[PCB_FORUM] Re: Metric to English - English to Metric
- From: chris.ball@xxxxxxxxx
- To: icu-pcb-forum@xxxxxxxxxxxxx
- Date: Tue, 30 Aug 2005 12:50:46 -0400
I recently began doing some of my designs in metric. I've been DIMENSIONING
prints in metric for a long time, but that's different.
I don't even think they tried to teach us metric when I was in grade
school. Maybe they showed us a meter stick beside a yardstick once.....
Anyhow, I too will always think first in inches, but can function OK in a
metric env as long as I stay focused in on the little stuff; 0.15 trace,
0.3 hole... that's kinda thing. Still glitch badly from time to time, but
it's do-able.
-Chris (el-CID)
"Schwartz, Jerome"
<jschwa01@xxxxxxxxxx> To:
<icu-pcb-forum@xxxxxxxxxxxxx>
Sent by: cc:
icu-pcb-forum-bounce@freel Subject:
[PCB_FORUM] Re: Metric to
ists.org English - English to
Metric
08/30/2005 12:31 PM
Please respond to
icu-pcb-forum
I have considered designing in metric only for a while. It would make
routing cleaner in BGA's etc. I have two reasons for not using metric.
These
might only be unique to me.
1. My designs can only be fabricated in the US. All of our vendors will
convert
the metric Gerber data to English. Thereby, creating the round off, and
offset, problem
I wanted to avoid in the first place.
2. Grade school, in the 1960's, tried to teach us metric. It still hasn't
taken. "You can't
teach an old dog new tricks." Therefore, I would always be converting
in my head.
IMHO (In My Humble Opinion) Although I am am seldom humble ;)
Regards,
Jerry Schwartz, CID+
IPC Advanced Certified Designer
"May The Schwartz Be With You."
Designer 3
Harris Corporation GCSD Voice (321)-727-5474
P.O. Box 37, MS 1-11F Pager (321)-690-9797
Melbourne, FL 32902-0037
mailto:Jerome.Schwartz@xxxxxxxxxx
http://www.harris.com
NOTE: IF SOMETHING I SAY CAN BE TAKEN TWO WAYS AND ONE OF THEM OFFENDS YOU.
I MEANT THE OTHER ONE.
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Gene Carman
Sent: Tuesday, August 30, 2005 12:05 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric
You guys are doing layouts in copper right? What kind of tolerance
do you think you get anyway?
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
Sent: Tuesday, August 30, 2005 8:33 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric
Whatever you say, Austin. PADS changed mathematics so there
would be no round off.
--
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
Austin Franklin
Sent: Monday, August 29, 2005 19:45
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to
Metric
George,
I'm not sure what reason you are referring to here, but
from what I can see, there is only one real reason and
that is because there is a problem with Allegro. If this
problem was fixed, there would be no reason not to switch
back and forth. It really isn't magic. People do it in
PADS (and other programs) all the time.
Regards,
Austin
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
Sent: Thursday, August 25, 2005 6:35 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to
Metric
All the more reason to...
( wait for it ... )
Stay in the same units you start with!
(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 richard moffat
Sent: Thursday, August 25, 2005 15:20
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English -
English to Metric
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
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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