Warning siren timers

[Dale87]

Does anyone know of a timer that keeps accurate enough time to close a set of contacts for 30 seconds on the first Tuesday of the month for two warning sirens in a small town? They both need to close at exactly noon and open 30 seconds later. I don't think any PLC will keep that kind of accuracy, need to see what Intermatic offers also. These will be outside so they will be exposed to changing temps.

 

[Ken Roach]

You would really think that Intermatic would build an option for a radio-controlled or GPS-input clock, wouldn't you ? But as far as I can tell even the ET2000 series that have enough events for 7-day/365 scheduling that could allow you to manually enter every Tuesday for a year will only be as accurate as your fingertip when setting the current time.

Another Forum member found a neat Modbus-equipped GPS unit that would let a nano PLC read the current time accurately, into which you could then program a calendar and a 30-second output.

 

[James Mcquade]

Before you do that, you need to think of this situation.
we did the same thing where i used to live, but on one of those days, there were tornado alerts. the sirens went off, everyone took shelter, but it was the regular storm warning test, no actual tornado. the all clear siren never went off. what a big confusion.
now, the sirens go off at noon on Saturday, UNLESS there is a severe storm alert of any kind. then they will go off on Wednesday at noon if it is a clear day.
james

 

[cardosocea]

Before you do that, you need to think of this situation.
we did the same thing where i used to live, but on one of those days, there were tornado alerts. the sirens went off, everyone took shelter, but it was the regular storm warning test, no actual tornado. the all clear siren never went off. what a big confusion.
now, the sirens go off at noon on Saturday, UNLESS there is a severe storm alert of any kind. then they will go off on Wednesday at noon if it is a clear day.
james

I've seen similar on a chemical site that tested the alarm horn at 11 every monday... On a particular monday, a real fire broke out at 10:58 (what are the odds, right??) and no one did anything because it was a test of the fire alarm.

That site installed a PA system (not feasible in a city or village) and the alarm test was at random preceded and followed by an announcement and called it a day. I then had to point out to the head of safety that without actual practice of alarm procedures this was still somewhat pointless as people should have noticed that the test was lasting far too long.


As for the question at hand, I think a GPS receiver is required. I use TimeNet Pro (600£ in my neck of the woods) and if you go with a PLC that has the ability to synchronize time (I know the Siemens ones do), you could have it done in a nice way.

Whether there's a time clock that is programmable to do what you want I don't know, but this would be my first instinct to create this solution.

 

[Puddle]

if you go with a PLC that has the ability to synchronize time (I know the Siemens ones do), you could have it done in a nice way.

Seems like a huge overkill for 2 or 3 lines of ladder, but a 1211 is less than £200 and can sync time to an NTP server. The 4G module is very expensive though if network access isn't available so would probably end up being a third party router.

 

[cardosocea]

Seems like a huge overkill for 2 or 3 lines of ladder, but a 1211 is less than £200 and can sync time to an NTP server. The 4G module is very expensive though if network access isn't available so would probably end up being a third party router.

To be honest, it really is and would easily be done with something like an Arduino with a GPS (or 4G) receiver and a relay module.

The idea of synchronizing to GPS is purely from a cyber security aspect as well as ongoing cost if you went with a 5G modem or something similar.

 

[BryanG]

Found this:
https://eshop.elkoep.com/documents/sht-6g/share_dokumentace/en/manual_sht-6g.pdf

Siemens used to have one, but I don't know if it has been replaced:
https://www.electricautomationnetwo...itch-expert-digital-230v-16a-1channel-2mw-gps

You might have to add a 30 second timer because the minimum output seems to be 1 minute.

 

[JordanCClark]

Came across these.

http://www.gpslightlock.com/index.html