CLX Time Sync

Andy Patel

Member
Join Date
Nov 2019
Location
Jersey City
Posts
11
Hello Everyone,

We have around 10 CLX with motion controls on them. They are provided by OEM, and I need to sync time on all of them. I have CLX of my own which is connected to all the other ones via Ethernet/IP. I am using it to read some data.

I am aware of the Logix5000 Clock Update tool.

Questions.
1. If I set up an automated time update by the tool, will it upset the motion controls on the CLX? especially while the machine is running?
2. If yes then I can write a logic to sync time from my CLX to other ones, while the machines are not running, but I don't know if we can do that. or how to do that?

can anyone help?

Thanks,
 
Check this box on the one you want to be the master and wait a bit. Then enable on the slaves.
I cant' recall the specifics at the moment but there is a voting that takes place and decides who the master is. You will need to look that up yourself.

The 5 indicators below the checkbox tell you who is what.

Time.jpg
 
See chapter 2 of this manual.
https://literature.rockwellautomation.com/idc/groups/literature/documents/at/ia-at003_-en-p.pdf

It explains the use and setup of CIP Sync and Grandmaster clocks.

On the advanced tab of the Time/Date you will find the details for the grandmaster clock. The description will show the current grandmaster device. The priority 1 and 2 determine the grandmaster clock device the one with the lowest value on the network will become the grandmaster. If all devices have the same priority value the devices will find the best clock on the network and automatically use that device as grandmaster.
Clock.jpg
 
Last edited:
While I don't have any motion controllers in my environment, I use a central PLC, and have written a routine that periodically checks clock drift and corrects it on all our PLCs in the field. We have several hundred controllers, and they are on different subnets. This works well in our environment.

I would not recommend syncing time on PLCs at a high frequency for anyone doing motion control. While I have never seen it myself, I have read where changing the time in the controller can have unexpected motion.

A coworker of mine also has stories about an automated timesync program at a manufacturing plant they worked at, which would cause the reports to be off by several seconds every time the PLC was time synced. They did not care about the timestamps, but more about the 24 hour totals. So they had logic in their reporting system that would correct the totals from the PLC after a time sync.
 
... and have written a routine that periodically checks clock drift and corrects it on all our PLCs in the field. We have several hundred controllers, and they are on different subnets. This works well in our environment.

I've never tried to update a CLX or CPLX clock yet over the wire and this is something I still need to create as I continue to transition old RTUs in the field from PLC'5s to CPLX. I update the PLC'5s clock by writing to the S registers, but just how do you change time on a CPLX (or CLX)? over the air... and in most cases over the VERY SLOW air? (if only they accepted NTP.... sigh)

Could you share your code or even some kind of template I can use to see if what you have accomplished would be possible in my telemetry? I'm using the Logix Clock Update tool but using a desktop as a sync source is just bad form, and only really works well locally and on the few cell modems I have scattered around that appear local to the tool. The slow VHF radio links need to be polled and I can't randomly throw out clock update transmissions into that, so I need to thread the update into existing polling.
 
I'm in the power industry right now and time-sync almost everything.

For ControLogix if you want great time-sync without much overhead. It may be worthwhile just to get a PTP enabled GPS unit. They are not cheap, but once you have one, CIP time-sync will be effortless. See Robobob's post for how to do it. Just set your GPS up to be the Grandmaster.
 
The time source isn't the issue it's the bandwidth required to do the update that I need to minimize. I only require 1 minute accuracy so a once a day update is plenty. If the sync payload is small enough I could do this a few times a day and get better accuracy. The bandwidth I have to some sites in the valley is about equal to a 9600 baud serial modem because of terrain hopping.
 
I've never tried to update a CLX or CPLX clock yet over the wire and this is something I still need to create as I continue to transition old RTUs in the field from PLC'5s to CPLX. I update the PLC'5s clock by writing to the S registers, but just how do you change time on a CPLX (or CLX)? over the air... and in most cases over the VERY SLOW air? (if only they accepted NTP.... sigh)

Could you share your code or even some kind of template I can use to see if what you have accomplished would be possible in my telemetry? I'm using the Logix Clock Update tool but using a desktop as a sync source is just bad form, and only really works well locally and on the few cell modems I have scattered around that appear local to the tool. The slow VHF radio links need to be polled and I can't randomly throw out clock update transmissions into that, so I need to thread the update into existing polling.

I'm at home right now (we all work 2 weeks on, 2 weeks off). I pinged a co-worker to send me the code. I'll PM it to you with some explanation of how it works once I get it.
 
See chapter 2 of this manual.
https://literature.rockwellautomation.com/idc/groups/literature/documents/at/ia-at003_-en-p.pdf

It explains the use and setup of CIP Sync and Grandmaster clocks.

On the advanced tab of the Time/Date you will find the details for the grandmaster clock. The description will show the current grandmaster device. The priority 1 and 2 determine the grandmaster clock device the one with the lowest value on the network will become the grandmaster. If all devices have the same priority value the devices will find the best clock on the network and automatically use that device as grandmaster.
View attachment 66479

Lowest priority1 is grandmaster.
Lowest priority2 is tiebreaker.
After that, the algorithm makes the call.
 

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