RSU's and computers.

sam.makins
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RSU's and computers.

Postby sam.makins » Sun Feb 19, 2017 9:39 pm

Hi all,

Bit of a strange one here! Has anyone else had trouble with computers and particularly pc monitors being affected by an RSU?

The reason I ask is there's a a pc on the floor below my modelling room and every time I press the pedal I get complaints of the screen going either pixelated or black depending how long I hold the pedal down!

I suspect it's something to do with the transformers magnetic field but my knowledge of such things is somewhat lacking!

Cheers,

Sam

Strandline
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Re: RSU's and computers.

Postby Strandline » Mon Feb 20, 2017 8:38 am

I know very little about it but it sounds like electromagnetic interference (EMI). I had a similar problem with a transformer (not an RSU) affecting a TV. I was able to get the owner of the transformer to move it which sorted it out. Might be worth Googling ways of reducing EMI.
Brian,
Sussex-by-the-sea

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David B
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Re: RSU's and computers.

Postby David B » Mon Feb 20, 2017 8:57 am

I have not had a problem with my RSU interfering with the computer but the computer causes interference on VHF/FM radio. Before anyone mentions using digital radio, we can't get it.

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Jol Wilkinson
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Re: RSU's and computers.

Postby Jol Wilkinson » Mon Feb 20, 2017 9:52 am

Most RSUs are built into metal cases, so I would think that EMI is unlikely. I have a PC, mains radio, London Road Models RSU, and Antex TCU in my workshop, all fed though a small ring main. I don't get any interference on anything.

Could it be a mains voltage "spike" when the RSU is turned on, that is affecting the PC.

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Guy Rixon
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Re: RSU's and computers.

Postby Guy Rixon » Mon Feb 20, 2017 10:00 am

I would guess that the computer is sensitive to radio-frequency emission from the RSU, generated either at the probe-work interface (tiny spark gaps are inefficient radio transmitters; early radio sets worked that way), or from the wire leading to the probe, or directly from the electronics of the RSU.

How you block the interference depends on the frequency spectrum. If it's mainly low frequency, then metal mesh, e.g. chicken wire, would block it. If there are high-frequency components, then you'd need a conductive shield with smaller holes or without holes.

The computer display is receiving signals that change state, I think, at a few hundred MHz (~million pixels x bit depth > 10 bits x refresh frequency), so it will be sensitive to noise in that frequency range. That's a fairly low frequency in RF terms: e.g. 408MHz has a wavelength of 49cm (a standard band in radio astronomy back in the day), and any mesh with a spacing well less than the wavelength is a possible shield.

dal-t
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Re: RSU's and computers.

Postby dal-t » Mon Feb 20, 2017 11:00 am

Given the reported symptoms (screen pixellation followed by blackout) I'd have thought it far more likely to be a voltage issue than EMI, which would normally manifest as sudden white lines or a 'scrolling' background pattern (not clear if its a CRT or flatscreen). I'd guess the RSU is causing a momentary voltage drop in the domestic supply, rather than a spike, which would be suppressed by the PC's passive power protection (assuming anyone with a computer has at least that these days). The best solution short of an upgraded consumer unit (or not using the RSU and PC at the same time!) would probably be to supplement the PPP with a BPS (backup power supply), which would not only carry the screen through the millisecond drop, but also give time to save files on the PC if a real power outage occurred, something we should all really consider (says he, still with passive protection only, living in a rural area where the power goes out often, saved at present purely by the Mac's exceptional recovery ability ...).
David L-T

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Jol Wilkinson
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Re: RSU's and computers.

Postby Jol Wilkinson » Mon Feb 20, 2017 11:23 am

It would help if we knew which brand of RSU this is.

The LRM version - and probably the Graskop or the Exactoscale ones that Bernard Weller sold - don't have any electronics.

The MIgnon Models RSU had a primary switched transformer and may have had some control unit. The American Beauty has rotary variable setting and that may have some sort of electronic control gear.

The LRM unit has, IIRC, a 3 amp fuse so draws appreciably less than that. Would switching that on cause an appreciable voltage drop?

dal-t
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Re: RSU's and computers.

Postby dal-t » Mon Feb 20, 2017 11:57 am

Jol Wilkinson wrote:The LRM unit has, IIRC, a 3 amp fuse so draws appreciably less than that. Would switching that on cause an appreciable voltage drop?


Not with anything like a reasonable domestic supply - most things in the kitchen will draw more than that, and a lot of other devices at switch-on (UK TVs used to have 3amp fuses, which was fine once running, but marginal as the CRT was warming up - so people wondered why they always blew as you switched them on.) Beginning to suspect there might be something peculiar about the ring circuit/spurs - try using the RSU from a different socket?
David L-T

sam.makins
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Re: RSU's and computers.

Postby sam.makins » Mon Feb 20, 2017 1:51 pm

Hi all,

Thanks for the replies so far.

The RSU in question is a LRM unit from the latest batch and the monitor is a flat screen LCD unit.

The RSU is plugged into the old part of the house currently so I'm going to try the new part which should hopefully have more reliable electrics and see if it effects anything that side.

I might also try sticking some chicken wire under the bench to see if that helps and maybe rule out EMI.

Also, It's currently plugged in via an extension lead which might or might not be a contributor?

Sam

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Jol Wilkinson
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Re: RSU's and computers.

Postby Jol Wilkinson » Mon Feb 20, 2017 9:26 pm

Sam,

try just operating the RSU without the probe connected. If the problem still happens then it is most likely a mains problem. EMI is unlikely to emanate from the transformer or the mains foot switch as they are both enclosed in metal cases.

sam.makins
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Re: RSU's and computers.

Postby sam.makins » Tue Feb 21, 2017 1:06 am

Jol,

I'll try that when I get back home on Friday and see what happens!

Thanks,
Sam

Pannier Tank
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Re: RSU's and computers.

Postby Pannier Tank » Tue Feb 21, 2017 7:40 am

Jol Wilkinson wrote:EMI is unlikely to emanate from the transformer or the mains foot switch as they are both enclosed in metal cases.
Maybe from the Mains Lead itself?
Regards

David

Maitland
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Re: RSU's and computers.

Postby Maitland » Tue Feb 21, 2017 9:08 am

Jol Wilkinson wrote:
EMI is unlikely to emanate from the transformer or the mains foot switch as they are both enclosed in metal cases.

Maybe from the Mains Lead itself?


Metal cases seldom do much to prevent EM radiation. They are as likely to act as an antenna as a screen- even if earthed. If it is really EMI that causes the problem, I'd suspect a sparking switch or a loose connection somewhere. This could then act like Marconi's spark transmitter, and desperately try to transmit a Morse 'S' to Newfoundland. The energy required to interfere with a modern LCD or LED screen must be massive though.

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Guy Rixon
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Re: RSU's and computers.

Postby Guy Rixon » Tue Feb 21, 2017 11:05 am

Maitland wrote:... The energy required to interfere with a modern LCD or LED screen must be massive though.


Yes, but only if computer and monitor are both working correctly in the first place. If the shielding in the monitor cable is poor, or if one or other device is producing almost-out-of-spec voltages onto the cable, then interference has more chance to change things.

Actually, changing the monitor cable might be a good move, if a spare is available. Not sure that it's worth paying silly money for a new HDMI cable, though.

garethashenden
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Re: RSU's and computers.

Postby garethashenden » Tue Feb 21, 2017 2:27 pm

Guy Rixon wrote:
Maitland wrote:... The energy required to interfere with a modern LCD or LED screen must be massive though.


Yes, but only if computer and monitor are both working correctly in the first place. If the shielding in the monitor cable is poor, or if one or other device is producing almost-out-of-spec voltages onto the cable, then interference has more chance to change things.

Actually, changing the monitor cable might be a good move, if a spare is available. Not sure that it's worth paying silly money for a new HDMI cable, though.


HMDI cable have gotten cheap. https://www.amazon.co.uk/AmazonBasics-High-Speed-HDMI-2-0-Cable/dp/B014I8SIJY/ref=sr_1_4?s=electronics&ie=UTF8&qid=1487686594&sr=1-4&keywords=hdmi

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PeteT
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Re: RSU's and computers.

Postby PeteT » Tue Feb 21, 2017 2:51 pm



But thats the point - the cheap ones are more likely to be susceptible to EMI interference due to incorrect (or poor quality control of) screaning.

sam.makins
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Re: RSU's and computers.

Postby sam.makins » Wed Feb 22, 2017 2:02 am

We should have a spare monitor cable so I'll try that and if that fails I'll try moving the RSU.

Thanks for all the suggestions,

Sam


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