SLC Clock Wipes During Update

[I_Automation]

I was online a SLC5/04 yesterday and one thing I did was go to processor properties and set the date and time to get the PLC clock current. It wasn't off a lot, but a good time to get it exact.



When I clicked the button I noticed the outputs that were enabled by clock time all flickered off quickly. Did it again and they flickered again.


When I got home I wanted to see what was going on so in my home automation SLC5/05 I set a few traps and logs.



Turns out when the time is set online the time goes to 00:00:00 for about 0.04 seconds and during that time since it's midnight officially the clock controlled outputs turn off or on as they should be at midnight.



I say about 0.04 because a couple of times it logged 0.03 seconds, but mostly 0.04 so if I put a 0.001 time base I'm guessing it's somewhere around 0.035



After the 0.04 seconds of midnight the clock then reads the new time.


EDIT: If you change the time by the program or entering a new value in the S2 file when online it jumps to the new time immediately, not even 1 scan of 00:00:00



Been working on SLC's since the 90's and never noticed this before yesterday.


EDIT 2: Now I'm wondering if the time is externally set by a message or time synch master if it does this. I don't have another 5/05 to test this with so I'll just keep it on my ToDo list.

 

[I_Automation]

In thinking about this now, if I had a critical operation I wouldn't read the S2 time directly.


I would copy the S2 time to N7 integers, and watch that it's NOT 00:00:00 unless it was 23:59 in the past minute, then use those N7 time values to run things.

Plus going to power up a ML1400 and see if a RTC does this. Wish I had a ControlLogix CPU now.

 

[drbitboy]

you could also check the year; I would expect the entire time value is being zeroed for those few milliseconds.

 

[I_Automation]

you could also check the year; I would expect the entire time value is being zeroed for those few milliseconds.

It does.


The data reads 0000-00-00 00:00:00


Oddly though S2:53 for Day Of Week does not change to 0 when tested on Thursday.

 

[I_Automation]

Micrologic Update:


The ML1400 processor does wipe the date/time to 0-0-0 00:00:00 when the RTC is set online.


Also the ML1400 sets the DayOfWeek to 0 that the SLC did not change.


But I was able to add NEQ RTC:0.YR 0 before the COP that copies the data to an integer file so that integer file is never all zero's and the PLC operation not effected.