Help with rslogix 5000

Daba,

After reading the comments in the AOI we could be here for some time.

Rockwell are saying it will run for 5.8 million years, and we all know how well Rockwell test things before putting them out to Joe Public.

Mark
 
Ah but wait !
There's a problem with the WallClock it's crashing out with a stupid year value, something like 563296 !!

I'm trying to determine the date that it doesn't like rolling over to
 
Maybe I've just been spending too much time writing software specs of late, but what is supposed to happen during daylight savings or more appropriately in this case British Summer Time?

I don't believe the clock in ControlLogix automatically adjusts for DST (I doubt CompactLogix is different). Does the time change by an hour or is one week of the year an hour short and one week an hour long? (I'm fortunate to live where we don't observe such silly rituals.)
 
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Actually most countries don't observe DST, by a margin of about 2:1, even the article you cite shows that, it's mostly a North American / Europe thing.

That wasn't really the point, rather I wanted the original poster to consider what happens when the clock does change and furthermore how does the clock change (manual reset, programmatically, or divine intervention).

I don't know exactly what the count is used for, so it might not be important at all. But in a 24 hour day operation where the number was used to measure production let's say. There could be 0.6% dip in production in the spring and a corresponding rise six months later.

Like I said, I've been writing a lot of specs lately, so I've been spending a lot of time working on these 'corner' cases.
 
OK, hands up, I didn't read the Wiki article close enough.

Anyway, DST in the UK is "Spring Forward, Fall Back"

In the spring, we put the clocks forward 1 hour, and call it "British Summer Time".

In the fall, we put the clocks back 1 hour, to restore it to UTC.

British Summer Time begins on the last Sunday of March and ends on the last Sunday of October. Clocks are "adjusted" at 0100 hrs on those Sundays.

That is enough given info to code when DST should be enabled in the Controller if required, all we need is to determine the "Last Sunday in March", to turn it on at 0100hrs, and the "Last Sunday in October" to turn it off. So knowing the day of the week is essential.


Anyway, I have determined that the WallClock (In a ControlLogix L62 Version 19 at least) has an issue being SSV'd which starts sometime around 17/04/2262 (dd/mm/yyyy)

It's hard to determine the exact time of day the problem arises, to be honest it seems to move around for some strange reason, as you try to "home-in" on it, dates and times that previously failed would work ok again.

The clock does seem to "ride" through if set before the problem was observed, and continue as a clock should, it's just a problem setting it. I suspect there is a glitch in the maths that the WallClock does to convert the DINT[7] array data supplied by the SSV into the 64-bit "CurrentValue", which has been observed to go negative when SSVing dates around then.

All very academic, and I won't lose any sleep over it... 2262 lol!

But if you are engaged in writing code for a "time-travel machine", just be careful where (when) you put yourself.


edit: On the subject of your "corner" cases, Timbert, most of the systems I have worked on have NOT used DST for production data for the reasons you stated. That doesn't mean they don't display DST times on the HMIs and SCADAs, but production data collected for statistical and historical purposes has mostly been stamped UTC.

Most production data revolves around rates, and that infers a time-period, so having all times UTC is beneficial... EndTime - StartTime = ProductionTime regardless of DST adjustments that introduce errors twice a year.

The WallClock on the Logix5000 processors can give you both attributes....

DateTime - unadjusted (UTC)
LocalDateTime - adjusted to the specified locale (DST) - if enabled !

The 64-bit "CurrentValue" is just a count of the number of microseconds since 00:00:00 on Jan 1st, 1970
 
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One which will accumulate errors over time, thereby requiring frequent intervention to fix. And as far as your "KISS" approach, the best approach to that is to put an alarm clock by the operator desk, and provide a button for him to press when it goes off. Even that would be more accurate and less error prone then a free-running timer.[/quote]

I had to take your word...For a week, at least...:site:
Meanwhile, two Logix class processors, 1756-L61 Rev.19.11 and 1794-L34 Rev.16.22 ran two "One_Week_Free_Running_Timer" RTOs
"hot wired" within their Main Continuous Tasks. Upon .dn true they've "time stamped" WallClockTime within two DINTs.
Guess what?!:geek: Magic....

THEY WERE ACCURATE TO THE SECOND!:cool:

After all, ALL TIMERS ARE RUNNING OFF THE CPU INTERNAL CLOCK TIME SLICE! THEY ARE AS AS ACCURATE AS THE WALLCLOCKTIME SYSTEM VALUE IS!

Give it a try... It's fun...:D
 

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