PWB reference designators

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(also called PCB reference designators)

You've seen circuit boards with cryptic little white words like "R129" and "C17". Those are the reference designators. You may already know what the "R" and "C" stand for -- but what are these parts labeled "Z1" and "Z2" ? And when I'm making a new board, how should I label this polyfuse ?

reference designators

reference designators (Is ``reference designations'' the same thing ?) [general PWB design]

• Electronics Design Checklist http://www.chipcenter.com/eexpert/hwallace/hwallace001.html lists the ``preferred component reference designators''
• standard reference designators http://www.google.com/search?q=cache:b61rjLt83b4C:www.pcbstandards.org/downloads/Metric%2520Environment/Instructions/Getting%2520Started/Getting%2520Started.doc+standard+inductor+capacitor+diode+%22reference+designator%22&hl=en
• Designator conventions "ANSI Y32.16-1975" www.ansi.org

  Here's a search result link from IEEE which has the full pdf versions (see items 40 and 41) If the link doesn't come across go to http://ieeexplore.ieee.org and search on "reference designations" I couldn't find the spec at ANSI's site either. Regards jmc

  http://ieeexplore.ieee.org/search97/s97is.vts?action=FilterSearch&QueryZip=%28reference+designations%29&Filter=adv%5Fsch%2Ehts&ResultTemplate=adv%5Fcrst%2Ehts&Collection=jour&Collection=conf&Collection=stds&Collection=pprint&SortField=pyr&SortOrder=desc&ViewTemplate=lpdocview%2Ehts&ResultStart=31&ResultCount=15

  -- "John M. Cardone" on 2001-02-14

  Dennis Saputelli wrote ``Z for a zener and TZ for a tranzorb''

  Graphic Symbols, Designations and Units http://standards.ieee.org/reading/ieee/std_public/description/gsdu/

  >the real fun comes in trying to get J $ P to be logical and consistent

  It's much easier than one might think, though most engineers don't know the standard.

  The primary distinguishing characteristic is that J is stationary and P is mobile. If both J and P are mobile, or are equivalent stationary, which usually means cables floating around to be connected together, then P is male and J is female.

  That's the standard. I'd add that if male and female are not distinguishable, as with some connectors which have both pins (male) and sockets (female), then I would make the hot connector (powered when unconnected) J and the other P, if there is any difference, which is what one would do anyway with good connector design.

  I.e., the wall socket is J and the lamp plug is P, because:

  • (1) The wall socket is stationary.
  • (2) The wall socket is female.
  • (3) The wall socket is powered.

  So an extension cord has a P on the end which goes into the wall, and a J on the other end, even though both ends are [mobile].

  -- Abd ul-Rahman Lomax on 2001-02-14 12:48:03 PM
• Q: ``How can i change the designator text size on my whole pcb, and set it as default for new components to be placed ?'' -- grossstuecki

  A:

  ``For the existing board, dblclk on one of the designators, click on Global, change it from "all free primitives" to "all primitives", and make the change you want. It should change them all.

  For future defaults, go to Default Primitives, Component, and select the Designator tab. Then just set the size you want there.'' -- Steve Hendrix on 2001-04-02 05:25:38 AM

  Baldwin Technologies PCB Design Check List http://www.baldwin-tech.com/checklis.htm suggests

  All reference designators will be renumbered from left to right, top to bottom, starting with the lowest reference designator number. ... (Not all customers want their PCB’s to be renumbered)

end http://massmind.org/techref/pwb_reference_designators.htm

Comments:

• found the ansi ref des spec# here with google easier than finding it on the ansi.org site, thanks!+

Questions:

• ~NOSPAM~martinESPAM at tamuracorp.com asks: " what does Ref des U stand for when used as an IC" James Newton of Massmind replies: Very good question. My best guess is "Unit" because the IC is a functional unit, but that is only a guess. Does anyone know the history of this?+

  +

• Does anyone know how I can have only certain ref designators show up on my final PCB? I have a lot of small components close together and having all the ref designators on would make it very confusing. James Newton replies: That depends on the software. In protel, each designator has a check box to specify that it be hidden.+

  + ... a gEDA user notes that "On the assembly drawing, you center the reference designators inside the component boxes" -- for example, see the assembly guide and PCB for megasquirt and see how the ref designators are centered underneath the components. ... SparkFun says "We don't actually use part indicators (R1, R2, C13, etc) on many of our tightly packed boards." (they only show up on paper, on the much-larger-than-life assembly drawings) ...

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