Solid state safety.

[keeperx]

Ok i have a serious question regarding certain standard safety features and how they apply to solid state laser systems.

In a solid state system, the laser is off all the time unless it gets a signal telling it to turn on.

In a ion/gas laser just the opposite is true.

That being the case, what is required for real safety.

If there is signal loss, the lasers turn off.

Now there is obviously a good reason for a shutter, because it is a way to completely enclose the laser and contain all optical/thermal threat.

But what about some of the other features.

Im asking because i really do not know much about this but what i have heard applies specifically to gas lasers.

[buffo]

what is required for real safety.

It depends on what you mean by "real safety"... If you mean "compliant with CDRH regulations", then you need a shutter, an interlock loop on the ILDA cable, a case-intrusion interlock, a time-delay between power-on and laser output, an emmission indicator, and a remote kill switch. The CDRH doesn't differentiate between gas and DPSS lasers.

Yes, I agree that it would seem redundant to have a shutter on a solid state projector when you already have direct control over the lasers operating state via the modulation input. (Unlike a gas laser, which is on all the time and must be blanked externally, a solid state laser is only on when it needs to be.) However, the CDRH hasn't seen fit to modify the regulations yet. Go figure.

As for what is "really required" just to be safe when operating your solid state laser projector in your basement, I would say the minimum requirements are an interlock loop on the ILDA cable and a remote kill switch. The shutter is redundant, the keyswitch, emision indicator, and time delay are all unnecessary (assuming that you have a reasonable idea what you're doing), and the case-intrusion interlock is essentially protecting you from yourself. (And, in fact, there is an exemption in the CDRH regs for this item if you state on the variance application that you built the projector and you will be the only one operating it.)

Personally, I added one extra safety feature to my projector. I think it's *implied* in the CDRH requirements, but I can't find it listed as a specific line item. Noentheless, it's something I've seen in medical lasers, and I believe it to be an important safety feature for projectors that will be used in public. This is the inclusion of a latching relay connected to a "start" or "run" switch that will not re-close once an interlock condition clears.

In other words, if you yank the ILDA cable (or do anything else to trip the interlock circuit), even if you plug the cable back in (which satisfies the interlock), the projector will remain in the shutdown condition until a separate restart (or "run") switch is pressed. And at that point the projector goes through the entire startup process again (complete with time delay) before resuming operation. This guards against unexpected start-ups. (The ILDA cable gets pulled out, you go to the projector to check the power cord, someone plugs the cable back in, and ZAP!)

Adam

[mixedgas]

I can speak from personal experience that depending on a single shutter cable and a TTL signal is a bad thing.

We were rehearsing a Pink Floyd tribute band show in a 3500 seat combo nigtclub/auditorium. When you have amateur actresses/actors backstage, their cross stage movements are co-ordinated and led by a stagehand. Earlier in the day they were briefed on not stepping on cables and the cables were taped and marked. One extremely cute but ill tempered young chick was playing Pink's nurse. The laser scaff was center stage and the cables ran to my control area backstage in a room centered on the stage. Because of flying scenery in the area the cables were down on the floor, not up in the air as I would prefer.

Said chick caught her shoe on gaffer tape on the floor. Muttered something about wires, and stomped my cable with a high heel, much to the disgust of the stage hand leading her and her "entourage" . I , however was, thinking about "correcting" her attitude. In ways too crude to express as a gentleman here.

The stileto spike heal of a 50 Kg female generates a force of roughly 8 times her weight walking ,plus she was stomping, so call it 24 times her weight , on a area about one square millimeter in size. That works out to roughly 40,000+ KPa on the poor cable, which stipped part of the jacket off and drove the shield into a few conductors. Her heel further lodged into my 64 conductor cable, tripping her.

I spliced the cable in plenty of time , but it makes it very clear why the CDRH likes current loop driven, manually controlled, spring return shutters. They are far, far, more likely to fail closed and safe in a theatrical environment then a signal that could pick up a stray voltage. Ie 300 mA flowing in a cable is more likely to quit then a 5 volt signal loaded by 100K input impedance in a noisy enviroment.

Many chinese lasers default to on when not hooked to the totem pole output stage in in a TTL circuit. James Lehman has one like that.


Since there is no standard for a failsafe blanking input , there is one for the shutter and interlock loop.Not all mass produced projectors have shutters, there are loopholes for projectors that have things like tamperproof screws. But that is not spelled out in the rules, and is negotiated at time of approval, For a one off, or even a 10 piece run, they will want to see the proper shutter and interlock switches and keys. Oh, and more then 1 interlock switch. Since microswitches get sticky if they are not used, the standard demands two in series.

The first thing my CDRH inspector does is look at paperwork and hand you a form to sign saying your inspected whether you consent or not by blanket order of a cabinet level secretary. You consented to FDA inspection at any time when you submitted the application. However they always call ahead, for the fact that they do not wish to travel 8 hours on per diem out of their own pocket and not get reimbursed. The next thing he does is pull the interlock plug. It had better wink out.

When I say perfromance standard,the standard is not in 21 CFR 1040.1,J, its in a guideline for manufacturers and a letter of recomendations published by
CDRH.

Chicks should rebel against tall stileto heels. They can cause long term back injuries. I like nice legs as much as any other red blooded male, but those damn things are dangerous.

Steve

[keeperx]

Wow.. thanks for that yarn...

Since im talking about diode lasers that are OFF unless they get a signal, i think that there should be some regulatory changes

Gas lasers require PHYSICAL safety as they are always ON..

Solid state lasers require solid state safety features.

I think that the safety circuits should have a battery backup as well...

[mixedgas]

There will be no changes. CDRH is very set in their ways. Laser show safety is based on medical laser safety, which is CDRH's day job. You simply can't trust anything less then a mechanical shutter with a current loop in medical. Medical often has redundant watchdog circuits as well. You certainly don't want to do software or solid state control over 100 mW or so.

Trust me, from years of field ops with long cables, you want the mech shutter. I know people who have had major problems at gigs like the Olympics from somebody keying a two way next to a galvo that had unshielded feedback wires at just a small portion of the cables. It now says in the cdrh advisory that no two way radios shall be permitted within 6 feet of a laser show projector because of that one event and a similar one in Canada. It blew the scanners into the next dimension, after scanning at a angle that broke the torsion bars. That same RF would rip right through the poorly shielded cases and cables of Chinese laser gear. It would also saturate the TTL input on a laser.

These regs are in place for a purpose, just like the one that says there shall be a manual way to shut down a show outside of software, and the one that says there shall be physical masking, and the one that provides extra requirements for unattended operation. These requirements were hammered out by years of field experience and trial and error, and written by folks who have PhDs in laser safety related fields.

CDRH makes no distinction between gas and solid state.

I have to build my systems in such a way that I can sleep at night, and not worry about my shutter coming open if a roadie climbs on top of my projector on its scaffold to adjust a intelligent light. And that has happened. Prometheus II is big enough and strong enough to stand on.
The fact that he was fired 5 minutes later not withstanding, if he had put his foot on a amphenol connector and sheared it off, the emission would have stopped. This was at the same gig as Miss Priss, the playboy star nurse. Very crowded place backstage. Spring loaded shutters and masks and emission interlocks save your a$$. They let you idle the lasers safely, something you don't have to think about under a watt, but do if you have big honking ion or solid state. It can take 20 minutes for older soild state to stabilize. You need that shutter.

We also lodged a complaint with the union on that one.
An hour later that projector was screwed down to the scaff with lagbolts
and lag bolts went into the stage floor to lock the scaff. Lesson Learned, because he could have put his foot through the safety mask as well.

You can't design your roadworthy projector to the low standards of a modern PC enclosure. Especially in a small theatre or on a tour.
The rules will not be changed, until you change UL, CSA , National Fire Protection , ANSI Z136, The harmonized IEC laser safety rules, and the National Electrical Code, which have more to do with projector setup then you might think. And then get rid of the world's village idiots.

I know one friend who personally observed a raver urinating on his setup, another case where you do not want a analog/digital shutter circuit. Urine is highly conductive, and odds are the driver would fail on.

There is trend everywhere else in the world but the US and China to go to more safeguards, not less. Ie things like scan fail circuits or PASS. Those here from the UK can get a UK standard scanfail from ELA, the English Laser Association, its voluntary, but it gives you some peace of mind. Since the Germans pay a couple of hundred euros to have their shows inspected and insured, they love scanfails.

You can do whatever the hell you like in your basement as long as you dont injure your guests or your children, but when you go into public, you have the moral and legal obligation to insure safety, as the people in the audience assume you will when they buy the tickets.

Safety systems as specified for laser shows are based on Good Practices and Redundent measures. The US is unique in that you self certify your own safety measures and that projectors are not inspected at manufacture or use by a third party.

Steve

Just on a personal note, is there anything in the world you don't want to rebel against?

[keeperx]

LOL im not rebelling, im learning...
im an ENTP and im out to change the world, ALL OF IT...

But back to solid state safety..

I think that you hit a goof point there when dealing with solid state lasers..

Shielding and waterproofing
This is something i can get behind..
a solid state rig could suffer greatly from radio signals or any kind of emf interference.
and since we are talking an ALL solid state system, water is obviously a possible hazard..

[Stuka]

LOL im not rebelling, im learning...
im an ENTP and im out to change the world, ALL OF IT...

.....

Lehman beat you to that lofty goal claim many, many pages of BS ago....

[keeperx]

damn.... well i guess ill just do my best to make it a better place...

[Stuka]

damn.... well i guess ill just do my best to make it a better place...

I don't think anyone here has a problem with that!

Now, I'm not saying that the following necessarily applies here, however -

What folks on this forum DO get tired of is people who try to shove their unsolicited versions of a new, improved world order down our throats; unprovoked, immature, non-constructive commentary and verbal attacks of organizations, companies, and personnel from those organizations and companies that many of us choose to affiliate with; and those who after a while might appear as "trolls" who don't do much more than stir up crap (however subtle) everytime they show up and decide to post here!

As I'm sure you are aware, there is another laser-related forum that recently formed. After dropping in for a look several times, it appears to me that one of the few ideas that gets consistent support from several of its members is the consistent anti-Pangolin, anti-ILDA immature BS that used to trash this forum. There IS a lot of good technical knowledge and many cool ideas floating around there, but that continued BS, unfortunately, tends to overshadow the positive aspects of that forum. However - if the BS is going to be posted, that is the place for it - not here.

Anyway, having said all of that, it is well known on this forum that anyone who wants to post, ask questions, and have fun here, and generally be a contributor, and not a distractor, is always welcome!!

[mixedgas]

Stuka, you know, all we have to do is get these guys to a LEM, and they are instantly assimulated. Most times we do not even have to strap them to the table or apply the widgets that hold their eyes open. Usually they are up in the balcony yelling, "hell yeah, I gotta get me one of those", in fact, rarely does it take more then one beer at the party the night before.

Signed, sincerely,

Species 4880