U.S. patent number 3,721,885 [Application Number 05/201,525] was granted by the patent office on 1973-03-20 for blasting machine with overvoltage and undervoltage protection for the energy storage capacitor.
This patent grant is currently assigned to The Bendix Corporation. Invention is credited to Irving E. Linkroum, James E. McKeown, Earl M. Phinney.
United States Patent |
3,721,885 |
McKeown , et al. |
March 20, 1973 |
BLASTING MACHINE WITH OVERVOLTAGE AND UNDERVOLTAGE PROTECTION FOR
THE ENERGY STORAGE CAPACITOR
Abstract
An electrical system for firing an explosive bridge wire device
or the like which includes a battery powered blocking oscillator to
charge a storage capacitor, a circuit controlling the maximum
energy to be contained in the storage capacitor, and a circuit that
determines the minimum energy in the storage capacitor before the
storage capacitor can be discharged into one or more explosive
bridge wire devices or the like.
Inventors: |
McKeown; James E. (Sidney,
NY), Linkroum; Irving E. (Hancock, NY), Phinney; Earl
M. (Oneonta, NY) |
Assignee: |
The Bendix Corporation
(Southfield, MI)
|
Family
ID: |
22746191 |
Appl.
No.: |
05/201,525 |
Filed: |
November 23, 1971 |
Current U.S.
Class: |
361/251; 102/219;
331/111; 331/112; 307/108 |
Current CPC
Class: |
H03K
3/53 (20130101); H02M 3/3381 (20130101) |
Current International
Class: |
H02M
3/24 (20060101); H02M 3/338 (20060101); H03K
3/53 (20060101); H03K 3/00 (20060101); H03k
003/30 (); H02m 003/22 () |
Field of
Search: |
;320/1 ;331/111 ;317/80
;307/108 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Konick; Bernard
Assistant Examiner: Hecker; Stuart
Claims
Having described the invention, what is claimed is:
1. A blasting machine comprising:
means for storing electrical energy;
means for supplying electrical energy to said energy storage means,
said means for supplying electrical energy comprising:
a source of electrical energy;
a transformer having a primary winding connected to said source and
a secondary winding;
a first diode means and said electrical storage means connected
together in series across said secondary winding to store energy
generated by the current flowing through said primary winding;
a solid state switch oscillator connected to said source and said
transformer to periodically interrupt current flow from said source
through said primary winding, said oscillator including:
a first transistor having collector and emitter terminals in series
with said primary winding, said transistor having alternate
conductive and nonconductive intervals to periodically interrupt
the current flowing from said primary winding;
a first voltage divider network connected across said first
transistor and said primary winding, said first voltage divider
network including second diode means connected to the junction
between said primary winding and said first transistor to direct
current from said winding in a predetermined manner; and
a second voltage divider network connected across said source of
electrical energy, said second voltage divider network including a
second transistor having alternate conductive and nonconductive
intervals to respectively control the conductive and nonconductive
intervals of said first transistor whereby the flow of current from
said source to said primary winding is periodically interrupted
causing current to flow in an oscillatory manner through said
primary winding.
means for producing a plurality of electrical pulses when said
energy storage means has reached a first predetermined energy
level;
switching means for receiving said pulses, said switching means
operable to permit the discharge of said energy storage means only
during the presence of said pulses, whereby said energy storage
means cannot be discharged below said predetermined energy level;
and
means for preventing said means for storing electrical energy from
exceeding a second predetermined energy level which is above said
first predetermined energy level whereby said energy storage means
is prevented from reaching energy levels above said second
predetermined energy level.
2. A blasting machine as described in claim 1 wherein said means
for preventing said means for storing electrical energy from
exceeding a second predetermined voltage level includes an
electrical circuit which comprises:
a gaseous conductor connected in series to a resistor and a
capacitor, said capacitor connected in parallel with a second
resistor, said electrical circuit connected across said means for
storing electrical energy whereby when said means for storing
electrical energy reaches said second predetermined energy level,
said gaseous conductor conducts to prevent said means for storing
electrical energy from exceeding said second predetermined energy
level.
3. The blasting machine as recited in claim 1 wherein the first
voltage divider network of said means for supplying electrical
energy to said energy storage means comprises:
a diode having a first terminal connected to the junction between
said primary winding and said source of electrical energy and a
second terminal connected to the base of said second
transistor;
a first resistor in series with the second terminal of said
diode;
a second resistor in series with said first resistor, and a third
resistor in series with said second resistor and having one
terminal connected to the junction between said first transistor
and said source of electrical energy.
4. A blasting machine as described in claim 3 wherein said means
for preventing said means for storing electrical energy from
exceeding a second predetermined voltage level includes an
electrical circuit which comprises:
a gaseous conductor connected in series to a resistor and a
capacitor, said capacitor connected in parallel with a second
resistor, said electrical circuit connected across said means for
storing electrical energy whereby when said means for storing
electrical energy reaches said second predetermined energy level,
said gaseous conductor conducts to prevent said means for storing
electrical energy from exceeding said second predetermined energy
level.
5. A blasting machine which comprises:
means for storing electrical energy;
means for supplying electrical energy to said energy storage means,
said means for supplying electrical energy comprising:
a source of electrical energy;
a transformer having a primary winding connected to said source and
a secondary winding;
a first diode means and said electrical energy storage means
connected together in series across said secondary winding to store
energy generated by the current flowing through said primary
winding;
a solid state switch oscillator connected to said source and said
transformer to periodically interrupt current flow from said source
through said primary winding, said oscillator including:
a first transistor having collector and emitter terminals in series
with said primary winding, said transistor having alternate
conductive and nonconductive intervals to periodically interrupt
the current flowing from said primary winding;
a first voltage divider network connected across said first
transistor and said primary winding, said first voltage divider
network including second diode means connected to the junction
between said primary winding and said first transistor to direct
current from said winding unidirectionally to said first voltage
divider network; and
a second voltage divider network connected across said source of
electrical energy, said second voltage divider network including a
second transistor having alternate conductive and nonconductive
intervals to respectively control the conductive and nonconductive
intervals of said first transistor whereby the flow of current from
said source to said primary winding is periodically interrupted
causing current to flow in an oscillatory manner through said
primary winding;
means for producing a plurality of electrical pulses when said
energy storage means has reached a first predetermined energy
level, said means for producing electrical pulses including a
second normally nonconductive gaseous conductor which is rendered
conductive when a predetermined voltage is applied thereto and a
resistor capacitor circuit in series with said second gaseous
conductor so that when said second gaseous conductor is rendered
conductive, said capacitor lowers the voltage applied to said
second gaseous conductor below said predetermined value and said
second gaseous conductor is rendered nonconductive;
switching means for receiving said pulses, said switching means
operable to permit the discharge of said energy storage means only
during the presence of said pulses, whereby said energy storage
means cannot be discharged below said predetermined energy level,
said switching means including a first normally nonconductive
gaseous conductor in circuit relationship with said pulse means,
said first gaseous conductor being rendered conductive upon
receiving said pulses, whereby when pulses from said pulse means
are transmitted to said first gaseous conductor, said first gaseous
conductor is rendered conductive to permit said storage means to
discharge and a switch connected between said first gaseous and
said pulse means, said switch operable in the ON position to permit
passage of said pulses to said first gaseous conductor, whereby the
energy storage means is discharged only when said switch is in the
ON position and when said pulse means is producing pulses; and
means for preventing said means for storing electrical energy for
exceeding a second predetermined energy level which is above said
first predetermined energy level whereby said energy storage means
is prevented from reaching energy levels above said second
predetermined energy level.
6. A blasting machine as described in claim 5 wherein said means
for preventing said means for storing electrical energy from
exceeding a second predetermined voltage level includes an
electrical circuit which comprises:
a third gaseous conductor connected in series to a resistor and a
capacitor, said capacitor connected in parallel with a second
resistor, said electrical circuit connected across said means for
storing electrical energy whereby when said means for storing
electrical energy reaches said predetermined energy level, said
third gaseous conductor conducts to prevent said means for storing
electrical energy from exceeding said second predetermined energy
level.
7. A blasting machine as recited in claim 5 wherein said first
voltage divider network of said means for supplying electrical
energy to said energy storage means comprises:
a diode having a first terminal connected to the junction between
said primary winding and said source of electrical energy and a
second terminal connected to the base of said second
transistor;
a first resistor in series with the second terminal of said
diode;
a second resistor in series with said first resistor; and
a third resistor in series with said second resistor and having one
terminal connected to the junction between said first transistor
and said source of electrical energy.
8. A blasting machine as described in claim 7 wherein said means
for preventing said means for storing electrical energy from
exceeding a second predetermined voltage level includes an
electrical circuit which comprises:
a third gaseous conductor connected in series to a resistor and a
capacitor, said capacitor connected in parallel with a second
resistor, said electrical circuit connected across said means for
storing electrical energy whereby when said means for storing
electrical energy reaches said predetermined energy level, said
third gaseous conductor conducts to prevent said means for storing
electrical energy from exceeding said second predetermined energy
level.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved blasting machine for
detonating blasting caps or the like. The invention is more
particularly related to a battery powered blasting machine of the
capacitor discharge type.
Basically, electrical systems for firing explosive devices include
a source of power such as a battery, an oscillator, a transformer
responsive to the oscillator for stepping up the pulses therefrom,
a storage capacitor which is charged by the pulses from the
transformer, and a trigger circuit which allows the energy stored
in the capacitor to discharge to fire an explosive device. The
energy stored in the capacitor is discharged through the explosive
device by means of a triggering circuit which may be operated
automatically or manually. Examples of such blasting devices may be
found in U.S. Pat. No. 3,417,306 entitled "Regulated Voltage
Capacitor Discharge Circuit" to J. L. Knak, issued Dec. 17, 1968;
and U.S. Pat. No. 3,275,884 entitled "Electrical Apparatus for
Generating Current Pulses" to L. H. Segall et al., issued Sept. 27,
1966.
In certain blasting operations such as those performed in tunnels
and shaft mining, it may be necessary to connect from as few as 1
blasting cap and as many as 150 blasting caps together in a
parallel circuit. Parallel connections are used because such
connections permit rapid connection of the blasting caps with
minimal possibility of error. To insure that all the blasting caps
are fired, the blasting machine must always deliver a given minimum
energy each time it is fired, otherwise all of the blasting caps
may not be fired. Further, it is also important that the blasting
machine does not deliver too much energy to the blasting caps,
otherwise malfunction of some of the blasting caps may occur.
Therefore, to insure that all blasting caps are fired, the blasting
machine must always deliver an amount of energy in a predetermined
energy range depending upon the number of blasting caps to be
fired.
Further, all too frequently, under heavy loading conditions,
existing charging circuits utilizing a transformer having a control
winding (teritary) experience high frequency oscillations that
affect the operation of the circuit and, therefore, the maximum
power that can be transferred to the load. The high frequency
oscillations occur because the amount of feedback to the control
winding that turns OFF the switch transistor in series with the
primary winding depends upon the voltage across the secondary
winding in parallel with the storage capacitor. At low magnitudes
of charge on the loads on the storage capacitor, the feedback to
the control winding is frequently insufficient to overcome a
positive bias on the switching transistor. Therefore, the switching
transistor is OFF for very short intervals, hence high frequency
oscillations occur.
SUMMARY OF THE INVENTION
This invention provides an improved blasting machine that prevents
low energy and high energy firing and is not susceptible to
spurious oscillations in the charging circuit that adversely
affects the operation of the machine. The invention is a blasting
machine characterized by a battery powered capacitor charging
circuit that includes a blocking oscillator to permit the rapid
charging of a storage capacitor while eliminating high frequency
oscillations when the number of devices to be detonated is
increased and an energy control circuit which controls the range of
energy stored in the storage capacitor prior to the discharge of
the energy into one or more explosive bridge wire devices or the
like.
In one embodiment of the invention, the blasting machine comprises:
a capacitor; means for supplying electrical energy to the
capacitor, said means for supplying electrical energy comprising a
battery, a transformer having a secondary winding and a primary
winding connected to the battery, a first diode means and the
capacitor connected together in series across the secondary winding
to store energy generated by the current flowing through the
primary winding, a solid state switch oscillator connected to the
battery and the transformer to periodically interrupt current flow
from the battery through the primary winding, the oscillator
including: a first transistor having collector and emitter
terminals in series with the primary winding, the transistor having
alternate conductive and nonconductive intervals to periodically
interrupt the current flowing from the primary winding; a first
voltage divider network connected across the first transistor and
the primary winding, the first voltage divider network including
second diode means connected to the junction between the primary
winding and the first transistor to direct current from the winding
in a predetermined manner; and a second voltage divider network
connected across the battery, the second voltage divider network
including a second transistor having alternate conductive and
nonconductive intervals to respectively control the conductive and
nonconductive intervals of the first transistor whereby the flow of
current from the battery to the primary winding is periodically
interrupted causing current to flow in an oscillatory manner
through the primary winding; means for producing a plurality of
electrical pulses when the capacitor has reached a first
predetermined energy level; switching means for receiving the
pulses, the switching means operable to permit the discharge of the
capacitor only during the presence of the pulses, whereby the
capacitor cannot be discharged below the predetermined energy
level; and means for preventing the capacitor from exceeding a
second predetermined energy level which is above the first
predetermined energy level whereby the capacitor is prevented from
reaching energy levels above the second predetermined energy
level.
Accordingly, it is an object of this invention to provide a battery
powered explosive ignition system that is not adversely affected by
the number of devices which it detonates and which supplies energy
to the devices that falls within a predetermined energy range.
It is another object of this invention to provide an improved
blasting machine that is safe and reliable.
The above and other objects and features of this invention will
become apparent from the following detailed description taken in
conjunction with the accompanying drawings and claims which form a
part of this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a blasting machine that utilizes the
principles of this invention.
FIG. 2 is a schematic diagram of a preferred embodiment of the
circuitry for a blasting machine shown in FIG. 1.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, FIG. 1 illustrates a block diagram
of a blasting machine which utilizes the principles of the
invention. The basic portion of the system includes a power supply
1, an energy storage device 3, such as a capacitor for storing
energy supplied by the power supply 1, a pulse generator 5 for
generating pulses when the energy in the capacitor has reached a
predetermined energy level, and a firing circuit 6 which permits
the discharge of the energy in the energy storage device 3 through
the load 8 which are the blasting caps or the like, when the
trigger portion 7 of the firing circuit 6 receives pulses from the
generator 5.
The power supply 1 may be either a.c. or d.c. and include the
necessary electrical components for charging an energy storage
device such as a capacitor.
The energy storage device 3 is preferably a capacitor. The voltage
regulator 2 may be used in electrical circuit relationship with the
energy storage device 3 to assure that the energy stored in the
energy storage device 33 does not exceed a predetermined voltage
level. The energy storage circuit may include a switch that, in the
ON position permits the energy storage device 3 to store energy,
and in the OFF position allows the energy storage device 3 to
discharge so that no energy remains in the energy storage device 3
when the blasting machine is not in use. The charge and discharge
switch 9 may be either a single switch or multiple switches and may
also be part of the firing circuit 6.
A voltage indicator 4 may be used in combination with the pulse
generator 5 to produce either visual or audible signals when the
pulse generator 5 is generating pulses.
The firing circuit 6 includes a trigger 7 which allows the energy
storage device 3 to discharge into the load 8. The trigger 7 may be
a gaseous conductor of the three-electrode type wherein the trigger
electrode upon receiving pulses from the pulse generator 5 allows
the remaining two electrodes which are in series with the energy
storage device 3 to conduct, thereby allowing the energy stored in
the device 3 to discharge into the load 8. If it is desired that
the blasting machine not be automatically triggered, a switch may
be located in series with the pulse generator 5 so that when the
voltage indicator 4 gives indication that pulses are present,
manually operating the switch to close the contacts will cause the
trigger to conduct and discharge the energy into the load.
FIG. 2 is a schematic diagram of a preferred embodiment of a
blasting machine that utilizes a battery and an oscillator to
charge the storage capacitor which will be discharged to fire a
blasting cap or other explosive bridge wire device or the like. The
dotted lines outlining portions of the circuitry indicate the power
supply 1, the energy storage device 3, the voltage regulator
circuit 2, the voltage indicator 4 associated with the pulse
generator, the pulse generator circuit 5, and the firing circuit
6.
The power supply 1 in this embodiment includes a battery 140, a
switch 9, a smoothing capacitor 130, and a transistorized
oscillator circuit in combination with a step-up transformer 150,
the output voltage of which is applied to the energy storage means
3. In operation, the power supply circuit 1 operates as
follows:
A solid state switch oscillator is powered by a battery 140 or
other direct current source. In one embodiment twelve one and
one-half volt batteries were used, which, because of the internal
resistance thereof, provided a voltage between 10 to 12 volts.
Connected across the battery 140 is a capacitor 130 which, when
charged, provides additional current to the oscillator. A
transformer 150 has its primary winding 101 connected into the
oscillator circuit and its secondary winding 151 connected to a
storage capacitor 153 through a diode 152 to store the energy
generated by the oscillator. The windings 101 and 151 of
transformer 150 are inductively coupled and wound and disposed in
the manner indicated by the dots.
The solid state switch oscillator operates to intermittently
interrupt current flow from the battery 140 through the primary
winding 101 of the transformer 150 and includes a first switching
transistor 103, a first voltage divider network (110, 111, 112,
113), a second voltage divider network (121, 122, 123), and first
diode means (102, 104, 106) connected between the first voltage
divider network and the primary winding 101 of the transformer 150
to direct the flow of current to and from the primary winding 101.
The oscillator circuit shown is capable of producing oscillations
in the range of 800 to 2,000 Hz.
The first voltage divider network includes a diode 110 and a
plurality of resistors 111, 112 and 113 connected together in
series across the primary winding 101 of the transformer and the
first transistor 103.
The diode means that directs the current from the primary winding
101 includes a first diode 102 connected by its anode terminal to
the junction between the primary winding 101 and the first
transistor 103. To permit current to flow from the primary winding
101 when transistor 103 is "off," diodes 104 and 106 are connected
in series with one anode terminal connected to the junction between
the primary winding 101 and the first transistor 103 and one
cathode terminal connected to the junction between the second
transistor 112 and the third transistor 113.
The second voltage divider network includes a transistor 121, a
resistor 122, and a resistor 123 connected together in series
across the battery 140. The base of the first transistor 121 is
connected, for biasing purposes, to the junction between the diode
110 and resistor 111 of the first voltage divider network. The base
of the first transistor 103 is connected to the junction between
resistors 122 and 123 to supply a current to the base of transistor
103 when the transistor 121 is in the conductive state.
The secondary winding 151 of the transformer 150 is connected to a
diode 152 and a capacitor 153. When the battery 140 is 10 to 12
volts, the maximum charge that can be obtained on capacitor 153 is
about 7,000 to 8,000 volts. However, voltages of this magnitude are
not generally required in battery powered explosive ignition
systems, therefore, an additional circuit (not shown) may be added
to limit the voltage across the capacitor 153. The energy stored in
the capacitor 153 is used for firing an explosive bridge wire
device or the like.
In this embodiment, when a constant current source having an output
voltage of about 10 volts is used in lieu of the battery 140 and
the capacitor 153 is a 100 microfarad capacitor, the capacitor 153
can be charged to 200 joules within 10 seconds and to 400 joules
within 20 seconds. Since batteries deteriorate with use, they are
capable of achieving the initial charged energy previously stated,
but tests reveal that when they are used to charge the capacitor
153 to 400 joules three times a day for 21 days, it would take a
maximum of 71 seconds of charge time to obtain 400 joules of energy
at the capacitor 153. The minimum charge time at the end of this
period to obtain 400 joules of energy at the capacitor 153 would be
49 seconds.
The energy storage means 3 includes a blocking diode 152 and
storage capacitor 153 in circuit relationship with the secondary
winding 151 of the transformer 150. The discharge resistor 154
allows the energy storage in capacitor 153 to be discharged when
the switch 9 in the power supply 1 is in the OFF position.
The voltage regulator 2 which prevents the voltage on the capacitor
153 from exceeding a predetermined value includes a two-electrode
spark gap 160, a resistor 163, a capacitor 165, and a resistor 167.
The function of the regulator circuit is to drain excessive energy
of the storage capacitor 153 to prevent the storage capacitor from
exceeding a predetermined upper energy limit. The spark gap 160 is
a normally nonconducting device that conducts when the voltage
across the device has reached a predetermined voltage. In this
instance, the breakdown voltage of the spark discharge device 160
is chosen to be the predetermined upper voltage limit desired
across storage capacitor 153. In operation, the voltage across the
storage capacitor 153 appears across the spark gap 160. As the
storage capacitor 153 is charged, the voltage across the spark gap
160 increases until the breakdown voltage of the device is reached.
The spark gap 160 then breaks down and conducts current to charge
capacitor 165. The current through the spark device 160 decreases
as capacitor 165 becomes more fully charged. Eventually the current
through the spark device 160 decreases to the point where it no
longer will support an arc in the discharge device 160. The arc
extinguishes and spark gap 160 ceases conduction. The charge on the
capacitor 165 is then discharged through resistor 167. As capacitor
165 discharges, the voltage across the spark gap device 160
therefore increases, and if the voltage across the storage
capacitor 153 is still greater than the breakdown voltage of the
spark gap discharge device 160, the discharge device 160 again
conducts and the cycle is repeated again. If desired, a neon
indicator light could be used in combination with this circuit to
give an indication when the voltage regulator is operating. The
suggested method with respect to a voltage indicating device would
be to place a neon indicator light and resistor across capacitor
165 which is responsive to the charging and discharging of
capacitor 165.
The pulse generator circuit 5 includes a two-electrode spark
discharge device 170, resistor 171, capacitor 177, resistor 173,
and resistor 175. The voltage indicator light 4, such as a neon
bulb, is in circuit relationship with resistor 173 and 175 and is
responsive to the charging and discharging of capacitor 177. In
operation, the two-electrode spark discharge device 170 will remain
in a nonconducting state as long as the voltage on the storage
capacitor 153 is less than the breakdown voltage of the spark
discharge device 170. When the voltage on the storage capacitor 153
exceeds the breakdown voltage of the discharge device 170, the
device conducts allowing current to pass through resistor 171 to
charge capacitor 177. As the voltage on the capacitor 177
increases, the voltage across the spark device decreases until the
spark device 170 returns to the original nonconducting state. At
this time, capacitor 177 then discharges through resistors 173 and
175 which further applies a voltage to the neon light 4 which gives
an indication that this circuit is in operation. When the voltage
across the spark discharge device 170 again rises to the breakdown
potential of this device, conduction begins again and the cycle
repeats itself. Each time capacitor 177 is charged, voltage is
applied to neon indicator light 4 through the resistor divider
network 173, 175. The neon indicator light 4 stays lit until the
voltage across the light drops below the minimum sustaining voltage
of the light 4. By this means, each time capacitor 177 is charged,
there is a visible light pulse to signal the operator that the
minimum voltage has been reached and the blasting machine may be
fired. With this circuit, when the minimum voltage across the
capacitor 153 is reached and pulses are being generated by the
pulse generator, pressing the firing switch 181 in the firing
circuit 6 will cause the pulses to be transmitted to the firing
circuit.
The firing circuit 6 includes a three-electrode spark gap discharge
device, a step-up transformer for raising the voltage of the pulses
received from the pulse generator 5 and applying them to the
trigger electrode of the spark discharge device 180, and a firing
switch 181 which permits the trigger pulses from the pulse
generator 5 to be transmitted to the primary winding 185 of the
step-up transformer. For further details concerning the particular
type of three-electrode spark gap discharge device required for
this circuit see U.S. Pat. Nos. 3,187,215 entitled "Spark Gap
Device" to I. E. Linkroum issued June 1, 1965, and 3,229,146
entitled "Spark Gap Device with a Control Electrode Intermediate
the Main Electrodes" to I. E. Linkroum issued Jan. 11, 1966. In
operation, when the firing switch 181 is in the OFF position, no
pulses are being supplied to the spark discharge gap 180 thereby
preventing the firing of any blasting caps attached to the output
terminals 190. Further, the firing switch 181 in the OFF position
is yet in combination with the power switch 9 in the OFF position
to place the discharge resistor 154 across the storage capacitor
153 to drain any charge thereon. When the firing switch 181 is
placed in the ON position, the storage capacitor 153 will discharge
if trigger pulses are present. Therefore, to discharge the energy
in capacitor 153 to blasting caps attached to the output terminals
190, it is necessary that the pulse generator 5 is generating
pulses and that the firing switch 181 is in the ON position. When
these two conditions are met, the output pulses of the pulse
generator 5 are transmitted to the primary winding 185 of the
step-up transformer where the pulses are stepped up to a higher
voltage and applied to the trigger electrode of the spark gap
discharge device through resistor 183 thereby causing ionization
within the spark gap discharge device and permitting current to
flow through the two main electrodes which allows the energy
storage capacitor 153 to discharge through the blasting caps
connected to the output terminals 190. If it is desired to
eliminate manual firing of the blasting caps and to have the
blasting machine discharge the energy in the capacitor 153
automatically when it has reached a predetermined energy level, the
firing switch 181 may be eliminated completely. In this instance,
as soon as voltage pulses are available from the pulse generator 5,
the three-electrode spark discharge device 180 would be triggered
to discharge the energy in the capacitor 153 through the blasting
caps (not shown) connected to the terminals 190.
OPERATION
Referring now to FIG. 2, the circuit operates as follows: When
switch 9 is in the OFF position, resistor 154 removes the energy
stored in capacitor 153. When switch 9 is closed, resistor 154 is
removed from the circuit and current flows from the battery 140
through capacitor 130 and through transistor 121, resistor 122 and
resistor 123. Accordingly, a voltage is applied across the voltage
divider network containing transistor 121 and the voltage dividing
network containing diode 110. Since there is a positive voltage
applied across the emitter base circuit of the transistor 121, the
transistor 121 conducts permitting a current to flow through
resistors 122 and 123 and through lead 124 to the base of
transistor 103 which is in the nonconducting state. When the
current to the base of transistor 103 is sufficient, transistor 103
conducts (ON). When the transistor 103 conducts, current flows
through the transformer primary winding 101 and transistor 103.
With current flowing to ground through the primary winding 101,
transistor 121 begins to return to the nonconductive (OFF) state as
the base to emitter current of that transistor begins to decrease.
Eventually transistor 121 becomes nonconductive, removing the
necessary base current to transistor 103 which also becomes
nonconductive (OFF). Once the transistor 131 turns OFF, the
electrical energy stored in the primary winding 101 during the ON
or conduction period of transistor 131 is removed as current leaves
the primary winding 131 and flows through diodes 104, 106, 110 and
resistors 111 and 112. This action also operates to back bias
transistor 121 so that it remains in the nonconductive state.
Further, since during this time the rate of change of current with
respect to time (di/dt) becomes sharply negative the voltage
induced across the secondary winding 151 for this period also
reverses and the secondary winding 151 becomes a current source.
Therefore, during the time di/dt is negative, most of the energy
stored in the primary winding of the transformer is transferred to
the secondary winding 151 in a manner that allows the diode 152 to
conduct and to supply energy to the capacitor 153 and to supply
energy to the capacitor 153 and to a load (not shown). Thus,
electrical energy which is fed to the primary winding during the
conducting period of transistor 103 is transferred to the capacitor
153 during the nonconducting period of transistor 103. The entire
action is cyclic for as the energy is removed from the transformer
150 the reverse bias on transistor 121 is removed allowing
transistors 121 and 103 to turn ON and repeat the entire operation
again. (About 800 to 2,000 Hz.)
As the energy stored in the capacitor reaches a predetermined
level, the pulse generating circuit 5 begins generating trigger
pulses. This occurs when the spark gap discharge device 170 reaches
its breakdown potential. To assure that the energy stored in the
capacitor is above the predetermined energy level but not in excess
of a second and higher energy level, a voltage regulator circuit 2
is utilized. This eliminates excessive energy levels that cause
adverse operation of the blasting machine.
Once the trigger pulses are present and the energy stored in the
capacitor is within a preferred range depressing the firing switch
181 applies trigger pulses to transormers 182 which causes spark
gap device 180 to conduct, thereby allowing the energy in capacitor
153 to discharge into the blasting caps (not shown) attached to the
outputs 190 and detonate explosives.
In one satisfactorily operable system, the blasting machine
described in FIG. 2 was powered by 6 one and one-half volt D size
batteries or one 12 -volt Energizer battery No. S-121 and the
circuit elements add the values or were of the types indicated
below:
Capacitor 130 3,300 microfarad, 30 Volts d.c. Capacitor 165 0.45 to
0.61 microfarad 3KV Capacitor 177 0.008 to 0.012 microfarad, 3.5KV
Capacitor 153 400 microfarad 2.5KV Capacitor 187 0.025 to 0.03
microfarad 3KV Resistor 122 6.2 ohms, 11W Resistor 123 33 ohms 1/2W
Resistor 111 100 ohms 2W Resistor 112 1,000 ohms, 1/2W Resistor 113
10K ohms 1/2W Resistor 154 3K ohms 10W Resistor 167 20K ohms 20W (2
in series) Resistor 163 2 ohms 20W (2 in parallel) Resistor 175
0.33 megohms 2W Resistor 173 1.36 megohms 4W (2 in series) Resistor
171 500 ohms 10W Resistor 186 20 megohms 1W Resistor 183 1K ohms 5W
Resistor 189 10K ohms 10W Transistor 121 Type MJE 341 Transistor
103 Type 2N3055 Beta 20-35 Diodes 110,102,104,106 GE A14F Diode 152
Motorola MR 995A Discharge Device 160 2,200 volts d.c. (breakdown)
Bendix Corp. Sidney, N.Y. Part No. 10-374105-21 Discharge Device
170 2,000 volts d.c. (breakdown) Bendix Corp. Sidney,N.Y. Part No.
10-374121-14 Three-electrode spark discharge device 3,750 volts
d.c. (breakdown) Bendix Corp. Sidney,N.Y. Part No. 1-28615-39
Transformer 150 Core H177; 0,010 air gap in each leg primary 42T
No. 15 120 volts; secondary 1500 I No. 29 8,000 volts Transformer
182 Ferramic Core 3/8" diameter primary 4T No. 20 secondary 32T No.
20 Switch 9 and 181 4 Contact-Bendix Corp. Sid- ney, N.Y. Part No.
10-348773-1
While a preferred embodiment of the invention has been disclosed,
it will be apparent to those skilled in the art that changes may be
made to the invention as set forth in the appended claims, and in
some cases, certain features of the invention may be used to
advantage without corresponding use of other features. For example,
different types of semi-conductors, or solid state control devices
may be substituted for the types illustrated. Accordingly, it is
intended that the illustrative and descriptive materials herein be
used to illustrate the principles of the invention and not to limit
the scope thereof.
* * * * *