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from the Automation List department...
Wire Numbering
PLCs and related questions. topic
Posted by Anonymous on 12 February, 2004 - 11:49 pm
I have been using I/O numbers for wire numbers mostely using SLC 500 platform. What is the trend for wire numbering schemes using ControlLogix platform where no addressing is required?


Posted by marc sinclair on 13 February, 2004 - 11:06 pm
You need a system, there are several established ones to choose from. the system I use has two rules, wires with the same number are connected and the wire number is derived from the page number and index of the first drawing it appears on. so for example wire 3-10 first appears on page 3 above index 10 (a line numbered 0-100 across the bottom of the drawing) It works very well and is easy to follow when building or fault finding. I have tried other systems that are software generate, but they are not intuitive, they simply generate the next available number. I did see one very interesting system used in heinz factories, in which all terminals are given a number and the far end of the cable connected to it is also given this number, they explained that with this system a technician could fault find a panel without drawings ! if you want to see how the system i use works in practise, there is an example at www.germainesystems.co.uk/drawings.pdf

Marc Sinclair
http://www.germainesystems.co.uk


Posted by Bouchard, James \[CPCCA\] on 17 February, 2004 - 10:02 pm
There are many numbering schemes. The main disadvantage of the one you mention is that if you want to change the drawing like adding pages, reorganizing or adding lines you have to change the wire numbers. If you have an installation that is never going to change OK. If you have an installation that changes a regularly, then this approach is problematic.

Another scheme it to assign wire numbers sequentially with no consideration for where the appear on the drawing, what I/O they are connected to etc. This avoids all the problems with changes but does require you keep a master
list of what wire numbers have been used ( and if you are smart where they were used ), Many electrical schematic drafting programs will do this automatically for you.

A third scheme is to use the PLC I/O address for the wire number. This of course only works for devices connected to the PLC. You need another system for the wiring that is not connected to the PLC. It also has the problem of what address to use for processors that no longer use a physical address such as Control Logix or IEC 11631 compliant ones. One problem with using the PLC address is that when you have to reorganize the PLC rack or move a
module, then you have to change all the wire numbers. That may cost you very much more than the other parts of the work. Again if things never change it is OK but at least in my world things are always changing.

Good luck with your choice.

James Bouchard


Posted by Bruce Durdle on 19 February, 2004 - 3:42 pm
The most useful wire numbering scheme I have used is based on the equipment tag number. So the positive to a transmitter or switch is FT123/1; the return FT123/2, etc. With a bit of care it is possible to have the postfix indicate the part in the instrument loop.

And at 3 am a technician sent to check loop TT124 had better not touch a wire labelled as FT123!

Bruce


Posted by marc sinclair on 19 February, 2004 - 5:56 pm
Not so, this system works from small machines to factory wide installation, if you need to add a page then it has a new number and hence new wire numbers, no need to change existing ones. (For example to add a new motor and inverter to a 23 page drawing, simply add page 24 using wire numbers 24-10, 24-15 etc. Adding a new IO block to the PLC is the same, add a new page) Likewise adding wires is as simple as re-issuing the affected page and adding the wire with an unused index. If your installation is changing regularly then it is again just a matter of re-issuing the relevant pages.

This is not to say that that this system is perfect, Terminals with the same number as the cable leads to extra, unmarked links on the rail, also on large drawings, a hundred wires can be tight, (although it is possible to move to a thousand index. :-0)

What I like about the system is the fact that it forces the drawings to be completed before wire hits panel, some machines i see in the field make me weep.

> if you want to see how the system i use works in practise, there is an example at http://www.germainesystems.co.uk/drawings.pdf

--
Marc Sinclair
http://www.germainesystems.co.uk


Posted by Michael Griffin on 21 February, 2004 - 3:13 pm
I have seen examples where people have added new pages to the back of the drawing set, and this is a terrrible solution. New pages should be inserted where they make sense in the context of the the overall drawing package. Simply adding the drawings to the back when they would logically belong nearer the front makes it likely that they will be overlooked by someone who is unfamiliar with the machine.

The only advantage of adding them to the back is that it makes less work for the person drawing the revisions. I don't think that is a good reason for making such a decision. It would (to use your example) probably be better to add a page 23A after page 23, and simply continue the numbers from the previous page (i.e. as if you were making the existing page longer).

Another scenario you haven't mentioned is where a modification to the machine requires completely re-drawing an existing page with re-arranged or new components. I such situations I would not renumber wires just because they were moved about the page.

The main thing the page+line numbering system has going for it is to make it easy to assign wire numbers on new designs. The clarity of the drawings however should not be sacrificed on subsequent revisions to preserve the purity of the "numbering system".


On February 19, 2004 17:54, marc sinclair wrote: <clip>
> if you need to add a page then it has a new number and
> hence new wire numbers, no need to change existing ones. (For example to
> add a new motor and inverter to a 23 page drawing, simply add page 24
> using wire numbers 24-10, 24-15 etc. Adding a new IO block to the PLC is
> the same, add a new page) Likewise adding wires is as simple as
> re-issuing the affected page and adding the wire with an unused index.
> If your installation is changing regularly then it is again just a
> matter of re-issuing the relevant pages.
<clip>

--

************************
Michael Griffin
London, Ont. Canada
************************


Posted by Matthew Hyatt on 14 February, 2004 - 12:06 am
It does not matter which platform or plc your using, as long as your wiring number makes sense and is documented on the drawings (is accurate) and is consistent, then do wha tever you were doing before.

I tend to use the following method:

these should be very obvious as to what they are.

AI001+
AI001-
(analog input)

AO001+
AO001-
(analog output)

DI001
(Digital Input)

DO001
(Digital Output)

ACI001
(AC input)

ACO001
(AC output)

K1 or R1
(Relay on a PLC or a stand alone relay)
K1-14
(pin 14 on relay 1)

RTN
(Digital input / output return or common)

+24vdc

H
(primary AC pwr input, to a pwr supply of plc)

H1
(switched pwr - usually after a CB or fuse or HOA switch)

N
(neutral)

GND
(ground - protective ground or earth ground)

MJH


Posted by Steve Myres on 16 February, 2004 - 8:31 am
I/O still has an address. For digital I/O in the local rack, the address is in the form: Local:slot:[I or O].Data.bit [grammatical period omitted] You could use the form Issbb or Ossbb where ss is slot number and bb is bit number. Analog addresses are in the form Local:slot:[I or O].Ch"n"Data (from Ch0Data to ChmaxData).


Posted by Bob Peterson on 16 February, 2004 - 8:46 am
The important thing is to document it and be consistant and make sure you have a system that does not allow duplicate wire numbers. I once did a job where they ended up with duplicate wire numbers because to shorten the wire numbers they omitted the leading zero in the node number and slot number, so you you could not tell for sure if it was nnspp or nsspp.

Bob Peterson

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