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| 1V Reference @ 1ppm |
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| tggzzz:
--- Quote from: spec on January 30, 2019, 04:04:35 am --- --- Quote from: tggzzz on January 30, 2019, 01:08:40 am --- --- Quote from: spec on January 29, 2019, 07:27:53 pm --- --- Quote from: tggzzz on January 29, 2019, 05:36:00 pm --- --- Quote from: spec on January 29, 2019, 04:32:04 pm ---Can I ask a question of the experts in this field: When you are checking the precision of an instrument, what is the shortest time that the instrument could be connected to the reference source? I have a reason for asking. :) --- End quote --- I would suggest "until the reading is stable and repeatable", where you have to supply the two obvious definitions. Are you thinking of a mechanical multimeter and a Weston standard cell? --- End quote --- My thought was to use a capacitor to lower the effective output impedance of a precision voltage divider but, in view of your and K's, remarks it is clear that a fair amount of time would be required to do the calibration so that idea goes down the tubes as only a film capacitor could be used. A supercap, which could allow sufficient time, would be too leaky, I think :) --- End quote --- Capacitors are crap components compared with resistors. Leakage, tempcos, non-linear voltage dependence, dielectric absorbtion, and more. --- End quote --- Oh yes I do know that, but there are capacitors and capacitors. Still overall you are obviously right. It was just a thought. UPDATE: just noticed that the LTZ1000 does use a capacitor internally. :) --- End quote --- At voltnut level there are no individual components, only black boxes with lots of hidden and poorly specified internal components :) People spend careers trying to minimise and work around that. Silicon capacitors are no different in that respect. BTW, you can get discrete silicon capacitors in the range 0.3pF to 3.3uF, but watch the availability, MOQ and price :) https://www.digikey.co.uk/products/en/capacitors/silicon-capacitors/68?k=silicon%20capacitor |
| spec:
--- Quote from: beanflying on January 30, 2019, 05:57:16 am ---xxx --- End quote --- Thank you for such a comprehensive summary. :-+ In view of what you and tggzzz say, it might be folly, but I would like to have a go at designing a stand-alone, low-impedance output Vef. So if I get around to posting a schematic, your comments would be appreciated. I have done a couple of outline schematics which, in theory, look promising, but I lack the specialist knowledge and experience that this field requires. My only qualifications are having read the threads on EEV and elsewhere on the net. |
| spec:
--- Quote from: beanflying on January 30, 2019, 05:57:16 am ---Back shelf is how to go 'part' of the way into the rabbit hole 7.5 digit Advantest on the top shelf, HP735A, Fluke Null meter, Fluke Portable Calibrator, Bottom row HP 740B working but mid renovation 1000V DC Calibrator/Null meter and Valhalla 1200V AC Calibrator. Won't mention my 'slight' time nut addiction either. Plus other assorted 'stuff'. No I don't feel I have a problem because TEA assures me I am 'normal' ;D Yes I am showing off the toys a touch ;) --- End quote --- Nice :) |
| tggzzz:
--- Quote from: spec on January 30, 2019, 11:20:51 am --- --- Quote from: beanflying on January 30, 2019, 05:57:16 am ---xxx --- End quote --- Thank you for such a comprehensive summary. :-+ In view of what you and tggzzz say, it might be folly, but I would like to have a go at designing a stand-alone, low-impedance output Vef. So if I get around to posting a schematic, your comments would be appreciated. I have done a couple of outline schematics which, in theory, look promising, but I lack the specialist knowledge and experience that this field requires. My only qualifications are having read the threads on EEV and elsewhere on the net. --- End quote --- Folly? No. You'll have fun and learn things. But personally I wouldn't tweak anything based on its output - first attempts are rarely perfect. You should understand what's behind the specs for professional high quality meters, especially those related to the drift over time. You might like to consider what will/won't happen if you short-circuit your low impedance output. |
| spec:
--- Quote from: beanflying on January 30, 2019, 05:57:16 am ---1 - Buy an AD-584 with measurements attached. With no measurements it is no better than your current best meter for Accuracy. --- End quote --- You have mentioned the AD584 a couple of times, but according to the datasheet, it is no big shakes (15ppm) compared to the other chips. So what is the story with the AD584? https://www.analog.com/media/en/technical-documentation/data-sheets/ad584.pdf |
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