Optimizing Engineering Revision Control

In order to guarantee that a drawing or a procedure is at the most current revision level and that it's the document associated with a particular instruction or bill of materials, the revision date and number should be visible in a predetermined location on each controlled document. (See: 5 Steps to Reducing Design Change Problems.)

A revision date and number in the Header of the document helps identify quickly if the document being reviewed is the same version number as indicated on the Engineering Change Order Release record. Please refer to the Procedures and Guidelines from Components Engineering for a detailed procedure for managing Revision Control.

Again, different companies have varying methods for handling revision control issues. There are systems that have a two placeholder identifier where both alpha and numeric indicators are used. In one company, an alpha in the first position may indicate that a drawing or a procedure is not yet released to manufacturing. When the first placeholder is changed to a number instead of a letter, it is an indication that Manufacturing has received the document and is assuming primary responsibility for informing Engineering of any changes. Documentation Control is showing the drawing as “Released.” The identifier scheme can just as easily be implemented where the first placeholder is a number and not a letter, also indicating “Pre-Release” status.

On procedure documents, there is usually a cover page that shows a table for revision entries. The table will include the “bump” to the next revision level shown as the next Alpha or Numeric in sequence. In other words, 1A may bump to 2A. The next column over in the table may be a brief description of the change. Another column will contain the name of the person entering the change.

The date of the change is shown and the last engineering change notice (ECN) number prior to this most recent change. After a period of time, this table contains the complete list of revision numbers and changes made to the document. Documentation Control retains all archive and earlier revisions, so anyone interested in the history of the document will be able to retrieve it via the document number and revision number.

When an engineering drawing is created, there is a section in the title block called “REV.” This is where the author indicates the first revision of the drawing. Up in the top right corner is where the table for revision tracking is located. It is similar to the procedure revision table in that over time, the table grows as changes are made to the drawing, and the revision letters are recorded for historical reference.

Software and firmware are also maintained under revision control. A bill of materials is often associated with a schematic diagram and a printed circuit board. As an example, a bill of materials at revision 1B might indicate the following:

  • 1 = 1st revision of the PCB fab
  • B = 2nd revision of the schematic

If on the schematic a resistor value changes, but the package type remains the same, then the schematic revision needs to bump a level, but the bare PCB does not change. Then we have the following change to implement on the PCB(A) assembly bill of materials documentation.

  • 1 = 1st revision of the PCB fab (No change)
  • C = 3rd revision of the schematic

If the schematic changes, causing a board change, then everything bumps up 1 revision. Hence:

  • 2 = 2nd revision of the PCB
  • C = 3rd revision of the schematic

A quick assessment of a revision number for a printed circuit board assembly at revision 8E would tell us the PCB has changed seven times and the schematic has changed four times — not necessarily simultaneously. We should be able to go to Documentation Control and ask for documents supporting bills of materials dated from the Release to Manufacturing, inclusive of Schematics 1 through 8, and PCBs A through E. Why would I want this? Because customer service is responsible for repairing every version, and all historical information on a product has to be readily retrievable.

Revision control is absolutely necessary for a multitude of reasons. Don't get caught waiting too long to control your company's documents.

15 comments on “Optimizing Engineering Revision Control

  1. Houngbo_Hospice
    October 24, 2011

    “Software and firmware are also maintained under revision control.”

    Revision control is very important for the enterprise expecially if mutiple developpers are working on the software project. It helps to track changes to the software or the firmware. Good documentation  of the changes over versions should be also provided.

  2. Eldredge
    October 25, 2011

    This whole topic can become quite confusing when a supplier deals with making assemblies for a number of customers. Each customer has their own reviswion control methods which they maintain at various levels of integrity (not always a high level of integrity!)

  3. Clairvoyant
    October 25, 2011

    Yes, Eldredge, that can be true. I'm assuming you are meaning outsource manufacturing? Ideally the outsource company could talk with their customers about improving their standards for revision control to make things easier for all companies involved.

  4. Nemos
    October 25, 2011

    Very nice and cleaver, specially the second part was very clear, and it described well enough.

    It would be great if you could visualize the first part also.

  5. dalexander
    October 25, 2011

    Nemos and All,

    I like the idea of a Part 2 that would actually show the revision tables with explanation to help the reader visualize the document. I will produce that in the next blog. For now, just go to

    You will see a full procedure that you can download and there is also a form under the “Forms” tab. I should have PART 2 next week. Thanks for the comment.

  6. Taimoor Zubar
    October 25, 2011

    Version control within software is very important and there's a whole science associated with it. Versioning in software might be slightly different than it is for engineering components. The versions take into account major software updates, minor software updates and bug fixes etc.

  7. t.alex
    October 25, 2011

    Without revision control, many projects that span across the globe could not easily be coordinated and integrated.

  8. prabhakar_deosthali
    October 26, 2011

    For proper revision control  proper systems support is a must. With a company outsourcing to many vendors and the suppliers catering to many comapnies it is a many to many situation and any gaps in the revision control documentation will result in a total confusion across. A well integrated ERP system only can take care of ensuring that the latest revision parts are ordered, manufactured and supplied.

  9. _hm
    October 26, 2011

    It will be nice to have these features explicit in ECAD packages. Also, there is need for some form of standardization. I have not seen it much. Is there any effort in this direction?

    October 26, 2011

    Nice post.  Cannot stress enough the need for companies to train their people in rev control and to audit procedure compliance regularly too.

    October 26, 2011

    Nice post.  Cannot stress enough the need for companies to train their people in rev control and to audit procedure compliance regularly too.

    October 26, 2011

    Nice post.  Cannot stress enough the need for companies to train their people in rev control and to audit procedure compliance regularly too.

  13. dalexander
    October 29, 2011

    TalmoorZ, Recently, I had to create a procedure for Software version control and I found some very good open source tools that did a great job. The revision automatically increments whenever there is a change to the source code and old revision is archived. Check out Wikipedia's list and you will see some really good free programs. If you need help with any of these, feel free to contact me and I can share what I have learned with you. I have a CE website and I have been considering adding a paper covering this topic. Is this something you think most CEs would be interested in?

  14. dalexander
    October 29, 2011

    Flyingscot and all, how do your companies handle Revision Control? Do you use a two place identifier to differentiate between a schematic/BOM change and a physical board change? One of the issues is, if the board/schematic changes on a sub-assembly, the revision has to be changed all the way up to top level. I have always asked for a serial eeprom on a system level board to be included in the design to track revision and serial number data that can be retrieved remotely if a product is at a customer location. Simply polling the EEPROM has expedited a lot of customer service related issues including warranty validation based upon cross referencing serial numbers to manufacturing dates. Having the revision level of the BOM and board really helps the R&R department troubleshoot existing problems with known solutions. How does everybody else do this?

  15. MarkSindone
    July 17, 2018

    There has to be an SOP when it comes to recording revisions I think. Even if you're the only person working on a project, you need to make sure that in case anybody else sees your work, that they'll be able to follow through on what you've been doing. Just in case.  And of course, it's really good housekeeping in case you need to come back to a project a couple of months, or even years down the line too! 

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