     Direction sensing means may be provided for selectively enabling 
either the first or the second timing signal steering means for allowing 
the receipt of timing signals travelling in either the first direction or 
the second direction.

     Timing signal storage control means may be included to allow storage 
of a timing signal when the first or second timing signal steering means 
are in the signal storage mode, and to prevent storage of a subsequent 
timing signal arriving at the delay device.

     The electrical delay device is preferably arranged to receive a 
triggering signal from the central control unit for activating the 
electrical load associated with the delay device a predetermined time delay 
after receipt thereof.

     Fault detection means are conveniently provided for detecting a fault in
the bidirectional timing signal path to which the delay device is in use
serially connected, the fault detection means being operative to prevent
the receipt of a timing signal in a direction corresponding to the
direction in which the fault was detected.

     The direction selection means may be responsive to a direction selection
signal arriving in a first or second direction along the bidirectional
timing signal path.

     Conveniently, the electrical delay device has first and second terminals
which are serially connectable to the bidirectional timing signal path.

     Each of the first and second timing signal steering means may include at
least two controlled switches, the controlled switches being arranged to
operate in combination in at least three states respectively corresponding
to the signal storage, bypass and blockage modes.

     The controlled switches may be in the form of a pair of unidirectional
buffers linked in series for accepting signals travelling in either the
first or the second directions.

     The first and second signal steering means preferably together 
comprise a bidirectional buffer arrangement constituted by at least two 
pairs of oppositely directed unidirectional buffers linked together in 
anti-parallel.

     Each of the two controlled switches may optionally include a first
controlled switch which is operative to maintain a first voltage level at
one of the terminals of the delay device, for allowing the receipt of a
timing signal at that terminal, and a second controlled switch which is
operative at a second voltage level to allow propagation of a timing
signal from one terminal to another, the output of the second controlled
switch being at least partly determined by the first voltage level.

     The first controlled switch may be in the form of a transistor 
arranged in series with a pull-up resistor to raise the voltage level of 
one of the terminals, and the second controlled switch is in the form of a 
transistor arranged to ground the other terminal.

     The direction selection means may be operative to set the first and 
second timing signal steering means so as to receive timing signals 
travelling only in the direction of travel established by a direction 
selection signal.

     The timing storage control means may optionally be operative to allow
storage of a timing signal in the delay device, and to prevent storage of
subsequent timing signals in the storage means after the first or second
timing signal steering means have operated in the signal storage mode.

     Conveniently, each electrical delay device includes charge storage means
for receiving a charge storage signal from the central control unit, the
charge storage means being arranged to power the delay device on receipt
of the triggering signal and to activate the electric load a predetermined
time delay after receipt of the triggering signal.

     The timing signals may be in the form of a real time signal, a digital 
word or any other signal which conveys timing information from the control 
unit to each delay device.

     The fault in the timing or other signal lines may arise as a result of 
a discontinuity in the signal lines due to a break in the harness, a faulty 
connection to one or more of the delay devices, a fault in the delay 
devices themselves, an undesirable short to ground or to a positive or 
negative voltage in the signal lines of the harness or in the delay 
devices, or any other spurious signal conditions arising in either the 
harness lines or in one or more of the delay devices.

Drawing Description

                     BRIEF DESCRIPTION OF THE DRAWINGS

     FIG. 1 shows a highly schematic representation of the main components 
of a timing apparatus of the invention;

     FIG. 2 shows a detailed functional block diagram of a central control 
unit or controller of a first embodiment of the invention;

     FIG. 3A shows a flowchart of the steps involved in activating the
controller and programming delay devices of the first embodiment of the
invention;

     FIG. 3B shows a timing diagram equivalent of the flowchart of FIG. 3A;

     FIG. 3C shows a safety level diagram illustrating the various safety 
levels of the timing apparatus of FIG. 2;

     FIG. 4 shows a functional block diagram of a first embodiment of a delay
device of the invention;

     FIG. 5A shows a timing diagram of the output of the controller when
programming in the clockwise direction;

     FIG. 5B shows a timing diagram of the output of the controller when
programming in the anti-clockwise direction;

     FIG. 6 shows a timing diagram illustrating how a reference timing 
signal is programmed into the delay device of FIG. 4;

     FIG. 7 shows a functional block diagram of a second embodiment of a 
delay device of the invention;

     FIG. 8 shows a timing diagram illustrating how a reference timing 
signal is programmed into the delay device of FIG. 7;

     FIG. 9 shows a schematic circuit diagram of a bidirectional buffer 
forming part of the delay devices of FIGS. 4 and 7.

     FIG. 10 shows a timing diagram illustrating the operation of the
bidirectional buffer of FIG. 9;

     FIG. 11 shows a schematic view of a third embodiment of the timing
apparatus of the invention showing a series of delay devices of the
invention which, incorporate bidirectional buffers.

     FIG. 12 shows a circuit diagram of the bidirectional buffer and the 
buffer logic circuitry of the delay devices of FIG. 11;

     FIGS. 13A and 13B show timing diagrams illustrating the manner in 
which the programming direction in respect of the timing apparatus of FIG. 
11 is set up for respective unbroken and broken harnesses;

     FIG. 13C shows a timing diagram illustrating the manner in which
programming of the delay devices of FIG. 11 is effected where no break in
the harness occurs;

     FIG. 13D shows a timing diagram illustrating the manner in which
programming of the delay devices of FIG. 11 is effected where a break in
the harness occurs, and

     FIG. 14 shows a flowchart indicating the steps involved in the 
programming and triggering of the timing apparatus of FIG. 11 for 
respective unbroken and broken harnesses.

Detail Description

                         DESCRIPTION OF EMBODIMENTS

     Referring to FIG. 1, a timing apparatus 10 is in the first embodiment 
about to be described intended for use in mining or quarrying operations 
for the detonation of explosives at predetermined times after a triggering 
signal. In broad terms, the timing apparatus 10 comprises a control unit or 
controller 12 electrically linked in series by means of a harness 14 to a 
number of remote electronic delay devices 16.1, 16.2, 16.3, 16.4, 16.5 and 
16.6, each of which are in turn connected to a corresponding electrical 
load or detonator 18 for setting off an explosive charge. The harness 14 is 
in the form of a loop having its ends connectable to first and second, or A 
and B ports 20 and 22 at the controller 12. As will be described in more 
detail further on in the specification, the harness 14 includes a timing 
signal path in the form of a programming line, which connects the delay 
devices together in series for serial programming thereof with timing 
signals from the controller. The harness also includes a number of power 
lines and a ground line which link the delay devices together in parallel, 
providing for the simultaneous powering up of the delay devices, and for 
allowing the transmission of a triggering signal for actuating the delay 
devices after predetermined time delays, which are determined by the timing 
signals which have been programmed into each delay device.

     This arrangement allows timing signals from the controller 12 to be
programmed serially into each delay device 16, each timing signal having a
specific duration or time interval. As will be described in more detail
further on in the specification, a subsequent firing signal simultaneously
initiates a count down of the time intervals stored in each of the delay
devices, thereby activating the detonator associated with each delay
device after the timing interval has lapsed. Owing to the loop-like
formation of the harness 14 and to the input/output configuration of the
delay devices, timing signals from the controller 12 can be programmed
into the delay devices 16.1 to 16.6 either in a clockwise or in an
anti-clockwise direction, indicated by respective arrows 24 and 26.

     Should a break 27 in the harness 14 occur, due to a rockfall for 
instance, it becomes necessary to implement bidirectional programming by 
sourcing timing signals from both the first and second ports 20 and 22 of 
the controller 12 in order to program all the delay devices. Delay devices 
16.1, 16.2 and 16.3 are programmed with timing signals emanating from the 
first port 20. The controller re-routes the further timing signals so that 
they emanate from the second port 22, allowing the delay devices 16.4, 16.5 
and 16.6 to be programmed in the anti-clockwise direction.

     In order to understand how this, and other functions of the timing
apparatus operate, the separate components, and the manner in which they
interact, will now be discussed in more detail.

     The controller 12 of FIG. 2 has a central microcomputer 28, which is
powered by a battery 30 operated by a key switch 31. The functions of the
microcomputer 28 are manually controlled by means of a series of switches
32 mounted on a control panel 34.

     The microcomputer 28 is connected via a bus interface 35 to a ROM 
look-up table 40 in which is stored a variety of reference timing signal 
patterns, one of which may be selected by means of selector switches 42. 
Programming may optionally be implemented via a keypad for more specific or 
unusual applications in which a non-standard blast pattern is applied. A 
stand-off clock 44 is linked to the microcomputer 28, and provides a 
stand-off time to allow the operators to vacate the area before the 
blasting sequence commences.

     A number of output lines lead from the microcomputer 28. These include a
PROG A line 46 and a PROG B line 48, which are connected to the
microcomputer 28 via first and second tri-state buffers 50 and 52
respectively. The buffers are actuable by means of signals from respective
first and second enable lines 54 and 56. The PROG A and PROG B lines
terminating in separate respective I/O ports 58 and 60 at the
microcomputer 28.

     Four separate lines lead from the controller 12 to a harness connector 36
at the first port 20, namely DETONATOR and LOGIC power lines 62 and 64,
the PROG A line 46 and a GROUND line 66. Likewise, four separate lines
lead to the harness connector 38 at the second port 22, two (the DETONATOR
line 62.1 and the LOGIC line 64.1) of which are offshoots from those lines
leading to the harness connector 36, the common GROUND line 66, and the
PROG B line 48. It follows that the harness 14 has four corresponding
lines; a DETONATOR line 62.2, a LOGIC line 64.2, a PROG line 47 and a
GROUND line 66.2

     Opposite ends of the separate lines of the harness are fed to male
connectors 36.1 and 38.1 which are operatively plugged into the
corresponding harness connectors 36 and 38. This results in the LOGIC
line, formed from the individual lines 64, 64.1 and 64.2, as well as the
DETONATOR line, comprising the lines 62, 62.1 and 62.2, forming continuous
loops. The PROG A line 46 and the PROG B line 48 form an open loop with
the PROG line 47.

     The DETONATOR, LOGIC, PROG A and PROG B lines 62, 64, 46 and 48 are linked
to the controller via a shorting switch unit 78 which comprises a series
of shorting switches 79. The DETONATOR line 62 is in turn lined to the
microcomputer 28 via an I/O port 79.1

     A motor 80 having a motor control unit 82 controlled by the microcomputer
28 is provided with a threaded shaft 84 which carries a slug 86, which is
mechanically linked to the shorting switches 79. Rotation of the shaft 84
causes the slug 86 to move from a disabled position indicated in broken
outline 87, in which the harness lines are earthed, in the direction of
arrow 88 to an enabled position in which the slug 15 is indicated in solid
outline, and the harness lines are connected to the controller 12.
Rotation of the shaft 84 in the opposite direction will naturally cause
the slug 86 to move the switches 79 back to the disabled position.

     A "safe" switch 89 is actuated by the slug 86 when in the disabled
position, transmitting a signal to the microcomputer 28 once so actuated.
If the microcomputer 28 does not receive such a signal after being
initially powered up, it will actuate the motor 80 via the motor control
unit 82 to move the slug 86 to the disabled position if the slug 86 is not
already in such a position. If, due to a faulty motor 80 or motor control
unit 82, the slug 86 does not move to the disabled position, the
controller 12 "times out" and the blast is aborted. A signal is
transmitted via a signal line 89.1 from the switch unit 78 to indicate to
the microcomputer 28 when the slug has reached the enabled position.

     The operation of the controller 12 will now be described with reference to
FIGS. 3A, 3B, and 3C. Once the operator has connected the harness 14 to
the controller 12, he subsequently turns on the key switch 31, thereby
bringing the safety level down from level 5 (the safest level) to level 4,
as is indicated in FIG. 3C. The controller 12 remains dormant until the
operator has selected the appropriate timing pattern (ie. the delay times
to be programmed into each one of the delay devices, and the number of
such devices which are to be programmed), by operating the appropriate
selector switch 42, and an ARM switch 90, causing the clock 44 to commence
timing for a stand-off time period which is typically two hours (refer to
both block 92 of the flow chart, and to step 4 of FIG. 3C). After this
time has elapsed, the motor 80 will be actuated to move the slug away from
the disabled position in the direction of arrow 87, thereby connecting the
harness lines 14 to the controller 12, as can be seen in block 94 of the
flow chart, and step 5 of FIG. 3C.

     The LOGIC line is then raised by sending a pulsed signal from the
microcomputer to a retriggerable monostable 96, which in turn actuates a
logic power supply 98 to power up the LOGIC line 64 (see block 100 of the
flow chart, as well as the rising edge of LOGIC pulse 102 in FIG. 3B). The
retrigerrable monostable 96 requires a regular pulse train from the
microcomputer 28 to hold the LOGIC power supply 98 on. Thus, should the
microcomputer 28 fail, it will no longer supply a regular pulse train to
the monostable 96, causing the logic power supply 98 to turn off, and
lower the LOGIC line 64.

     A signal from the microcomputer 28 along enable line 54 then enables the
buffer 50, thereby allowing programming of the delay devices 16.1 to 16.6
to commence by raising at 104 the PROG A line 46 (see block 106). The
programming of each of the delay devices 16.1 to 16.6 is monitored by
observing the return signals on the DETONATOR line 62, which at this stage
is in high impedance mode, so as to permit feedback. The return signal 108
appearing on the DETONATOR line 62 indicates when the delay device 16.1
has commenced timing, and the PROG A line is pulled low to indicate the
end of the timing period in which a first timing signal 104.1 is
programmed into the first delay device 16.1, causing the DETONATOR line to
be raised. The following timing signal 104.2 is transferred to the next
delay device 16.2. The actual delays to be programmed are drawn from the
blast pattern stored in the ROM look-up tables 40, and the programming
procedure is repeated until all the delay devices 16.1 to 16.6 have been
programmed.

     Once all the delay devices have been programmed, an additional pulse 
109 is sent via the PROG A line. Since all the delay devices have been 
programmed, this additional pulse is transmitted through all the delay 
devices and is received at the PROG B I/O port 60. Upon the reception of 
the additional pulse 109, the controller assumes that all the delay devices 
were programmed correctly and raises the DETONATOR line 62 (at 115) by 
switching on the detonator power supply 116. This charges the energy stores 
or capacitors in the delay devices, as will presently be described. The 
detonator power is then turned off, the falling edge 120 acting as a 
trigger for all the delay devices to begin timing their respective delay 
times.

     If, during programming via the PROG A line, a discontinuity is 
detected by the lack of a return signal via the DETONATOR line, the 
controller continues to send out the programming pulses until all the delay 
devices still linked to the controller via the PROG A line have been 
programmed. An additional pulse is still sent out via the PROG A line and 
the PROG B I/O port 60 is monitored for the return pulse. The lack of a 
return pulse confirms the discontinuity.

     In response thereto, the controller disables the PROG A buffer 50 and
enables the PROG B buffer 52. The programming procedure is completed via
the PROG B line 48 in the anti-clockwise direction by the controller
drawing the timing pattern out of the ROM table in the reverse order. This
procedure can be seen more clearly in FIG. 5B, in which the PROG A line is
low and timing signals 104.6, 104.5 and 104.4 are sourced in reverse order
from the PROG B line for programming the respective delay devices 16.6
16.5 and 16.4.

     The progress of programming the outstanding delay devices is once again
monitored via the DETONATOR line. The number of delay devices to be
programmed is preset into the ROM tables, and this number must correspond
with the number of delay devices actually connected to the harness. It is
thus possible to determine the span of the discontinuity by determining,
via the DETONATOR line, how many delay devices have been successfully
programmed. On the basis of the number of delay devices which have been
successfully programmed (indicated by the number of feedback signals
received on the DETONATOR line 62), the microprocessor 28 then ascertains
whether the entire operation should be aborted or whether it should
continue. For example, if only one of eight delay devices have not been
programmed, then the operation may continue. If more than one delay device
has not been programmed, the blasting procedure may be aborted by shutting
off the LOGIC power, and rewinding the motor 80 to move the slug 86 to the
disabled position, thereby shorting the lines to ground. (See blocks 112,
114 and 114.1).

     As was described previously, once the delay devices have been 
successfully programmed, the DETONATOR line 62 is raised (at 115) by 
actuating a detonator power supply 116, which is turned on by means of a 
retriggerable monostable 118 fed by pulses from the microcomputer 28 (see 
block 119). As with the logic power supply 98, failure of the microcomputer 
will interrupt the pulse train and cause the detonator power supply 116 to 
turn off. Once all the capacitors in the delay devices 16.1 to 16.6 have 
been charged, the detonator power supply 116 will be turned off, thereby 
lowering the DETONATOR line at 120, the falling edge 120 acting as a 
trigger signal for the delay devices to commence timing their respective 
delay times. At the same time, the motor 80 is powered to move the slug 86 
to the disabled grounded position 88 (see block 114.1), thereby grounding 
the harness lines, and returning the system to its initial state. A buzzer 
12.1 is connected to the microcomputer 28, and it sounds whenever the 
switches are connected to the harness and the harness lines are unearthed.

     Referring now to FIGS. 4, 5A and 6, the operation of the system will 
now be described with reference to the delay devices. The delay device 16.1 
of FIG. 4 is connected in parallel via protective circuitry 122 between the 
GROUND line 66.2, the LOGIC or LOGIC POWER line 64.2, and the DETONATOR or 
DET POWER line 62.2, and is linked in series between the PROG A and PROG B 
lines. The latter two lines are connected to one other via a bidirectional 
buffer 124, which will be described in greater detail further on in the 
specification.

     In broad terms, the delay device 16 has a logic unit 126 which 
receives a reference timing signal from either the PROG A or the PROG B 
line via the bidirectional buffer 124 and bidirectional buffer control 
circuitry 127. Onboard timing is provided by a local oscillator 128, which 
is used to increase a set counter 130.

     Once the LOGIC line goes high at 125 in FIG. 5A, it powers up both the
logic unit 126 and all other active components of the delay device 16.1
via a voltage regulator 131, as is indicated by broken lines 132 in FIG.
4. On being powered up via the voltage regulator 131, reset circuitry 137
generates a reset pulse to reset the logic unit 126 and to set up the
bidirectional buffer 124 and its control circuitry 127. At the same time
as the LOGIC line 64.2 is raised, the DETONATOR line 62.2 is pulled high
at 130 to the level of the LOGIC line by means of a pull-up resistor 133
located in the controller 12 of FIG. 2. The voltage level of the DETONATOR
line is limited to a level which does not permit zener diode 134, which is
connected to an energy storage device 136, to conduct.

     The logic unit 126 receives the timing signal 138 from the PROG A line 
via the bidirectional buffer 124 and its control circuitry 127. As a result 
of the PROG A line going high, the logic unit 126 transmits a reset pulse 
142 to clear both the set counter 130 and a run counter 146. At the same 
time, a forward direction signal 148 is raised to disable the reverse 
buffers and only to permit passage of reference timing signals travelling 
in the forward direction, along the PROG A line. Further on in the 
specification, the operation of the bidirectional buffer 124 and its 
circuitry 127 will be described in more detail.

     At the rising edge 150 of the first pulse 151 generated by the local
oscillator 128 after the PROG A line has been raised, the logic unit 126
pulls the DETONATOR line low at 152 via an open collector transistor 154,
thereby indicating to the controller 12 that it has started to generate a
time period. Simultaneously, the local oscillator 128, starts to increment
the set counter 130. The lowering at 152 of the DETONATOR line, which
monitors the starting period of the set counter 130, is detected by the
controller 12, which pulls low the PROG A line at 154 once the appropriate
period has been clocked into the set counter 130 by the local oscillator
128. The DETONATOR line goes high at 156 in response to the PROG A line
going low, causing the set counter 130 to freeze with the number of
oscillations which have been clocked into it by the local oscillator.

     In response to the DETONATOR line going high at 156, a bidirectional 
buffer enable line goes high at 158 so that the subsequent reference timing 
signal travelling along the PROG A line bypasses the delay device under 
discussion and travels to the next delay device in the series which 
requires programming, and for which the timing signal is intended. This 
routine is repeated successively with each delay device. Once all the delay 
devices 16.1 to 16.6 have been programmed, the voltage in the DETONATOR 
line is raised to a level above that of the zener breakdown voltage (see 
115 in FIG. 3B) so as to charge all the capacitors 136 to enable them to 
independently power their respective delay devices 16.1 to 16.6. Once all 
the capacitors of the delay devices are fully charged, both the DETONATOR 
line and the LOGIC line (see 120 in FIG. 3B) are lowered to provide a 
trigger signal. The capacitor 136 then takes over the powering of the 
voltage regulator 131 where the LOGIC line left off to continue supplying 
the local oscillator 128, the set counter 130, the run counter 146 and the 
other active components of the delay device circuitry with power.

     The trigger signal is received at the logic unit 126 via a voltage 
limiter 140, which limits the voltage of the trigger signal to the voltage 
levels acceptable by the logic unit 126.

     On receipt of the trigger signal, the delay devices then commence 
timing the specific delay which has been programmed into each of their set 
counters 130 by using the local oscillator 128 to increment the run counter 
146 via the logic unit 126. A comparator 160 actuates a switch 162 as soon 
as the value in the run counter 146 equals the value which has been stored 
in the set counter 130. Actuation of the switch 162 causes the remaining 
charge stored in the capacitor 136 to be discharged into the electrical 
load or detonator 18, thereby detonating the explosive charge.

     If the GROUND line 66.2 leading to a delay device is broken or
disconnected, then there is the possibility that the circuitry will float
and perhaps even oscillate. This may then affect the PROG A and PROG B
lines, which in turn may adversely affect the adjacent delay devices, in
particular if the delay device oscillates, as this may cause the adjacent
delay devices to be programmed with spurious signals. A diode 164 is thus
placed between the DETONATOR and GROUND lines of each delay device to
ensure that, during the programming phase, should the GROUND line to that
delay device be disconnected it will be held at a level governed by the
DETONATOR line.

     Proceeding now to FIG. 7, a second embodiment of a delay device 165 is
shown, in which components similar to those in FIG. 4 are indicated with
the same numerals. The comparator 160, set counter 130 and run counter 146
of FIG. 4 are replaced with a shift register 166 and a preset counter 168.
The operation of the delay device 165 will now be described with reference
to the associated timing diagram in FIG. 8.

     The programming routine is initiated by sending a positive address pulse
170 along the PROG A line. The delay device 165 detects this pulse and
responds by sending a return signal 172 to the controller along the DET
POWER line which is proportional to the signal from its local oscillator
128. The period 174 of the signal is then measured accurately by the
controller 12 by means of a crystal-controlled oscillator which operates
in the MHz range. The controller then proceeds to calculate the precise
value that must be loaded into the shift register 166 of the delay device
in order to obtain the correct delay time. If, for example, a 12
millisecond delay is required to be programmed into the delay device, and
the period of its local oscillator is measured by the crystal-controlled
oscillator to be 1,5 milliseconds, then the microcomputer will calculate
that a digital word representing eight periods of the local oscillator
(ie. 1 0 0 0) is required. The digital word 176 representative of such
delay is then transmitted serially to the delay device along the PROG A
line, using the local oscillator signal 178 as a clock signal for the
serial transmission.

     Once the digital word 176 has been received by the delay device, it is
loaded into the shift register 166. The bidirectional buffer 124 is set so
that all the information along the PROG A line bypasses the first delay
device and is relayed on to the next delay device in the series, which is
addressed with a second pulse 180 along the PROG A line and subsequently
supplied with a second digital word 182. This process is repeated until
all the delay devices are programmed. Once the DET POWER line is lowered
at 120, the digital data stored in the shift register 166 of the delay
devices is then transferred in parallel to the preset counter 168. The
preset counter 168 then proceeds to count down, and as soon as the preset
counter reaches zero, the switch 162 is actuated and the detonator is
triggered as described previously.

     An advantage of this embodiment is that the actual frequency of the local
RC oscillator 128 is used to program the delay device. As the frequency of
the local oscillator is dependent on temperature and component tolerances,
it varies in respect of each delay device. The digital word sent by the
controller to each delay device compensates for such variations caused by
these differences and allows the delay time to be set very accurately
using a relatively inexpensive RC oscillator, provided such an oscillator
is stable. Furthermore, by transmitting a digital word rather than a real
time signal, the time taken to program all the delay devices is completely
independent of one or more of the actual delay times programmed into each
delay device. In fact, the programming time is generally reduced, thereby
lessening the period for which the harness lines are unearthed, and
potentially unsafe.

     The operation of the bidirectional buffer 124 and its control 
circuitry 127 will now be described in greater detail with reference to 
FIGS. 9 and 10. Under normal operation, terminals 46.1 and 48.1 to which 
the PROG A and PROG B lines 46 and 48 are connected, are pulled to ground 
by means of pull down resistors 184 and 186 respectively. The PROG A 
terminal 46.1 is joined to an INTERNAL 1 bus 188 via a forward input buffer 
190 which is controlled by a signal IN1* originating from the Q output of 
flip-flop 191. The INTERNAL 1 bus 188 is in turn connected to the PROG B 
terminal 48.1 via a forward output buffer 192 controlled by a signal OUT1* 
originating from the Q output of flip-flop 193. The PROG B terminal 48.1 is 
connected to an INTERNAL 2 bus 194 to receive timing signals in the reverse 
direction via a reverse input buffer 196 which is controlled by a control 
signal IN2* sourced from the Q output of flip-flop 197. The INTERNAL 2 bus 
is connected to the PROG A line 46 via a reverse output buffer 198 which is 
controlled by a control signal OUT2* emanating from the Q output of 
flip-flop 199.

     Once power is applied to the delay device by raising the LOGIC line (see
125 in FIG. 5A), the logic unit 126 generates a RESET pulse 200 which
travels along an input line 204 connected to the set input of flip-flop
191, causing the Q output of the flip-flop 191 to go high, thereby raising
the IN1* signal at 208 and disabling the forward input buffer 190 to
prevent the passage of reference timing signals along the PROG A line to
the INTERNAL 1 bus 188. The logic unit 126 then generates an S RESET pulse
210 at the clock input of the flip-flop 191, causing the signal level at
the D input, which is connected to the PROG A line, to be clocked through
to the Q output. As, under normal conditions, the PROG A line would be low
at this stage, the IN1* signal is lowered at 212 to enable the input
buffer 190 and to allow timing signals to travel along the PROG A line 46
to the INTERNAL 1 bus 188. The flip-flop 197 is also controlled by the
RESET and S RESET signals from the logic unit 126 in an identical fashion
to the flip-flop 191, the pulse 216 IN2* emanating from the Q output of
the flip-flop 197 being identical to the pulse 208. The reverse input
buffer 196 is thus disabled and subsequently enabled in exactly the same
manner as the buffer 190, initially preventing and subsequently permitting
the passage of reference timing signals along the PROG B line 48 through
to the INTERNAL 2 bus 194.

     During the period when the IN1* and IN2* signals are high, and the input
buffers 190 and 196 are disabled, the logic level of the PROG A and PROG B
lines 46 and 48 are continuously monitored by being linked via monitoring
lines 218 and 220 to the D inputs of the flip-flops 191 and 197. Thus,
should the logic level of the PROG A or PROG B lines go high during this
period as a result of either of them being shorted to high, the Q outputs
will be held high after being clocked through by SRESET pulse 210 and the
input buffers 190 and 196 will be permanently disabled to prevent any
spurious signals from entering the INTERNAL 1 and INTERNAL 2 buses, and
from being programmed into the delay device. At this stage, the INTERNAL 1
and INTERNAL 2 buses are pulled to ground by pull-down resistors 221.

     The rising edge of RESET pulse 200 also causes the outputs of OR gates 
222 and 224, connected to the SET inputs of flip-flops 193 and 199 to go 
high, thereby raising the OUT1* and OUT2* signals at 230 and 232. This has 
the effect of disabling the output buffers 192 and 198, thereby preventing 
programming signals from passing through the delay device, and preventing 
spurious signals generated at the delay device from being transmitted to an 
adjacent delay device via the sensing lines 218 and 220.

     Provided both the PROG A and PROG B lines are low on the rising edge 
of the S RESET pulse 210, both input buffers 190 and 196 are enabled as a 
result of the IN1* and IN2* signals going low, thereby allowing free access 
for timing signals travelling along the PROG A or PROG B lines to the 
respective INTERNAL 1 and INTERNAL 2 buses. The bidirectional buffer is 
thus ready to receive a timing signal, whether it arrives along the PROG A 
or PROG B line. Should a reference timing signal 234 arrive at the PROG A 
terminal 46.1 in which case programming is occurring in the clockwise 
direction, the INTERNAL 1 line 188 will also be raised at 236 as the input 
buffer 190 is enabled. This will cause the output of OR gate 238 to go 
high. In view of the fact that the RESET pulse 200 has already caused the Q 
output of flip-flop 240 to be held high, the output of AND gate 242, namely 
the PROG line 243, will go high at 246 in response to its input from the OR 
gate 238 going high. On completion of the timing signal 234 from the 
controller, signified by the PROG A line being lowered at 248, the INTERNAL 
1 line will be lowered at 250. This will cause a positive signal to travel 
via NOT gate 252 to the clock input of flip-flop 193, thereby clocking in 
the grounded D input level so as to lower the OUT1* signal at 254 to enable 
the forward output buffer 192, and to connect the INTERNAL 1 bus 188 to the 
PROG B line 48.

     At the same time, the flip-flop 240 will toggle as a result of the output
of the AND gate 242 going low after the output of OR gate 238 has gone
low. The output from the AND gate 242 is fed back via an inverter 256,
thereby holding the Q output of the flip-flop 240 at zero and preventing
any further programming information from being fed to the delay device via
the PROG line 243.

     The OR gates 222 and 224, which have one of their inputs connected to the
Q* outputs of opposite flip-flops 193 and 199 respectively, prevent the
flip-flop 199 from enabling the output buffer 198 when programming is
occurring along the PROG A line, and also prevent the flip flop 193 from
enabling the output buffer 192 should timing signals be travelling in the
opposite direction, along the PROG B line.

     The PROG line 243 is used to convey the programming signal 246 which
programs the delay device via the logic unit 126, as has been described
previously with reference both to FIG. 4 and to FIG. 7.

     When the next pulse 256 arrives along the PROG A line, both the input
buffer 190 and the output buffer 192 are enabled, which allows the pulse
256 to ripple through the buffers 190 and 192, thereby bypassing the delay
device under discussion and continuing along the PROG B line to the next
delay device which requires programming. Under normal conditions, the
pulse 256 will be the first pulse travelling along the PROG B line 48, and
it will thus be programmed into the next delay device in the manner
described.

     Should break in the harness 14 occur, as has been discussed previously,
before programming of the delay device under discussion has occurred,
timing signals are rerouted by the controller in the manner previously
described in the opposite direction from the I/O port 60 along the PROG B
line. Programming in the reverse or anti-clockwise direction along the
PROG B line occurs in exactly the same manner as has been described with
reference to the PROG A line, as the circuitry of the bidirectional buffer
124 is totally symmetrical.

     Referring now to FIG. 11, an alternative embodiment of the bidirectional
buffer and its logic circuitry is shown in which a series of delay devices
1,2, . . . N, N+1 and N+2 incorporating this embodiment are connected in
series to the A and B ports of a controller 12. For clarity of
illustration, only the PROG line 47 of the harness 14 is shown. Each delay
device 1 to N+2 includes a bidirectional buffer 302, the operation of
which is controlled by buffer logic circuitry 304, which is illustrated in
more detail in FIG. 12. The buffer logic circuitry 304 is in turn
connected to the remainder of the delay device circuitry 306, which may
resemble that illustrated in either one of the two embodiments of FIGS. 4
and 7.

     The basic steps involved in the setting up and programming of the timing
apparatus are as follows:

     Initially, as is illustrated in FIG. 13A, the LOGIC line 64 is raised at
314, thereby powering up a regulated internal 5 volt power supply line 308
for supplying power to the bidirectional buffers 302 and the buffer logic
circuitry 304. The delay devices 1 to N+2 have respective PROG A and PROG
B terminals. The PROG A terminals receive timing signals travelling in a
clockwise direction along the PROG line 47 from the A port 20 of the
controller 12, and the PROG B terminals receive timing signals travelling
in the anti-clockwise direction from the B port 22 of the controller 12.
For the sake of simplicity, only three delay devices are shown in detail
in FIG. 11; three hundred or more delay devices may be connected together
in a practical implementation of the timing apparatus.

     After the internal power line 308 has been raised by the logic line the
controller 12 transmits a test signal 316 from the B port 22. If there are
no breaks in the harness 14, the test signal 316 ripples through the delay
devices in an anti-clockwise direction, and is received at port A of the
controller after a short delay, as is illustrated by pulse 318. In
response to receiving the pulse, the controller 12 pulls the B port low,
as is shown at 320. This in turn causes a "0" to propagate through the
delay devices in the anti-clockwise direction, the presence of a "0" at
the respective B terminals of the delay devices 1 to N+2 indicating that
programming should occur in the clockwise direction.

     By monitoring its port A, the controller 12 can determine whether there is
a break in the harness 14 or not. If port A receives a high input, as a
result of the test signal 318, then there is no break in the harness 14,
and the system is probably undamaged. However, if the input at port A
remains low, as is shown at 322 in FIG. 13B, then this indicates that the
harness 14 is broken; some of the delay devices will therefore need to
programmed in the clockwise direction, and some in the anti-clockwise
direction. As the controller 12 does not receive the test signal 318 at
its port A, it holds the test signal emanating from port B high as is
shown at 324, thereby indicating that at least some of the delay devices
should be programmed by means of timing signals emanating from port B.

     The manner of operation of both the bidirectional buffer 302 and the buffer
control logic circuitry 304 will now be described in more detail with
reference to FIGS. 12, 13C, 13D and 14.

     Both the A and B terminals of each delay device have respective pull-down
resistors 326 and 328 linked to earth and respective pull-up resistors 330
and 332 connected to the internal power line 308 via respective first and
second controlled switches 334 and 336, which are in the form of pnp
transistors. When turned on, controlled switches 338 and 340, which are in
the form of npn transistors, link the A and B terminals directly to earth.
On powering up of the delay device, a reset signal emanating from reset
circuitry 137 in FIGS. 4 and 7 resets the D-type flip-flops 341, 342 and
344, thereby causing flip-flops 344 and 346 to be set with their Q outputs
high and flip-flops 341, 342 and counter 348 to be reset with their Q
outputs low. As a result, AND gate 350 will have a low output, and OR gate
351 will have a high output, thereby turning off the transistors 340 and
336 respectively. The transistors 334 and 338 will cause the output at
terminal A to follow the input at terminal B as follows. If terminal B is
low, it will be inverted by inverter 352 so as to provide a high input for
AND gate 353. As both of the other inputs of AND gate are latched high, a
high output from the AND gate 353 will turn on the transistor 338. A low
input from terminal B will also be inverted by inverter 354, resulting in
a high output from OR gate 356, which in turn causes a high output at OR
gate 358 via AND gate 360, thereby turning off pnp transistor 334.

     If, on the other hand, terminal B is high, transistor 334 will switch on
and transistor 338 will switch off by opposite action of the same gates,
thereby causing the high signal at terminal B to propagate through to
terminal A. The arrangement of transistors, resistors, the AND gates 350
and 353 and the inverters 352 and 361 constitute the bidirectional buffer
circuitry in this embodiment.

     A high signal at port B of the controller 22 will be propagated in the
anti-clockwise direction from the B to the A terminals of the delay
devices in the manner described, only failing to reach the A port 20 if
there is a break in the harness 14. Whenever a break in the harness 14
occurs, for example at 362, the resistor 328 of the delay device N whose B
terminal is adjacent the break, and which is consequently disconnected
from the adjacent delay device N+1, will cause the B terminal to be pulled
down, thereby causing a low signal to be propagated back via delay devices
N . . . , 2 and 1 to port A of the controller 12, as can be seen at 322 in
FIG. 13 B, resulting in the output at port B remaining high, as is
indicated at 324.

     As was described previously, if no faults are detected, the controller 12
then lowers port B, the low signal being rippled through all the delay
devices in the anti-clockwise direction to become a low at the A port,
thereby setting up the harness 14 for programming in a clockwise
direction, as will become apparent further on in the specification.

     On powering up of the delay device N of FIG. 12, the local oscillator 128
provides a clock signal vis AND gate 363 to the clock input of the counter
348, causing the Q1 output of the counter to provide a high DIRN STORE
signal after a period of approximately 10 milliseconds, once it has been
established by means of the test signal during which time period it has
already been established whether there is a break in the harness or not,
and all the terminals of the delay devices have settled. The DIRN STORE
signal is in turn transmitted to the clocked input of flip-flop 341,
clocking the level at terminal B into the Q output of flip-flop 341. After
a further delay of approximately 10 milliseconds, a DIRN SET signal
emanating from the Q2 output of counter 348 clocks in the level at
terminal B, as stored in flip-flop 341, into flip-flops 342 and 344. If
terminal B was low, then transistor 338 would be held off due to the AND
gate 353 receiving a low input from the Q output of flip-flop 344.

     The low output at AND gate 360, one input of which is fed from the low Q
output of flip-flop 344, results in a low output at OR gate 358. This low
output in turn causes transistor 334 to be turned on, raising terminal A
and thereby enabling it to receive negative-going programming signals
which originate from port A of the controller 12.

     The transistor 336 is turned off via a high output from OR gate 351 as the
Q* output of the flip-flop 342 is high due to the low D input thereof,
which has been clocked in by the DIRN SET signal. Transistor 340 is still
free to switch, depending on the input level at terminal A. If terminal A
is low, terminal B would be pulled low as transistor 340 would be turned
on via the AND gate 350, whereas if terminal A was high, transistor 340
would be turned off, thereby releasing terminal B and allowing it to be
pulled up by terminal A of the adjacent delay device. Therefore, those
delay devices which have their B terminals low before arrival of the DIRN
SET and DIRN STORE signals are set up with their transistors 334 on,
thereby pulling up their A terminals and enabling negative-going
programming pulses to be transferred to their B terminals.

     If, on the other hand, terminal B had been high when the PROG line 47 on
the harness 14 had "settled", this would indicate that there was a break
362 in the harness 14 between the delay device N+1 and port A of the
controller 12. After DIRN SET goes high, transistor 336 is turned on via
OR gate 351, transistor 334 is turned off via a high signal from AND gate
360 and OR gate 358, and transistor 340 is turned off via a low signal
from AND gate 350. The bidirectional buffer 302 would thus be set up with
a configuration that is the reverse of that just previously described. The
B terminal of the delay devices N+1 and N+2 would be pulled high, ready to
receive negative-going programming signals in the anti-clockwise
direction. On receipt of a negative-going programming signal at terminal B
of delay device N+2 from port B, transistor 338 of the delay device N+2 is
then able to switch, allowing the low signal level at its terminal B to be
transferred to its terminal A, and hence to terminal B of delay device
N+1, by pulling down terminal A of delay device N+2 against the current
drive from the transistor 336 of the delay device N+1. This procedure will
be described in greater detail further on in the specification.

     After the DIRN SET output has gone low, the Q3 output of counter 348 
goes high, and is inverted by inverter 347. A low PROG ENABLE signal from 
the output of inverter 347 removes the set control at the flip-flop 346, 
and the reset control from either one of flip-flops 368 or 370, depending 
on the state of flip-flop 344, the outputs of which determine the direction 
of programming. If the Q output of flip-flop 344 is high, indicative of an 
anti-clockwise programming direction from terminal B to terminal A, then 
flip-flop 368 remains reset via OR gate 371, and will not participate in 
the programming procedure. On the other hand, if the Q* output of flip-flop 
344 is high, indicating a clockwise programming direction, flip-flop 370 
will remain reset via OR gate 372 and will not participate in the 
programming process.

     At this stage, the delay devices are individually set up to receive 
all the timing signals in the clockwise direction, from terminal A to 
terminal B, if no discontinuity has been detected in the harness 14. The 
pnp transistor 334 will be turned on to enable the buffer 302 to receive a 
negative-going programming pulse arriving at terminal A. Where terminal B 
is connected to a functioning delay device, it will be held high by the pnp 
transistor of the A terminal of that delay device. On the other hand, the 
other pnp transistor 336 will be turned off, and its corresponding terminal 
B will be held low by pull-down resistor 328 if connected either to the 
non-programming port B of the controller, or to a faulty delay device or a 
broken section of harness. In the case of a discontinuity the delay device 
with its terminal A adjacent the B terminal of the aforementioned delay 
device, the buffer 302 may be set up to receive negative-going programming 
pulses arriving at its terminal B in the anti-clockwise direction with its 
pnp transistor 336 turned on and its pnp transistor 334 turned off, thereby 
allowing the signal level at terminal A to follow that at terminal B.

     The controller 12 then places both its A and B ports 20 and 22 in a 
high impedance state which allows them to float high under the influence of 
the adjacent delay devices, except in cases where there is no harness 
damage, in which case port B of the controller will then be pulled low by 
the resistor 328 of the adjacent delay device N+2.

     In the event of a discontinuity arising at 362, for example, it 
becomes necessary for the controller 12 to determine the exact location 
thereof, so that the correct timing signals can be programmed into the 
delay devices on either side of such a discontinuity.

     To this end, after having been set up for clockwise or anti-clockwise 
programming, each delay device undergoes a quasi-programming routine in 
which it is programed with a short negative-going pulse from the controller 
12, during which time it responds via the DETONATOR line in the manner 
described hereinafter.

     In the event of a break being detected, such as that at 362, a string 
of short negative-going pulses are transmitted out of port A by the 
controller for quasi-programming of the delay devices 1,2 . . . to N. The 
delay devices 1 to N have been set up for programming in a clockwise 
direction, and the first quasi-programming, or counting pulse transmitted 
from port A of the controller bypasses the delay devices 1 to N-1, which 
are set up in the signal bypass mode, with their B terminals pulled high by 
the pnp transistor 334 of the adjacent delay device. Due to the fault 362, 
the delay device N has its B terminal pulled low by pull-down resistor 328 
which causes it to operate in a signal storage mode, allowing it to accept 
the first negative-going counting pulse. After programming has taken place, 
the A terminal of the delay device is pulled low by the pull-down resistor 
326, causing the B terminal of the adjacent N-1 delay device to be pulled 
low, thereby permitting it to operate in the signal storage mode for 
acceptance of the next negative-going quasi-programming signal. In this 
manner, quasi-programming of the delay devices occurs in the reverse order 
N to 1. Once delay device 1 has been "programmed", its A terminal is pulled 
low, which in turn pulls low the signal level at port A, as its buffer is 
caused to "float" in a high impedance mode.

     During the testing and delay device counting procedure as described 
above, each quasi-programming signal is returned via the DET POWER line, 
which is linked in parallel to each delay device, as was shown in FIGS. 4 
and 7, once "programming", or counting of the delay device has taken place. 
If the break at 362 had caused all the lines in the harness 47 to sever, 
the counting signals would be returned into port A of the controller 12 via 
the DET POWER line. If, on the other hand, the break at 362 had only caused 
the PROG line to sever, the quasi-programming signals would be returned 
into both port A and port B. The number of signals returning on the DET 
POWER line is then counted by the controller, and this number is then 
stored in the controller.

     A string of negative-going counting pulses is then transmitted by the 
B port of the controller 12 so as to "programme" the delay devices N+1 and 
N+2. By monitoring the DET POWER line, the number of delay devices which 
need to be programmed in the anti-clockwise direction can be ascertained.

     By storing the number of delay devices on either side of the break 
362, the controller 12 is able to access from its ROM table the correct 
timing signal for each delay device. Furthermore, by establishing the 
programming pattern, the approximate location of the break 362 can be 
ascertained, as well as the number of delay devices which are available for 
programming. The situation could arise where the harness 47 is broken in 
two places, both at 362 and at 363 for example. In this case, the counting 
pulses would count only four delay devices, namely 1, 2, N+1 and N+2, in 
communication with the controller 12. Assuming that the total number of 
delay devices should be linked together in the system is known to be fifty, 
it can thus readily be ascertained that not all of the devices are linked 
to the controller 12, and as a result the entire routine will be aborted.

     If there is no break in the harness, and the delay devices are set up 
to programme in a clockwise direction, the same count routine may be 
followed to confirm that the correct number of delay devices are connected 
to the controller 12.

     After the delay devices have been set up and counted, powering down of 
all the delay devices occurs by lowering the logic power line so as to 
reset the delay devices and erase the counting signal which as been 
programmed into each set counter of the delay device. The delay devices are 
then powered up and the direction set routine is then followed by the 
raising port B, in the case of the break of the harness, or by lowering 
port B, in the case of no break having been detected. The buffers 50 and 52 
of respective A and B ports are then placed in the high impedance mode 
prior to actual programming of the timing signals into the delay devices. 
During actual programming, the delay devices operate in exactly the same 
manner as has previously been described with reference to the 
quasi-programming, or counting routine.

     After the timing signals have been programmed into the delay devices, 
the DET POWER line is raised to charge the capacitors in each delay device, 
as has been described previously with reference to FIG. 3B at 115, and the 
DET POWER line is then lowered at 120 to trigger the delay devices, causing 
them to activate their associated detonators after the expiry of the time 
delay which has been programmed into each of the delay devices. The flow 
chart of FIG. 14 clearly sets out the procedure described above, and 
requires no further explanation.

     Reference will now be made to FIG. 13C, which shows a timing diagram 
of programming in the clockwise direction, where no break in the harness 14 
has occurred. The controller 12 raises its DETONATOR line to a monitoring 
level 400. Port A of the controller is held at 402 by the pull-up resistor 
330 and the pnp transistor 334 of the adjacent delay device 1. The 
controller 12 then lowers port A at 404 to indicate the beginning of the 
first programming pulse. The Q output of flip-flop 344 is low, indicating a 
clockwise programming direction from terminal A to terminal B. The reset 
condition is consequently removed from flip-flop 368 via OR gate 371, 
thereby enabling it, and the Q* output of flip-flop 344 causes the 
flip-flop 370 to reset via OR gate 372, thereby effectively disabling it.

     The delay devices 1 to N+2 are now set up for the propagation of 
negative-going programming pulses in the clockwise direction, with their B 
terminals being held high by the pnp transistors 334 of the adjacent delay 
devices. The signal level at terminal B will thus follow that at terminal A 
via AND gate 350 and npn transistor 340 after a short propagation delay. If 
terminal B of delay device 1 is high, indicating an adjacent unprogrammed 
delay device 2, the high input at terminal B is inverted by inverter 376 to 
provide a low D input for flip-flop 368.

     Once terminal A of delay device 1 goes low, it is inverted by inverter 
378, thereby clocking the low D input into flip-flop 368, so as to hold the 
Q* output of flip-flop 368 high. As the flip-flop 370 has its reset input 
held high via the OR gate 372, both the Q* inputs of AND gate 380 are high, 
providing a high output for OR gate 382. Any change on the output of OR 
gate 382 is thereby prevented, and the flip-flop 346 is left unaffected. As 
the PROG output of the AND gate 386 is low, a programming pulse is not 
programmed into the delay device, but is propagated through the delay 
device 1 out of the B terminal to the next delay device 2 in the series.

     If, on the other hand, terminal B of a delay device is low, this 
indicates one of the three abovementioned conditions. The delay device N+2 
is thus ready to be programmed with a timing signal in the following 
manner.

     The D input of flip-flop 368 will be high via the low input from 
terminal B when terminal A goes low, the inverter 378 clocking the inverted 
high D-input into flip-flop 368, thereby causing the Q* output of flip-flop 
368 to go low. This in turn causes the respective outputs of AND gate 380 
and OR gate 382 to go low. Consequently, inverter 384 provides a high input 
at AND gate 386, which together with the high input provided by the Q 
output of flip-flop 346, raises the PROG line, as is shown at 410, and a 
positive pulse 412 having the duration of the negative-going pulse 405 is 
thus stored in the set counter 130 of the delay device N+2.

     When terminal A of delay device N+2 goes high, as is shown at 414, the
output of OR gate 382 also rises, thereby clocking in the low on the input
of flip-flop 346 to lower its Q output. The PROG output of AND gate 386 is
thus lowered, as is shown at 416. At the same time, the high Q* output of
flip-flop 346 ensures that the outputs of OR gates 351 and 358 are held
high, thereby switching off pnp transistors 334 and 336 by raising their
bases. The Q output of flip-flop 346, which is held low, provides low
inputs for AND gates 350 and 353, thereby ensuring that npn transistors
338 and 340 are held off. This ensures minimum current drain when
programming of the delay device N+2 is complete.

     As the A terminal of the delay device N+2 is held low subsequent to the
programming thereof, the B terminal of the delay device N+1 is held low,
signifying that it should receive the next negative-going programming
signal 418 which emanates from port A of the controller 12. The
programming of the delay device N+1 occurs in exactly the same manner as
has previously been described, with a timing signal 420 being stored in
its set counter 130.

     Between generating the programming signals, the controller 12 switches 
its port A to high impedance to allow it to determine if the delay device 1 
adjacent port A has been programmed. This will be indicated by the port A 
output of the controller 12 being pulled low by pull-down resistor 326 of 
delay device 1. Should this not be the case, the sequence as described 
above is repeated until all the delay devices in electrical communication 
with port A have been programmed.

     In FIG. 13D, a timing diagram corresponding to the configuration of delay
devices as is illustrated in FIG. 11 is shown, with the break 362 present.

     N negative-going programming signals 428 are transmitted from port A 
of the controller, with the signal 430 being programmed into the delay 
device N at 431. Due to the break 362, both the B terminal of the delay 
device N and the A terminal of the delay device N+1 are held low, as is 
illustrated at 432. After programming of the delay devices 1 to N has 
occurred in the clockwise direction, programming of the delay devices N+1 
and N+2 then takes place, with the first timing signal 434 being programmed 
into the delay device N+1, as is shown at 436, and the second timing signal 
438 being programmed into the delay device N+2, as is shown at 440.

     Programming in the anti-clockwise direction occurs in exactly the same
manner, with the timing pulses being sourced from port B of the controller
12 and the delay devices in electrical communication with port B
configuring themselves so that the pnp transistors 336 are turned on, as
has previously been described.

     The apparatus of the invention has a number of noteworthy features which
distinguish it over the prior art. In addition to the bidirectional
configuration of the central control unit, the harness and the delay
devices, it enjoys a number of safety features which have been described
in some detail with reference to FIGS. 2 and 3. The mechanical switch
provided by the motor 80 and the slug 86 ensures that electronic failure
cannot trigger the detonators when the slug is in the earthed position 88.
Furthermore, as the lines of the harness 14 are shorted together and
earthed during all periods when the delay devices are not being programmed
by the controller, and especially just after the delay devices have been
triggered, the existence of potentially dangerous triggering signals in
the harness lines resulting from RF interference is avoided, and the
problem of live harness wires being blown around by the subsequent
explosion is eliminated.

     Moreover, electronic interlocks are provided by the retriggerable
monostables 96 and 118, ensuring that any electronic failure in the
functioning of the microcomputer 28 or its associated software will result
in the pulse trains enabling the power supplies to the LOGIC or DETONATOR
lines being adversely affected, thereby disabling the power supplies and
ensuring that the system can only be powered providing the microcomputer
28 is fully operational.

     An additional safety feature results from the provision of separate lines
(namely the LOGIC and the DETONATOR line) to respectively program the
delay devices and charge up their capacitors. The capacitors are only
charged up just prior to blasting, and thus even if the switch 162 is
accidently triggered, the detonator will not be activated as no charge
will have been stored on the capacitor.

     Programming of the timing apparatus of the invention is interactive, with
the result that absence of a feedback signal from a delay device allows
rapid detection of a faulty detonator or a section of harness. The ability
of the apparatus to monitor exactly how many detonators have been
programmed also allows a quick decision to be made as to whether repairs
should be effected, whether the whole operation should be aborted, or
whether the blasting operation should be continued with.

     Naturally, the invention is not confined to use in sequential 
blasting, but may also be used in conjunction with pyrotechnic displays and 
with multiple fuses.

     The interactive communication between the controller and the various 
delay devices enhances the timing precision of the imprecise local 
oscillator at each delay device; timing signals or digital words are 
transmitted from the control unit to calibrate the local oscillator. Errors 
caused by unpredictable phase knowledge of the local oscillator are reduced 
by using the local oscillator signal to initiate programming of the timing 
signal from the controller.

     The bidirectional programming ability of the controller means that a
discontinuity or bad connection in the harness, or a single faulty delay
device will not necessarily result in the aborting of the blasting
operation, as the reference timing signals can merely be re-routed in the
opposite direction. This feature increases safety and reduces costly
down-time.

Claims
We claim:

     1. A method of activating a plurality of electrical loads after
predetermined time delays comprising the steps of:

 a) connecting a plurality of remote electrical delay devices in series with
  a central control unit using a signal harness, each delay device being
  associated with an electrical load;

 b) addressing a first delay device with a polling signal from the central
  control unit;

 c) transmitting a representation of an imprecise timing signal from the
  first delay device to the central control unit in response to the polling
  signal;

 d) generating at the central control unit a precise timing signal;

 e) computing at the central control unit a timing control signal based on a
  measurement of the representation of the imprecise timing signal relative
  to the precise timing signal;

 f) transmitting the timing control signal to the delay device, and storing
  the timing control signal therein;

 g) repeating steps b) to f) in respect of all subsequent delay devices
  until all the delay devices have been programmed; and

 h) producing the predetermined time delays in respective delay devices by
  applying the timing control signal stored in each respective delay device
  to the imprecise timing signal associated therewith.

     2. A method as claimed in claim 1, which further includes the steps of:

 prior to programming of a delay device, operating the delay device in a
  signal storage mode, and steering the timing control signal into the delay
  device; and

 subsequent to programming the delay device, of operating the delay device
  in a signal bypass mode, in which polling and timing control signals
  transmitted from the central control unit are permitted to bypass the
  delay device for polling and programming of a subsequent delay device.


     3. A method as claimed in claim 1, which further includes the step of
monitoring a number of electrical delay devices which have been programmed
with the timing control signals by sensing, at the central control unit,
the imprecise timing signals transmitted from the delay devices, and
aborting the activating procedure in the event of at least one of the
delay devices not having been programmed correctly.


     4. A method as claimed in claim 1, wherein the timing control signals
comprise digital words, and which includes the steps of transmitting the
digital words serially along the signal harness and clocking the digital
words into the delay devices using the imprecise timing signal of a delay
device in which a digital word is to be stored.


     5. A method as in claim 1, wherein for each respective delay device, the
computing step comprises:

 1) measuring number of cycles of the precise timing signal corresponding to
  the representation of the imprecise timing signal associated with the
  respective delay device;

 2) computing a number of cycles of the imprecise timing signal associated
  with the respective delay device needed to produce a desired delay time
  based on the measured number of cycles; and

 3) generating the timing control signal for the respective delay device as
  a representation of the computed number.


     6. A method as in claim 5, wherein for each respective delay device, the
producing step comprises counting cycles of the imprecise timing signal
associated therewith corresponding to the computed number.


     7. Apparatus for activating a plurality of electrical loads after
predetermined time delays comprising:

 a) a central control unit for generating timing calibration signals, the
  central control unit including a precise timing signal generator,
  measurement means and computation means;

 b) a plurality of remote electrical delay devices, each remote electrical
  delay device being associated with a corresponding electrical load and
  arranged to be serially programmed by a timing control signal originating
  from the central control unit, each said remote electrical delay device
  including an imprecise timing signal generator, steering means for
  steering said timing control signal from the central control unit into the
  remote electrical delay device, and storage means for storing the timing
  control signal; and

 c) at least one timing signal path for allowing the timing control signals
  to be transmitted in series from the central control unit to each said
  remote electrical delay device, wherein;

each said remote electrical delay device is arranged to transmit a
representation of an imprecise timing signal to the central control unit
in response to a polling signal received from the central control unit,
for measurement by the measurement means in relation to a precise timing
signal, and computation by the computation means of a factor which is
transmitted as said timing control signal to a delay device for storage in
the storage means.


     8. Apparatus as claimed in claim 7 in which the timing calibration signal
is a digital word, the precise timing signal generator is a precision
oscillator, the imprecise timing signal generator is a local oscillator,
and the storage means is a shift register.

RFID Technologies © / rfid@pixie.co.za