EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Jbliss on April 18, 2015, 05:19:01 am
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Hi just brought my first osilscope and it has a CRT just wondering if they were in any way dangerous or emit and dangerous radiation
Thanks
\ :-BROKE
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They are not dangerous in the way of emitting xrays or anything like radiation. What is dangerous, possibly lethal, is playing around inside with the CRT and it supporting high voltages without proper instruction and experience. Use it with confidence. Don't poke around inside unless you understand the risks.
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My monitor proclaims (on an internal panel) that it produces something like 0.5uSv/hr of x-ray output; somewhere around background radiation. Most CRTs should have similar performance, but I suppose you could always find an unlucky brand:
http://i.imgur.com/Oi96lcm.jpg (http://i.imgur.com/Oi96lcm.jpg)
Tim
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Hi just brought my first osilscope and it has a CRT just wondering if they were in any way dangerous or emit and dangerous radiation
Thanks
\ :-BROKE
Yes. Look at all these people who have been using CRTs for 30+ years. They are all slowly dying. They say you will be older by a year every year you use a CRT. |O
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[Yes. Look at all these people who have been using CRTs for 30+ years. They are all slowly dying.
Life: The incurable, fatal sexually transmitted disease.
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Yeah, all vacuum tubes that use high voltages > several hundred volts occasionally create an high-energy photons in very low levels, soft x rays. Pre-transistor TVs were even worse because they not only had the CRTs, but also around 50 other vacuum tubes to run it. Anyway, nothing to worry about. A few microsieverts are not going to kill you, you will probably get more from natural potassium exposure.
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I wouldn't worry too much about the X-rays from an oscilloscope as much as the lead that you're exposed to while soldering / desoldering.
Or how about the toxic chemicals and epoxies that go into PC boards.
If you eat a CRT, you might get sick.
:scared: :-DD
Life: The incurable, fatal sexually transmitted disease.
@BradC: So funny! but so true. :-+
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Using an oscilloscope CRT is ok, anyway everything has more or less been proven to give cancer nowadays. However every time I disassemble a device with glass under vacuum stuff in it and see stickers like "Handle with care! Risk of implosion!" it creeps me out.
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If you eat a CRT, you might get sick.
:-DD
I wouldn't be surprised to find this on some safety sticker!
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If you got yourself an 80 inch CRT, sat in front of it for months with it showing a bright white image at maximum brightness and minimum contrast, you will get the equivalent of eating a bunch of Bananas in that period.
As somebody who, when growing up, had a garden that was more than half banana plants, and where we regularly had 3 40kg bunches hanging on a steel hook where we had to either eat them, cook them or make banana bread by the freezer full out of them before they went too bad to touch ( was rare, I like bananas) I ate a lot of them. I have normal radiation levels in my body ( confirmed a few times going into a nuclear plant, you could trigger the alarm with a bunch of bananas in your lunch) after all that.
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Thanks guys just paranoid.
:)
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Thanks guys just paranoid.
:)
Serious question, i do not want to be mean, i am just curious :)
Might i ask you how old you are?
Until a few years ago CRTs were everywere, multiple ones in each household.
You could not walk 100 meters in a straight line without running into one.
It seems that we reached the point were they have become something the youth only knows from pictures?
Greetings,
Peter
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It seems that we reached the point were they have become something the youth only knows from pictures?
Like self control, self censoring and the ability _not_ to share their entire lives on-line?
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you need in the teens of kilovolts to start generation of x-rays.
Your 'scope is probably 1 to 5kv.
Make and model?
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you need in the teens of kilovolts to start generation of x-rays.
Surely this depends on the method of generating the X-rays?
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If you break the glass and eat it yes it could be dangerous, BTW avoid looking at the wrong end that could be Dangerous. high voltage there.
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It's the stopping of the electron, that emits a photon, energy /frequency = voltage. The rate of radiation is very low and the energy similarly so. I recall there were some 'tricks' to reduce the radiation but it is very low. Be more worried about the mains voltage and some of the dodgy chemicals.
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My understanding is that there was some significant radiation from early shadow-mask color CRTs, from the electron beam hitting the metal surface of the mask, rather like an X-ray tube. But then they started using leaded glass to block most ionizing radiation.
IIRC, The amount of radiation from monochrome CRTs (i.e. virtually all CROs) was only a laboratory curiosity and not considered harmful by any measure.
Of course the high voltage used by any fire-bottle is potentially lethal, and the extra high voltage used by CR tubes even more so.
Note further that many (most?) TV tubes actually have an intrinsic capacitor formed by the aquadag conductive coating on the inside of the tube, the glass envelope of the tube, and an outer coating of aquadag which is grounded. This forms a filter capacitor for the accelerating voltage when it is generated by the 15,750 Hz flyback transformer. Same effect as a Leyden Jar.
Many people have been seriously zapped by tubes which they assumed were "inert".
http://en.wikipedia.org/wiki/Aquadag (http://en.wikipedia.org/wiki/Aquadag)
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stay away from back of the CRT as I said .
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CRT necks aren't usually too bad... depends though. Scopes, and maybe some very old TV sets, use -HV on the cathode and ~0V on the anode. (Fancy Tek tubes usually do this, but have a final HV in the 5-15kV range anyway. The voltages are kind of all over the place. :) ) Almost all magnetic deflection tubes use ~0V around the neck, with up to 100-200V for grid/cathode voltage (which admittedly is still enough to be dangerous to those leaky meat-sacks with fingers :P ) and one pin in the ~kV range (focus anode).
Of course, TV sets are usually not isolated, so touching anything inside carries line potential with it, with respect to earth ground, as well. Whether you're in the HV area, around the LV signals, or the power supply line area itself.
Tim
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I wouldn't worry too much about the X-rays from an oscilloscope as much as the lead that you're exposed to while soldering / desoldering.
Or how about the toxic chemicals and epoxies that go into PC boards.
If you eat a CRT, you might get sick.
:scared: :-DD
Life: The incurable, fatal sexually transmitted disease.
@BradC: So funny! but so true. :-+
Heartburn presumably. Heck, it is not that long ago we had leaded-gasoline. Or when the car came back from the workshop it said "dust from drum brakes cleaned". Read: we used the compressed air hose to blow out the asbestos dust.. :o
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Xrays are not an issue with an intact tube/mounting system. But be careful with possible implosion of TV tubes - wear safety glasses, watch out for high voltages stored in the tube, and if the tube breaks open dispose of it with care due to heavy metals in the getter. A CRT is a huge capacitor with a glass dielectric and aluminum and dag conductors. When the unit is turned off the tube will store thousands of volts. There is often a bleeder resistor to take the voltage down, but even after discharging it and disconnecting the anode lead, charge will slowly migrate from within the glass and you can still get a painful poke, even days later. I worked in the CRT industry, standard lab practice was to push an insulated handle screw driver, with a grounded wire clip on the metal shaft, under the anode cap to discharge the tube before disconnecting the anode. This assumes the outside dag coating is grounded - just be sure the anode button is shorted to the dag. The rimband is probably connected to the dag so it's mounting ears can make a good attachment point for the lead clip.
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When you push that screwdriver under the anode cap make sure you do not scratch the glass, or
be prepared for a face transplant. Nice if screwdriver had no edges or pointed contact points.
Regards, Dana.
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I don't think the OP uses that CRT scope anymore, because it broke (mentioned in another thread). This thread is almost a year old.
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When you push that screwdriver under the anode cap make sure you do not scratch the glass, or
be prepared for a face transplant. Nice of screwdriver had no edges or pointed contact points.
Regards, Dana.
Not to worry, they're a lot more sturdy than you might expect and the leaded glass is not easy to scratch, especially deep enough to compromise it's mechanical integrity.
If you do compromise the vacuum it is most likely to occur by breaking the neck which is more fragile but that will not cause an implosion.
Another caution, never remove the implosion protection which is generally a rimband which usually doubles as the mounting bracket. The tension band greatly minimizes the possible damage from an implosion.
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CRTs don't explode, they implode. The problem with early TV CRTs and many scope CRTs was they didn't have a reinforced faceplate and a steel rimband to prevent it fracturing catastrophically, so any scratch or impact could possibly crack the tube neck launching the base and gun assembly straight through the screen, showering the viewer with high velocity glass and metal shrapnel if the toughened glass or plastic implosion protection shield was missing.
Damage to the rear of a modern tube that doesn't compromise its faceplate rim is almost always far less dramatic, though any time you are handling glass under vacuum, safety glasses should be worn.
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I always thought that the purpose of the implosion protection band was to hold the base of the curved face of the CRT in compression (a bit like the chain around the dome of St Pauls Cathedral) to prevent it from imploding under a heavy front impact. I don't think it would have any effect on internal components being projected into the rear of the screen. In that case all the heavy glass of the cone is domed outwards too and the neck components are relatively low mass.
I've never seen a flat faced oscilloscope CRT with a protection band. They're always required to have a front plastic shield fitted (according to the Tek manual anyway).
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When I was a kid of about 14 in the '60s our B&W TV died and we had to get a new one. This was a big deal for us. A new TV was an event that ranked just short of buying a “new” car. This was exciting enough but when it arrived they then gave me what was probably the best present I have ever received and it wasn’t even Christmas. I got the old TV (sans picture tube) to do with as I pleased. This was, to me, the next best thing to money. In fact it was better than money since if I had any I wouldn’t know what to do with it and probably would have wasted it on junk food or comic books. No, with the old TV I could take it apart and wonder what each of the diverse and strange pieces did and how.
As I said, I did not get the entire TV. The picture tube I was not allowed to touch. It was known to be dangerous, and rightly so, at that time. Disposing of it fell to the capable hands of my bigger brother, Bob, nine years my senior who was deemed more worldly wise than I since he was already working at a steady job and making his own money. He had already taken a course in electricity and electronics in high school and so was assumed to be more expert than I when it came to this kind of stuff. In those days picture tubes were not made as they were later with an inch and a half of resin covering the display surface as a safety measure to prevent implosion or to protect one from it. The sets themselves were built with a sheet of tempered window glass fixed to the front of the cabinet in front of the picture tube so that should the worst happen then the glass shards would probably not come through the front of the set to dice us all. I was later to find out, in fact, that tube implosions during handling at the factory where they were made were then not uncommon. The manufacture of picture tubes was not as automated as later on so they were handled by people at several stages during their assembly with the inevitable spectacular failures due to weaknesses in the glass falling susceptible to the odd bump. I do not know what the casualty rate was for those in those jobs nor do I know if they got extra danger pay. They should have.
Bob wrapped it in a couple of my dads’ old WW II army blankets and set it into a cardboard box in the trunk of our old ’55 Chevy for the trip to the dump. Dad drove with Bob in the front seat and me in the back as I would be hanged if I didn’t come to see the action. The tension was palpable. The trip was slow as we all felt as though we were a transporting a nitro-glycerin bomb. After lifting it out of the trunk and placing it gingerly face-down in the middle of the trash heap without its protective blankets we scurried back to take refuge behind a pile of garbage some eighty feet away. Bob hoped that this would be far enough away to save us should the dump be rocked by the explosion we felt must surely come. We were not to be disappointed. Then choosing a moment when we were sure there were no passers-by within shrapnel range, Bob heaved a pop bottle at it and at once we were answered by a loud bang and the sound of a million pieces of glass which shot straight up ten or twenty feet and came straight down to the place it just departed. If Bob was nonchalant, then I, at least, was relieved that we survived to go home and tell the tale.
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My monitor proclaims (on an internal panel) that it produces something like 0.5uSv/hr of x-ray output; somewhere around background radiation. Most CRTs should have similar performance, but I suppose you could always find an unlucky brand:
http://i.imgur.com/Oi96lcm.jpg (http://i.imgur.com/Oi96lcm.jpg)
Tim
Tim, to put that radiation in to some context, when I was at secondary school in the early 1970s you could still buy uranium IV oxide to make up stunning red, orange and yellow glazes, and it was far cheaper to buy than the inferior selenium oxide (5g of selenium cost £5, whereas 100g of uranium oxide cost me 99p). I used to make it up in a blue plastic bucket with a wooden stick to stir and then dipped my pots in by hand, with no protective gear on whatsoever. I'm still going strong and have never suffered from any radiation related cancers. If uranium oxide were available today I would still happily use it, but sadly it is deemed too dangerous these days. :) ;D