CRT monitor radiation measurement project

[regulaz]

hi im new here so hello fellas!

i'm using an old school 21 inch CRt monitor as those used in graphics industry around 6 years ago.

i was curious about how much radiation it was actually outputting.

there is an anti radiation screen in front of this with a grounding cord which goes into the ground of the electrical outlet.

i took a multimeter set it on AC 2 volts setting and it measured 300 millivolts.

now im curious if this is actually the electric radiation being measured or is this something else?

does this prove the anti radiation screen is necessary for CRT type monitor?

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one more question my 29 inch CRT TV has a 2 pronged plug and measured in the same way as above shows 40 volts... the cable box when turned on increases this 40 volts figure to around 100-200 volts fluctuating. when i touch the base of the cable box with one lead and the ground with another lead it read 90 volts.

it looks a little dangerous to me, but im not sure if im measuring the radiation or something else. i have 220 volts 50 hz power system here.

thanks.

 

[Nigel Goodwin]

No it's not 'radiation' - and assuming there is any 'radiation' from CRT monitors, then measuring it would be a fairly complicated affair - first off you would need to decide what type you were looking for.

 

[regulaz]

No it's not 'radiation' - and assuming there is any 'radiation' from CRT monitors, then measuring it would be a fairly complicated affair - first off you would need to decide what type you were looking for.

thanks for the quick reply, what is the meter showing then? where is 300 millivolts coming from and 40 - 200 volts?

i thought the filter was netting all variety of waves and their energy dissipating through the ground cord?

 

[cowboybob]

I'm assuming the first reading you mention (300mVAC ) was between the "radiation screen" and ground.

There is, indeed, some electromagnetic radiation being emitted from the CRT face that is interacting with the screen, generating some, if not all, of the 300mVAC.

The other values you mention I would suggest are "ground loop" values generated by the lack of a properly grounded eqiupment.

And, yes, they can be dangerous.

Now, as far as the radiation from the screen is concerned, determining its composition would require some rather more sophisticated equipment than the meter you have at hand.

That said, as the radition's strength is a ratio of the inverse of the distance squared from the screen, most safety studies have concluded that there is little danger from that radiation if the monitor is used as specified by the manufacturer.

And the screen, properly used, can reduce that value even more, although I don't think that I would bother.

 

[regulaz]

I'm assuming the first reading you mention (300mVAC ) was between the "radiation screen" and ground.

There is, indeed, some electromagnetic radiation being emitted from the CRT face that is interacting with the screen, generating some, if not all, of the 300mVAC.

The other values you mention I would suggest are "ground loop" values generated by the lack of a properly grounded eqiupment.

And, yes, they can be dangerous.

Now, as far as the radiation from the screen is concerned, determining its composition would require some rather more sophisticated equipment than the meter you have at hand.

That said, as the radition's strength is a ratio of the inverse of the distance squared from the screen, most safety studies have concluded that there is little danger from that radiation if the monitor is used as specified by the manufacturer.

And the screen, properly used, can reduce that value even more, although I don't think that I would bother.

thanks for the reply, yes your assumption is right.

is this ground loop issue due to house wiring (it has a separate ground cable) or the equipment being two pronged? tips on where to begin fixing this will be useful.

 

[cowboybob]

From what you've posted, I'd say it is the two prong plugs, that lack a separate "safety" ground lead, that are the problem.

You might want to consult with a qualified electronics technician before attempting to add a safety ground lead to the equipment.

If it were me, I'd do it, but I have no idea of your level of expertise.

 

[Nigel Goodwin]

thanks for the quick reply, what is the meter showing then? where is 300 millivolts coming from and 40 - 200 volts?

High impedance meters and scopes pick up all kind of crap floating around - including mains hum and any RF transmissions.

Monitoring 'radiation' from a CRT would require much more substantial test equipment, and I wouldn't have a clue how you'd do it? - ask the Swiss

 

[regulaz]

From what you've posted, I'd say it is the two prong plugs, that lack a separate "safety" ground lead, that are the problem.

You might want to consult with a qualified electronics technician before attempting to add a safety ground lead to the equipment.

If it were me, I'd do it, but I have no idea of your level of expertise.

i called a crt repairman he told me two prongs is how it works and talked about shorting something if he provided an extra ground ?

anyway i did start isolating equipment. the cable box on its own is okay.. no voltage from its metal base to ground if plugged in the mains.

the 29" tele is still showing 40 volts even when separately plugged in the mains.


the odd thing is that 21" CRt monitor also has 40 volts showing but when i plug in the vga cable (it has a ground i guess) the voltage reading drops to 300 millivolts. on the other hand in the tele when i plug in the cable box and turn it on the voltage goes up to 200volts

i can do the 2 prong to 3 prong at the plug but inside the tele is not my thing, i could do it if there was a howto/walkthrough though.

 

[regulaz]

High impedance meters and scopes pick up all kind of crap floating around - including mains hum and any RF transmissions.

Monitoring 'radiation' from a CRT would require much more substantial test equipment, and I wouldn't have a clue how you'd do it? - ask the Swiss

i guess so , but i gotta do with the meter i have for now

 

[cowboybob]

I say this only as a cautionary statement:

Lethal voltages may be present!!" Use extreme caution!!

anyway i did start isolating equipment. the cable box on its own is okay.. no voltage from its metal base to ground if plugged in the mains.

Might be that the cable box metal base is "floating", i.e., connected to nothing, just an electrically isolated support for the electronic guts.

the 29" tele is still showing 40 volts even when separately plugged in the mains.

Whatever test point you are using on the tele is connected to the electronic guts.

the odd thing is that 21" CRt monitor also has 40 volts showing but when i plug in the vga cable (it has a ground i guess) the voltage reading drops to 300 millivolts.

What is connected to the other end of the VGA cable?

on the other hand in the tele when i plug in the cable box and turn it on the voltage goes up to 200volts

With the tele un-plugged from the mains and everything else, connect any portion of the tele chassis metal frame holding the electronics (this might be accessaible at an external antenna/cable connector [the threaded part], for example) to a known household ground. NOT the "return" lead of the mains, but the separate ground (earth) lead.

This could be done temporarily with an appropriate "jumper' cable.

With the tele again connected to to the mains, check fro the ground loop voltage again. It should be zero.

 

[regulaz]

on the other hand in the tele when i plug in the cable box and turn it on the voltage goes up to 200volts

What is the VGA cable connected to at the other end?



i can do the 2 prong to 3 prong at the plug but inside the tele is not my thing, i could do it if there was a howto/walkthrough though.[/QUOTE][/QUOTE]



the vga cable is connected to the desktop pc which then goes to a UPS which goes into the powerpoint in the room..

(the computer/monitor is in a different room and tele in a different room - both circuits on separate MCBs but same ground wire running through the house)


vga cable is for the monitor/desktop connection. coax cable for cable box and tele

 

[cowboybob]

regulaz,

Please re-read post #10. Somehow I posted gibberish.

I've edited the post such that it makes more sense.

CBB

 

[regulaz]

I say this only as a cautionary statement:

Lethal voltages may be present!!" Use extreme caution!!



Might be that the cable box metal base is "floating", i.e., connected to nothing, just an electrically isolated support for the electronic guts.



Whatever test point you are using on the tele is connected to the electronic guts.



What is connected to the other end of the VGA cable?



With the tele un-plugged from the mains and everything else, connect any portion of the tele chassis metal frame holding the electronics (this might be accessaible at an external antenna/cable connector [the threaded part], for example) to a known household ground. NOT the "return" lead of the mains, but the separate ground (earth) lead.

This could be done temporarily with an appropriate "jumper' cable.

With the tele again connected to to the mains, check fro the ground loop voltage again. It should be zero.

it measures 2.8 volts with tv unplugged and when connected to mains 145 volts. its not zero.

the vga cable question ive answered in the previous post.

 

[cowboybob]

OK.

The quote above looks horribly out of context.

Let's start over.

With the tele unplugged and still with 2.8VAC showing I'd say you have a lot of 50Hz spurious radiation flying around in the room. Nothing much to do about that.

But with 145 VAC showing with the tele on mains you, for sure, do not have a grounded device. If I may ask again, if you ground the point that your are using to measure the 145VAC, do you still have a significant voltage present?

I'm beginning to wonder about your earth grounding point...

 

[regulaz]

OK.

The quote above looks horribly out of context.

Let's start over.

With the tele unplugged and still with 2.8VAC showing I'd say you have a lot of 50Hz spurious radiation flying around in the room. Nothing much to do about that.

But with 145 VAC showing with the tele on mains you, for sure, do not have a grounded device. If I may ask again, if you ground the point that your are using to measure the 145VAC, do you still have a significant voltage present?

I'm beginning to wonder about your earth grounding point...

the point where im connecting the lead in the tele is the centre pin of the coax input, that is too tiny a point to ground separately and stick the lead into simultaneously. if there is some other point on the outside for the tele where i could ground and separate point where i could stick the lead then i'll be able to answer your question. any ideas where else can i stick the lead?

if you tell me where you're going with this i could have a tele repairman come in to check it.

lot of 50 hz spurious radiation? that couldnt be good for health... or the earth point is probably bad?

 

[regulaz]

yes i did it using the outside of a RCA cable connector. it does read zero now instead of 145 vac and 0.4 VAC instead of 2.8VAC .

 

[cowboybob]

Good.

Sounds like you're on your way to correcting the grounding problems. And it sounds like you have, for the most part, a decent earth ground.

Just so you know, the center pin of most two wire, circular connectors with a single center post, is the "signal" lead, which is never ground.

<EDIT> The spurious 50Hz (or 60Hz) is everywhere. Depending on who you ask, it can be bad for you, or not. I subscribe to the school of thought that believes, as a rule, it's generally harmless in the long run.

 

[regulaz]

Good.

Sounds like you're on your way to correcting the grounding problems. And it sounds like you have, for the most part, a decent earth ground.

Just so you know, the center pin of most two wire, circular connectors with a single center post, is the "signal" lead, which is never ground.

great thanks for getting the earth point verified. now what should be the next step? the equipment when connected as usual goes back tobehaving poorly.

while the tele chasis shows a 0 voltage with a separate ground provided... the anti radiation screen still catches 200 volts and the chasis of the cable box (without a separate ground) is at 90 volts..

 

[cowboybob]

great thanks for getting the earth point verified. now what should be the next step? the equipment when connected goes back to behaving poorly.

Behaving badly how??

 

[regulaz]

Behaving badly how??

i have an anti radiation screen in front of the tele) when i connect a lead of the meter to the screen and the other lead to the ground i get a reading of 100-200 volts fluctuating rapidly (even while providing the tele a separate ground).