Patent ID: 7869172

Claim:
A digital controller that converts an analog input signal from a signal output device that is connected to an input signal line into a digital input signal to output a control signal obtained by conducting a given calculating process on the digital input signal, the digital controller comprising: an analog/digital converter that is connected to an input terminal connected with the input signal line, and converts the analog input signal into the digital input signal; an input processing unit that obtains a control input value taking into consideration ground, ground fault, and disconnection of the input signal line according to an output of the analog/digital converter; and a signal output device power supply that is connected to the input terminal within the digital controller, wherein the input processing unit comprises: ground determining means for determining that the input signal line is grounded when a voltage from the input terminal that is connected with the input signal line is equal to or lower than a ground determination value; failure determination invalidating means for outputting a first specified value as the control input value regardless of the voltage from the input terminal during a first given period immediately after the digital controller starts; ground fault detecting means for conducting a ground fault determining process on the input signal line when the voltage from the input terminal is lower than a ground fault determination value which is a lower limit of an output range of the signal output device after the first given period, outputting a value based on the voltage from the input terminal as the control input value when the voltage from the input terminal is equal to or higher than the ground fault determination value and equal to or lower than a disconnection determination value that is an upper limit of the output range, outputting a third specified value as the control input value during a second given period after the first given period when the voltage from the input terminal is lower than the ground fault determination value, and outputting the first specified value as the control input value when a state in which the voltage from the input terminal is lower than the ground fault determination value is maintained for the second given period or longer; and disconnection detecting means for conducting a disconnection determining process on the input signal line when the voltage from the input terminal is higher than the disconnection determination value after the first given period, outputting a second specified value as the control input value during the second given period, and outputting the first specified value as the control input value when a state in which the voltage from the input terminal is higher than the disconnection determination value is maintained for the second given period or longer.