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| 7.5 digit bench DMMs comparison |
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| plesa:
For your applications I will purchase instead of one instrument at least two. The modern DMM with graphical LCD look nice and for basic statistic it is OK, but for normal use I needs to use PC it is more comfortable (consider BenchVue or logging with some Visual basic scripts or Python). Small factor PC (e.g Infocus Kangaroo for $150 including Win10 )Raspberry Pi or any small form factor PC and some old DMM like 2001/3441xA/34401 can be good enough. For nA current measurement I will buy Keithley 6485, 6414/6517 is little bit overkill if you needs on sub nA measurements. |
| acbern:
Also for precision gear, such as 7 and 8 digit DMMs I would only go with used ones. That always provided they are not badly worn. At least for hobbyist use, they dont run often, so the remaining lifetime is most likely not an issue at all (some preventive cap replacement on certain ones may be a good idea, as has been pointed out here, altough I do not share that experience...), and they have a well aged reference and other parts, with related low drift, and of course the price is a fraction of a new one. This is why some metrologists only buy the used 732As... I would not think a second if I had to decide between a used and warrantied 3458A and a new 7 digit DMM. |
| plesa:
--- Quote from: acbern on September 26, 2016, 11:24:39 am ---Also for precision gear, such as 7 and 8 digit DMMs I would only go with used ones. That always provided they are not badly worn. At least for hobbyist use, they dont run often, so the remaining lifetime is most likely not an issue at all (some preventive cap replacement on certain ones may be a good idea, as has been pointed out here, altough I do not share that experience...), and they have a well aged reference and other parts, with related low drift, and of course the price is a fraction of a new one. This is why some metrologists only buy the used 732As... I would not think a second if I had to decide between a used and warrantied 3458A and a new 7 digit DMM. --- End quote --- I will add that used are good in case there is schematic available, otherwise it can be painful to repair. PArts availability is important factor as well. In this segment is "better" Keithley with only few custom parts against HP/Agilent. Used does not mean it is fully working within spec, only few customers are using all functions to their limits. So lot of issues are not know to the seller. This was my experience mainly on low current measurement devices. There are only few applications where 6.5 digit DMM is not enough and you needs 7.5 or 8.5 digit. I needs to return new 3458A after few months for convergence error. In case I'll buy used one for $2500 and after that return it to Keysight for repair $2851 and calibration the total cost will be >50% of new unit ( $9778 with 3 years warranty). So the used 3458A is worthwhile only if it was recently tested/calibrated and checked for drift. |
| ebclr:
I would like to know what kind of electronic hobbist circuit need a 7 1/2 digits meter accuracy , I stoped on 50000 count's meters and never need anything more than that for hobby, would be interesting to evaluate hobby application to support the investment on this class of meter for hobby |
| TiN:
ebclr High resolution DAC/ADC testing, voltage references design and experimenting, ratiometric measurements (e.g. bridges, comparators). How these areas fill into home hobby? Well, that's a question outside of the choosing DMM here. It's often not resolution what justify such instruments, but their stability and accuracy. But that's only if 7.5/8.5 meter is tested and calibrated. Otherwise calibrated 6.5-digit meter in such cases often provide better accuracy than uncalibrated unknown 8.5-digit one. |
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