Analog quantity output diagnosis method for safety-level PLC system of nuclear power plant

The invention discloses an analog quantity output diagnosis method of a nuclear power plant safety level PLC system. Analog quantity output is diagnosed through an analog quantity output signal operation circuit. The analog quantity output signal operation circuit comprises a processing unit, a DAC module, an ADC module, a relay K1, a relay K2, a current conversion module and an amplification filtering module. The DAC module is connected with the processing unit through an isolation module; the ADC module is connected with the processing unit through an isolation module; the processing unit is connected with the relay K1 and the relay K2. The relay K1 is connected with the DAC module, the current conversion module and the amplification filtering module; and the relay K2 is connected with the ADC module, the current conversion module and the amplification filtering module. The output state of the analog quantity can be flexibly changed, whether the analog quantity output side is in an abnormal state or not is