Fail-safe digital filter

摘要

A simple fail-safe digital filter is to be created for monitoring an input signal which is subject to tolerances, which can be constructed of non-safe filters and which can be used for monitoring the significant errors of an input signal. According to the invention, the filter is constructed of more than three, preferably four identical mutually parallel and intrinsically non-safe filter channels (I to IV) which are ANDed (5) at the output end, the filter channels (I to IV) being supplied with derived pulses (1) of the differentiated rectified input signal (f) for monitoring the frequency and duty ratio of the input signal (f), which filter channels cause a subsequent channel monostable flip flop (18) to output a continuous-1 signal (7) as long as these pulses (1) fall within the defined window time ( DELTA t) of a 2nd filter monostable flip flop (17) which is controlled by a preceding 1st filter monostable flip flop (16> and, for monitoring for pulse overshoots and break-HAZARDS, each of the filter channels (I to IV) is connected in parallel with an arrangement in which detector monostable flip flops (22, 23) respond to irregularly collapsing edges of the input signal (f) during defined test times (ttest) of preceding monostable flip flops (20, 21) and activate a turn-off monostable flip flop (24), the signal (6) of which turns off the associated channel monostable flip flop (18). <IMAGE>