Emergency Shutdown procedure with MIAC

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go233
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Emergency Shutdown procedure with MIAC

Postby go233 » Wed Aug 24, 2016 2:08 pm

Hello,
I would like to ask your opinion on what is the best way to handle a critical alarm with the MIAC and flowcode 6.

In a nutshell I have an Atmosphere Oxygen Depletion sensor/box and I must execute an emergency shutdown procedure
of the Argon gas switching system when this box raises an alarm.

So, in essence MIAC is doing is "normal controlling daily routine" (as usual) and suddenly the above box sends an alarm to the MIAC!
I need to act quickly and at ANY point of the program.......

Any suggestions?
Thanks
Giovanni

(it is difficult man arg!!! :?)

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medelec35
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Re: Emergency Shutdown procedure with MIAC

Postby medelec35 » Wed Aug 24, 2016 2:44 pm

Best way it to use the INT2 interrupt:
Miac INT2.png
Miac INT2.png (73.17 KiB) Viewed 4650 times

When voltage on I8 goes from low to high ( above 8V, assuming rising edge within interrupt properties is selected )the INT2 interrupt should fire and INT2 macro will be instantly serviced.
I can't test to see if works until this evening.

Martin
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Re: Emergency Shutdown procedure with MIAC

Postby EtsDriver » Wed Aug 24, 2016 2:46 pm

EtsDriver wrote:You should use interrupt to catch change on input that gives out the ALARM as medelec stated... But generally, i dont like software based EMG stops anywhere, havent seen anything that has made good impression on electronics manufacturing industry or automation systems.

Because were here talking about oxygen depletion, i make conclusion that this might be life threathening situation, and your system should behave in all possible scenarios in same way. Make sure your system handles correctly if MIAC goes offline... You could wire it so miac loses power when alarm goes off and your system behaves accordingly? So its "Failsafe".

As far as i know, someone might have more correct information about this:

MIAC is not rated for safety applications (Meets only IEC60950-1), so use correct safety relay for your application if you cant be sure that system goes to lower risk state when miac "blows up, gets jammed etc".

Here is something for a good read:
http://literature.rockwellautomation.co ... _-en-p.pdf

Using a safety relay, you can get miac to notice that there is alarm gone off, and your system behaves correctly no matter what miac is doing/not doing.


******

OH, sorry, did thought i readed emergency stop there, but emergency shutdown is completly different thing :lol:
Ill just keep the good work up!

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Re: Emergency Shutdown procedure with MIAC

Postby go233 » Thu Aug 25, 2016 11:12 am

nonononono you are correct!!!!! it is an life threatening scenario, because the room where the system is very small and the system is connected to a massive central tank of Argon which can potentially fill the all department.

However, I have my bottom covered by other safety systems: there is an o2 sensor in the room (and adjacent rooms) monitored by the University security 24h centre, plus I have sealed the whole gas switching system in an air tide big box made in Plexiglas (it is like an aquarium) AND I have connected this acquarium to an exhaust which (in theory) is constantly sucking up the Argon (in case of leak) to a chimney located on the roof liberating the Argon in the atmosphere .

BUT it is university!!!!! and anything can happen here....the sucking system could stop, the O2 sensor alarm is not picked up quickly enough by security, the power can go off and...ufff!!!! I am a bit of a pessimist here ...in fact the earth could be hit by a meteor today at lunch time!
:roll:

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Re: Emergency Shutdown procedure with MIAC

Postby go233 » Thu Aug 25, 2016 11:17 am

ah sorry I forgot to add that I have connected the MIAC to a bank of batteries always under charge!!!
Giovanni

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Re: Emergency Shutdown procedure with MIAC

Postby go233 » Thu Aug 25, 2016 12:19 pm

Hi Martin,
yes it works! a raising edge on I8, execute immediately my macro!
:D

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Re: Emergency Shutdown procedure with MIAC

Postby medelec35 » Thu Aug 25, 2016 12:39 pm

Hi Giovanni,
Glad it works.
Thanks for letting me know. :)
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Re: Emergency Shutdown procedure with MIAC

Postby go233 » Thu Aug 25, 2016 12:56 pm

Hi Martin,
how can you activate an interrupt if a variable associate with an ADC reading goes above a certain threshold?
Giovanni

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Re: Emergency Shutdown procedure with MIAC

Postby LeighM » Thu Aug 25, 2016 2:04 pm

Hi Giovanni,
You probably need to be thinking about designing your program as “state machines”.
That is, have a main loop that calls separate routines/macros where the processing time for each one is kept to a minimum. Don’t “wait for something to happen” in any of them. Each process can keep a state for that process, read inputs and change state and outputs accordingly.
Hope that helps,
Leigh
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