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| 1V Reference @ 1ppm |
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| beanflying:
When not in outside use yes. I have a hacked wine fridge at 25C. and 34970A loggers with DMM cards fitted. Still a WIP and it also has two newish LTZ1000 Refs and the bits for two more coming. If it wasn't out of interest there is nothing I do that requires more than 4.5 digits but having that known 6.5 digit and references gives me very good confidence at that 4.5 has very good confidence. The consideration to jump to 8.5 is a total indulgence and I am still weighing up that or a modern 1/2 rack 7.5 digit option. Either way it would be kept in Current Cal. |
| spec:
CROSSED POSTS :) --- Quote from: beanflying on January 29, 2019, 11:46:19 pm ---LM399 and LTX1000 [LTZ1000] based devices are POINTLESS unless you have a 'known' accurate standard or meter to set them with their initial accuracy varies widely. They will only be as 'accurate' as the device YOU measure them with but generally they are more stable than other References due to Temp but can take weeks to years to settle. They are a can of worms in the Rabbit Hole with you in free fall but always just out of reach --- End quote --- Isn't, 'They will only be as 'accurate' as the device YOU measure them with' true of any Vref that you make? Both the LTZ1000 and the LM399 are oven controlled. The LTX1000 is top of the chip heap, so why not use it. OK you may not realise it's full potential, but so what. Is it because of the $50 price tag? At a lower spec (0.5ppm) and price ($12), the same goes for the LM399, or is it because the LM399 is a shunt type, which complicates the design, compared to a series type? It would appear that the basic vref of the LM399 cant be that good if it only achieves 0.5ppm/degC performance with oven control. My thinking is that there may be big gains in performance by oven controlling one of the au natural chips we discussed, which as you say, also have an initial absolute accuracy around two orders better than the LM399. https://www.analog.com/media/en/technical-documentation/data-sheets/199399fc.pdf https://www.analog.com/media/en/technical-documentation/data-sheets/LTZ1000.pdf |
| beanflying:
In the case of Ref's like the LM and LTZ their initial accuracy varies heaps so without a good meter they are no good for a walkup 'accurate' home built reference. The Max6350 runs rings around them for initial 'accuracy'. So if you have no 'known' source don't build one IMO there is simply nothing to be gained unless you already have a very good calibrated meter which in Raphael's case he gives no indication of. LM399 6.75 - 7.3 V initial 'accuracy' LTZ1000ACH 7.0 - 7.5 V initial 'accuracy' MAX 6350 4.999 - 5.001 V initial 'accuracy' (0.02%) |
| spec:
--- Quote from: beanflying on January 30, 2019, 05:00:02 am ---In the case of Ref's like the LM and LTZ their initial accuracy varies heaps so without a good meter they are no good for a walkup 'accurate' home built reference. The Max6350 runs rings around them for initial 'accuracy'. So if you have no 'known' source don't build one IMO there is simply nothing to be gained unless you already have a very good calibrated meter which in Raphael's case he gives no indication of. LM399 6.75 - 7.3 V initial 'accuracy' LTZ1000ACH 7.0 - 7.5 V initial 'accuracy' MAX 6350 4.999 - 5.001 V initial 'accuracy' (0.02%) --- End quote --- Agree. But at one stage you were suggesting that the Vref be used as as a transfer standard, which implies another precision reference- or have I got that wrong. To put a stake in the ground can I suggest that we consider two approaches * Transfer standard (with high output R and adjustment) * Stand-alone absolute Vref, with low output R (suitable for a load of 10M or higher) and initial calibration (if required) by resistor AOT. I have an interest in two above. |
| beanflying:
With no calibrated gear it becomes a chicken and egg type of thing you still need an 'Accurate' Reference to make that Transfer Standard. So your choices are buy or make the best one you can. Vref best options without going broke. 1 - Buy an AD-584 with measurements attached. With no measurements it is no better than your current best meter for Accuracy. 2 - Build a MAX6350 based reference and make it YOUR volt. It wil be better than just about any 4.5 digit meter I am aware of for initial accuracy? 3 - There is 399 Refs in the for sale section at present for not to many $$ but I am not sure of what there long term aging or stability is as I haven't looked at the project other than a glance in the for sale section? Personally I would stay away unless you already own a meter capable of tracking and looking at its drift (6.5 digits) 4 - DMM check or similar other devices are also available online. How you get to the various voltage points to transfer YOUR Volt from there is a topic in itself and really to large for here and outside basic dividers and not Beginner material in particular. Depending on the meter you want to Cal as I put a few posts back you need to hit a huge number of different points even for a couple of meters. This is why I own a couple of Calibrators both AC and DC to 1000V+ but they are not sensible for most apart from their boat anchor dimensions as per the photo below. One other possible option is you go down the path Ian Johnson has with his LM399 based Reference http://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-v2-detail using a good quality DAC/micro on the reference but this is way out of Beginner level and will cost real money. 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 ;) |
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