DEVICE AND METHOD FOR PROTECTING AN AIRCRAFT TURBOMACHINE COMPUTER AGAINST SPEED MEASUREMENT ERRORS

The invention concerns a device for protecting an aircraft turbomachine computer against speed measurement errors comprising: - on a speed control channel (10): a turbomachine gearbox shaft speed sensor (21), a speed measurement circuit (24), and a speed control circuit (26), - on a monitoring channel (11): a turbomachine gas generator shaft speed sensor (31), a speed measurement circuit (34), and a control circuit (37) stopping the turbomachine, in which each channel (10, 11) uses dissimilar characteristics capable of eliminating common-mode errors, in which each speed sensor delivers a pseudo-sinusoidal frequency signal and in which this device comprises, on each channel, a speed monitoring circuit (25, 35) that compares the frequency signal to a minimum threshold and that delivers an error signal when the measured frequency is lower than this minimum threshold, and a shared circuit (36) for cross-checking the speeds in order to detect the exceeding of a predefined discrepancy between the two frequencies such that the monitored discrepancy is greater than a maximum discrepancy or the monitored discrepancy is lower than a minimum discrepancy corresponding to the loss of a frequency period on one or other of the sensors (21, 31), and means for analysing said error signal and said signal indicating a predefined discrepancy has been exceeded in order to control the stopping of the turbomachine. L'invention concerne un dispositif de protection d'un calculateur de turbo-machine d'aéronef contre les erreurs de mesure de vitesse comprenant un capteur de vitesse de l'arbre de la boite d'engrenage de la turbo-machine, un capteur de vitesse de l'arbre du générateur de gaz de la turbo-machine, un circuit de mesure de vitesse, un circuit de surveillance de vitesse qui effectue une comparaison du signal de fréquence à un seuil minimum et qui délivre un signal d'erreur lorsque la fréquence mesurée est inférieure à ce seuil minimum , et un circuit de vérification croisée des deux vitesses obtenues, configuré pour détecter un écart anormal entre ces deux vitesses, en détectant la perte d'une période sur l'un des deux signaux ou même des deux signaux simultanément, et qui délivre un signal de problème de vitesse, en cas d'un écart anormal entre les deux vitesses.