Info on scan fail systems

Hi

Can anyone give some info on what scan fail detection systems are on the market. I know about the Scan Guard system from Laser Visuals which is software based with setup done on a PC via USB. Are there any other forms of scan fail detection out there? Looking for something to work with Scanpro 20's from LSP.

Also I would like to know exactly how the laser is to be shut down by such a system and how do you test such a system with out trying to stop the scanners with your fingers?

How many of the people on PL have scan fail systems fitted to there projectors?

Carl

Hi Carl,

This is a great question!! You will find my own personal opinions below (for whatever you think they are worth).

I do applaud that you have an interest in safety and that you want to apply a scan fail safeguard to your scanners. Unfortunately, as I have evaluated a number of scan fail safeguards out there, it's difficult for me to make a strong recommendation for any single product, since I haven't found one that I really like a whole lot myself (aside from our own -- more on this below).

However, if I had to pick a single scan fail safeguard out of the vast pool of ones that are available, I would probably go with the one made by HB. It is an all-analog circuit made by people who are generally pretty reputable, and I think the price is pretty decent. If you don't know HB, you can see their web site at www.hb-laser.com (I am not sure if their scan-fail system is listed in the products or not.)

In my opinion (for what it's worth), I personally don't like scan-fail systems that are microprocessor-based. Microprocessor-based systems require software. Software is written by humans, and humans make mistakes, thus the software has mistakes. As IBM concluded in a famous paper years ago "all software has bugs" (yes, including Pangolin software). So, the very last thing that I personally would want in a safety system is software. (And heck, I'm a software guy, right?)

Yes, all-analog scan-fail safeguards are also made by the same fallible humans. But for some reason, all-analog circuits don't seem to have the same incidence of "bugs" as microprocessor-based systems. So my own personal recommendation to you is to look into all-analog scan-fail safeguard systems. If you buy it from the right company, it should work well, and theoretically be less expensive than the digital ones anyway.

Now about our own scan-fail system. As some of you know, we invented a system that we call PASS. This is a combination of hardware and software, although the software is implemented in a kind of special way, such that it is "supplemental" in nature, and not safety-critical. The PASS system is incorporated into laser projectors made by LSDI, and in fact it's the only safety system ever approved by CDRH for what we might call "general audience scanning" (as opposed to specific, limited time, limited effects).

PASS is actually far more than a scan-fail system, because it also monitors the light coming from the projector as well as the scanning and laser control signals coming from the computer. And PASS incorporates redundant circuits within itself, and is constantly checking itself. The PASS hardware is implemented almost entirely in analog circuitry, with logic only used for the internal "voting" system. And finally, PASS has been peer-reviewed by top safety professionals, including staff members of CDRH. This means that, even if there was a mistake in the design of PASS, it would be caught by others who have reviewed the circuitry and techniques. (Note that this is in strong contrast to software-based systems since, as far as I know, no software-based safety systems have made their source code and schematics available for peer-review.)

Sounds pretty good, eh? The problem with PASS, in the context of this board is that PASS is way out of the price range of most of the people on this board. It also requires some additional things to be added to the projector (such as the light sensor and damn-fast shutter). The whole system might wind up to be a factor of 10 or 20 times more expensive than the simple scan-fail circuits out there. But for the Disneys and Pink Floyds of the world, who need to absolutely guarantee safety, and where price is secondary, PASS is a great system.

Nevertheless, I would say that PASS is probably overkill for a lot of people. If you are a hobbyist doing shows in your own garage, for your own entertainment and family (who won't likely sue you if something goes wrong), then a more simple scan-fail system will certainly do the trick. And I certainly applaud anyone for looking into this.

But there is one more thing to think about. A lot of people have the attitude that, simply adding a scan fail safeguard to the projector will automatically make the projector safe for audience scanning. This isn't true, and not even PASS will help you if the projector isn't configured correctly. Of greater importance is the DIVERGENCE, which must be purposefully made high in order for the audience scanning to be safe. Normally, the topic of purposeful increasing the divergence is like blasphemy to laserists but... what do you want? Do you want it to be safe or not?

There is another benefit to increasing the divergence (and thus the safety) and that benefit is that the show becomes more appealing. As the effects scan past your eye, they won't leave an after-image, so it winds up being a more pleasant show.

Increased divergence is actually far more important than the scan-fail circuit, and if I had to choose only one of these, I would choose increased divergence. For more information, please see the following two links:
http://www.pangolin.com/resguide09a.htm
http://www.pangolin.com/resguide09b.htm


Best regards,

William Benner

PS: It should be obvious, but since we make our own safety system, therefore it might seem like I have a vested interest in convincing you that other products are inferior and to buy our product. This is certainly not the case with PASS, which is something we try hard NOT to sell, and something that has only been made available to a small number of quality-conscious clients. However, I tried to set forth some of my own philisophical beliefs above about the type of system that I would be looking for if I were you.

Thanks Bill for your comments on the original question asked by Carl, and for also changing the original text in your post above about “lace curtains” in the same sentence as our Scanguard Monitoring device. Since our private correspondence, I now understand it was supposed to be a complement about our product, but on balance it was probably more confusing than anything else.

Returning to the original question, I would say Carl that if you are going to point lasers at an audience via galvanometers, then you should seriously think about employing some sort of scan fail detection system. The result is that if the SF is set up correctly, you will more than likely end up exposing an audience to less laser radiation than you would if you were relying on noticing a static beam zapping out into the display area.

Scan-fail detection systems vary with complexity, and have over time evolved into more sophisticated devices that consider more different types of failure modes. What is important, is to know the limitations of the system being used, and that just having a scan fail system in a projector does not make it inherently safe.

As some of you will know, I regularly work as an independent laser safety consultant to many of the UK’s larger entertainment venues, as well as production companies themselves. More often than not I come across confusion with Scan-Fail boards and even Beam Attenuation Maps. Laserists, to be fair to them, are mainly concerned with the artistic effects of the display, and the safety implications are often viewed as being a secondary “pain in the backside”. Ideally what is needed is a mini “Laser Safety Officer” in a box that sits in the system considering every possible exposure and failure mode. Back in 2003 with the help of UK government we realised as system that would do a pretty good job at this, but quickly reached the conclusion that market would not bare the cost of having a safety critical monitoring device in large numbers of projectors. (We are dealing with an industry that sometimes can’t even be bothered to put e-stops on projectors, so it is doubtful that the £15K-£20K safety system would be popular) So the product was mothballed, but instead some of the findings from the development carried forward onto other things.

One of these being a low cost digital scan-fail board that would be more user friendly than existing products. Bill is correct in stating that using a microprocessor to monitor emissions can be less transparent than using discrete components, (and would certainly be harder to get CDRH approval), which is why on the systems we have been recently trialling with a select group of users have multiple monitoring points and fallback scenarios to mitigate against errant code, a glitch, or processor malfunction etc. And for those requiring extra assurance there is even the capability of adding a second processor board and photodiode input of a completely different architecture to increase redundancy. The system is software configurable via a USB port, and self calibrating to check extinguishing time every time it is used. Ease of use and reliability have been two key areas we have concentrated on through the development of this.

A Scan-fail system is not the whole story though. Most velocity based scan-fail devices will not stop a dangerous emission from, say, a large scanning circle, for example. The scanners are moving fast, so as far as the scan-fail knows, (and has been designed to do), there is nothing wrong, and the system is working correctly. But what could be happening (and is far more likely than a scanner not working) is that the tunnel is producing a too higher exposure in the first place, when it is scanning correctly. This is the case for all the "velocity-only" commercially available devices I have seen whether analogue or digital by design. Therefore another part of the story is that the emissions need to be checked too, so as not to expose people to excessive laser radiation, …even when the scanners are working correctly. You can carry this out by measuring the emissions, or making the tricky calculations.

Some of you will know about our Emissions Analysis software called Scanguard Analyser, which has been designed to make the emissions checking of laser effects easier, and at a relatively low cost. We are about to release a new version of the software which will be available in four different editions, and is completely different to anything shown in the past. (there will be an announcement on this in the next two weeks). Combine a hardware failure monitoring system (the scan-fail monitor) with an emissions analysis program such as our Scanguard Analyser, and you go along way to increasing the safety of the people’s eyesight you are pointing the laser effects at, and making the assessment process easier.

So to summarise…
Scan-fails – yes if you are using galvanometers to scan an audience with. But remember they only protect against a scanner failure mode, (some better than others), and not against the normal operating exposures of properly working scanners.
Check the emissions – physical measurements and analysis needed here.
Don’t rely on a scan-fail as being a magic box that will make laser shows safe. Safe shows need to start off with safe design…

Hope this helps make things a bit clearer Carl

Thanks Bill & James.

The info you both posted on this matter has been very informative to read and points out a lot more on safety for laser projectors than just scan fail systems. I have Read the HS(G)95, The UK guide to setting up safe laser shows, from front to back many times and this also states that scan fail systems should only be used in adition to other safty fetures with in the system and an opperator that is familiar with the system and the safty guide lines.

Would like to know what safty fetures other laser show hobbyist like my self on PL have fitted to thire systems.

Carl

Hi Carl

Some very interesting comments regarding scan fail systems from both Bill and James.

I read with great interest any threads regarding laser safety especially when it comes to audience scanning. It seems that most laser users miss most of the point of laser safety, they assume that the main danger is the beam itself.

I agree that a static beam into the audience can be a great hazard, but only if the beam exceeds the MPE. How many would know if the beams that were moving would be over the MPE? or even how to measure or use the equipment never mind understanding the results!

As the cost of laser power drops and more easily obtainable, it is not uncommon to have the hobbyist use 1,2 or even 5W of CW power to play with, we all have seen some scary video clips of materials bursting into flames, or very high powers scanning the audience. It is almost impossible to shut off high power beams fast enough in order to keep the single beam exposure below the MPE. I only said almost as PCAOM used in PASS is capable depending on laser power (don't think it would work with a 20W CW ??)

It is common place in the UK and europe to use high power beams above the audience as long as you have a assessed the risk to take into account all of the issues related to flammable materials, public access to areas etc. My view is that it is more of a hazard if the 1500 capacity venue burnt down killing some or all, or one person potentially getting blinded in one eye before the shutter reacted.

As James is aware I attended his training course some time back now, and found it very good and worthwhile for anybody interested in laser safety (No Charge for the plug James), but this leads people who attend the course to assume that they are laser safety officers, I have meet some of these people on my visits to venues after installs.

I have been told that the PASS system is retrofittable and will be available soon as standard in some high end systems from China, can Bill confirm this as some of my contacts have told me this.

I think it is time for some serious thought regarding laser safety as the industry is moving fast and it will be very difficult for any of us to exist after a major laser incident. I know that James and myself have spoken about low cost high power systems from China being installed all over the UK without local authority approval never mind CE marks, scan fail, E stops or adequate risk assessments. local authorities and HSE are only active when there is an incident, so when they respond it my be too late for the industry.

Smaller lower power (100mw?) laser systems with simple overall scan fail equipment and hard shuttering (not electronic attenuation) and a divergent beam, installed and passed by licensed or certified laser safety experts could be a solution to remove the confusion regarding audience scanning.

Has anybody any information regarding costs of scan fail systems available as I have looked and found only two ?

Regards

Kevin

Hi Kevin

As I don't intend to use any lasers higher than 150mW CW, setting fire to venues with the beam is a low risk factor but I do know what you mean.

I got some Aproximate calculations for minimum distences for audience scanning with a laser system I got a few years ago and use this as a guide when setting up, but I use the calculations given for 200mW with the 150mW lasers this being 27m with no smoke and beam divergence of 2 mrad at 532nm, 8.5m in low dencity smoke. do these sound about right?

Thanks

Carl

Hi Carl

I calculate the NOHD (nominal ocular hazard distance)to be just under 50m with 2mm initial dia, 2mr and 200mW this reduces to 42m with 150mW.

I have not had time to double check my figures maybe some one can confirm (one person cannot do a risk assessment on their own !!)

You cannot rely on smoke or haze to improve a safety margin although it does help.

Most venues I am aware of that use lasers are not that big and certainly do not have 42-50m from the stage or truss to the audience, even if you can obtain 3m above head height .

The HSG95 is an old document that certainly does not give any indication on how to measure beams or how to complete an adequate risk assessment.

It would be very helpful if some one could provide examples of an adequate audience scanning risk assessment that has been accepted by any local authority or HSE or even HPA (health protection agency). I am certainly not aware of any !!
Maybe James could help on this one !!


Regards

Kevin

Hi Kevin

If you are right about the the distence calculations in you last reply for a scanned emission I think audience scanning will be going out the window.

Thank for the info.

Carl

Quote:

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Originally Posted by Lynx

even if you can obtain 3m above head height.

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???? Which bit of legislation specifies this?

Are we talking about beams here?, if so, I believe that you have this information completely wrong. 3 meters above FLOOR height yes, but NOT 3 meters above HEAD height. Or have I not been reading the correct literature?

Jem

Hi Jem

Sorry mate typo, not thinking when writing !!

See how simple errors can cause problems.

To correct, beams need to be above 3m from floor level or if a staging or mezzanine is accessible 3m above that floor level.

Sorry Jem you can smack me very hard the next time ;)


Regards

Kevin