Method and apparatus for a calibrated electronic timing circuit

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.