On Mon, 17 Aug 2009, Steve Blackmore wrote:
> Date: Mon, 17 Aug 2009 01:42:02 +0100
> From: Steve Blackmore <[email protected]>
> To: EMC2-Users-List <[email protected]>
> Subject: Re: [Emc-users] Realistic spindle encoder count for parallel port?
>
> On Sun, 16 Aug 2009 12:10:50 -0500, you wrote:
>
>
>> OK, base period is 62.5 us. For safety, we should never have encoder
>> counts coming faster than twice that period.
>> So, that is 125 us or 8000 Hz. Just to pick round numbers, 3600 RPM is
>> 60 rev/second, or 16.67 ms. So, we can read no more than 8000
>> counts/second, and need to fit that into .01667 seconds. 8000 * .016667
>> = 133. So, you need a 128 or 100 count/rev encoder. Encoders are
>> usually specified as cycles/rev (also written pulses/rev) and that is 4
>> x less than the count rate. So, you need a 25 or 32 cycle/rev encoder!
>> That's why people use hardware assist to handle these encoder counting
>> chores.
>
> Looks like a Mesa card may be a good bet, but...
>
> $199 + 22.5% import duty + carriage + 15% VAT = a lot :(
>
> I wonder how well I can get away with 1 pulse per rev?
>
> Steve Blackmore
> --
Can you use both encoders at once?
High resolution for low speed and Low resolution for high speed?
You could also do this with the high resolution encoder and a gizmo
like the USdigital divider, only with 2 selectable divide ratios run from a
single I/O bit, say 1/1 and 1/64. This is easily do-able in a $ 1.20 CPLD
Would you need the index at high speeds?
Peter Wallace
Mesa Electronics
(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
