CRT monitor radiation measurement project

[cowboybob]

Is the rad screen somehow attached to the tele? Is it (the rad screen) grounded?

 

[regulaz]

the rad screen is not grounded and not attached to the tele in the sense no metallic parts touch , only plastics.

 

[regulaz]

ah i grounded the rad screen and now that too is showing 0 VAC. thanks so much cowboybob.

but im surprised to see 200 VAC on the rad screen in the 29 inch Tele while just 300 millivolts on the 21" monitor that meets tco 95.

 

[cowboybob]

Plastics can conduct, or deveop a static charge (not unlike a comb rubbed on the hair of your head).

Is the rad screen touching the glass of the CRT of the tele. Or even just very, very close? There might be a capacitive effect between the two. There are very high electrostatic voltages on the interior face of the CRT that might be causing a charge to develop on the rad screen.

Anyway, if there is a reasonable way to ground the rad screen, you could try that.

Although, I'm pretty sure the voltages you're seeing are very low current and, as such, generally non-lethal.

 

[regulaz]

yes the rad screen is very very close to both but one is tco 95 certified one isnt. do you suppose it is unnecessary given the very low amount of current ? or should i have one for the 29inch non tco tele which develops 200 VAC on the screen surface?

 

[cowboybob]

This from the TCO 95 Standards description:

Emissions
- Considerable reduction of magnetic and electrical fields.
- Minimized electrostatic fields.

Operative concern for the tele is a lack of these reductions. But even at their worst, generally of little concern, unless you plaster your face to the front of the tele and sleep with it there. Most likely long term effect would be a severe sunburn. Years of it might cause cataracts.

 

[regulaz]

This from the TCO 95 Standards description:

Emissions
- Considerable reduction of magnetic and electrical fields.
- Minimized electrostatic fields.

Operative concern for the tele is a lack of these reductions. But even at their worst, generally of little concern, unless you plaster your face to the front of the tele and sleep with it there. Most likely long term effect would be a severe sunburn. Years of it might cause cataracts.

well i guess ill let the rad screens stay, have been used to them.

that wraps up about 95% of the discussion. in the end id just mention the rad screen measurements from one tco certified monitor of 22inches at 1 volt and another non tco certified lcd with wled backlight 24 inches at 1.5 volts which were surprising since these were more than the CRT while the lcds are considered far more benign. this matters for people who spend most of their time on the displays

 

[unclejed613]

the electromagnetic radiation is measured with a magnetic pickup for low frequencies (such as 50-60hz and up to a few hundred khz) and an antenna for higher frequencies. when you measure with a 10MEG meter, or an oscope (which has a 1MEG input impedance) you really don't know how much of the voltage meaurements you are seeing are the result of leakage currents, where a few hundred microamps will show up as hundreds of volts. with a "real world" loading path, (such as 50-60k ohms for the human body with dry skin), those voltages drop a lot, to less than 1% of what they appeared to be with the high impedance of the meter or scope attached. when properly attached to other devices that also provide a low impedance path, those incredibly high voltages drop to next to nothing.

as for other forms of radiation possible from a CRT screen, low level Xrays can be produced by the collision of the electron beam with the shadow mask and phosphors, and this is one reason there are devices to limit the anode voltage on the tube. this is also why CRT tubes are so heavy, as there's a lot of lead (Pb) in the glass, especially on the thick glass on the face of the tube. the lead absorbs xrays.

 

[Nigel Goodwin]

well i guess ill let the rad screens stay, have been used to them.

that wraps up about 95% of the discussion. in the end id just mention the rad screen measurements from one tco certified monitor of 22inches at 1 volt and another non tco certified lcd with wled backlight 24 inches at 1.5 volts which were surprising since these were more than the CRT while the lcds are considered far more benign. this matters for people who spend most of their time on the displays

Again, you're 'measuring' just random rubbish and it's totally meaningless - your 'radiation screens' are just a scam and a total waste of time and money (but if it makes you happy, then that's all that matters).

 

[KeepItSimpleStupid]

This whole thread is just getting too wierd.

What is the mains voltage and frequency where the OP lives? Is the US and 120 VAC or some 240 V system?

That shield is made of muMetal and electromagnetic shield. It HELPS prevent the Earth's magnetic field from messing with the deflection. The CRT happens to get magnetized in operation and there is an automatic Degaussing circuit near that shield.

Usually a NTC resistor applies power to this degauss coil when the monitor starts up to demagnetize the CRT. You might be seeing the effects of this. It's like a small EMP pulse when the TV starts up. I used to hear it as a thump in early sets made in 1968.

If this is a Sony Trinitron monitor, there is a metal grid barely visible from the front. It's part of the monitor design. The Trinitron doesn't have to be aligned, if I remember right.

 

[ronsimpson]

CRT monitor radiation measurement project

What type of radiation? When we made CRT monitors we measured many different types of radiation.

The Trinitron doesn't have to be aligned, if I remember right.

I designed CRT monitors for Sony and they need aligned.

Toward the end the 'government' was very hard on us about 'radiation'. We made special yokes that reduced magnetic radiation at 60-80hz and 30-100khz. (vertical and horizontal frequency of a typical 21" CRT monitor) We put shielding on transformers to keep the 100khz power frequency from radiating. CRTs got more metal. The plastics received special metal spray on the inside. The video amplifiers went into metal boxes to keep the RF radiation down. We tried to keep the HV down.

 

[KeepItSimpleStupid]

@ronsimpson
The Trinitron didn't require convergence adjustments.

This article: https://en.wikipedia.org/wiki/Trinitron says no adjustments post manufacturer.

 

[unclejed613]

i've replaced trinitron tubes, and yes, they do require some alignment (however, purity, and convergence were simplified to the point where it took 1 hour or less compared to the 3 or so hours required before), but not as much as tubes that had the 3 guns arranged in a triangle. "inline" tubes later copied the gun structure of the trinitron, and that simplified the adjustments, but they still required some tweaking after replacement. when i repaired computer monitors, new tubes often came without yokes and alignment rings, so the old yoke and alignment rings had to be transferred to the new tube, and the whole process of tube alignment and convergence had to be done. the convergence electronics and active convergence electromagnets were no longer required (the constant tweaking of the interactive controls on a convergence board could take up to 3 hours because you'd do one pass, but since the controls interacted with each other, you'd do another pass and get it closer, and so on....), , but the ring alignment had to be done and the yoke had to be wedged properly. i had a special crosshatch pattern made of red, green, and blue segments that worked extremely well, because all you had to do was line up the segments in straight lines.

 

[ronsimpson]

The Trinitron didn't require convergence adjustments.
This article: https://en.wikipedia.org/wiki/Trinitron says no adjustments post manufacturer.

I am thinking from a manufacturer view point. Sounds like UncleJed has been there to.
I think we are off topic again.

 

[regulaz]

What is the mains voltage and frequency where the OP lives? Is the US and 120 VAC or some 240 V system?

That shield

I used to hear it as a thump in early sets made in 1968.

If this is a Sony Trinitron monitor

its 240V system

which shield ? internal to CRT or the one rad screen attached separately?

yes it even now causes ear pressure changes even though its not very audible

yes it is a sony trinitron.

 

[regulaz]

What type of radiation? When we made CRT monitors we measured many different types of radiation.

I designed CRT monitors for Sony and they need aligned.

Toward the end the 'government' was very hard on us about 'radiation'. We made special yokes that reduced magnetic radiation at 60-80hz and 30-100khz. (vertical and horizontal frequency of a typical 21" CRT monitor) We put shielding on transformers to keep the 100khz power frequency from radiating. CRTs got more metal. The plastics received special metal spray on the inside. The video amplifiers went into metal boxes to keep the RF radiation down. We tried to keep the HV down.

designer of CRT for sony? im on the right forum for sure. im just measuring the volts flowing between a anti radiation screen ground cord and the wall socket ground using a multimeter. it shows 300 millivolts when the VGA cable is connected between the monitor and the desktop, if the cable is disconnected it shows 40 volts. i'm not sure how it shows 40 volts because the monitor has a 3 prong plug which goes into the wall socket that has a separate ground wire for the 40 volts to drain out.

 

[regulaz]

'radiation screens' are just a scam .

well you can use a copper mesh with 100 dots per inch instead of the rad screen and get the same results.

 

[regulaz]

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

.

hi cowboybob i forgot about asking on the VGA question that remains, why does it shows 40 volts when the monitor has a 3 prong plug with proper grounding? why does the monitor need the VGA cable ground to show 300 millivolts instead of 40 volts?

 

[Nigel Goodwin]

Usually a NTC resistor applies power to this degauss coil when the monitor starts up to demagnetize the CRT.

It's called a 'posistor' and normally consists of an NTC and PTC in a single casing.

If this is a Sony Trinitron monitor, there is a metal grid barely visible from the front. It's part of the monitor design. The Trinitron doesn't have to be aligned, if I remember right.

Exactly the opposite - the Sony Trinitron was the only non-PIL (Precision In-Line) tube of recent decades - the ONLY type which required alignment (or indeed was capable of it). The shadowmask in a Trinitron is also not a metal grid, it's a mesh of vertical wires only - with a couple of very thin horizontal wires for support, which you can see if you look closely, particularly on computer monitors.

 

[regulaz]

okay i've resolved the VGA cable question, it was another grounding problem due to using the 6 point surge protector, ive got the monitor plug hooked directly in the wall socket and now it is showing 0 volts even with vga cable unplugged.

now the only question remains what is this 300 millivac for crt and 1000 millivac for LCD that is being shown from the rad screen ground? is it spurious radiation?