- Either the CPU is configured in NTP client mode, and the NTP server is no more reachable or there was a disruption bigger than 2 seconds in NTP served time
-> in order to resynchronize the RTCs, set the process system word %SW128 to 16#1AE5 and then to 16#E51A .
-> in order to manage this situation, use the safety device-DDT diag bits in the logic to warn if the NTP service is down : EIO2_d1_r0_s0_SRA31200/S_COM_DBG/M_NTP_SYNC and EIO2_d1_r0_s0_SRA31200/S_COM_DBG/CPU_NTP_SYNC

- Or, the CPU is configured in NTP server mode, and the user has updated the CPU time  with a value more than 2 second different from the previous time value.
-> update the CPU real time clock using UnityPro
-> use the same method using %SW128.

see the attached example screenshot

important Note : when using a CPU that wasn't powered for a long time, prior to install it, it must be powered, and the Real Time Clock must be set to present date & time using Unity Pro

Basics :
in order to deal with safety I/Os, a safety CPU and his remote I/O drop head (CRA) use their Real Time Clocks (RTC) to time stamp their safety exchanges, cross-checking the time stamps of his counterpart exchanges vs its own RTC in order to maintain the accuracy of their RTC, the CPU and CRA rely on the NTP protocol, and need a reachable NTP server.

if the NTP server is not reachable, then the RTC of each element (CPU and CRA(s)) are no more updated, and start to drift and when the RTC difference reaches a given value (2 seconds), the safety communication synchro gets invalid, then after a while, the safety communication becomes invalid, and the I/O go in fall back state.

Note : the NTP is not used for safe communication between CPU and IOs starting from FW CPU >=3.20. So, this FAQ is valuable only when application level set into Control-Expert is lower than 3.20

Опубліковано для: Schneider Electric Україна