Sure this is also correct, but if you run realtime equipment through
485 it is not worth it to run unisolated interfaces.
It takes one voltage glitch or an inductive discharge close by or a
lightning strike far away or a charge buildup on the guard to induce
current in ground loops which are present in non-isolated converters.
It is not worth your workpiece missing a critical command in realtime.
If you use it for terminal programs like networking etc with error
correction, fine then it is not an issue, but for real-time, I will
never do that. Just one glitch and the workpiece is destroyed.
My company was one of the first to use RS485 in specific industries
back in 1988 with massive multi drop systems. We built a lot and learnt
a lot and see folks making the same mistakes we encountered and
resolved almost 20 years back.
You have a ground loop, it is just a matter of time.
Javid Butler wrote:
Isolation is commonly used to deal
with large common mode differentials. While that can blow a 485
tranciever it does not happen alot unless there are vey long cable runs
or the cable runs between buildings. When running 485 for distances of
a few hundred feet connecting equipment powered off the same mains
transformer it's unlikely that enough differential will occur, but a
quick check with a voltmeter before connecting equipment is always a
good idea.
So both comments are correct. In
many cases 485 will run just fine without isolators, but some
applications definitely require isolation. I build 485 isolators, but
they are rarely tested to their limits. Often the isolation is more of
an insurance policy-it ensures that a single device cannot take down an
entire network segment.
Javid
-----
Original Message -----
Sent:
Sunday, February 03, 2008 9:15 PM
Subject:
Re: [Emc-users] Modbus RS-485 Transceiver
At 6 bucks a pop, buy 2.
Seriously, I worked with 485 at a
previous job and I never blew out a non isolated converter.
Of course it might depend on what
your doing I guess.
-----
Original Message -----
Sent:
Sunday, February 03, 2008 8:42 PM
Subject:
Re: [Emc-users] Modbus RS-485 Transceiver
Good advice is never to buy non-isolated converters.
You will replace them regularly if you do.
This does not seem to be isolated.
Kirk Wallace wrote:
On Sun, 2008-02-03 at 03:06 -0500, Dean Hedin wrote:
Interesting if you have the time..
But for six bucks and free shipping...
http://www.dealextreme.com/details.dx/sku.6040
Obviously, I didn't look hard enough when went looking for these. Thanks
for the link Dean.
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