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Thread: Interlock question

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    Default Interlock question

    So Im building a projector and going to try a get a variance for it. Ive been searching this forum for info on variences for hours. I will be adding the IDLA board for stanwax. One thing Im confused on is the interlocks. Im not going to put case interlocks becasue it doesnt look like they are needed if I the only one who will ever use the projector. I see on some projector pics here that people use a 1/4 headphone jack and shorted plug as an interlock of some sorts. So does that meet the requirement for interlocks?

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    I know the 1/4" phono jack an mine is actually for an E-stop. I don't think you're really supposed to use a shorted plug.

    What i think you can do, since you're the only one using the projector, is label each panel with a warning sticker about there being no serviceable parts inside and the potential for being exposed to radiation if the cover is removed. YOUR the one certifying it meets the requirements so, it's really on you as the "manufacturer". My understanding is there is not a set of guidelines that says, "It must have this or that." Remember, an "interlock" could conceivably be reported as a lab room entry door with the laser sitting exposed in the lab.

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    thanks for the info

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    I've read on here that if you use security type fixings (such as Torx) for the access panel then you don't require the interlock.
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    I've heard that sort of thing too. As long as it's an uncommon sort of tool you would need to open the case.

    Again, as the manufacturer, what you're explaining to the CDRH is that, as another safety feature, this type of screw to gain access requires an uncommon tool, unlike a regular screwdriver or worse, thumb screws.

    From what I understand, with show variances and manufacturing variances, it's a bit like preparing a legal case and demonstrating what you, as the manufacturer, have done to satisfy the types of things they are looking for.

    For example... lets say for one reason or another, you can't place your projector at the 3 meter height. Doesn't mean you can't do the show... but what it does mean is you have to explain what measures you are taking to ensure safety and satisfy that requirement. Maybe you're going to add physical barricades to prevent audience access, or add an additional trained individual to be positioned with the projector watching the area during operation.

    There was a thread about aperture glass and the fact that, a way around the issue of cleaning and not having the customer open the box was to simply leave the aperture glass off. That way scanner mirrors can be cleaned without removing a cover and exposing them to radiation. And of course... the hope that an idiot doesn't try to clean the mirrors with the laser running. (I don't remember how that argument worked with dicros though.)

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    Quote Originally Posted by norty303 View Post
    I've read on here that if you use security type fixings (such as Torx) for the access panel then you don't require the interlock.
    As long as you have to use a 'tool' to gain access then that is sufficient. You don't have to use Torx security heads, its only a safer method than a standard screwdriver as not everyone has torx security tools.
    It's to stop the fitting of Quick Release catches so that anyone and everyone can gain access.
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    Hi f150.. (nice...

    Don't have a lot of time, right now - waiting on some renders for a client, to finish, but... wanted to at least try and give you some 'links' / food for thought....

    Quote Originally Posted by f150trk21 View Post
    So Im building a projector and going to try a get a variance for it. Ive been searching this forum for info on variences for hours.
    a) not sure if you've noticed (..many peeps miss it..) but we've got a rather-wealthy 'chest of info', right in the PL-Wiki - http://www.photonlexicon.com/wiki/in...fety_Overviews (..I 'fast-forwarded', a little for ya.. - But, if you're willing to put a little 'cerebro-grease' into it, once you 'drill-down' a little-deeper, you'll find a trove of links / info, that will (eventually) get you everything you could need.. ie:

    http://www.photonlexicon.com/wiki/index.php?title=CDRH, then, from down at the bottom, http://www.fda.gov/Radiation-Emittin...118907.htm#lrs - and http://www.fda.gov/Radiation-Emittin.../ucm116422.htm and http://www.fda.gov/MedicalDevices/De.../ucm094361.htm - bada-bing, bada-boom..

    Quote Originally Posted by f150trk21 View Post
    One thing Im confused on is...Im not going to put case interlocks becasue it doesnt look like they are needed if I the only one who will ever use the projector.
    Not trying to be a *, but.. Could you show me where you're getting this idea? What happens if / when you sell the unit? IF - and I say *if* - you were to, somehow, get a non-interlocked pj Certified, on the basis that, 'you'll only ever be the only-one who will ever use the projector' - technically, that means you could never, ever sell it, w/o, then making it 'uncertified'.. :/

    Once you understand the 'motive' behind the interlock-requirements, really, every-one should *want* interlocks - sure, you could put 'torx screws', etc, but... why would you do that - to yourself?? Trust me, you'd curse yourself out, the first time you needed to get at your optical-deck for alignment / cleaning, etc, and 'what the heck did I do w/ my torx??!! - whata PITA!

    ..Far-better to simply have *defeatable* interlocks, that positively-terminate laser-operation, until you, the Operator, are 'back in control' - which, can simply be the act of 're-engaging' the interlock - with the cover, off, (so you can get at yer shizz.. - then re-starting the lasers, etc - but, since that is a *positive-action* - NOT something that can 'start by accident' (thus heightening the risk of injury to you or someone else..) well, now you begin to understand the 'logic behind this Reg'...

    ..Even in the case of a 'room interlock', like in lab, the Regs require that 'opening the interlock' (the lab door..) would instantly-STOP the laser-operation, *untill* you, the Operator, took positive-action to re-start it - intentedly, once 'all is safe' / glasses-on, etc, etc..

    By all-indicators still-eminating from the CDRH, they have only 'relaxed' the standards, as they-relate to the OEM laser-sources, themselves, since many of the 'orig-regs' were all centered-around Ion, (or other 'legacy-medium' lasers) - where 'opening the head-cover' (thus, accessing laser-radiation) was not only regular-practice, but often-needed (ie: cleaning-brewsters / measuring tube-voltage, etc), But, for the most-part, nowadays, you don't usually need to 'open' a diode-module or DPSS - in fact, if ya do, 'poof goes the warranty'..

    ..However, this does not-mean that interlocks - for Projectors - are therefore, 'now-moot' - see this Doc, http://www.fda.gov/MedicalDevices/De.../ucm094361.htm notes under: "2. Guidance / "Which applicable sections of 21 CFR are unaffected by this guidance?" - Interlocks are not 'just a good idea, they're (still) the law'..

    Here's one example of how a (properly / complete-designed) interlock-circuit should be..

    Click image for larger version. 

Name:	DSLS_Intlk_ILDA_v2.jpg 
Views:	40 
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ID:	37321...'implementation' and components can vary (ie: Rob Stanleys' fine-board / others..), and, this does not show / spec the 'remote-interlock / e-stop' - just shown as an 'int. loop extra', but.. this is the 'core' / in-projector standard - needs to have defeatable door-interlocks / switches / reset-relays, and so-forth, and, then be 'labeled-accordingly' - ie: if there are-no interlocks (ie: on a DPSS laser-head) there is a specific label-requirement.. If there are interlocks, but they can-be defeated, then, that's a different label / wording, etc..

    Quote Originally Posted by f150trk21 View Post
    ..I see on some projector pics here that people use a 1/4 headphone jack and shorted plug as an interlock of some sorts. So does that meet the requirement for interlocks?
    No, that would be an example of an 'interlock-defeater' - As-mentioned, something that would (temporarily) sub-in for a 'remote-interlock' ('E-stop', which would be part of that same-circuit..) Case / door-interlocks, are more-often like the one shown in the drawing, or, 'micro-switches' of another kind / design, but in all-cases, something that - if the case / door is opened, where anyone - Op-included - can-access the laser-radiation... *pop* should go the laser-output.. Use of a 'hard beam-shutter' is seen as more of an 'arguable-value layer of protection', but interlocks - like keyswitches - ain't..

    There are probably other 'experts', here, more well-versed on all the 'nitty-grit', than-I, but... that's pretty-much the 'current poopie', afaik... We haven't seen, for-example, any more-recent 'Guidance' from the CDRH than 'Laser Notice 50', there, so... Again, interlocks = smart idea / best-practice, and the surest-way to 'CYA'... and...still the law..

    Hope this helps, gotta jet..
    j
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  8. #8
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    As per Casey Stack and confirmd by Woody-

    Not trying to be a *, but.. Could you show me where you're getting this idea?
    Case interlocks *DO NOT* have to be an electo-mechanical device to terminate lasing. The bolts/fasteners, what have you, that are used to keep your panels on are considered a case interlock. Provididng that the "fasteners" require a tool to remove and providing that the panel is clearly marked as non-interlocked.

    In my product report, I *specifically* addressed this issue with the question when asked. I put N/A and a brief explnation like i just put above, and i had no problems with the luminance being certified.

    In fact, IIRC, case electro-mechanical interlocks are actually *NOT* desired. This provides many more possibilities for the CDRH to say, "well....we dont like this switch. we dont like your circuit. we want this. we want it on ALL removeable panels. It bcomes VERY silly. Woody and i had this exact conversation quite some tim ago and he said, if you have removeable panels and you put some sort of E.M. interlock on it to stop lasing, than you better have the same thing on *ALL* panels and you better make sure That ALL of them fail safe.

    *HOWEVER* You still need to satisfy the beam attenuation and remote interlock requiremnt. This is where your remote shutter or "kill Box" coms into play.

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    wow thanks for all the info dsli_jon and Marc. Those links will really help out. Just got my custome case, now to put everything in it.

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    Quote Originally Posted by gottaluvlasers View Post
    As per Casey Stack and confirmd by Woody...i had no problems with the luminance being certified.
    ..and herein lies the conundrum - Perhaps, for *your* projector-consideration / submission, they said 'ok, no, fine..' BUT, untill the CDRH publishes a 'Laser Notice' for the industry, telling ALL manufacturing Variance-holders 'door / case lasing-interrupting-interlocks are no longer needed, period', I don't see how the industry can use your-case as a 'blanket policy'...

    Sure, 'no more interlocks-required for laser HEADS', makes perfect-sense, since, what OEM would allow you to open a DPSS / diode head, w/O voiding the warranty? That's where the 'no user-servicable parts' etc comes-in - So, little-problem to 'prevent access to radiation', as who is going to want to bork their warranty.. Plus screws / seals, blah, blah..

    Also, sorry, but not seeing how 'screws' ARE an 'interlock' - they are screws. Yes, having to use a 'tool' is a deterrent, but not part of that 'interlock circuit', which, as you confirm, still, in fact, needs to be part of a safety-chain.. Please show me, Chapter and Verse, where they say anyone can gain free-access (by only removing screws) to 'laser-radiation levels above (limits)', ie: In a projector, where an x-Watt multi-source (RGB) class IIIb / IV, etc is running full-bore, when you open the business-end panel.. Please share..

    ..And, arguments against 'all panels needing EM-interlocks' can easily be gained, *where there is no access to any laser-radiation*, (ie: electronics 'bunker', below the optical-deck, etc) but saying 'then, all case-interlocks are moot', does not wash...

    So, unless they issued one that (most of us) missed, Para. 2 of LN-50, explicitly-confirms that 'demonstration products' (aka, pj's..) are still-subject to the orig. standards... it's right here: http://www.fda.gov/MedicalDevices/De.../ucm094361.htm Otherwise, why would Kvant / RGB / Arctos / Sollinger / etc, all spend boku-$$$ on laser-section-interlocks - since 2007 - if 'none were-needed'... Just 'going the extra mile'?? Nah..

    Again - not saying 'Casey / Woody did not say 'ok' for *you* / the Luminance', I'm saying don't see that as a 'blanket-ok' from the CDRH, until they issue a Laser Notice, that addresses / supercedes #50. Feel-free to show me 'chapter and verse', otherwise.. Not a 'challenge', I merely want my understanding / posts to be correct, if somehow I've missed a 'new notice / guidance'.. Capiché?

    ciao
    j
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