Hi all,

Could some one explain to me about time synchronization in DCS system from GPS as following question:

How often does DCS system receive time synchronization signal in a hour? And how long is it between received times?

 

jianjian2112,

the target of time synchronization in DCS from GPS that if we have more than one controller system ,so by default each system will have its clock adjusted basically from the PC which downloaded the program in the system ,so if any trip or trouble occur in the system if all the system doesn't have the same time ,the reports will be messy and confused about at which time the problem occur due to difference in reporting time.

So a main controller or using GPS signal to every controller is sent in a specified time to every system in which every system readjust its clock.

and this signal is to be one (pulse signal) per day (or according to customer needs)

Hope you got the point,
Regards
Ahmed

 

We are not very sure , but time synchronization plays very critical role in Multiple Node system we are not sure about GPS

typically, time synchronization cycle varies from DCS to DCS

HONEYWELL - EXPERION C300 10-100 ms
YOKOGAWA - CS3000 - 100 ms

This is Global system parameter , it has to synchronise simultaneously & top-most priority as far as the operating system Controller.

You have to specifically ask this parameter from DCS vendor.

This also plays very critical information , when on ETHERNET Highway , No of Nodes increases more than 8.

You may please varify this data from DCS vendors.

Regards

Jari
iconcnl [at] vsnl.net

 

I feel that it is firstly required to understand as to why the synchronization is required. Generally for a critical continuous application which has more than one control system (e.g. DCS, PLC, UCP etc) communicating with master control system, requires the time synchronization. I remember earlier days, it was DCS which was used as Master Control System and use to send the Time Synchronization Pulse to all its subsystems. And this was done only to the systems which it was communicating.

Now a days, there are cases where you have multiple systems working independently (e.g. Process control System viz. DCS & PLC, Vibration Monitoring System, BMS, F&G, Well SCADA etc). If this is the case, then it is worth using GPS for time Synchronizing. GPS will give pulse at a specific time period(to be defined based on the accuracy of the clocks of every system) to all / any of the system. This will ensure that all the systems will have the same time and the analysis of the parameters(which created the disturbance) is accurate. E.g. Trip condition (accuracy is very important in this case as to what made the area/plant/unit trip and what was the exact time sequence).

Regards,
Ketan Lakhani

 

The system clock for most systems nowadays are very unlikely to drift more than a seconds in a day. For this reason, we sync the time of our DCS and subsystem only once per day. Unless your have a time critical requirement which require all the system to be in sync, then you may consider to do it more frequent.

 

Hi All,

DCS system receive time synchronization in form of Pulse which can be defined for second and available through Serial ports which can be configured for IRIG-B port or Ethernet port. Normally each GPS do parallel tracking with satellites for time synchronizing and provide pulse per second output. Please make sure when you are buying GPS it must support NTP (network type protocol) to connect multiple devices on Ethernet like slave clocks, PLCs ,RTUs etc. if you want to have first hand information visit any 415KV substation to get exact details like GPS, Time stamping, and SOE details.

 

Hello all,

Thanks for all have taken care and explained for me.
And now we have another related GPS problem need to clarify: In the DCS system, which one of stations should be connected to GPS is the better way? History Data Server, Engineering station, configuration server, calculation server, real time data server or directly to the bus?
Thanks for all again!

Best regard!

 

Hi,

please connect GPS to DCS directly through PPS or Ethernet in turn DCS will sync all other devices which are connected. One more option is connect GPS to LAN using NTP. All other devices which are connected in automatically get sync

Best regards

M.Bhaskar

 

Can anyone explain to me how a time master send time message to other slaves in the network?

Example: in DCS I have a Hopf 7001. It send synchonization pulse every 30s to controllers and every 5s to analog & digital clocks. So, if at the beginning, the time set in the clock are wrong, how it can be corrected after receiving these pulses.

Thank you in advance.

 

HA,

Using my preferred Internet search engine to ask:

"How does NTP work?" (without the quotes)

this was the first result it returned:

http://www.ntp.org/ntpfaq/NTP-s-algo.htm

NTP is an open-source time synchronization application that is widely used around the world for synchronizing multiple controllers in a network.

The explanation may be a little much for what you're asking, or it may be too little--but it does talk about packets and sanity checks and such, and as such that may be what you're looking for. NTP is usually implemented over Ethernet networks, using UDP/IP (you can look that up, too, with your preferred Internet search engine). But basically, messages are sent (in this case from the "client" to the "server" asking for the current time, and the "server" sends back a message with several bits of information from which the "client" can determine how long it took for the request to get there, how long it took for the request to get processed, what the time was the request was sent back, and so on.

The "client" then adjusts the clock of its host to reflect a time that should be within micro-seconds of the "server's" time signal. If the host clock is the PCs BIOS clock, then that's what gets adjusted since most applications take their time from the host's PC BIOS clock (at least those running most modern-day operating systems). It would be akin to a person checking the time of the controller (PC; DCS; etc.) using some command-line or other application, and then changing the time based on some other clock using that application or utility to do so.

Most clocks have some drift, for various reasons, but time synchronization keeps them all very close to a master signal. The master signal can come from the server's clock, or from a third-party "clock" (a satellite signal; another DCS or computer; etc.).

Hope this helps!

 

Dear CSA,

Thank you very much for your explanation.

One specific case: a DCS system (installed >12 years ago) with PC run in Linux an not supported NTP. They have master clock system which receive time signal from GPS. But the way the deliver synchonization information to node in the system (controllers, PCs) are is 1-sec and 5-sec pulses via mechanical relay. Thus, I don't understand how it can send time message to these node. If it sends only the synchonization pulse, it can keep the time offset to be constant, but can not make this offset become zero. Am I right?

Best regards,
HA