DIAGNOSTIC CIRCUIT OF CROSS COIL TYPE METER

摘要

PURPOSE:To perform diagnosis even if a change-over switch is not provided, by supplying a predetermined diagnostic signal from a diagnostic signal supply means started by the detection signal from a detection means as a measuring signal. CONSTITUTION:The car speed signal from a car speed sensor 1 is passed through LPF3 at first to have noise removed from said signal and subsequently supplied to an input waveform shaping circuit 102 through an input synthesizer circuit 5. A disconnection detection circuit 9 monitors the output signal from the sensor 1 through LPF3 to detect whether the wiring from the sensor 1 to LPF3 is disconnected. The detection output signal is supplied to a disconnection time discrimination circuit 11 and discriminates true disconnection when disconnection continues for a predetermined time or more. A dummy sensor signal generator 13 is started by the disconnection discrimination output of said circuit 11 and a predetermined dummy sensor signal for diagnosis is outputted from the generator 13. This signal (diagnostic signal) is supplied to the circuit 102 through the circuit 5. Thereafter, a cross coil is driven through an F/V converter circuit and the value corresponding to a predetermined diagnostic signal is specified to judge whether a cross coil type meter is normal.