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| 7.5 digit bench DMMs comparison |
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| tggzzz:
--- Quote from: Dragony on September 24, 2016, 03:51:13 am ---Right now I have one bench DMM, the Rigol DM3068, but the device was not able to fulfil the following tasks I actually encountered: - Measuring current flow of 10nA failed. Too noisy. - Measuring current consumption based on cap discharge hardly works. I don't trust the results. The problem is DC Bias. I also encountered the phenomenon that the unconnected DMM set to 10G input impedance rises on voltage 1V/s. Looks like DC Bias as well. Of course this does not happen with 10M, but I can't use 10M for this task as it would bias the measurement. I use 10G for this. --- End quote --- Neither of those requirements implies need for a 7.5 digit resolution. The "10nA" implies amplification before measurement. Of course that will directly expose fundamental measurement problems (e.g. noise, thermal and acoustic effects, maybe even number of electrons/s...) that can't be solved by a higher resolution measurement. The "DC bias" issue implies you have a very high source impedance, which has other knock-on consequences. |
| e61_phil:
--- Quote from: Dragony on September 24, 2016, 03:51:13 am ---Right now I have one bench DMM, the Rigol DM3068, but the device was not able to fulfil the following tasks I actually encountered: - Measuring current flow of 10nA failed. Too noisy. --- End quote --- Did you try measuring 10nA in 100mV range with 10Meg input imepdance? |
| bson:
--- Quote from: Kjelt on September 24, 2016, 08:37:04 am ---For a cheap lab with cal instruments suitable for 6,5 digits dmm this will already cost you the price of half the new meter (400-500) , --- End quote --- I paid $99 to have the 34465A calibrated after a year. There is nothing to adjust - all that's done is installing of the new calibration data, which is automatically done by the calibration process, to compensate for drift. I'm not aware of any modern DMM with anything to adjust; it's going to measure whatever it measures, and if it's out of spec (so far off the measurement can't be used for a linear reading based on calibration data) it needs to be repaired. |
| Kjelt:
--- Quote from: bson on September 27, 2016, 07:48:08 am ---I paid $99 to have the 34465A calibrated after a year. There is nothing to adjust - all that's done is installing of the new calibration data, which is automatically done by the calibration process, to compensate for drift. I'm not aware of any modern DMM with anything to adjust; it's going to measure whatever it measures, and if it's out of spec (so far off the measurement can't be used for a linear reading based on calibration data) it needs to be repaired. --- End quote --- That depends on the calibration service. Normally they only measure your meter against known standard references and print out the deviation from those reference, they do not adjust anything, they just give you a piece of paper stating how much your meter deviates. That costs here in Europe between €140 and €300 If you want that they adjust your meter to the reference, then they measure the deviation, adjust and measure again the deviation, this costs twice or sometimes even more. I know that in the US there are more cal labs and also cal labs that charge way less than here in Europe. For $99 measuring and adjusting would be an absolute bargain. |
| HighVoltage:
I just spoke to Keithley Germany about the DMM7510 and also asked about calibration. The guy quoted me Euro 330 over the phone (without adjustment) plus VAT and 1 week turnaround. If adjustments are needed it will cost much more, depending on the adjustments, he said. |
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