JPS6411458A - Signal break detection system - Google Patents

Abstract

PURPOSE:To detect a signal break stably without reference to variation in the level of an input signal to be monitored by varying the decision level for the signal level according to the variation in the signal level of the input signal to be monitored. CONSTITUTION:When the input signal S arrives continuously, the outputs FS1, FS2 of LPFs2 and 3 are at the same signal level and the level of the attenuation output MS obtained by attenuating the output FS1 to 1/l is invariably lower than the level of the output FS2. If the signal S enters a break state, the outputs FS1 and FS2 begin to attenuate from this point of time according to the time constants of the LPFs2 and 3, but the outputs FS1 and MS which are larger in time constant attenuate according to a curve relatively gentler than the other output FS2. Consequently, MS=FS2 after a constant time determined by the difference in time constant and the attenuation factor is elapsed, and then MS>FS2 thereafter. A comparator 5 compares the output MS with the FS2 and generates a signal indicating the signal break when MS>=FS2.