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| 7.5 digit bench DMMs comparison |
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| bson:
--- Quote from: Kjelt on September 27, 2016, 08:42:29 am ---That depends on the calibration service. Normally they only measure your meter against known standard references and print out the deviation from those reference, --- End quote --- I take my instruments to a well-regarded used equipment vendor in Santa Clara who regularly sends batches of equipment off to a local lab for calibration. I find out when the next shipment is and drive down there, and drop it off. I don't pay for a full report, only the standard NIST traceability certificate, and on return can verify that the calibration data has been updated both from the updated calibration date and from the fact that the readouts differ for my DMMCheck. Since the readouts differ and there is nothing to adjust it implies there is new calibration data installed. It's even possible the 34465A won't permit setting the calibration info string without also installing calibration data - some makes and firmware won't permit this. They charged $150 for my Keithley 2001 (7.5d) two years ago if memory serves. This is all quite cheap. A lab that only compares the displayed readouts to a standard is worthless. Proper calibration procedures for DMMs follow a specific SCPI based script that both validates measurements are within specification and installs new calibration data. If they don't have the software to do this I'd go somewhere else, but any decent lab will. |
| kj7e:
--- Quote from: HighVoltage on September 24, 2016, 10:51:57 am ---I have the Keysight 34470A for a while now and like it a lot for my VoltNuts addiction. The calibration of this one is 1 1/2 years old Now I have brand new Keithley DMM7510 This one was calibrated in 8/2016 In the next few days I will make some comparison measurements between the two. But so far I see the following on my LTZ1000A reference: The 34470A reads about 18 uV high And the DMM7510 is about 20 uV low What is really impressive with the 7510 is how quick it is warmed up to show a stable reading. I have not measured it, but it is less then one minute, it seems. Both instruments are recommended. The handling is just very different. If you are in to low current measurements, the 34470 has a 1 uA current range and the DMM7510 has a 10 uA current range. And the 34470A is just amazing, in measuring this low current. I have not tested this on the Keithley meter. --- End quote --- I've noticed this too, it only takes about 3 min to stabilized to sub PPM levels. Here, I powered mine on with my 10v reference already fully stabilized. Overall, from cold startup to 8 min; First 90 seconds zoomed in; Reaching 2 min mark; Final stabilization; |
| HighVoltage:
--- Quote from: kj7e on March 23, 2018, 04:16:01 pm --- I've noticed this too, it only takes about 3 min to stabilized to sub PPM levels. Here, I powered mine on with my 10v reference already fully stabilized. --- End quote --- It is truly amazing, how fast the DMM7510 will stabilize after a coldstart. And you do not need to use the ACAL feature of the 7510, to get reliable readings. |
| Kleinstein:
The jagged curve suggests that the 7510 uses some periodic corrections to compensate for drift about every 2 seconds. This could be temperature measurements and numerical corrections or maybe short adjustment cycles for the ADC gain (so kind of a partial ACAL). In the 10 V range there is no need for that many parts to stabilize: its mainly the reference and some amplifier offsets to a point that the internal corrections / AZ works. The 1 V or 0.1 V range might need considerably more time. The slightly larger jump at about 80 seconds looks a little odd. If such a jump (around 20 µV, if a judge the scales right) would happen in the more normal working range it could be really bad. It looks like those corrections also show some errors/noise. |
| HighVoltage:
Here is a good comparison of a Keithley DMM7510 and a Keysight 34470A Both hooked up to a 10V reference |
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