Patent ID: 6118190
Filing Date: 2000-09-12
Classification: G01F

Abstract:
A fail-safe electrical circuit for use with a sensor, said sensor providing an electrical output indicative of a sensed condition, said circuit and said sensor provided with an alternating electrical drive signal, said circuit comprising:a conductor, connected to said sensor, to provide an attenuated drive signal output, said attenuated output comprising said electrical output indicative of said sensed condition;a first comparator (IC2) for comparing said attenuated drive signal output with a threshold value signal, said comparator providing an alternating output signal when said attenuated drive signal output corresponds to a sensed normal condition;a second comparator (IC3) for providing a second comparison output signal when said alternating output signal has a predetermined phase with respect to said alternating electrical drive signal;a selector to establish normal and abnormal conditions to be sensed, said selector setting the threshold value signal applied to the first comparator and setting the phase of the alternating electrical drive signal which is applied to said second comparator;a fail-safe output stage, responsive to said second comparator output and having normal and fail-safe states, said stage going to said fail-safe state when said second comparator output fails to indicate said predetermined phase between said alternating drive signal and said alternating output signal; andan error detector (IC1), responsive to the attenuated drive signal output and a preset voltage, for providing an error signal if the attenuated drive signal output is less than a minimum value determined by said preset voltage, said error signal being, in at least one setting of said selector, coupled to said output stage whereby said output stage reverts to its fail-safe state when said error detector detects a short circuit at said conductor.