Control system wiring numbering schema

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Thread Starter

Victor Zaltsman

We are trying to establish a standard for Plant Control(PLC) system wiring numbering. Two methods have been proposed and we have a problem to pick up a right one.
Method 1: Start a numbering at PLC TB (our PLC TB are numbered according to RACK:SLOT:SIGNAL pattern, so a terminal, belonging to RACK 1, Slot 5 Signal 14 would be numbered as 1514) and keep the number unchanged all the way via various junction boxes up to the field instrument terminals.
Method 2: Start a numbering at PLC TB and change the wire's number (according to terminal's number) each time the wire entering/exiting a terminal up to the field instrument terminal. This way both ends of the same wire will have different numbers.
What method would you recommend ? (one of above or any other "good practice").
Thank you,
Victor Zaltsman
 
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Thomas Swift

ISA Standards and Practices for Instrumentation. ISBN 1-55617-051-3

These standards cover control systems documentation from device to electrical elementary drawings. Your tags (numbers) should be consistent throughout the project.
 
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D W Heinecke

Victor, I would think that the first method would be more appropriate, I have in the past designed, built and supported systems in both formats. I know when it comes to trouble shooting systems I want to know that I have the same wire at each test point and usualy I would also put an Identifier Letter for type of signal I= input O= output this is important if you are using isolated source power for each area of your circuit. In systems with remote racks or networks then a drop identifier is added as well as a prefix as you listed. these schemes can make your wire numbering a bit of a pain for your assemblers but when it comes to analysing a fault it pays for itself in downtime reduction. The second method I find that it is often used in the "electronic" type circuits where your prints are in a point to point wiring scheme, Good Luck
 
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Brian Kukulski

We have adopted the following:

Panel Wiring side of PLC panel T/Bs. - Use the acutal PLC I/O address as a wire label. When troubleshooting from the PLC outward, you know the address and this makes the field wire and T/B is easy to find. Good for finding blown fuses fast. The addresses being sequential mean you terminal blocks are sequential. I tried using the Rack/Slot approach - good but but now I need a cross reference to the PLC I/O address - addresses and slot location are not necessarily the same . This works if the I/O cards are wired
sequentially out to terminal blocks and also quickens loop sheet drawing design. You can now have the panel built before you assign I/O to process instruments.

Field wiring side of PLC panel T/Bs - Use the Instrument tag (say LSHH123 ) and keep that tag until you touch the next device. Then change the tag to LSHH123-1 , -2, -3 etc. until you get back to the PLC. Now when you get back to the PLC you have a set of terminal blocks with the Instrument tag and a suffix on 1 side and the I/O address on the other side. This makes finding the PLC I/O point easy for ladder troubleshooting.

It will be interesting to hear other good ideas.
 
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Troy Stearns

> We are trying to establish a standard for Plant Control(PLC) system wiring
> numbering. Two methods have been proposed and we have a problem to pick up
> a right one.
>
> Method 1: Start a numbering at PLC TB (our PLC TB are numbered according
> to RACK:SLOT:SIGNAL pattern, so a terminal, belonging to RACK 1, Slot 5
> Signal 14 would be numbered as 1514) and keep the number unchanged all the
> way via various junction boxes up to the field instrument terminals.
>

I am not a fan of the method you describe above, but I have encountered many who use it. If you use this method, make sure that leading zeroes are
strategically placed. Your example of wire # 1514 could also mean RACK 15, SLOT 1, SIGNAL 4. If leading zeroes are used these wire numbers would be 010514 and 150104 respectively.

> Method 2: Start a numbering at PLC TB and change the wire's number
> (according to terminal's number) each time the wire entering/exiting a
> terminal up to the field instrument terminal. This way both ends of the
> same wire will have different numbers.

Having the same wire with different numbers depending upon where it is connected, each time, would be a nightmare. If you have any daisy-chaining of wires you could have several different numbers for the same electrical signal. I would not want to have to debug anything labelled in this fashion. YUK!!!


Troy Stearns
 
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I have always taken as invarient the idea that a terminal does not change a wire number. Method 1.

Speaking of which... I am currently working on a project with a German company and they do not use wire numbers at all. Connector numbers, harness
and cable numbers, terminal numbers, and wire colors and pin numbers... but no wire numbers. I am told by my vendor this is typical for Europe and IEC schematics. It's different, to say the least.

Paul T
 
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Bouchard, James [CPCCA]

I would not recommend using the PLC address as part of the wire number. Four major reasons:
1) if you change the addressing of the I/O point you have to change all the wire numbers
2) If you have more than one PLC you will have
duplicate numbers
3) you will need a different numbering scheme for wiring that does not go to the PLC
4) Using the PLC address does not allow you to
have devices in series connected to the PLC without going to suffixes etc.

We use a sequential numbering system which requires you keep a list of numbers used and where they are used.

For more discussion see Chapter 9 in "Fundamentals of Industrial Control " by Charles Albert and Don Coggan published by ISA

James Bouchard
 
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R A Peterson

I would beg to differ. Using the PLC I/O address dramatically simplifies troubleshooting in the field, and makes it much easier to find wires on
drawings, and improves your ability to go directly to the PLC I/O point.

Most systems using PLCs do not have a lot of wires connecting between different PLCs so duplicate numbers is rarely a problem. The few wire numbers that interconnect between such systems can be handled separately if needed. In the few cases where I have added interconnections, generally I have appended a prefix to the wire number to indicate what PLC the wire comes from. For example: 01:I001300 is I:13/0 in PLC #1, and 02:I001300 is I:13/0
in PLC #2. I usually use the PLCs highway address for the prefix. In a few cases I have just used A, B, C, ... for the prefix.

Keeping track of a long list of random-like wire numbers is a much more daunting task.

Changing the I/O address is a problem, but is not that big of a deal in most cases. Most of the time when you change I/O addresses, its because you have changed PLCs. You can either renumber the wires to the new I/O address when you do so, or just live with it (not any worse then the more or less random number you advocate for the wires), as long as the drawings are accurate.
Changing the wire numbers is not all that daunting a task. You can print up new ones and install them fairly quickly (maybe a couple hundred an hour if you use self laminating wire labels). In a few days they can all be
converted to the new numbers.
 
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Bruce Durdle

The most user-friendly system (for maintenance and troubleshooting) I have used is based on the tag number - after all, in most cases, this is the
common reference for operators, maintenance, engineers.

If a tech is looking to fault-find on LSH421, and sees a wire labelled LH421-1, it's probably the right one. If the number is 02-I12:24, who knows?

And then there are the grid-based systems - OK if you have the drawings.

If possible, base numbers on tags.

Bruce.
 
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Similar to this, I have seen where the wire number at the PLC terminal is the Device Tag Number that the wire goes to. So LS-123 would be the wire number at the discrete PLC input. At the other end of the wire, at Device LS-123, the wire number would be the PLC address that the wire goes to, Perhaps I:010/00. Thus, a maintenance person can walk up to any device
without schematics, and know exactly where the wire goes to, or at the PLC know exactly what device is connected to that input. You have a different wire number at each end of the same wire, but it identifies where the wire goes.

FWIW

Bruce Axtell
 
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Hi all,
I just though I would add my 2-bits worth on this topic. PLCs change, using PLC address on cables going to the field could be a big mistake.

regards,
Richard King
 
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Roderick K. Duet

We use the I/O type input or output followed by address.
Ex:: I:1.1/04
This scheme is used from the PLC to the field device.
The input and output devices or then labeled as type of device and address.
Ex: AV-1.1/04
AV = Air Valve
SV= Solenoid Valve, Etc.
Analog is done in the same scheme
Ex: I:4.0
LT-4.0
LT = Level Transmitter

From the time we implemented this wiring scheme the familiarization of a system and devices seams to be easier followed by plant engineering
staff. The wire labels can get wide depending on the system but thats what high cpi on the printer helps. I use as high as 17 and or still very
legible. Labeling the device with the address extension also helps in labeling panel components. Ex: MS-1.1/04 or CP-1.1/04 or PDP-1.1/04
Well you get the idea.
 
Our plant prefers 'destination-based' labels. We use the Rack/Slot/Point label inside the PLC cabinet so from the IO card to the intermediate
terminal the wires are labeled like: DI010215 for a digital input, rack 01, slot 02, point 15. Then from the intermediate terminal out to the field the wires are labeled with their destination. An example might be:

Wire from PLC IO card to terminal in PLC cabinet:
IO Card Terminal Strip
-------- --------------
DI010215 <-----> DI010215

Wire from terminal in PLC cabinet to field junction box:
PLC Cabinet Field JB
----------- -------------
JB00201-19 <-----> CAB00205-1-25

Wire from field junction box to device:
Field JB Device
-------- ----------
LSH-0001 <-----> JB00201-19

That is a worst case example. Usually, there isn't a field junction box, so the intermediate terminal in the PLC cabinet shows the PLC IO point as the internal label and the device tag as the outgoing label. This makes trouble shooting a total breeze for our techs.

Mike Ryan
Aerojet Fine Chemicals
 
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Blanco, Felix

We use a combination of the tagging procedures posted to the list. We have a ITB (Intermediate terminal Block) which uses Rack/Slot/Group/Channel (R/S/G/C) numbers (octal). For instance 0/1/0/1 means Rack #0, slot #1, group #0, channel #1. This ITB is in between PLC I/O and FTB (Field Terminal Block). The FTB uses the P&ID tag numbering, say LSH421. With this schema, both Operator and Instrument people can troubleshooting an instrument easy, from the field to PLC memory data table.

Felix Blanco
Venezuela
 
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Bouchard, James [CPCCA]

We have machines with several different PLC's on them along with servo drives and lots of other equipment so the multiplication of addresses is a
concern. Since only about one half of the wiring is associated with the PLC I/O you still have to maintain the wire list.

Recently we had to relocate two cards in a PLC rack to make room for a module that had to be installed in a particular place. Changing the wire
numbers on those two modules took a technician 4 shifts so it is not negligible. We have also in the past combined two PLC's and had to change two racks of addresses.

When you consider that PLC's that use device net do not assign I/O addresses but only internal registers the argument for using the I/O as the wire number is less useful.

When you consider that newer PLC's and the IEC 1131 standard uses aliases instead of hardware addresses the reason to use the I/O address is even less valid.

What I prefer to do is to use the device number of the field device as the tag or unique identifier in PLC programming software. This allows you to simply search on the device number and you will get the part of the program you want. Since we put a device number tag on each field device the tracking is easy to follow.

James Bouchard
 
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> We have machines with several different PLC's on them along with servo
> drives and lots of other equipment so the multiplication of addresses is a
> concern. Since only about one half of the wiring is associated with the PLC
> I/O you still have to maintain the wire list.

Maintaining the wire list in this case would be relatively easy if you made the wire number keyed to the drawing page number and index for wires not
connected to a PLC I/O point. This is by far the most common way of assigning wire numbers for PLC based control systems.

> Recently we had to relocate two cards in a PLC rack to make room for a
> module that had to be installed in a particular place. Changing the wire
> numbers on those two modules took a technician 4 shifts so it is not
> negligible. We have also in the past combined two PLC's and had to change
> two racks of addresses.

Four shifts to change the wire numbers on just 2 cards? Even if they were 16 point cards, and there were three wires on each point that had to have new wire numbers, thats less then 100 new wire numbers. 32 hours seems really excessive unless you were using something other then self-laminating wire labels. Thats 20 minutes per wire number. I would expect more like a minute
per.

> When you consider that PLC's that use device net do not assign I/O
addresses
> but only internal registers the argument for using the I/O as the wire
> number is less useful.

But device net is a very small part of installed systems. I would grant that some thinking may need to be done when/iff you use device net or other similar busses that do not have traditional I/O addresses. But for MOST PLC based control systems, this is not an issue.

> When you consider that newer PLC's and the IEC 1131 standard uses aliases
> instead of hardware addresses the reason to use the I/O address is even
less
> valid.
>
> What I prefer to do is to use the device number of the field device as the
> tag or unique identifier in PLC programming software. This allows you to
> simply search on the device number and you will get the part of the program
> you want. Since we put a device number tag on each field device the
tracking
> is easy to follow.

This does make some sense when you have tag numbers for all the field devices (such as in a chemical plant). Most of the time PLC based controls make the device tag number a function
 
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Scot Sutherland

The system I typically use is based upon Chrysler's controls design standards.
The wire number is based on the line number.
For instance, on line #324 the wire number would be 324.
If there is more than one wire on line 324 (if there are a series of relay contacts, for instance) then the subsequent wire numbers would be 3241, 3242, 3243...
Additionally, the devices are numbered per the line number they are drawn on.
A push button drawn on line #512 would be named 512PB.
This method accomplishes a couple of things:
1) Choosing wire numbers is easier. There is no "Did I use wire number 53 already?"
2) Finding the sheet number where the wire is referenced is easier.

Scot Sutherland
Software Engineer
Spire Corporation
1 Patriots Park
Bedford, MA 01730
(781)275-6000
[email protected]
 
P
Very well put. We are also grappling with the "wire number" question, and I am not pushing for controller I/O numbers on the wires for the same reasons James mentions. I have in the past been successful with wire numbers that are derived from line numbers on the schematics rather than I/O numbers or the device numbers themselves. The wire numbers on each side are the same when the wire passes through terminal blocks. There are some wire numbers that for convenience are not schematic line numbers- those related to phase conductor feeder and branch circuits, or the neutral conductor, or to a DC
+ and the corresponding DC common for example- but using line numbers from the schematics does a few things.

First, you can assign line number ranges to particular types of I/O. For example, we're presently using 2000 - 2499 for DI. When I grab the wire in the field, I know what it is and since the line numbers are unique, I can also find it in the prints quickly. If I have more than 500 DI on the machine (not often) there are some "overflow numbers" in the scheme that are used if a range runs out.

Second, I can have multiple people working on the drawings at the same time. Since the wire numbers are not assigned by the software and they are not sequential, I can work on DI loops, you can work on DO loops, somebody else has AI/AO, etc. Nothing is stepped on by someone else.

Third, as I design the machine my numbering stays consistent. If I start out with 40 air solenoids and leave 48 outputs to drive them, then solenoid
41, added during debug, falls after the existing solenoid 40 and the wire numbers follow as well. If all wires were numbered sequentially as they
were drawn in, then any grouping you might try to do is lost. Quickly. &lt;g> Trying to leave unused numbers in a sequential scheme is possible but hard to manage.

Fourth, as I physically make and apply wire lables, I have at most 5 characters- the number and then A, B, C, etc. if the wire runs through
multiple devices. If the wire runs through a device the number changes (2000A, 2000B, 2000C, etc); if it runs through a terminal block it does
not. Which way you want to work the A, B, C- from the final element or from the controller- is up to you &lt;g>.

Is it perfect? Nope. I've used most of the schemes put forth in the last few days and they have all worked. I do think that as we move to
controllers without fixed I/O addresses as in the past, that some sort of wire numbering that does not depend on the controller I/O address is
important. Also, I freely admit that your mileage may vary; I've used the above approach on OEM process equipment and machines that are typically run by a single PLC, with less than 500 points and 100 analog channels. For large systems, spread over several thousand square feet, something else may be more appropriate.

Paul T
 
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Michael Griffin

At 11:15 22/12/00 -0500, paul_tolsma wrote:
<clip>
>Is it perfect? Nope. I've used most of the schemes put forth in the last
>few days and they have all worked.

I think this is part of the problem. Everyone has at least one method and each method has some merit to it. I have used several methods,
and have been dissatisfied with all of them. I should think this would be a suitable topic for an official standard. I hate creating my own 'standards'. I have a copy of an old JIC standard, but this uses the simple 1,2,3 method
on a small relay logic system.
The most common method I have seen involves wire numbers being derived from PLC I/O addresses or drawing page/line numbers (for wires not directly associated with I/O). The PLC I/O based numbers haven't really been a problem for us, it's the page/line number ones that seem to have the most trouble. Some designers seem to get so obsessed with maintaining the purity of it that they let it affect their electrical design.
Is anyone aware of a recognised standard suitable for numbering wires on small PLC controlled machines whose drawings are layed out in typical JIC ladder format? This standard should cover assigning wire numbers, how wire numbers relate to device tags, etc. If such a suitable standard does exist, is there any reason why everyone is not using it?


**********************
Michael Griffin
London, Ont. Canada
[email protected]
**********************
 
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Bouchard, James [CPCCA]

With this method you can never change the line number without changing the numbers on the wires or devices. If the line number is based on the sheet number you can't change the sheet number either.

James Bouchard
 
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