Forum Post: RE: [A/D converter] How to detect A/D abnormal, disconnect abnormal and short abnormal

Something like this is normally done by bounding the sensor to a range of values.  This may be done by selecting appropriate resistors or may already be built into the sensor.  For example a sensor may produce pull a line low through a resistor which is already pulled up at the measuring point (your A-D input) if the reading goes full scale then the sensor must be disconnect. The sensor can also be arrange to provide valid outputs between say 1V and 2V where 1V means 0mph and 2 means 200mph anything outside these ranges would be a failure, which may be a transient spike on the line for instance. These are just examples you would have uses values that apply to your hardware and situation.  Momentary glitches for instance should be removed from any calculations done but persistent out of range or varying in a manner that you wouldn't expect on the sensor would give the abnormal indication. You probably need a tighter spec on when these cases should be reported. Paul.