Time Synchronisation for DCS

D

Thread Starter

Dave Millett

The DCS will be operating a combined heat and power plant. DCS clocks, and PC clocks, all drift. The plan is to synchronise the DCS with GMT, so that our operating times match the National Grid when we decide to export power.

The solutions I have found so far are by Galleon and HKW Elektronik, but both rely on RS232 comms. All I really want is a radio-synchronised alarm clock, tuned to the Rugby transmitter, but which will give me a volt-free contact instead of the alarm.

Unless anybody has any completely different solutions?!
 
Dave:
> I want to synchronise a DCS accurately with GMT. I am looking for
> something that will provide a regular (daily?) synchronisation pulse for
> a dig input on the DCS.

Have a look at the Network Time Protocol (NTP) - the documentation mentions
related things (like the radio clocks etc).

It might even do what you want, if you can use a PC as the source of the signal for the DCS. You could use the ntp package to synch that PC either over the Internet, or using a radio clock or something.


You can definitely use ntp to synchronize all the PCs together.

Jiri
--
Jiri Baum <[email protected]>
http://www.csse.monash.edu.au/~jiribvisit the MAT LinuxPLC project at http://mat.sf.net
 
We use two redundant GPS based time servers to synchronize a network of 250+ DCS workstations and PCS's using Network Time Protocol (NTP). The system works flawlessly, sychronizing to within 1 millisecond. Many GPS time server products on the market are available, some with serial interfaces to your stratum server.
 
N
Have a look at http://www.datum.com they have units that are sync to GPS
satellites that will broadcast both NTP and SNTP packets on a network. We
use these to synch our PC's then the HMI running on the PC's synchs our PLC
networks. There not cheap (at least in Aus$)! But they are supplied with
everything you need. Search for tymeserve2100L.

Neil Firmin
Yallourn Energy Pty Ltd.
 
A
There are several servers that provide standard time on the Internet.
You could use one of these servers and periodically get the accurate
time and pass it on to the DCS system either as a contact using PC based
cards or by comm ports, ethernet etc..
Search for tardis (i believe that name has changed now but you will get
the link) on earch engines.

Anand
 
D

Dave Millett

Thanks for the suggestions. However, all the proposals rely on PC's and networking. This is a stand-alone DCS, and it is not clear yet whether a PC will be part of the system - apart from my laptop when I commission it!

At the same time I was investigating this, the DCS supplier had arranged with Galleon to set up their own automatically synchronised outstation, and I am expecting a Beta version shortly. This links directly to the RS232 port on the outstation, and I assume that the Galleon radio receiver sends a text message which sets the outstation's clock.

Thanks again for the comments.
 
Time Synchronization for DCS.
Please note that there are several issues that you need to verify with your vendor before embarking on Time Synchronization. reasons are

Time Synchronization could play havoc in a DCS. Suppose the time is 11:55:00:155 and my value of tag 1 is 200 and then I record it, and then the time is adjusted to below 11:55:00:155, then i could have multiple values for the same time.
Some systems may hang or fail due to this.

Time synchronization can be done by using a publicly available time synchronization
tool. There are several servers that provide a standard time or for a single complex use, you could use one station as the master time keeper and then using tools, synchronize the time at regular intervals.

Since you want GMT you may have to connect a master PC synchronizing time with the time masters available on the internet. A long time ago i used a tool called tardis. Please perform a internet search on tardis time synchronization
with GMT and you will come with several tools (name of tardis is now changed). Use one of this. Ensure that you implement proper firewalls and safeguard tools so that unauthorized access to your network from the internet is prevented.

For safety visit <a
class="moz-txt-link-abbreviated"
href="http://www.smbd.org">www.smbd.org</a> for more details.

Please note that your DCS vendor may be needed for this implementation.

Anand
 
Anand:
> Time Synchronization could play havoc in a DCS. Suppose the time is
> 11:55:00:155 and my value of tag 1 is 200 and then I record it, and then
> the time is adjusted to below 11:55:00:155, then i could have multiple
> values for the same time. Some systems may hang or fail due to this.

The better time synch programs can adjust by slewing - changing the clock frequency (slightly) rather than the time. That avoids this problem.

Usually slewing is the default if the difference is small; you might need to put in an option to force it to slew large differences.

For instance, ntpd on Linux will default to slewing if the difference is less than 128 milliseconds; the slew rate is 0.5ms per second, ie the clock frequency is adjusted by up to one part in two thousand. To force it to slew always, use the -x option to ntpd, but large differences will take a long time to fix up (about half an hour for each second of adjustment).

Jiri
--
Jiri Baum <[email protected]>
http://www.csse.monash.edu.au/~jiribvisit the MAT LinuxPLC project at http://mat.sf.net

 
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