13 – Let’s Compare RF And Glass Tubes

0:00well it’s a nice sunny day welcome to another session with my tangerine tiger

0:07this is not a tangerine tiger no it’s in the workshop behind you and that’s where it’s going to stay

0:12today because we’re going to have a little bit of a reflection day we’re going to take what i consider to

0:18be an honest look at the difference between a glass tube laser

0:23and an rf laser now i know i haven’t got a great deal of experience with the rf laser so far but i’ve dug in

0:30pretty deeply and i’m pretty sure i’ve come to some pretty strong conclusions already even though we’re probably only

0:3720 20 of the way through our test program not only have i had the opportunity to gain

0:42a great deal of experience with the glass tube laces i’ve also had a great opportunity

0:48afforded to me to play with a fiber lacer

0:53now i’ve always sat back and i wouldn’t say envy because that’s the

0:58wrong word marvelled no that’s still not the right word

1:03wondered probably that’s a better word i’ve wondered why the rf laser has got such a great

1:09reputation why it cost so much money what’s so fantastic and marvelous about it

1:17and then claude ray with great generosity gave me a 20 watt

1:24rf laser to fit to a machine that i bought now that gave me the opportunity to try

1:30and really understand what an rf laser is all about

1:36i’m afraid any magic that i thought was attached to these devices has

1:42disappeared even though i’ve only spent a small amount of time with the rf laser

1:49i’ve done a lot of research and i can already tell you that this project as it stands at the

1:56moment is likely to be a bit of a damp squid it’s going to work don’t get me wrong

2:02we’ve got a machine that will run extremely fast but we’ve got a 20 watt laser that will not keep up with the machine

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

2:10and that’s my problem now i was hoping that i might be able to make this machine comparative

2:16to something like an epilogue zine okay it would never look like an epilogue zing but it might well perform

2:23the same except when i start looking a bit more at the detailed specification the zings

2:30run anything from 40 to maybe 80 watts i think you might even be able to get 100 watts in as well that’s a big

2:37difference from what i’m trying to do with 20 watts now 20 watts is not even enough

2:43to light a bonfire to be honest um i mean a k-40 has got more power

2:48than the 20 watt tube and i suppose you’d use 20 watts for

2:54dermatology you certainly wouldn’t use it for cutting or for

2:59doing any serious work but hey that’s what i’ve got it was gifted

3:05to me and you know what they say about a gift horse i’m going to make the most of it i’m going to see just how fast it will go up

3:13so what i want to do today is to just take you through an honest set of comparisons between

3:20a glass tube laser and an rf laser to try and take away the magic aura

3:27that seems to be hanging around this very expensive technology

3:35so as i always say to you come on in and let’s get started you will still have to suffer some of my kindergarten drawings but

3:42hey i’m interested in getting the principles and the ideas over and not producing a van gogh type

3:47artwork now one of the most important things about the laser is power watts now

3:55i’ve given you this analogy before of a candle flame and how when you put

4:01your hand over a candle flame if you hold it still you know what’s going to happen but if you move across

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

4:07it at a certain speed then yeah it will not hurt let’s try and

4:12turn that analog upside down now and here we’ve got a piece of material and we’ve got a miraculous machine that

4:20i’m going to be using because it burns square dots

4:26okay now i i need you to suspend reality for a few moments and go along with this idea

4:32now very conveniently this happens to be one millimeter by one millimeter yeah we’ve got a

4:38pretty coarse lens in here as well okay now let’s assume through my special

4:43magic lens here i’m able to focus one watt

4:49okay and i keep that one watt on that spot there for one second

4:58okay so we’ve got a one watt for one second energy density on that

5:05square millimeter now i don’t know how you technically express that in terms of units um

5:11but let me now move on and say look if we now instantly move on to another dot

5:18which is here and again we apply one watt for one second we’re going to

5:24do the same amount of burning damage on the second dot

5:29because one watt for one second gives a certain depth or type maybe just a scorch

5:36on the material it doesn’t really matter but it’s going to produce damage of some sort and so

5:43if i carry on like this and we produce instantly jumps

5:50of one millimeter we should produce eventually a line like that all the same density of

5:57depth of cut or color [Music] now that’s because we’ve used one watt

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

6:04for one second now this would work we do not have to move instantly from unit to unit because we

6:11could move smoothly along there at one millimeter per second

6:18which is effectively what we’ve got every second we’re going to move along here one millimeter so that’s effectively the

6:25uniform speed that we’ve just used so at one millimeter per second with one

6:32watt we should produce this amount of damage okay now i’m building this up gradually

6:40so what happens if i go to two millimeters a second

6:49remember the candle flame we’re now moving twice as fast how much damage will i do

6:57well the answer is obviously half as much damage because i’m spreading the same one watt over

7:04the same distance times two in the same period of time so

7:12i’m now moving two millimeters a second so i’m applying half as much energy to each one of these little

7:17blocks here so therefore i’m going to do half the amount of damage

7:23now it is a long-winded way of getting around to showing you that look to produce the

7:29same amount of damage on that line we need to move two watts

7:34of energy at two millimeters a second

7:39or four watts at four millimeters a second if i increase the speed

7:46to keep the same amount of damage into the material i’ve got to increase the watts as well

7:54and there is my problem with this 20 watt machine

8:0220 watts is 20 watts whatever sort of laser you use to

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

8:08generate 20 watts that’s it so

8:14slightly different with the 20 watt fiber laser because the fiber laser was not only was

8:21it 20 watts if you like uniform power where that represents 20 watts

8:27this was able to produce spikes of energy very short spikes of energy which were up in the

8:34kilowatts region because it was storing energy between the pulses

8:41and building it up the rf laser and the glass tube laser

8:50do not do that they have got 20 watts continuous energy

8:57and with the rf laser you switch on and off with a glass tube you keep it on all the time and you

9:03switch it on and off so there are differences between these two

9:08but the principle is still the same we do not have any magic amplification

9:13with either of these and that was my problem i thought there

9:20was some sort of magic associated with an rf laser the only difference between these two

9:27laser sources let’s call them that is the manner in which the

9:33laser beam is produced now i have no intention of going inside these boxes so here we’ve got

9:41an rf laser and here we’ve got a glass tube laser

9:50now the one thing we do know is that what comes out of there is 20 watts

9:59and what comes out of here is 20 watts

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

10:07but what goes in to make that 20 watts well in this instance we’re putting in

10:14rf which means radio frequency we’re feeding into this unit 48 volt dc to create a very very high

10:22frequency 100 megahertz signal within here which is vibrating

10:29the gas molecules and making them effectively become lightning just like

10:36we see in our glass tube but we can’t see what’s happening in here because this is a solid block of metal

10:41very crudely in here we’ve got two plates with this 100 megahertz zipping between them and that causes the

10:49breakdown of the gas and it ionizes within that section there okay

10:56now the ionized gas again what we’ve got is two mirrors very crudely we’ve got two mirrors and

11:01exactly the same system operates here as it does with our glass tube

11:07okay we’ve got two mirrors in our glass tube we’ve got two electrodes here in our glass tube

11:13where we feed 25 000 volts dc

11:220 volts and we’ve got gas in between here which and it’s in a tube

11:30this is not a tube this is two plates whereas this is a tube and the light reflects off these mirrors

11:38and amplifies and comes out the end the pink beam that you see in here is ionized

11:43nitrogen that ionized nitrogen is used to bump into is a very crude analogy

11:51the co2 molecules and change their energy temporarily raise their energy and as the energy drops down

11:58that’s how we create our laser beam now exactly the same thing that’s happening within here now this 48 volt

12:05dc probably is using something like about 12 ounce that’s the power that we’re

12:12feeding into this device here we’re feeding 25 000 volts dc and we’ve got a current

12:19flow through here which is somewhere in the region of about say for 20 watts it’s ridiculously small

12:28at something like about 14 milliamps

12:33now the reason i’m pointing this out to you is what happens inside these black boxes is

12:40relatively unimportant what is more important is that when we look at the input

12:45we find that if i do a quick calculation there that’s 576

12:53watts of energy 48 times 12 defaults dc times

13:00current as watts that equals 576 watts that we’re putting in and what are

13:08we getting out 20.

13:14that’s interesting isn’t it what are we putting in here well to be honest although we put 25 000

13:22volts dc in once the tube has what they call struck or ignited

13:28we only need probably something like about 9 000 volts to sustain

13:35the beam so in this particular instance what we’ve got we’ve got 9000 volts

13:43times point zero four amps

13:54volts dc times amps and what does that give us

14:00126 watts so immediately you can see that

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

14:08the power requirement of this device is a lot less than this device this is a

14:14very power hungry device now not only is it power hungry and relatively inefficient as you can

14:20see we’re getting a little out for a lot in we’re getting a much better return

14:25on our investment with a glass tube when you’re putting all these watts in we get a huge amount of

14:36i really ought to draw it like this don’t i waste heat

14:42now for 20 watts on the device that i’ve got in there we have about 570

14:50watts of waste heat well look that’s more or less all of what we’re putting

14:55in i mean the numbers don’t compete exactly and i’m sure if i did it very exactly and they would balance but very crudely

15:04we’ve got something here which shows you clearly that this is throwing a lot of this energy away as

15:09heat which is why the fans are on there and why they they cause so much noise now you can

15:16have it water cooled but it doesn’t change this fact you’ve still got to drag away 570 watts and you’ve also then got to

15:23have a cooler or chiller that’s capable of cooling 570 watts so this starts to get quite expensive in

15:30terms of power i don’t have a 20 watt glass tube

15:35i have a 70 watt glass tube here we’ve got a chart so across the

15:42bottom we’ve got tube wattages so i’ve been able to check for rf tubes

15:49wattages right up to about 400 watts and at 400 watts this

15:55chart down the side here tells me that i’ve got 400 times 15.

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

16:02well 400 times 15 is 4 000 so that that is effectively 6 000

16:10watts of heat energy that i’m going to output so

16:17for 400 watts i’m going to create six kilowatts of heat energy

16:24that’s stupidly inefficient okay so that’s a factor of 15. but look as we

16:30start going down lower and lower for an rf tube the fact it gets even worse so let’s take a look here at

16:38something like about 10 watts at 10 watts we’ve got a factor of

16:43370 something like that so for a 10 watt output we’ve got 370

16:49watts of waste energy so my 70 watts if it was an rf tube

16:57would have something like about 1.2 kilowatts of heat now that’s that’s a small

17:03electric kettle now 10 liters of fluid in my reservoir

17:12would be up to boiling probably within about 10 minutes

17:18i was to put 1.2 kilowatts of heat into it i never get anywhere near those

17:23temperatures i mean i get maybe a one or two degree c

17:29temperature rise depends what the ambient is because we’re getting obviously lost through the side of the tank

17:34but but the point i’m really making here is we have minuscule amounts of heat generation

17:40from this system in relation to what we see here well let’s let’s just keep the mass

17:46simple shall we let’s just say we’ve got 20 watts in and therefore we’ve got 100 watts out

17:51well 100 watts is not going to cause a great deal of heating in 10 10 liters of water

17:57okay i’m going to finish up with 570 watts over half a kilowatt of heating that is

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

18:02going to have a big effect on a bulk of 10 liters of water so the point is this is a very

18:10inefficient system as far as power is concerned and energy conversion okay so that’s

18:17a big negative as far as it’s concerned but nobody ever worries about that because you just buy one of these machines you plug it in

18:24and you use it just to keep things nice and simple we’ll keep rf on the left hand side of

18:29the page and we’ll keep glass on the right hand side

18:36i’ve got a whole set of data sheets here from a company called syntec optronics

18:42they’re in singapore and they make they make huge numbers of all sorts of

18:48laser systems from uv laces right the way up to ir lasers like

18:54this and everything in between fiber optics you name it they make it and the great thing about

19:01them is they’re very honest with their data sheets so this is a great source

19:07to do comparisons when i look at other famous products like roofing and maybe coherent and other things

19:14you will find exactly the same sorts of performance specifications

19:20it’s a feature of the physics not of the manufacturer okay

19:26now the one thing that’s common throughout all of these rf laces is this factor here

19:34which is the mode quality now what is mode quant the energy of the light intensity within

19:41our beam is something called a gaussian distribution and here we’ve got a gaussian

19:48distribution and here we’ve got another gaussian distribution and another one and another one these are all gaussian distributions

19:56the only difference is if we look carefully we shall see that if you squash the base up you get a tall

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

20:04thin distribution and if you start stretching the base out like this you get a short fat like me oh no sorry

20:11i’m tall and fat um distribution this thing here called mode quality

20:20is how close to a gaussian distribution the

20:28light intensity is within the beam this is the perfect distribution and what they’re saying is

20:34well you know our distribution is pretty good look it’s it’s less than 1.2 now m

20:42squared equals one means it’s a perfect match for a gaussian distribution

20:49so at 1.2 it’s not a perfect match for a gaussian distribution

20:55whereas if we get a tall gaussian distribution like this and it has the top knocked off like that that is not a

21:01gaussian distribution so that’s you know it may well be that the problem is there

21:06or it may well be that the problem is down here somewhere like this you know either of those factors would

21:12make this a non-conforming gaussian distribution

21:17so the quality of the b is defined by this m squared number and the m squared

21:24number for all these rf laces is 1.2 now wherever you look

21:32on these spec sheets 1.2

21:371.2 1.2 add that to our list on the left hand side here m squared

21:44equals 1.2 our glass m squared equals

21:55beam quality is less than or equal to 1.1 but typically if you look through

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

22:04any specification for a glass tube you’ll find that the m squared value

22:09equals 1.1 so glass tubes if you want to use the

22:15word quality have got a much higher quality of beam than an

22:22 rf laser now that’s slightly contrary to the words that i’ve heard mentioned exhibitions by the sales guys for these

22:31machines who dramatically berate the chinese glass tube machines

22:40and greatly enhance the performance of their own rf tubes

22:47the facts don’t bear that claim out now the second fact that needs to be

22:55talked about something called beam divergence angle

23:01now beam divergence angle is exactly what it says but it’s expressed in a funny unit called milli radiance now

23:09one milli radian mrad basically what that means is the beam

23:18is going to expand from a starting point here over one meter a thousand millimeters

23:29it’s going to grow by one millimeter for a glass tube

23:36somewhere in the region of approximately three milli red beam divergence

23:44okay so what do we see for a rf tube 30 watts

23:52here we’ve got it seven seven

23:58[Music] 40 watts seven seven

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

24:09sixty watts and eighty watts seven seven seven so the rf b is not as

24:16compact it grows rapidly at least twice as fast as a glass tube laser i start off with a

24:24beam diameter of two millimeters diameter and i finish up with a beam diameter of

24:29nine millimeters diameter we don’t modify the beam we just fire our beam at mirror three

24:37with this you cannot fire the beam at mirror three you have to control the beam and in

24:43doing that what i’ve had to do i’ve had to increase the beam from two

24:49up to six millimeter diameter i actually put a

24:55times two beam expander in there which technically should have taken me from two to four

25:00millimeters didn’t work that way quite but hey i’m happy with the six millimeter beam

25:06that’s parallel so it hits mirror three at six millimeters diameter whereas here when i hit mirror three

25:12i start off at about four millimeters diameter

25:18and i grow over the same distance one millimeter and i’m gonna hit my beam i’m gonna hit

25:24mirror three with a slightly expanding five millimeter

25:29maybe even six millimeter b so i’ve got roughly

25:36the same amount of beam diameter hitting my mirrors the only difference is

25:43that this is a an element in the path which is going to consume something like

25:48about eight percent of my energy this does bring us on to another point as well

25:55and that is this look we started off with a two millimetre beam

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

26:03and okay so look it wasn’t perfect because it was an m 1.2

26:09maybe looking like this with a blunt a blunt point but because we’ve had to expand it we’ve

26:16had to take it from two millimeters here out to maybe six millimeters

26:23here now in taking it out to six millimeters

26:30look what we’ve done we’ve not changed the shape of the beam the beam has remained gaussian to the

26:37extent of 1.2 not gaussian but we’ve changed it from something that

26:44looks like this nice and sharp and pointy to something that looks like this

26:49which is a bit like a blunt pencil before i even get to mirror three

26:55i’ve degraded the beam that i’m going to be using for working through my lens so i’ve got

27:02a much better quality beam here from a glass tube by the time i get to my lens

27:08that i have here now the chances are i’m not going to be able to do as much damage because i’ve got a much softer

27:16beam now there’s an argument here which which goes something like this if you use a beam

27:22expander then you get a better focused point that’s what lens theory says and i agree entirely

27:28with what len’s theory says how do we get a focus point let’s start the other side here we’ve

27:35got this beam here it passes through this material and it gets changed its direction through refraction

27:42and it comes out the other side here and does this and this one here does the same

27:49it comes out here and does that and look focus

27:57and that’s the whole point of a lens it can it re-guides the beams from parallel down

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

28:03to a small point but hey that isn’t the end of the story but what about these beams here they

28:09come in like this and very crudely i’m going to just draw this

28:14slightly wrong and exaggerated but they do not come down

28:21to the same focus point we’ve got another focus point here

28:26and those rays so all the rays passing through this lens

28:32focus at different points now this ray that’s passing down the

28:39center the magic ray as i call it it’s a ray on its own

28:45how can it focus if it’s on its own you need another ray coming in from another

28:51direction to focus so that ray carries on

28:57to infinity theoretically and never focuses okay let’s just

29:04imagine what happens to these rays that are right right close to this one

29:11now you know what happens to two parallel lines they run parallel and if you change them very very

29:16slightly so they’re not parallel hang on that means that that’s going to focus some way

29:23out distant point what i’m really getting to here is there is a not a blind spot but almost a

29:31hole where the rays are out of control they’re not really being focused

29:38properly onto what you would expect to be the focus point it’s a we’ve got i like to call these rogue rays

29:44i’m not i’m not an optical engineer i’m just looking at this purely as a logical set of conditions we’ve seen this effect

29:52with some of the cutting experiments that i’ve done you know and i can show you that there is power

29:57way beyond the focal point let’s come back to this picture

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

30:03if we stretch our beam from two millimeters to eight or ten millimeters diameter sd

30:10you damage with light intensity look we’ve lost all the light intensity at the

30:15center and we’ve much more turn this into a uniform

30:21light pattern where the effect of these rogue rays has basically been

30:27minimized and what we’ve done we’ve actually corralled these rogue rays that are near to the center and we’ve now

30:33made them come back much closer to the correct focal point so yes

30:39increasing the diameter of the beam with a beam expander will allow you to focus the rays

30:47into a specific point much better that’s fine for engraving

30:54but it doesn’t help your cutting you don’t want the rays to be focused onto a specific point

30:59you need these rogue rays to get good cut basically concludes a bit of a comparison between the two

31:07systems the two laser source systems so on balance you would never buy

31:15an rf laser it’s inefficient it doesn’t do much for the beam

31:23and the other thing is if i want to buy 100 watt

31:30rf what’s it going to cost me

31:36well you’ll find it very difficult to find out but it’s in the region of

31:43probably 15 000 to 20 000

31:55if i want to buy a 100 watt

32:00glass tube what’s it gonna cost me let’s exaggerate and say something like

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

32:08about 500. if you want to waste your money on a recce then yeah you’ll pay a thousand dollars or more

32:16all right but discount different people claim different numbers

32:21for their systems five to ten times the lifetime of a glass two firms they will assume that

32:28this takes probably about two years and its life is gone whereas in fact from all practical experience of not

32:34only myself but other many people around the world that have got tubes at five six seven years old

32:40we know that glass tubes do not expire in two years i do know people that say that these

32:46only last about five years but let’s just give it the benefit of that and say 10 years

32:51if i have to replace the tube twice in the lifetime of the machine 20 years

32:58what’s it cost me it’s cost me 40k

33:04because it’s cheaper to replace than it is the regas and i hate the idea of regassing because you don’t get a chance to

33:10clean the cathodes which is where all the oxidation takes place okay so this is four four of these

33:17four years four times five years so

33:23so it’s going to cost us 2 000

33:29to replace the tube four times in 20 years

33:34now it doesn’t require a genius to say why would you spend your

33:41money on an rf laser tube that costs the earth does not perform as well as a glass tube

33:51i mean i’m not an advocate for either of these two systems i’m just putting the facts in front of you i

33:57really wanted this to succeed and be a fast really good machine

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

34:03that would run rings around the glass tube machine i didn’t think it would ever be in terms of cost

34:09how do you control the power that you get out of these machines well with the rf they always use something

34:16called pwmc it’s a square wave like that which is normally at the uh transistor

34:23level five volt d and then along here we’ve

34:29got hertz frequency this frequency here is a roundabout maximum of 20 sometimes 25 kilohertz

34:40okay now that’s got nothing to do with the 100 megahertz that’s used

34:49to generate the arc that’s within the tube these are two completely separate

34:54frequencies that do not get involved with each other this one has a control of the output

35:00signal and this one is for generating the laser itself

35:05as we’ve already discussed in earlier sessions when i’ve talked about this control system the five volt dc is only

35:12switching on fully switching on the power that’s coming out of the laser so if you’ve got

35:18a 60 watt laser you will be switching on 60 watts

35:26it can’t do anything else it either turns the laser on or off the idea of this pwm signal

35:33is pretty simple if you allow the signal to be zero

35:40five volts like that in other words what you do you close down these gaps here so that

35:47the signal is on all the time then you have something called cw continuous wave you don’t have a chopped

35:54up 60 watt power you have 60 watts of continuous output power and that’s what you need for cutting you

36:00don’t want to compromise your power when you’re cutting you need it all now 100 power means we’re going to switch it on

36:05and it’s going to stay on all the time like that and if you want 50 power this is the

36:11frequency from here to here this is one cycle what you do you put a certain proportion

36:18of the cycle 50 percent of the cycle on and 50 of the cycle off

36:25so it’s delivering 60 watts for that amount of time and delivering zero watts for that

36:31amount of time the argument goes that on average what you’ve done you’ve decreased the power

36:37to 30 watts we’re not talking about doing average damage we do

36:42real damage over a period of time so there’s a very complex relationship

36:47between frequency power and what they call duty cycle

36:54in other words the amount of time you spend on and the amount of time you spend off

36:59now i’ve already demonstrated this to you the way in which i’ve been able to

37:05manipulate and play with these numbers to get let’s call them dots but they’re

37:10not really dots because this machine cannot produce photographic dots it can only produce

37:16lines this is a very complex way of controlling the power for

37:24engraving if you look at the reader handbook for the controller they recommend that

37:30for glass tubes you use something called analog output which basically means something very simple like zero

37:36and five volts there’s a scale which a signal which comes out which is

37:42anything between these two voltages here and whatever that number is is fed into

37:48the hv power supply and the hv power supply then supplies

37:56a percentage of its maximum output so say this 8 volt power supply could supply 30 milliamps

38:05zero volts equals zero milliamps

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

38:12and five volts equals thirty milliamps and everything in

38:19between everything in between is proportional so if you want 50 the output of the power

38:26supply you call up for 50 okay of that so two and a half volts and that’s the

38:33way that this works very simply when you want to change power you change power by just calling up your

38:39percent power and you’re not fiddling with this you’re purely adjusting the current that

38:46flows through the tube directly here you’ve got simply power and speed now that brings us round

38:55full circle to where we started from power for a given period of time with this system

39:01it’s intuitive so pwm is outside many people’s sphere of

39:08understanding or knowledge the only problem with the glass tube is the linear relationship is between the

39:14percent power and the current flowing through the tube and there isn’t a relationship between

39:20the current flowing through the tube and the watts that come out of the tube so at the end of the day there is not a

39:26linear relationship between here and the watts

39:33so speed is a much more logical way to control the power with the glass tube i understand how both these systems work

39:38now and i can see clearly that it would be possible to run a glass tube with an rf

39:47control system now bear in mind that rf is the mechanism by which the laser beam

39:52is being produced not the mechanism by which it’s being controlled so there is no logical reason why i

39:59couldn’t use this complex system for running a glass tube now the great advantage

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

40:08of this and its only great advantage is its speed of switching

40:15the speed of switching is all to do with the way in which any gas discharge tube works before you

40:22get power out of a gas discharge system you have a zone let’s call that power

40:31watts if you like there is a zone in here where

40:40things are very uncertain and it takes time for the beam to establish a constant

40:46output power okay now there’s the constant output power let’s call it 60 watts

40:56okay now this picture here applies to both glass and rf laser tubes now you can see i put

41:04this strange block here and that’s because this is something called pre

41:12ionization

41:19it’s a zone that exists for all gas discharge systems regardless of whether it’s rf or

41:27constant current glass tube and during that period of time

41:35there is huge uncertainty about exactly what’s going on inside that tube and i don’t mean

41:41uncertainty from the outside because we know that there’s things going on but they’re not under control

41:47you get incredibly high spikes of very very high frequency energy that

41:53can be taking place during that period of time okay before it settles down to a nice

41:59steady controllable output so it’s a region of uncertainty

Transcript for Let’s Compare RF And Glass Tubes (Cont…)

42:06and on the glass tubes you can exploit that because it is very high frequency very

42:12high pulses it’s superb for doing glass engraving for cutting card without scorching it’s got all

42:19sorts of great uses but the problem is

42:26if you switch your signals i want to switch on the laser tube now

42:32what has to happen is this is the this is the if you like the switch on signal from the controller

42:39that signal then has to go through the power supply and the hv power supply has to generate

42:44some high voltage to make the tube switch on and the switch on

42:49time is such that it could be

42:54it does something like this before it reaches 61. a normal glass 2 power supply claims that you can

43:01get to 90 of your demand value in less than

43:08one millisecond now one millisecond is like a year in electronics time so it takes a finite

43:16amount of time for the power to appear when you’re trying to switch on an hv power supply

43:25with this system here with an rf system what you do you have this

43:32switch on period nullified because you hold the beam with a special thing called a tickle

43:38current you hold it here so it’s just hovering there all the time not it’s not doing it’s not got enough power to do anything

43:45but it’s sitting there so at the moment you switch on the moment you say i want to switch the power on it

43:52instantly switches on and you’ve got 60 watts there so that’s the big advantage of an rf

44:00tube you lose the pre-ionization zone because the pre-ionisation zone is

44:06nullified by what they call a pre-ignition signal is sitting there waiting to switch on

44:11the instant that you ask for the power to be available but from what everything that i’ve gathered

44:17that’s really the only positive advantage for an rf system it’s switching speed

44:26but now i’m going to surprise you and say because i understand this

44:31i could make a glass tube system do exactly the same thing

44:40that’s for another day i think we’ll stop at that point and say yes we’ve confirmed several

44:48things first of all i haven’t got enough power to do much damage with this machine at 20 watts

44:54and secondly i’m very disappointed that there is no magic in the rf system after all i’ve shown you both sides of

45:01the argument you can work out for yourself whether either side of the argument is right or wrong

45:06and you can wire up the pluses and the minus for yourself i’m afraid the whole thing on this side

45:12appears to be minus except for this final point here which is response speed well if i can do it for

45:20here i can probably do it for here as well so the only message i can really finish up with is maybe you’re not going

45:28to rush out after all and buy an rf machine so i’ll leave that with you thank you very much and i’ll catch

45:33up with you in the next session

Transcript for Let’s Compare RF And Glass Tubes