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mmohamed15
Junior
Joined: 13 Feb 2012
Posts: 18
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 Posted: 20/05/2016 12:31 Post subject: Galvanic isolation |
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Hello friends
recently i had made a contract for my company to provide an upgrade for our automation system
for the automation panels i asked that every digital i\o should be organically isolated
so i described the system with two power supplies one for the field and the other for the panel that contains the PLC cards and the interface between the field signals and the PLC cards is done through opto-couplers (As same as the concept of the Dry contact)
[url=http://www.99poze.ro/p/83d94e7ac31bcf5aeaa4c59aa19952dd.jpg] [/url]+
i had received a lot of negative comments and bad mouthing about what i did some people called it total stupidity and not necessary and a lose of money
also some people said that i put extra components and this means that i added an extra source of troubles
what do you think am i wrong or what
best regards |
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tortuga
Junior
Joined: 21 May 2016
Posts: 11
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| Posted: 21/05/2016 13:40 Post subject: Re: Galvanic isolation |
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| mmohamed15 wrote: | Hello friends
recently i had made a contract for my company to provide an upgrade for our automation system
for the automation panels i asked that every digital i\o should be organically isolated
so i described the system with two power supplies one for the field and the other for the panel that contains the PLC cards and the interface between the field signals and the PLC cards is done through opto-couplers (As same as the concept of the Dry contact)
[url=http://www.99poze.ro/p/83d94e7ac31bcf5aeaa4c59aa19952dd.jpg][/url]+
i had received a lot of negative comments and bad mouthing about what i did some people called it total stupidity and not necessary and a lose of money
also some people said that i put extra components and this means that i added an extra source of troubles
what do you think am i wrong or what
best regards |
I saw this and I want to to help you
Your requirement is of good sense but probably your contractor do not know how to cope with.
It happened few days ago on an old installation a cable with 220VAC enter in atingere with an +24VDC cable for Input and destroy the entire Input Module of about 300 dollars
Look how to proceed. Normally you have to isolate all digital I/O contacts.
1. As rule the PLC have to have it's own Source and eventually with battery Backup if necessary.
2. Even if use Digital Inputs which are galvanically isolated you better can use miniature relays on all Inputs/Outputs. On Inputs all the Digital sensors and miniature relays are supplied from a different source.
3. For Outputs use also miniature relays which contacts are supplied from the same source of Inputs or a different source.
So what you need supplementary are the miniature relays (which are very cheap) for every Input/Output and a Source for supply the external digital circuitry for Inputs/Outputs .
Even if at first sight seems to have a little bit to spend some money you have sure your PLC is safe .
This is the normal procedure for a professional design.
Siemens uses a so called Marshaling Cable components which include these relays.
We use Schrack relays mounted directly on rail which is a little bigger than a normal connector.
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mmohamed15
Junior
Joined: 13 Feb 2012
Posts: 18
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| Posted: 09/07/2016 22:55 Post subject: |
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| ٍso you think that i did this job correctly |
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mentor
Junior
Joined: 10 Jul 2016
Posts: 2
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| Posted: 10/07/2016 10:20 Post subject: |
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| mmohamed15 wrote: | | ٍso you think that i did this job correctly |
If the industrial site you intend to use is having a potential risk (heavy industries, oil&gas, etc. ) then it is advisable to follow the above solution.
If the site have not potential risks you can use only the isolation for modules (galvanically isolated).
So everything depend on the medium you are about to install.
Normally if at least one sensor has 220VAC cables intersecting with +24VDC cables the solution is to use above solution. |
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