Synching 2 PLC's Start Time

[kyle 0]

I am trying to sync 2 PLC's start time. One PLC will be the master and the other will recieve the time from the master and input it into the second PLC the slave. They are RSLogix 5000. Is there a way to add something to the main program to sync this time once a day at a certain time each day? Edited 20 Oct 2006 by kyle

[OkiePC 14]

I think you'll get an expert reply with a few more answers about the problem... First, how are the two CPUs connected? Second, are you trying to synch process start times, or the PLC clocks? Third, how much error in timing can be tolerated? PEC

[kyle 0]

1)Cat-5 connection between the two PLC's both control logix 5000 2)PLC clocks, we have to go in about a month later after synching them and re-sync them because one of them trails off by a few minutes and starts our lines up later than the other. 3)Looking for maybe somewhere in the range of seconds.

[TConnolly 13]

The hard (but not really hard) and not precise but maybe close enough and cheap way: Each PLC will need a DINT[8] array. Decide which PLC is to be the master and which is to be the slave. In the master PLC execute a GSV instruction to place the current date and time in the first seven words (0-6) of the Dint array. Then set DINT_ARRAY[7].0. MSG the dint array to the slave PLC to the matching dint array in the slave. When the slave detects that DINT_ARRAY[7].0 is set, it executes an SSV instruction to update its clock using the first 7 words (0-6) of the dint array. Then the slave clears DINT_ARRAY[7].0 and messages just the word DINT_ARRAY[7] back to the master, thereby clearing the matching bit in the master and acknowledging that the time has been updated. If the master does not get its DINT_ARRAY[7].0 cleared within a few seconds, it can be used to trip an alarm to indicate that the sync failed. The easy expensive way with high accuracy for motion control: Use Synchlink. EDIT: I wouldn't put this in the main task. I would put it in a periodic or event task. Edited 20 Oct 2006 by Alaric

[svn 0]

OK you already have Ethernet communication in this case. In one event recording application there was no communication link between PLCs. I set digital output of the master PLC at 7:00 AM. This is wired to input of other PLCs and they are programmed such that on positive edge of the input, RTC is set to 7:00 AM. The PLC scan times were very fast and I got good accuracy. SVN

[Ghettofreeryder 0]

If u have a HMI computer running, why not just use the Logix 5000 Clock Update Tool. Then the plc clocks will be synched with an internet time server