Compactlogix Time Warp

So a few weeks ago I had an issue with the PLC clock and HMI clock going balistic and resetting to strange values on the HMI.

I now believe these issues have been resolved.

However the site have now contacted me and claim that the time has lost two hours in the three weeks since the visit! Think I have worked out roughly 30 minutes a week.

Can anyone explain this? I am using wallclock etc. etc. and as I was unsure if time was being altered at the HMI by operators I wrote a simple routing to sync the clocks at 6am and 6pm each day.

The operative who contacted me also said the PLC clock (at HMI) appeared to freeze for approx. 20 seconds...although am sure this is nothing to do with issue.

Any thoughts as I am now baffled.

Can you tell us more about the HMI and how you've written the synchronization feature ?

I had an HMI system some years ago that somebody had built using a PanelView Plus that was reading the time from the PLC, using that to set the HMI time, then writing that time back to the PLC. Depending on exactly when it triggered, it would lose one or two seconds every time it ran, so it was losing an hour a week.

I wish that RA had built a simple code-triggerable Network Time Protocol (NTP) client into ControlLogix, but they just haven't.

Ken Roach said:

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I wish that RA had built a simple code-triggerable Network Time Protocol (NTP) client into ControlLogix, but they just haven't.

Click to expand...

I was told by an integrator that Contrologix will automatically seek out a PTP server and sync to it. True?

ControlLogix uses IEEE 1588 Precision Time Protocol (PTP) as a way to manage device synchronization for motion and safety.

PTP clocks are usually built into high-end switches or into the 1756-EN2T/EN3T modules themselves.

For the more mundane feature of just setting the system clock so that it matches your wristwatch or the time on the clock on the wall, ordinary Network Time Protocol is used. And ControlLogix doesn't support that.

The only good way I know about to keep a ControlLogix-based control system adjusted to keep up with an ordinary PC system is to use the RSLogix 5000 Clock Update Tool.

And the usual disclaimer: I don't work for RA Tech Support anymore and have no internal knowledge about new features that may have been added to the product line.

This is a feature I have quite a bit of interest in, so I keep my eyes open for updates and changes related to it, but it's certainly possible for things to get by me.

Thanks for the feedback.

In essence at 6am and 6pm each day I use the 'SSV' command to read the wallclock and set system time, this then latches a bit to 'SetHMIClock'for HMI Clock for a time of three seconds.

I am currently running the code on a desktop to look at the error a bit more deeply as it was thrown together in haste and I was not aware of the subtleties and believed this would help with the original problem.

If helps I may be able to get a printout of the associated ladder.

Date time code.

Out of interest can you do the sync the other way i.e. HMI > PLC rather than PLC > HMI

This logic looks a little over-complicated to me.

Rungs 3 and 4 appear to both use an SSV to set the WallClockTime in the CompactLogix.

Those rungs also both re-use the boolean tag L_DBS6PLS as the memory tag of a One-Shot instruction, which is not proper. I don't think Rung 4 will execute when PON_Stage6 becomes true.

Can you explain the intended difference between the individual tags CW_PLCYEAR (Month/Day/Hour/Minute/Second) and SYS_PLC_CLOCK.Year (Month/Day/House/Minute/Second) ?

One thing that Rung 3 does is ignore the fractional part of a second twice a day, but that should only add up to 1 minute a month.

When do you intend to execute Rung 2 ?

It looks like the time value is going in a circle, from CW_PLCYear -> SYS_PLC_CLOCK.Year -> CW_PLCYear, losing the fractional part of a second every time.

Take a step back and describe how you intend the time handling to work on this system.

Are there Numeric Entries on the HMI that allow a user to set the time ?

Are you attempting to use the Global Connections in FactoryTalk View to set the time in the HMI ? Post details about how that is configured.

Ken

It may appear over complicated but given the issues previously reported I was overly enthusiastic to prevent the previous issue and may have inadvertently had another effect on the system.

Agree rungs three and four are in effect doing the same thing, will delete one during the test and see what effect it has.

CW_PLCYEAR comes from the HMI to allow operator resetting of the time.

Rung two is intended to be executed when the page is initially load for setpoints, not sure if I this how it is but will confirm.

Not sure if it circular but will review.

Taking a step back;
1. PLC Clock is sent to HMI
2. Due to HMI clock previously going into error at start up when power is applied reset HMI clock from PLC.
3. As reports of clocks being different being reported and in the absence of firm cause being established set HMI time to PLC time twice a day BUT not at midnight as all totalisers are read then.
4. Operator can set clock from HMI if required.

And yes an attempt is being made to use global connections.

This is like a boomerang. The issues would now appear to be resolved in terms of synchronizing... however it has been noticed that the time on the alarms page and the system time differ by an hour, I am waiting for screen shots to confirm but I assume they refer to the the time stamp for the alarm.

Does anyone have an explanation for this?