Redundancy device unit and method for determining fault in industrial control system, industrial control system and industrial system comprising redundancy device unit

A method for determining a fault of an industrial control system, wherein the industrial control system comprises a first device connected with a field device via a first link and a second link in series and a second device connected with the field device via the second link and a third link in series, the first device is configured to be initially active in use, and the second device is configured to be initially passive in use, the method comprising steps of:

• obtaining from the first device first diagnostic information indicating, when the first device is active, whether there is a fault in the first link and/or the second link;
• when the first diagnostic information indicating that there is a fault in the first link and/or the second link, switching the first device into passive and switching the second device into active;
• obtaining from the second device second diagnostic information indicating, when the second device is active, whether there is a fault in the second link and/or the third link;
• when the second diagnostic information indicates that there is no fault in the second link and/or the third link, determining that there is a fault in the first link;
• and
• when the second diagnostic information indicates that there is a fault in the second link and/or the third link, determining that there is a fault in the second link.

A method for determining a fault of an industrial control system, the method comprising steps of:

• obtaining from a first device, when active, first diagnostic information indicating whether there is a fault in a first link and/or a second link;
• when the first diagnostic information indicates that there is a fault in the first link and/or the second link, switching the first device into passive and switching a second device into active;
• obtaining from the second device, when active, second diagnostic information indicating whether there is a fault in the second link and/or a third link;
• when the second diagnostic information indicates that there is no fault in the second link and/or the third link, determining that there is a fault in the first link;
• when the second diagnostic information indicates that there is a fault in the second link and/or the third link, determining that there is a fault in the second link;
• and
• wherein the industrial control system comprises the first device connected with a field device via the first link and the second link in series and the second device connected with the field device via the second link and the third link in series, the first device is configured to be initially active in use, and the second device is configured to be initially passive in use.