Timer circuit for use in protective relaying applications

Abstract

The timer circuit includes ramping circuit means for producing a substantially linear ramping voltage output signal. Control circuit means is provided for receiving a timer input signal and controlling the ramping circuit means wherein the presence of the timer input signal causes the ramping voltage output signal to ramp with a positive slope. Level detector circuit means is coupled to the ramping voltage circuit means to receive the ramping voltage output signal and to produce a level detector output signal when the positively ramping voltage output signal is of a predetermined threshold. The level detector output signal continues as long as the timer input signal continues and is coupled back to the control circuit means. The presence of the level detector signal develops a truncating signal which causes the positively ramping voltage output signal to truncate. When the timer input signal terminates, the ramping voltage output signal ramps negatively and the level detector signal terminates. Output circuit means is coupled to receive the level detector output signal. The output circuit means produces the timer circuit output signal. The timer circuit output signal continues as long as the level detector output signal continues and for a predetermined dropout time after the level detector output signal terminates.