AB PLC time sync

fullanitox

Member
Join Date
Jan 2020
Location
Argentina
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Hi, I need to synchronize a PLC but I have no experience with this. I would like to know which are the common alternatives to achieve this and what is the best option for a PLC that controls the followers in a photovoltaic solar plant?
Thanks!.
 
Welcome to the PLCTalk forum community !

What model of A-B logic controller are you using ? How are they networked ?

Are these small controllers that control one solar panel frame each, or a larger controller that controls many follower mechanisms ?

Do you have any sort of HMI (PC or hardware based) that gets an accurate time value from an Internet or other reliable time server ?

There are several ways to set PLC time clocks, including a software utility that runs on an HMI or server computer, or a high-precision ControlLogix module, or some roll-your-own clock data setting logic.
 
Hi sorry for the late reply and thank you!. We have a CompactLogix L35e PLC installed in a photovoltaic solar plant that loses synchronization in case of a power outage causing trackers not to follow the sun according to the time of day. When the electric power returns, the PLC starts from the time that the electricity was lost. The BAT LED of the PLC remains off indicating that the battery is in good state. My doubt is that if the battery is in optimal conditions then the RTC of the PLC should not continue counting regardless of the power outage. Should i install a UPS?

How i can sync the this PLC?

Another question I have, is the same a GPS module as an NTP server?
 
Allen-Bradley has a free program that can run on a PC or server using the Lite version of RSLinx that will keep your PLC synced to that PC. You can schedule it to sync as often as you want.


A UPS is always a good idea. But get a battery-less type. Panduit makes a nice one they put in their networking cabinets.


The Reynolds company make a CompactLogix GPS module that would give time time as well.
 
For your purpose, you probably don't need super precision so you can just get the Clock Update Tool from Rockwell and run it on a HMI PC that's already synced.

For extreme precision, you will need a PTP server. L35e should support it.

Some GPS module also acts as NTP and/or PTP server but not always.
 
From your description, this doesn't sound like a sync problem or at least not just a sync problem. A CompactLogix controller should keep the RTC running for days on loss of power.

When you say "PLC starts from the time that the electricity was lost." Does the clock continue like no time has elapsed during the power outage? (for example power is lost at 1130, is off for one hour, and when power is restored the PLC thinks it is still 1130 or does it read 1230)

Or is it that your solar panels lag 15 degrees behind the sun because they didn't move during the power outage? If it's the later than there is an issue with the program driving at a set speed vs calculating what the position should be based on the time.
 
It sounds like someone has created their own clock in logic instead of using the built-in real time clock. If I create my own clock using timers and counters, it would stop updating when power is lost and then resume when power is restored. There isn't a quick fix to this other than to prevent the PLC from ever losing power. That's where a UPS would come in.

The built-in clock does not pause due to a power failure and then resume when power is restored. It continues to update as long as the battery is good whether it has power or not.

We need to identify if they have created their own clock. Any chance you can post the program? You can send it in a private message instead of posting here where it would be publicly available.

OG
 
If you have a Rockwell TechConnect, the 1756-TIME might be the thing you are looking for.

If you have a server connected to an NTP, the server is the best way to sync times.
 
Thanks to all of you for take your time to reply.

When power is lost for example at 12 : 00 and it keeps 1 hour, then when it returns the PLC thinks that is 12 : 00 yet and this causes an error tracking the sun, like Timber explain.

I think that who programmed the PLC didn't use the RTC as describe Operaghost.

Sorry for the lack of information but i didn't have access to the program because the plant is so far to me and the operator doesn't have much knowledge about PLCs.

I'll opt for the software because is simple and economic solution.

Thanks again.
 
If the program is not referencing the PLC real time clock then syncing to a network source will not help. If the program cannot be accessed then using a UPS is probably the only effective course.
 
Can't OP copy from the NTP-Synced wallclock into their custom clock in case they are using one?

I am imagining that drift would become an issue sooner than later, maybe not that drastically?
 
Given that your application involves tracking the sun with solar panels (if I understand it correctly) I'd say precision is important at least to the minute (I would guess) in order to maintain a high level of efficiency. If that is the case then I'd be looking at UPS systems, using the PLC's real time clock and even a backup with RSLinx or maybe an external time server that the PLC can get updates from. I'm guessing there are several ways of doing that however I do know that Spectrum Controls Universal Gateway can connect to an internet time server and send time stamps (via Strings) to a PLC. It's not something I've done so there are some gray areas and like I said I'm guessing there is other stuff out there that can accomplish the same goal but the long and short is (from what I understand of the application) keeping accurate time is important so having some redundancy should be looked at.
 

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