Patent ID: 8799707

Claim:
A redundant system comprising: an input device; a plurality of arithmetic devices that receive input data from the input device; and an output device that receives output data output from the arithmetic devices, the redundant system causing the arithmetic devices to perform the same processing, wherein each of the arithmetic devices includes: a first communication unit that acquires the input data from the input device; a second communication unit that sends the input data acquired by the first communication unit to other arithmetic device and receives the input data acquired by the other arithmetic device from the other arithmetic device; a control/arithmetic unit that calculates the output data by performing a predetermined arithmetic operation based on the input data; and a storage unit that stores an intermediate value dataset, which is a plurality of data items obtained during the process of calculating the output data, wherein the second communication unit sends the intermediate value dataset stored in the storage unit to the other arithmetic device and receives the intermediate value dataset sent from the other arithmetic device, the storage unit stores the intermediate value data received from the other arithmetic device in association with the input data, and the redundant system further comprises at least three of the arithmetic devices, wherein each of the arithmetic devices includes a data selecting unit that, if at least one of the input data acquired via the first communication unit and the second communication unit does not match, selects a value with the highest occurrence frequency from among at least three of the input data as changed input data, and the data selecting unit, if at least one of a plurality of the intermediate value datasets stored in the storage unit does not match, selects a value with the highest occurrence frequency from among the intermediate value datasets as a changed intermediate value dataset and, if the selected intermediate value dataset differs from the intermediate value dataset based on the input data acquired via the first communication unit, determines that the output data calculated from the input data acquired via the first communication unit is not correct and sets the intermediate value dataset with the highest occurrence frequency as a changed intermediate value dataset.