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'Now kind of [OT) Re: Quadrature decoder'
1999\04\19@034159 by Stefan Sczekalla-Waldschmidt

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Hi Wagner,

Wagner Lipnharski wrote:
>
> Hi Stefan, yes, the noisy environment requires more care.
>
> (...)
> is the metallurgic electric metal melting chamber... man, if you heard
> about EMI that is where it was born... mainly when the electrodes are
> pouring thousands of amps over the scrap melting metal and they inject
> pure oxygen in the middle of it... do you know that they avoid to use
> electronic wrist watches around there? hehe.

Well - I visited one while I was still in school. They did aluminium
( Al ) melt there ... The magnetic fields where so strong that you
could hook coins together like a daisy-chain holding only on coin, the
others looked like they where glued to the edge of each other...
>
> Why don't you tell us in which situation, and how the sensor was
> connected, cable, filtering, when you got those noise problems?

The application was a "winch-level( position )-display-and-control"
for 12 winches used in theater

The problems I had, where in with (given) quadratur sensors, mounted to
electrical controled winches. Unfortunately there where several
problems with the assembly I had to migrate my controller. Beside this
- at this time I 've been very new to this kind of enviroment.
( and very unexperienced )

After the first test we discovered that every f***ing relais forces
resets in my circuit. The rack where I had to migrate my system was
build like they never heard about emi. After adding absorber networks
to all relays the system started to work more reliable. but whats this ?
when looking onto the display of the controller - operating one winch
gave also counts to other displays.

operating several winches at once made the system fail.

to make it short,

the winches used "normal closed" magnetic actuated brakes and no
care was taken to emi matters - so the release of a brake triggered
almost everything on every I/O-Port I had ...

but back to the quadratur sensors. The given sensors uses a unbalanced
transmition with an open collector output. the cable length where up to
30 meters, the cable was shilded but laid the same way like the power
cable for the winche.

After the mentioned first test run I reworked the design of the counter
to the full-state-machine-way. this reduced the amount of unwanted
counts
significantly. befor reworking this I used the one chanel-clock
other chanel-data approach. I also did a lot of filtering on the input
lines.

maybe this story is somewhat confuse, and emotional biased -
but if I had used a fully-state-machine design right the first time
for counting the quadratur-encoder pulses, I would have had more
time to discover the problems which where caused by the magnetic brakes.

This project also made it clear to me that working as a freelance
engeneer will cost a lot of nerves sometimes. So I'm now working as
System Administrator and doing "Pic-Ing" as a hobby.

>
> A lot of people can learn about it if we share our experiences, right?

right !

Kind regards,

       Stefan

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