Method and apparatus for a calibrated electronic timing circuit

• US 5,117,756 A
• Filed: 09/20/1990
• Issued: 06/02/1992
• Est. Priority Date: 02/03/1989
• Status: Expired due to Term

• Current Assignee: Orica Explosives Technology Pty Limited (Orica Limited)
• Original Assignee: Atlas Powder Co.
• Inventors: Goffin, Glen P. II
• Primary Examiner(s): Kyle, Deborah L.
• Assistant Examiner(s): Johnson, Stephen
• Application Number:
  US07/585,631
• Time in Patent Office: 621 Days
• Field of Search: 331/1 R, 331/1 A, 331/30, 331/18, 331/11, 331/14, 331/25, 375/10, 375/11, 102/217, 102/218, 102/220, 102/206, 102/200
• US Class Current: 102/217
• CPC Class Codes: F42D 1/055 specially adapted for firing multiple charges with a time delay

Abstract

A timing circuit includes a variable frequency oscillator which has a control signal that determines the output frequency of the oscillator. The control signal and a reference signal are stored in the circuit. A precision calibration pulse is applied to the timing circuit which counts the output cycles of the variable frequency oscillator during the period of the pulse. This count is stored and compared to the reference count to produce an error count. This error count is combined with the previously stored control signal to produce a new control signal that drives the output of the oscillator to a new frequency. The timing circuit can be utilized as a part of a delay circuit is an electronic blasting system wherein a control unit transmits the calibration pulse concurrently to each of the delay circuits to cause each circuit to calibrate its local oscillator in accordance with the calibration pulse. The control unit transmits a delay count to each of the delay ignition circuits. A fire command is transmitted from the control unit to each of the delay ignition circuits to cause the outputs of the calibrated local oscillators to be compared to the previously received delay count until a predetermined relation is reached. When this relation is reached, each delay ignition circuit generates a fire signal which ignites a corresponding explosive element.

Claims

1. A method of operation for a time delay blasting system having a plurality of time delay ignition circuits connected to a control unit which has a time reference therein, comprising the steps of:

transmitting from said control unit concurrently to said plurality of said time delay ignition circuits a calibration pulse derived from said time reference,

at each said time delay ignition circuit producing a rate signal proportional to a count of output cycles produced by an oscillator during said calibration pulse, wherein the frequency of the output signal of said oscillator is determined by a control signal provided thereto,

at each said time delay ignition circuit, comparing said rate signal to a predetermined reference signal to produce an error signal,

at each said time delay ignition circuit, changing said control signal by a proportion to said error signal to produce a new control signal which causes said oscillator to produce an output signal having a frequency closer than the previous output signal frequency to a predetermined timing relation to said time reference,

transmitting respective time delay counts from said control unit to each of said time delay ignition circuits,

transmitting a start signal from said control unit concurrently to said time delay ignition circuits subsequent to the transmission of said calibration pulse,

at each said time delay ignition circuit, comparing the output produced by the corresponding oscillator to a predetermined relation to said time delay count and producing a fire signal when said predetermined relation is reached,

and,

at each said time delay ignition circuit, igniting a corresponding explosive element in response to the first signal produced at the time delay ignition circuit. explosive element in response to the fire signal.

2. A method of operation as recited in claim 1 wherein the steps of transmitting a calibration pulse, producing a rate signal, comparing said rate signal to a predetermined reference, and changing said control signal are repeated to produce a sequence of said output signals having frequencies which converge toward said predetermined timing relation to said time reference.

3. A delay ignition circuit for igniting an explosive element after a predetermined time delay, comprising:

an energy storage element connected to input terminals of said delay ignition circuit,

a switch for connecting said energy storage element to said explosive element,

a delay count storage connected to receive a delay count through said input terminals wherein said delay count determines said time delay,

a variable frequency oscillator having a control signal input which determines the frequency of the output signal of said oscillator,

a control signal storage connected to provide said control signal to said oscillator,

a reference signal storage for storing a reference signal therein,

an accumulator for storing a rate signal proportional to a number of output cycles of said oscillator during a selected time period,

a difference circuit connected to said reference signal storage and said accumulator for producing an error signal proportional to the difference between said reference signal and said rate signal,

a combining circuit connected to said control signal storage and said difference circuit for combining said error signal and said control signal to produce a new control signal to replace the previous control signal in said control signal storage, and

a comparator for comparing the output of said oscillator with said delay count to produce a fire signal when a predetermined relation is reached, said fire signal connected to activate said switch to connect said energy storage with said explosive element for igniting said explosive element.