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glen herrmannsfeldt
Guest
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 Posted:
Sat Sep 17, 2005 1:21 am Post subject:
Re: Ethernet breaker |
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Robert Redelmeier wrote:
| Quote: | Rich Noonan <rnoonan@gmail.com> wrote:
Yes, it's safety critical and when the equipment is installed
in the US I'm sure it's covered by OSHA. But it's covered
by much more stringent industry regs which is what I'm
helping respond to.
When fully operational, areas of our equipment have >3KV
running through. It can arc almost 3 inches and you can be
injured just pointing in the wrong direction. OSHA regs,
if any relevant ones exist, would not adequately cover this.
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The one I remember was 10kV/cm or so, but that would be
for DC. RF can go much farther than that. In any case,
yes, be careful.
(snip)
| Quote: | This is a LOTO (lock-out, tag-out) situation. A strapped down
(security Torx-head) wall-wart on a lockable breaker is OK.
But for more reliability (uptime) and less bypassibility,
I'd simply put jack and patchcord inside a lockable box.
When the tech needs isolation, he follows the written procedure
including a signoff step to open box, pull RJ45, leave air gap,
and lock box with LOTO hasp.
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How about a mechanical interlock that won't open the box
until the cable is removed? Remember in the days of
TV tubes that were user replaceable, the power cord went through
the back in such a way that it was disconnected when you removed
the back. Not that you couldn't cheat, but they could have done
better if it was required.
-- glen |
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Dale Farmer
Guest
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| Posted:
Sat Sep 17, 2005 9:27 pm Post subject:
Re: Ethernet breaker |
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Rich Noonan wrote:
| Quote: | Thanks for the replies. Maybe I should describe the actual
application.
We have a machine with multiple PC based operator interfaces. During
machine servicing it is sometimes necessary to disable control of the
machine at all but one interface PC. We are looking for a way to
disable control that is a) not software based (we already have numerous
s/w interlocks built in to the system and b) doesn't involve removing
power to the PC. What we'd like to do is simply disable the data line
to the PC.
Two easily implemented methods are currently under consideration.
1) Use a managed ethernet switch at the center of the control system
and disable individual switch ports as needed. The problems are that
switch silicon
(arguably or provably) has a higher failure rate than say a
mechanical/electrical switch and to the user/safety inspector it still
looks and feels like a software switch.
2) Install a low-density ethernet (branch) switch between each PC and
the central (core) ethernet switch with an electrical relay controlling
power delivery to those branch switches. The relay states can then be
selected with a traditional mechanical knob switch. The problems here
are that we just greatly increase the number of potential failure
points in the control system and introduced a whole bunch more unused
ethernet ports which we are trying to limit for other safety reasons
(e.g. factory staff plugging in computers without having to follow
procedure).
My imaginary solution is a fairly simple, two port device that would
sit inline on the PC ethernet link and when it lost power would break
the link. Do you know of such a device?
|
Okay. Safety control of an industrial machine for servicing. Proper
procedure is for a lockout switch to be used. Turn your ethernet
topology around. Have a small three port ethernet switch that
connects to the machine, the priority control PC, and the other
ethernet switch. The other ethernet switch connects to all the other
PCs. Depower the second ethernet switch with an approved lockout
switch and you are good to go.
--Dale |
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Al Dykes
Guest
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| Posted:
Sun Sep 18, 2005 3:45 am Post subject:
Re: Ethernet breaker |
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In article <S71Xe.2728$3V6.2271@newssvr11.news.prodigy.com>,
Robert Redelmeier <redelm@ev1.net.invalid> wrote:
| Quote: | Rich Noonan <rnoonan@gmail.com> wrote:
No question, this would be the best approach and we're
looking at how it could be accomplished, but unfortunately
physical constraints are numerous. Let's just say the
ethernet switch and PCs are in an unfortunate location
relative to the rest of the equipment. This is why the
design proposal (and this is very preliminary stuff at the
moment) gaining traction is a multi-position switch in a lock
box, the switch controling "breakers" on the ethernet lines.
Well, I don't think any passive switch exists that is Cat5
rated. You might be able to find an ethernet A-B box, but it
will be light-duty rated. You could try putting the Rx pair
through a DPST explosion proof box. and the Tx pair through
another. This will probably work so long as the runs are well
under 100m. It sure won't meet the untwist requirements, but
the explosion-proof aluminum housing should cut stray fields.
-- Robert
|
Are you worried about the conduction of HV or the tcp bits? If the
former you could use fibre optic ethernet to eliminate any DC
conductivity to the equipment.
--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore. |
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Robert Redelmeier
Guest
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| Posted:
Sun Sep 18, 2005 3:53 am Post subject:
Re: Ethernet breaker |
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Rich Noonan <rnoonan@gmail.com> wrote:
| Quote: | No question, this would be the best approach and we're
looking at how it could be accomplished, but unfortunately
physical constraints are numerous. Let's just say the
ethernet switch and PCs are in an unfortunate location
relative to the rest of the equipment. This is why the
design proposal (and this is very preliminary stuff at the
moment) gaining traction is a multi-position switch in a lock
box, the switch controling "breakers" on the ethernet lines.
|
Well, I don't think any passive switch exists that is Cat5
rated. You might be able to find an ethernet A-B box, but it
will be light-duty rated. You could try putting the Rx pair
through a DPST explosion proof box. and the Tx pair through
another. This will probably work so long as the runs are well
under 100m. It sure won't meet the untwist requirements, but
the explosion-proof aluminum housing should cut stray fields.
-- Robert |
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Al Dykes
Guest
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| Posted:
Thu Sep 22, 2005 4:20 pm Post subject:
Re: Ethernet breaker |
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In article <cei5j15d523h1imqc1skeopfdi6eq1cjlu@4ax.com>,
William P. N. Smith <> wrote:
| Quote: | "Rich Noonan" <rnoonan@gmail.com> wrote:
I'm looking for a device which could act as an ethernet breaker switch
Found the mechanical switchbox:
http://dalco.com/ProductDetails2.aspx?sku=38636
Down to $12.60 from $33.10 last time I looked at them.
You're welcome. 8*)
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It says "CAT5" but I'm sceptical. It may work at 100Mb with short
cables but that's way different from CAT5 compliance.
I'm sure it works fine at 10Mb.
--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore. |
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William P. N. Smith
Guest
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| Posted:
Thu Sep 22, 2005 4:20 pm Post subject:
Re: Ethernet breaker |
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"Rich Noonan" <rnoonan@gmail.com> wrote:
| Quote: | I'm looking for a device which could act as an ethernet breaker switch
|
Found the mechanical switchbox:
http://dalco.com/ProductDetails2.aspx?sku=38636
Down to $12.60 from $33.10 last time I looked at them.
You're welcome. 8*) |
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Guest
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| Posted:
Thu Sep 22, 2005 4:20 pm Post subject:
Re: Ethernet breaker |
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There are a couple of things that were designed for exactly
this purpose. i.e. disconnect a network conenction when
required (usually when a device was not working).
1.
This one, fortunately (or fortunately - I don't know),
is for Fiber Optic networking.
It is called an Optical Bypass Relay.
(Optical Bypass Switch too apparently)
The intention was to cut off the two fibers that connect to a port
and re-connect the external pair to maintain a FDDI ring.
The FO spec for GE and 100M Ethernet is I think the
same as for FDDI. Maybe you can still get them.
Google for [optical bypass relay]
There you go:-
http://luxlink.com/products/os-1002.htm
"Failsafe return to bypass mode with loss of power"
You could put more than one in series if one was
not reliable enough. (in a disconnecting sense).
The consequence of looping the ethernet would have
to be considered (spanning tree protocol, split IP networks,
others?), however this could be avoided with two OBRs
back to back.
Maybe you don't want to change to FO networking
and is does sound as if using convertors would be
unaceptable.
I would guess that these devices were made to be VERY
reliable.
Oh, maybe they are used today by Telcos for SONET.
2.
Using relays (mechanical and solid state) to switch networking
signals was standard practise with token ring hubs. T/R used
signalling that was very similar to ethernet and Cat5 cables.
A T/R hub is formally called a MAU.
Multi-station Access Unit.
I am sure that you could probably find someone to
dig out their old T/R drawings and design something for you.
You could hear the relays clicking as stations came on to and left the
ring.
Maybe you could stick to lower data rates if 100M was problematic. |
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William P. N. Smith
Guest
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| Posted:
Thu Sep 22, 2005 10:14 pm Post subject:
Re: Ethernet breaker |
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adykes@panix.com (Al Dykes) wrote:
OK, I'd imagine the OP would be able to slap a Cat5 certification tool
on it, but what's so hard about Cat5 in a giant box like that one? An
{four,eight}-gang rotary switch and a bit of care with your twists and
it should be just fine, IMHO... |
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