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Old March 2nd, 2018, 01:25 AM   #1
Dudge1981
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Plc on off

Hi

Can anyone tell me what the on off point in plc is called ?

Cheers
Ryan
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Old March 2nd, 2018, 01:48 AM   #2
cardosocea
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Can you clarify what you are looking for?
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Old March 2nd, 2018, 01:52 AM   #3
Dudge1981
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Hi ..

It was a question thst my friend got in a test, it ask what are the on off points in a plc are called ? . He said digital.
Is there anything you can think of that they may be referring to .

Regards Ryan
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Old March 2nd, 2018, 01:58 AM   #4
cardosocea
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Your friend needs to look at a better school.

I would say Digital to be "correct"... but if your friend ever mentions on-off points professionally he will not be taken seriously.

By the way, what are analog points called in your colleague's school?
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Old March 2nd, 2018, 02:04 AM   #5
Dudge1981
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Thanks

It's a question on the new ECITB skills test ..

Thanks for the information, greatly appreciated.

Analog... would they be called inputs ?
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Old March 2nd, 2018, 05:39 AM   #6
KingPresident
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analog can be input or output. on off should be called IO.
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Old March 2nd, 2018, 05:51 AM   #7
rdrast
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I'd call it "The Power Switch"

...

Is this by chance a question from that, what was it called, HNC course in Europe?
Or its successor?
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Old March 2nd, 2018, 06:02 AM   #8
Geospark
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PLC 101 (< pun) - I'm not hearing the magic words?...

EDIT: KingPresident - I was trying to compose a post below to guide our friend towards the answer here, more so than just giving it to them. You've now mentioned the magic words that were missing. But, I feel, you are still not quite correct in your understanding of the general terminology used with respect to PLC "Points", or you have over simplified them (more later).

I'll continue and finish the post as was intended...

Ryan,

Welcome to the Forum!

Quote:
Originally Posted by Dudge1981
...Can anyone tell me what the on off point in plc is called ?...

...It was a question thst my friend got in a test, it ask what are the on off points in a plc are called ? . He said digital...
"Digital" would not quite be correct, in my opinion.

I won't give you the answer. I'll just attempt to guide you towards it. That way you, and your "friend", might learn to think about these things a bit more, rather than just having the answers given to you. That's how we best learn, is it not, after all?

The question is essentially asking this -

On / Off Points - What is another way of describing these "Points" for a PLC?

With respect to "Points" on a PLC, "On" and "Off" may describe the status that these type of "Points" may hold, but what is the best term to use for describing PLC "Points" in general?

Clue 1: For a PLC, "Digital" decribes the type of "Points" where the only status available is either "On" or "Off" - Example: a switch contact or an indicator lamp.

"Analog" describes the type of "Points" where the status available is not simply "On or "Off" but is a potentially dynamic value - Example: measuring or controlling temperature.

Clue 2: For all types of PLC "Points", how are the signals from the connected devices directed to and from the PLC "Points"? How do we best describe the sending and receiving of signals between the PLC and the connected devices?

While KingPresident has esentially given you this answer, it needs to go a step further...

Quote:
Originally Posted by KingPresident
...on off should be called IO.
KingPresident,

You are now missing a descriptive term before "IO". There are different types of "IO", as you have pointed out, but how do we best describe "IO" that may be either "On" or "Off"?

There are actually 2 common terms used to describe this type of "IO", and they both start with the same letter. Bonus point for getting both of them?

(No Gurus need apply, but of course may add their comments if they so wish).

EDIT: That was funny rdrast - it is a poorly worded question, if it has been relayed here correctly. So I do hope my interpretation of its meaning is at least in the ball park?

Regards,
George
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Last edited by Geospark; March 2nd, 2018 at 06:24 AM.
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Old March 2nd, 2018, 09:30 AM   #9
boneless
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Could it be BITS?
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Old March 2nd, 2018, 09:54 AM   #10
Tom Jenkins
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Quote:
Originally Posted by rdrast View Post
I'd call it "The Power Switch"

...

Is this by chance a question from that, what was it called, HNC course in Europe?
Or its successor?
+1

Actually, because of the wide use of "digital" communications and other uses of the word "digital" I think the current preferred term is "discrete" I/O.
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Old March 2nd, 2018, 10:04 AM   #11
cardosocea
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Quote:
Originally Posted by KingPresident View Post
analog can be input or output. on off should be called IO.
IO = Input Ouput... so it may be "On Off" or analog values which I suppose are called numbers in the exam in question.

@TomJenkins,

Good point... nowadays most IO will be digital at one point as fieldbuses gain popularity.
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Old March 5th, 2018, 06:58 AM   #12
PLCnovice61
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doesn't take much to get him started.
whats the bet that the person who devised the plc never ever said on/off point.
But of course as l sit here with a port l will be corrected.
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Old March 5th, 2018, 01:54 PM   #13
janner_10
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Quote:
Originally Posted by PLCnovice61 View Post
whats the bet that the person who devised the plc never ever said on/off point.
.
Apparently he did, I found this.


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Old March 5th, 2018, 04:44 PM   #14
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TRUE / FALSE
HIGH / LOW
ON / OFF
ENERGISED / DE-ENERGISED
ACTIVE / INACTIVE


Steve
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Old March 5th, 2018, 05:39 PM   #15
Geospark
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You are too modest...

Quote:
Originally Posted by Geospark
...how do we best describe "IO" that may be either "On" or "Off"?...

...(No Gurus need apply, but of course may add their comments if they so wish).
Quote:
Originally Posted by Tom Jenkins
...Actually, because of the wide use of "digital" communications and other uses of the word "digital" I think the current preferred term is "discrete" I/O.
Tom,

Perhaps you don't look at yourself this way, but to me you are undoubtedly a member of the Guru brigade here on the Forum, and I'm sure in your profession, held in high esteem. Alas, it was my hope that the OP, and perhaps other novices, might try to guess the answers here, in the interest of them learning, while the rest of us refrained from stating what is most likely quite obvious to us. But of course, you are perfectly entitled to reply how you see fit.

I've now failed in my endeavours here twice, so I'll not try again. It's not anyone's fault. It's just the nature of the Forum here and how it tends to flow, often beyond any one member's control.

Quote:
Originally Posted by Geospark
...There are actually 2 common terms used to describe this type of "IO"
Here, I was just stating that those 2 terms are "commonly" used to describe "On / Off" type PLC I/O. They are both widely used, in my experience. For me, either would be acceptable as an answer here. I was not stating which one may be preferred over the other, as you have suggested. Just that they are both often used. It is still common to hear both used in day to day business. You may be correct in that there has been a slight shift in preference, but the Digital World is not a relatively new concept with respect to PLC digital I/O; so much so that it should confuse or force it off its "perch". That is just my opinion. I do know how manufacturers tend to latch on to buzzwords in order to better market their products.

Personally, it would not confuse me to hear digital I/O mentioned with respect to a PLC/PAC in the ever increasingly crowded digital spectrum. It should be somewhat self explanatory for a moderate to experienced PLC user. I could suggest that if a relatively experienced user needs digital I/O referred to as discrete I/O, so as to better understand what is meant, then they really have missed or require further training on basic PLC concepts.

Technically, I believe that "On / Off" type PLC I/O should only be referred to as digital I/O and not discrete I/O. Why might I believe that?

That question is open to the Forum in the interest of discussion and further perspective on the topic. We often don't stop to think about or try to understand why something is so.

Quote:
Originally Posted by boneless
Could it be BITS?
Bits would be more used to refer to the internal bit addressing in the program for digital I/O i.e. software, as opposed to the external physical I/O points i.e. hardware.

Quote:
Originally Posted by nehpets
TRUE / FALSE
HIGH / LOW
ON / OFF
ENERGISED / DE-ENERGISED
ACTIVE / INACTIVE
There is another very common, if not the most common, opposing term to describe PLC digital I/O status. (I alluded to it in my "pun" earlier).

Just another curve ball here...

Another possible meaning to the somewhat vague question of "...what the on off point in plc is called ?" is that they are referring to the switching threshold of the Off-to-On and On-to-Off states for PLC digital inputs. That is, the minimum voltage the input signal must supply to guarantee the input is in the On-state and the maximum voltage the input signal must be below to guarantee the input is in the Off-state. But that would probably be a slightly more elevated type question to include in a basic technical apptitude test, such as the ECITB.

Regards,
George
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