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| The Rigol DS1052E |
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| EEVblog:
--- Quote from: Simon on October 22, 2009, 06:57:14 am ---the other thing to remember is being 8 bit there will be a +-1 bit uncertainty, this will show up in any case as a 3 pixel thick line, just the nature of the beast, personally I can't understand why Rigol did not screen all of the analog circuitry --- End quote --- Because it most likely would have done nothing. They shielded what was important, the high impedance analog front end. The support circuitry is much lower impedance so does not need the same shielding. Remember also that noise can be conducted, not just electromagnetically and capacitively coupled. That noise isn't coming from the switching regulator, you can shield it all you want it's not going to do a thing. When the cheap Rigol has the same noise floor as a $5000+ Tektronix, you know something a lot more complicated than simple PSU noise and shielding is at play here. If you wanted to stop all noise from that supply, you would have to not only magnetically shield it (al-foil does nothing in this respect, you need mu-metal), but also put suitable chokes on all the wires coming out of it. But you are chasing a red-herring with the supply. Dave. |
| Simon:
Dave, whats mu metal ? I did notice that screening the supply made practically no difference at all, personally to anyone wanting to have a go I'd say just inser the foil above the analog support circuitry, this is quik and easy: just cut a sheet of foil of appropriate size and tape it to the analog input box, if you use decently thick foil (15 um) then it will support itself. |
| EEVblog:
--- Quote from: Simon on October 22, 2009, 10:25:01 pm ---Dave, whats mu metal ? --- End quote --- http://en.wikipedia.org/wiki/Mu-metal Regular metal shields only stop electric fields, not magnetic fields. Dave. |
| Simon:
thats interesting, where do I get this stuff, what sort of thickness does it come in ? if this is the answer thats probably why the scope (being quite cheap) was not sheilded in the first place because of the exspense of setting it all up. |
| Dago:
--- Quote from: Simon on October 23, 2009, 06:39:24 am ---thats interesting, where do I get this stuff, what sort of thickness does it come in ? if this is the answer thats probably why the scope (being quite cheap) was not sheilded in the first place because of the exspense of setting it all up. --- End quote --- The reason why it was not done was because it will not help, like Dave said. You could prolly cast every component invidually in mu-metal and you'd still get noise, just get over it :P Not all noise comes from external sources, it can be thermal noise, sampling noise etc. |
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