[PCB_FORUM] Re: Metric to English - English to Metric
- From: "richard moffat" <richard.moffat@xxxxxxxxxxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Fri, 26 Aug 2005 10:19:40 +1200
Sorry - I wrote a " when I shoulda put mils. Same maths and numbers apply.
>>> annoonan@xxxxxxxxx 26/08/2005 10:14:23 a.m. >>>
Hi Richard,
I think we talked about using 2 decimal places in MILS, not inches. Again, I
haven't taken any time to go through the motions yet myself.
I can see though, how 2 decimal places in INCHES would cause undesirable
results.
Regards,
Andrew
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of richard moffat
Sent: Thursday, August 25, 2005 3:08 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric
This will work most of the time, sometimes it will trip you up. eg:
0.0009mm -> 0.0354"
0.0354" rounds to 0.04"
0.04" -> 0.001016mm
0.001016mm rounds to 0.001mm
so you see you've lost some accuracy already. Caveat emptor ...
>>> annoonan@xxxxxxxxx 26/08/2005 3:56:24 a.m. >>>
Hi Kanak,
Someone made an interesting suggestion yesterday. When you must switch back and
forth, set the accuracy in millimeters to 4 decimal places, and the mils to 2
decimal places. Apparently this removes the rounding errors. I haven't tried it
my self, but it's worth a try if you need to use this approach.
Andrew
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Kanakaraj
Sent: Wednesday, August 24, 2005 9:11 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric
Hi,
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
placesUsing this process, allows you to switch back and forth without any round
off errors.Patrick JabbazSr. PCB Design Eng.Xilinx2100 Logic DriveSan Jose, Ca
95124Direct: 408-879-4709M: 408-621-6533email: 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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