[PCB_FORUM] Re: Metric to English - English to Metric

MessageHi,

In my project, the customer has given the mechanical dimensions of the 
connectors and mouting holes in mm. ( with three digit accuracy like 21.213 
mm). I place the connector with milimeter as measurement unit and switch back 
to mils for routing.

When we are doing the dimensioning, we again switch back to milimeter, then we 
encounter errors upto two decimal points. ( the connector fixed at 21.213mm is 
showing as 21.192 mm.. for an example).

have any one encountered issues like this? how can this be fixed.

Regards
~Kanak

  ----- Original Message ----- 
  From: george.h.patrick@xxxxxxxxxxxxxx 
  To: icu-pcb-forum@xxxxxxxxxxxxx 
  Sent: Thursday, August 25, 2005 3:39 AM
  Subject: [PCB_FORUM] Re: Metric to English - English to Metric



  The question remains:

      WHY switch back and forth?

  If the board is started in one unit, you are making it harder on yourself and 
others switching back and forth, even with NO round off errors.  The grids are 
different, the trace widths are different (unless you LIKE typing two decimal 
places all the time).  It is senseless to be switching it around, unless it is 
just to make extra work for yourself or your international partner.  Why not 
just KEEP IT SIMPLE (K.I.S.S.) :)

  -- 
  George Patrick
  Tektronix, Inc.
  Central Engineering, PCB Design Group
  P.O. Box 500, M/S 39-512
  Beaverton, OR 97077-0001
  Phone: 503-627-5272         Fax: 503-627-5587
  http://www.tektronix.com    http://www.pcb-designer.com

  It's my opinion, not Tektronix' 

    -----Original Message-----
    From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Patrick Jabbaz
    Sent: Wednesday, August 24, 2005 14:58
    To: icu-pcb-forum@xxxxxxxxxxxxx
    Subject: [PCB_FORUM] Re: Metric to English - English to Metric


    Here is the trick to make it work, In Allegro,

    You can switch units from metric to mils, and vise versa without errors, if 
you have the following setup:

    User Units mils use 2 decimal places 

    User Units  millimeter  use 4 decimal places

    Using this process, allows you to switch back and forth without any round 
off errors.

    Patrick Jabbaz

    Sr. PCB Design Eng.

    Xilinx

    2100 Logic Drive

    San Jose, Ca 95124

    Direct: 408-879-4709

    M: 408-621-6533

    email: patrick.jabbaz@xxxxxxxxxx

     


----------------------------------------------------------------------------

    From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
    Sent: Wednesday, August 24, 2005 2:26 PM
    To: icu-pcb-forum@xxxxxxxxxxxxx
    Subject: [PCB_FORUM] Re: Metric to English - English to Metric

     

    Hi Richard,

     

    Perhaps more than a decade ago, the CPU and code speed may have been an 
issue.  But, in the realm we are talking about (a printed circuit board and the 
range of numbers and precision necessary) IMO and IME the compiler imposes no 
significant restrictions, nor does the "math processor" in the CPU.  Again, it 
is simply a matter of knowing where the decimal point is.

     

    In Allegro, you don't convert because the tool can not handle it.  In a 
tool that can adequately handle it, this is not an issue.

     

    Regards,

     

    Austin 

     

     -----Original Message-----
    From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of richard moffat
    Sent: Wednesday, August 24, 2005 5:15 PM
    To: icu-pcb-forum@xxxxxxxxxxxxx
    Subject: [PCB_FORUM] Re: Metric to English - English to Metric

      Cadence is probably making a compromise for speed.  The way that other 
tools may allow a seemless interchange is to have a greater length of 
significant numbers in the internal database, especially converting 
metric->imperial.

       

      The programmers are restricted to that they are given:  The C compiler, 
and the maths processor on the CPU.

       

      In short:  don't convert!


      >>> austin@xxxxxxxxxxxx 25/08/2005 9:08:15 a.m. >>>

      Hi,

      > Conversely, 1/10 (0.1) cannot be exactly represented in base 2...

      I design ASICs, and I have done a LOT of arithmetic functions in ASICs, 
and
      use decimal points all the time.  All hardware arithmetic functions are 
done
      in base 2.  It's simply a matter of knowing where the decimal point is and
      using enough digits.  Yet, it goes on to explain the solution (as I said,
      knowing where the decimal point is)...so I fail to see the *real* problem.

      As was pointed out, PADS has no problem switching back and forth between 
the
      two unit systems, so I simply don't believe Allegro can't do it as well.  
It
      seems like this may be a self imposed restriction:

      > The real issue is that some numbers can't be represented exactly in the
      > standard floating point representation.

      Why do they have to use "standard" floating point representation anyway?
      Sounds like someone programmed themselves into a corner, and instead 
fixing
      it, they are trying to come up with explanations...instead of solutions.
      Sigh.  To me, this is a huge weakness of Allegro.

      Regards,

      Austin



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