Re: [CAD_CAM_EDM_DRO] RE:Chinese Scales to Glass Scales DRO Interface

Kenneth Emmert wrote:

> The Shumatech DRO reads Chinese scales directly. There is a quadrature to
> Chinese converter so that standard scales can also be used, but nothing that
> goes the other way. He's looking for a Chinese to quadrature converter
> useable with an existing DRO, and I haven't run across that as a stand alone
> unit yet. Far as I know, the Shumatech is still the only one around that
> will read both.

If you think about the problem, you will see that the Chinese to
quadrature conversion is simply not practical. The Chinese scales output
a 24bit number ( and it's two's compliment version as a check ) every
300mS in slow mode or 20mS in fast mode. One needs to generate enough
'edges' to display the difference between two readings in this 20mS
window, and even throwing away some of the accuracy still leaves the
potential for a high number of these edges.

Added to this, there is always an amount of 'jitter' in he readings from
the scales, which means that numbers jump reading to reading. This could
be processed in the same way as the Shumatech filters the scale input,
but the chances of the quadrature output drifting with respect to the
scale reading is still very high.

The conversion the other way is obviously not a problem as the
quadrature feed is a much cleaner signal, and only needs a 24 bit
counter synchronized to it from which to generate the Chinese data stream.

Just for the record, the Digimatic protocol uses a 52 bit message
including 6 BCD digits rather than a simple 24bit binary number.

http://www.shumatech.com/support/chinese_scales.htm has all the detail
that Scott ha assembled,
( and the DRO:int4 from YADRO is available from
http://home.lsces.co.uk/ModelEngineersDigitalWorkshop/YADRO/index.html
;) hope to have machined cases by the end of the month! - another watch
this space item :) )

--
Lester Caine - G8HFL
-----------------------------
L.S.Caine Electronic Services - http://home.lsces.co.uk
Model Engineers Digital Workshop -
http://home.lsces.co.uk/ModelEngineersDigitalWorkshop/
Treasurer - Firebird Foundation Inc. - http://www.firebirdsql.org/index.php