Keithly DMM7510 Fresh Off Calibration from the Mothership - Page 1
Forum section: electronics / general

author: Zenwizard
author_rank: Regular Contributor
timestamp: July 17, 2022, 12:03:58 am
content: I though this information might be of interest here in the Meteorology section. I am planning on doing a video for this for the channel but I will leave the excel sheet here. I am going to add to the log so I can get some drift over time so The center section will fill out once I get a second year History of the unit : It is my personal meter for the lab and it most accurate one that I have at the moment. My plan is to maintain this with keithly as this currently sets "Truth" for my lab. My every day meter is a DMM 6500 and a bank of DM502A'sThis is an excel document created from the data Keithly sent me. I had the meter sent through their accredited calibration along with the data for longer term records this is the first data point.Zen

author: HighVoltage
author_rank: Super Contributor
timestamp: July 17, 2022, 07:49:09 am
content: The DMM7510 is very stable in keeping its calibration value.Thanks for sharing your Cal Data

author: Andreas
author_rank: Super Contributor
timestamp: July 17, 2022, 10:05:46 am
content: Hmm,what I am wondering:Even the calibrator is never "spot on" e.g. on the 10V value. (and ususally there is always a different calibrator used for each calibration)so what was the actual value given for the 10V value from the calibrator?In some protocols I can see this when calculating the average of the usually non-symmetrical low/high limits.But in your case it is 10V +/-152uVAnd what is the uncertainity of the calibration? (uncertainity from calibrator at the time of your calibration and the measurement setup?)If I want to observe drift which should be <2 ppm/year after the first year of operation then I also want to keep track what was actually given from the calibrator for the reading in the protocol.with best regardsAndreas

author: mendip_discovery
author_rank: Super Contributor
timestamp: July 17, 2022, 05:30:59 pm
content: Very good. I would also record the UoM from the certificates this would allow you to put the measurments into perspective. Also I added some maths so show the error from non all and then check that its within the spec and then graph it all.I suggest you make another sheet to compare the unit to a few of your lab standards and record that periodically so you can compare it all and see how good your kit is and how that drifts over time.

author: Zenwizard
author_rank: Regular Contributor
timestamp: July 18, 2022, 01:28:53 am
content: Thanks for the info. I have the UoC data from Keithly. I am still working on my 8.5 meter the DMM7510 is the best I have in the lab at the moment. The gear used to calibrate the DMM7510 is as follows:Fluke 5720AFluke 5725Fluke 8505AIET 1423IET HACS-Z-A-2E-1ufKeihly 3390The accreditation was ISO 17025For the 10V uncertainty I haveFull scale - 0.000029half scale - 0.000016I do have my eyes on the fluke 8.5 as for gear in the lab I am working with aVoltageFluke 343A - DCFluke 5200A - ACFluke 5205A - High ACCurrent - best I have is a Keithley SMU 2450Resistance - none yetI do have a decade inductor box for Henry's - 6625Frequency I am at a GPSDO -> 1pps -> Rb

author: Kleinstein
author_rank: Super Contributor
timestamp: July 18, 2022, 06:22:35 am
content: The deviations for the positive and negative readings are still well inside the accurracy specs, but a bit large to be explained with the expected degree of INL. The sign also changes from the +-10 V to +-5 V test points, so it should not be an offset either.So chances are some of that error is also from the calibrator, with the test point not exactly at the nominal values. While OK to check if the meter meets it's accuracy specs, it may not be good enough to see the expected drift over time.

author: DH7DN
author_rank: Regular Contributor
timestamp: August 19, 2022, 05:34:10 am
content: Quote from: Zenwizard on July 17, 2022, 12:03:58 amThanks for sharing the results! I was "thrilled" to see a real A2LA accredited calibration certificate instead of an "ISO" rubbishyaaayThe calibration lab's Voltage Standard was probably a Fluke 8508A 8.5 digit DMM which was used for comparison. The Fluke 5920A calibrator was probably used as a stable voltage supply so the nominal value difference isn't of importance. The important stuff is the actual measured value, its expanded uncertainty and the decision rules for the statement of conformity (e. g. DMM specifications).They also have a very short recalibration intervals of only 3 months. I guess they need a high confidence in their calibration results because of high throughput. Building up a calibration history will be very expensive if you're aiming for a 12 month calibration interval. You could increase it to 24 months once your Fluke DMM7510 proves its stability over time.Last but not least: it's calledmetrology(not meteorology) although metrologists also like to discuss the current weather situation (our air conditionings are suffering right now due to hot/moist weather)

author: mzzj
author_rank: Super Contributor
timestamp: August 26, 2022, 07:04:00 pm
content: Quote from: Andreas on July 17, 2022, 10:05:46 amsome calibration labs ”shift” the results to nominal value in the certificates, ie 99.999mV reference and 100.000mV UUT reading is shifted to ref=100.000mV and UUT 100.001mVNot huge fan of the idea as it can cause its own set of problems but it is done sometimes.