Hi Frank, I use my private 3458A mostly as a ratio meter. Therefore, I'm not that much worried about the temperature (changes), but I should have a look at the filter ;).
I would also have no doubt, that the 3458A could compete with the Fluke meters, if HP had installed expensive components. But the 3458A is a box of cheap parts (my opinion) which are regularly calibrated against the two internal standards. It is a great marketing stunt to make the customers believe that ACAL is something great. In my opinion it is only to cover/compensate the mediocre ingredients. Many meteorologists don't like such self adjusting boxes, but that (in combination with the superb ADC linearity) made it possible to create a "cheap" metrology DMM. The 8508/88 are specified with 2.75 ppm/year not 4 btw. Our 8508A drifted by 0.8ppm in the first year and I assume this rate will go down with age. I don't think Keysight will offer a second (metrology) version of the 3458A. I also think that 10V are good enough on all the meters. If you really need less uncertainty, one should use a 10V standard in combination with the 3458A. But there are other differences between the 3458A and the Fluke meters. Especially low and high ohms are much better on a 8508/88A. Real ratio measurements, low TC and no Auto Zero are other points which lead me to buy a 8508A and now a 8588A instead of an additional 3458A (we already have more than one). But I don't want to start a Fluke vs. 3458A discussion again ;). Best regards Philipp Am Sa., 26. Okt. 2019 um 22:12 Uhr schrieb Frank Stellmach < [email protected]>: > Hi Philipp, > > you definitely have to clean the fan filter of your unit.. standing free > on a table, and with a clean filter, the internal temperature rise is > 12..13°C at most. > > Defining a metrology grade 3458A would explicitly require to define and > control the environmental conditions in the specification, like reduced > temperature range, specifying the ventilation requirements, like no use > in a rack, by using a different filter, and also by regularly checking > the internal temperature by firmware. > > The 3458A is designed and specified as a system DMM, inside a rack, in a > hot manufacturing environment, like in a electronics manufacturing line, > but never was intended and built as a metrology DMM, as hp and KS still > try to advertise. > > Your argument, that a sample distribution is root cause of these wide > specification limits, does not convince me: > > The annual and temperature drift (with ACAL) is mainly determined by the > drift of the two internal references, due to the ACAL technique, the > rest of the circuit does contribute only marginally, but on the w/o ACAL > specifications . > > Therefore, the 8508/88A simply beat the 3458A, because they use an LTFLU > running at 45..55°C only, instead of 95°C, and due to the heavy usage of > stable Vishay BMF resistors, which also contribute to the superior > short- and midterm stability of these instruments. > > So only the sample distribution and yield of the LTZ and 40k resistor > affect the annual drift specification limits for the 3458A. > > Concerning the LTZ reference, that is already covered by their > monitoring / selection process, where they have for sure have yield > problems already. > > If they would simply reduce the temperature for metrology purposes, like > in practice done on the FLUKE DMMs, they would directly get near 100% > yield for 2..3ppm/year (@65°C), due to the ACAL DCV feature.. > > The 8508/88 on the other hand have to account for the drift of other > components, to achieve e.g. these 4ppm/year, although the LTFLU very > probably performs more like 1..2ppm/year (inside the 732B, @ 47°C, for > example). > > I think the 3458A would at least be on par with the FLUKE DMMs if KS > would simply chose the same metrology grade resistors and oven > temperature as DATRON/FLUKE had done... > > Frank > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/volt-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/volt-nuts_lists.febo.com and follow the instructions there.
