Breakage detection device of the analog input signal line

摘要

PURPOSE:To prevent an erroneous output by providing a voltage follower comprising operational amplifier between an input resistor and a T type filter, detecting a broken signal line for an analog input signal early and latching a current value to a value just before the broken line takes place. CONSTITUTION:An analog input signal from a signal source 1 is delivered to an A/D converter 4 in a controller 6 via an input resistor R2, an operational amplifier 8 and a T type filter 3 and converted into a digital conversion value 4a. A broken line detection section 7 outputs a broken line detection signal 7a when an input voltage to the operational amplifier 8 is lower than a prescribed value. The operational amplifier 8 is a component of a voltage follower circuit and an output voltage 8a of the operational amplifier 8 depends on an input voltage VIO independently of the effect of voltage VIN across a capacitor C in the T type filter 3. Thus, the occurrence of a broken line till its detection is implemented momentarily, and should a broken line be detected during A/D conversion, the digital conversion value is invalidated to latch a value just before the broken line takes place. Thus, it is prevented that an erroneous digital coversion is outputted to a control system.