Reply by Phil Hobbs January 31, 20162016-01-31
>I'm guessing the sensor conditioning/detection
threshold stuff isn't really complex. It's a picoamp linear/log TIA and a couple of LM358s. The photon budget and low cost are the most interesting parts.
>If you want to make sure the sensors don't lose power, you could have the >logic signal be laser on = OK, and maybe laser off = failure and laser >flashing = fire detected.
Not that simple. It isn't just a fire alarm, it finds the first signs of fire (a spark) and kicks open a solenoid-powered divertor door to dump the burning material someplace safe. The panel will poll each concentrator box periodically. Fibre isn't a good solution here because its installation and maintenance requires a level of cleanliness and skill that's unlikely to be available on site. It's also expensive, at least if you get the armoured kind, which we'd certainly need. Cheers Phil Hobbs
Reply by Jon Elson January 31, 20162016-01-31
John Larkin wrote:


> I wonder what burning cotton "sounds" like, namely converting the > light to audio. > >
Ok, here's a crazy idea or two. Have the sensor and detection logic on the machines. Power from whatever source is available. When fire is detected, sound a sonalert. The sonalert fires into plastic water pipes, and the sound is detected at the other end in the control room. Somewhat more down to earth, a scheme I thought up for a remote rain gauge that would be lightning-resistant, would be your sensor/detector flashes a laser into a fiber that is detected at the control room. By sending a LOGIC signal on the fiber instead of the raw sensor input, you can't possibly not have enough signal. I'm guessing the sensor conditioning/detection threshold stuff isn't really complex. If you want to make sure the sensors don't lose power, you could have the logic signal be laser on = OK, and maybe laser off = failure and laser flashing = fire detected. Jon
Reply by Phil Hobbs January 29, 20162016-01-29
>I don't suppose the ducts are willing to be straight, to give you a >long view.
I need timing information so we can make sure the diverter door opens at the right time. A glass multimode fibre bundle of at least a millimetre might work, but that's no longer so cheap, and needs more than a wrench and screwdriver to install. Cheers Phil Hobbs
Reply by Joe Hey January 29, 20162016-01-29
On Thu, 28 Jan 2016 09:32:29 -0800
Joerg <news@analogconsultants.com> wrote:

> On 2016-01-28 08:37, Joe Hey wrote: > > On Thu, 28 Jan 2016 10:35:40 -0500 > > Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > >> On 01/28/2016 10:15 AM, Joe Hey wrote: > >>> On Thu, 28 Jan 2016 10:03:51 -0500 > >>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>> > >>> }snip{ > >>> > >>>> Roight. I'll probably use another of those 150 uF coupled > >>>> inductors > >>> ^ > >>> Shouldn't that be 'micrometer'? ;-) > >> > >> Nah, these ones are about 10 feet tall. 10000H, 150 uF. ;) > > > > Hah :) > > > > With capacitance or Leyden flasks, shouldn't it be liters? > > Oh wait, litres, of course. >
You got it. :) joe
Reply by Jan Panteltje January 29, 20162016-01-29
On a sunny day (Thu, 28 Jan 2016 20:26:49 +0200) it happened
upsidedown@downunder.com wrote in
<ramkabdu0bgusob4p4lnllpf3bep8ig61j@4ax.com>:

> >1.) you can use non-isolated RS-232 for equipments in the same room >2.) use galvanic isolation (2 kV) RS-422/485 in the same building >3.) use fibres between buildings
^^^^^^^^^^^^^^^^^^^^^^^^^^^ Exactly.
Reply by Jan Panteltje January 29, 20162016-01-29
On a sunny day (Thu, 28 Jan 2016 10:34:32 -0500) it happened Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote in
<n8dc91$rhm$1@dont-email.me>:

>I wish. The design requirement is "It has to work through repeated >thunderstorms in an old wood/steel/cinderblock/mud/thatch/whatever >building in the hills of Bangladesh, with 200 metres of rusty steel >ductwork that may be carrying mains current, and very few grounds."
I have seen that situation, and we decided to go optical fiber. that worked, and had not speed limit due to capacitance,
Reply by krw January 28, 20162016-01-28
On Thu, 28 Jan 2016 20:26:49 +0200, upsidedown@downunder.com wrote:

>On Thu, 28 Jan 2016 10:34:32 -0500, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>> You might check the relevent sections of IEC61000 and IEEE/ANSI C62 to >>> figure out just what level of transient or surge immunity that you >>> intend and what exposure level is targeted. >> >>I wish. The design requirement is "It has to work through repeated >>thunderstorms in an old wood/steel/cinderblock/mud/thatch/whatever >>building in the hills of Bangladesh, with 200 metres of rusty steel >>ductwork that may be carrying mains current, and very few grounds." > >I have been working with industrial communication systems for decades >also in tropics with daily thunderstorms. I have used the thumb of >rules: > >1.) you can use non-isolated RS-232 for equipments in the same room >2.) use galvanic isolation (2 kV) RS-422/485 in the same building >3.) use fibres between buildings
How about variations of ISM radios (whether it be WiFi, Bluetooth, or some sort of mesh) available for cheap, these days? It's probably cheaper and more reliable than wires, especially for low bandwidth uses.
> >After my customers also understood these rules, I haven't heard >complaints by the end users in the tropics > >Rule #1 for lightning protection: There is no such thing as a ground >potential, the best that you can get is equipotential bonding !!
Reply by John Larkin January 28, 20162016-01-28
On Thu, 28 Jan 2016 19:05:11 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 01/28/2016 05:38 PM, John Larkin wrote: >> On Thu, 28 Jan 2016 14:43:59 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 01/28/2016 01:11 PM, Cydrome Leader wrote: >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> So I'm looking at lightning protection for the mezzanine units of the >>>>> cotton spark detection system. >>>>> >>>>> I have a copy of Standtler's book, "Protection of electronic circuits >>>>> from overvoltage", which is useful but a bit out of date (1989). (He >>>>> doesn't know about HV depletion MOSFETs or polyfuses, for instance.) >>>>> >>>>> It looks as though I can protect the isolated RS485 pair and the >>>>> power/common pair with a cascade consisting of >>>>> >>>>> (3-terminal spark gap) 500v 1a depl MOS >>>>> 0-------*-----------* *--*-----*-----*--* *-------*-----(Iso RS485) >>>>> A | | V | | | V | | >>>>> | ---------- | --------- V >>>>> | -------* | *------- /---/ bidirectional >>>>> | | | | A TVS >>>>> | *-----*-----* | >>>>> V | >>>>> -----GND | >>>>> A | >>>>> 0-------* .... similar.... .... * ... >>>>> B >>>>> >>>>> Lighter-weight lines are easier to protect, of course--Ethernet just >>>>> uses transformers. >>>>> >>>>> Any wisdom about other ways of proceeding? >>>> >>>> fiber media converter. >>>> >>>> They make them for serial as well as ethernet. Complete isolation between >>>> end points, and distance limiations for serial and interference is no >>>> longer a problem. The only issue is price and where to plug in the power >>>> packs for each side although they do make rack mount concentrators as >>>> well. >>>> >>> >>> Relying on having mains wiring up in the attic of a cotton mill well >>> outside Dhaka is going to be problematic, I think. Relying on anything >>> staying plugged in is also a problem. >>> >>> Cheers >>> >>> Phil Hobbs >> >> It would be cool if you could collect and transmit the light from the >> burning cotton with a fiber. Something big and tacky like Toslink. >> >> >Interesting idea--pipe the signal all the way to detection modules >installed in the panel, and so avoid the whole mess. > >There's a bit of an etendue issue, though, and a lot of the signal is in >the IR where plastic fibre isn't any good. My first official act on >this project was to spend about a week and a half doing photon budgets >for various scenarios. We wound up with a small InGaAs diode as the >most cost-effective choice, interestingly.
I don't suppose the ducts are willing to be straight, to give you a long view. Stuffing wide-angle light into a tiny fiber is inefficient, so you'd need a lot of light for that to work. I wonder what burning cotton "sounds" like, namely converting the light to audio. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by Phil Hobbs January 28, 20162016-01-28
On 01/28/2016 04:31 PM, legg wrote:
> On Thu, 28 Jan 2016 10:34:32 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 01/28/2016 07:55 AM, legg wrote: >>> On Wed, 27 Jan 2016 21:25:14 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> > <snip> >>> >>> You might check the relevent sections of IEC61000 and IEEE/ANSI >>> C62 to figure out just what level of transient or surge immunity >>> that you intend and what exposure level is targeted. >> >> I wish. The design requirement is "It has to work through repeated >> thunderstorms in an old wood/steel/cinderblock/mud/thatch/whatever >> building in the hills of Bangladesh, with 200 metres of rusty steel >> ductwork that may be carrying mains current, and very few >> grounds." >> > > Then the first thing to do is to include a 4-foot passivated ground > rod in the instrument's kit, to be pounded into the ground at the > duct port entry to the receiver's building location.
Which very likely would instantly be stolen and sold for the metal value. In rural Bangladesh, folks are super poor. (You can tell a first-world country because the poor people are fat. That's far from true elsewhere.) And of course people steal copper wiring and plumbing even in Canada and the US.
> This needs to couple into the wire bundle's ground/drain/earth > conductor using braided grounding wire or strap. Supposedly the same > arrangement can be expected at the TX end, using the same kit. This > is actually the best location for any air-gapped suppressors on your > bill of material, if access to data or power conductors is > physically possible. Same principal as a domestic residence's antenna > lead-in suppressor.
> > Transient suppression works on the assumption that there's a route to > redirect the current involved, that does not involve the sensitive > circuitry, or other sensitive leads exiting the equipment container. > The bulk energy entaileded is expected to dissipate in the tailored > transient path, with any residual local voltage disturbances (shorter > duration peak, lower amplitude tail) being handled by lower-powered > limiters. > > Most circuits that you see published already expect that this basic > protection level is present. Limiters at the service entrance levels > can be expected to degrade with use and to require regular > inspection/ replacement. > > The northern districts of the Indian Subcontinent aren't the worst > place for lightning, being on par with the American gulf states, but > an average of 1 strike a week per square kilometer isn't something > to ignore. > > RL >
Part of the fun of this project is that I can't make a lot of assumptions of that sort. The customer has been in the business for quite awhile, and so can provide good guidance about what has and hasn't worked in the past, but this system's architecture is quite different from what they've done before. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by Phil Hobbs January 28, 20162016-01-28
On 01/28/2016 05:38 PM, John Larkin wrote:
> On Thu, 28 Jan 2016 14:43:59 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 01/28/2016 01:11 PM, Cydrome Leader wrote: >>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> So I'm looking at lightning protection for the mezzanine units of the >>>> cotton spark detection system. >>>> >>>> I have a copy of Standtler's book, "Protection of electronic circuits >>>> from overvoltage", which is useful but a bit out of date (1989). (He >>>> doesn't know about HV depletion MOSFETs or polyfuses, for instance.) >>>> >>>> It looks as though I can protect the isolated RS485 pair and the >>>> power/common pair with a cascade consisting of >>>> >>>> (3-terminal spark gap) 500v 1a depl MOS >>>> 0-------*-----------* *--*-----*-----*--* *-------*-----(Iso RS485) >>>> A | | V | | | V | | >>>> | ---------- | --------- V >>>> | -------* | *------- /---/ bidirectional >>>> | | | | A TVS >>>> | *-----*-----* | >>>> V | >>>> -----GND | >>>> A | >>>> 0-------* .... similar.... .... * ... >>>> B >>>> >>>> Lighter-weight lines are easier to protect, of course--Ethernet just >>>> uses transformers. >>>> >>>> Any wisdom about other ways of proceeding? >>> >>> fiber media converter. >>> >>> They make them for serial as well as ethernet. Complete isolation between >>> end points, and distance limiations for serial and interference is no >>> longer a problem. The only issue is price and where to plug in the power >>> packs for each side although they do make rack mount concentrators as >>> well. >>> >> >> Relying on having mains wiring up in the attic of a cotton mill well >> outside Dhaka is going to be problematic, I think. Relying on anything >> staying plugged in is also a problem. >> >> Cheers >> >> Phil Hobbs > > It would be cool if you could collect and transmit the light from the > burning cotton with a fiber. Something big and tacky like Toslink. > >
Interesting idea--pipe the signal all the way to detection modules installed in the panel, and so avoid the whole mess. There's a bit of an etendue issue, though, and a lot of the signal is in the IR where plastic fibre isn't any good. My first official act on this project was to spend about a week and a half doing photon budgets for various scenarios. We wound up with a small InGaAs diode as the most cost-effective choice, interestingly. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net