Keithley DMM 6500 10VDC Calibration NOT as expected - Page 1
Forum section: electronics / general

author: View[+]Finder
author_rank: Unknown
timestamp: October 12, 2024, 04:59:59 pm
content: If you were to do an "old-school" adjustment and calibration with a 10VDC reference, the DUT meter would show "10.00xxx" when you finished, right? {yes, there are many reasons why not so, this post is not about those}My problem is with a modern Keithley DMM 6500 meter that can be calibrated at discrete points (e.g. 10VDC positive) using commands from TSP (not SCPI) over a variety of remote connections to the DUT. The simplified process is "unlock CAL", "connect 10V ref", "measure ref" and finally, "save and lock CAL". Do I see 10.0000 on the display? NO! The display shows "9.99970", which is at the low end of the published specs for the meter on 10VDC.Here's the puzzle: on 100VDC range, the display is "010.0000" and on 1000v range, "0.010000k". It appears that the meter is less accurate on the 10VDC range than on the higher ones.Unlike the calibration procedure for the Keithley 196 (the 'brown' 6.5 digit meter) that accepts a "value from the calibrator," the 6500 has no such provision and generates an error message. {NOTE: other calibration points do allow, just not voltage.)How then was Keithley able to sell a meter that is "spot on" from the factory? I suspect that there is an alternative calibration routine that instals the nominal value in the EEPROM.I would very much like to find that routine or something with the same result: closer than 100uV from nominal.FYI, the 10VDC reference measures 9.99997x on two DAQ6510 meters, not likely the problem. Likewise, the settle time in the CAL has no apparent effect.

author: HighVoltage
author_rank: Super Contributor
timestamp: October 12, 2024, 08:26:23 pm
content: Quote from: View[+]Finder on October 12, 2024, 04:59:59 pmYou must follow the calibration instructions step by step in the correct sequence on all voltage settings, (+ and -), as shown in the calibration manual. You can not just adjust the 10V range.

author: View[+]Finder
author_rank: Unknown
timestamp: October 12, 2024, 10:08:58 pm
content: QuoteNot in this case; Keithley CAL manual for DMM6500:“Remote calibration adjustment proceduresThe front-panel display does not show calibration progress or completion.The following sections provide the preparation and command parameters that you need to complete adjustments to you DMM6500. The preparation sections provide information necessary for making connections and other equipment needed for that adjustment.The command parameter tables are meant to run through in any order allowing you to adjust just the parameters you need.For a complete adjustment, run through these sections in order, making the preparations and running all of the command parameters. “Source: DMM6500 61⁄2-Digit Multimeter with Scanning Calibration and Adjustment Manual Section 3: Adjustment (page 3-7){italics added}And yeah, I thought so too. Keithley meters permit discrete adjustment (as do Datron's, maybe others)Just another case of RTFM for me. The problem--as laid out above--is not that calibration adjustment doesn't work; it's that it defaults to the same value regardless of what is presented as a reference.I would REALLY like to be shown wrong on this point, so thanks for your comment.

author: View[+]Finder
author_rank: Unknown
timestamp: October 13, 2024, 09:50:57 pm
content: QuoteToday I ran a 10V calibration, using the same reference (PDVS2), on two Keithley meters (6500, 6610) and when they were restarted after to CAL, they did NOT display the same voltage for the reference. In fact, not even close: one was above 10v nominal and the other was below 10v. Although both were within the band of certainty Keithley publishes for those meters on 10V range.My next trial was to investigate the relationship betweensetupandexecuteand the time to settle the reference voltage. The verdict was to do multiple passes through the core CAL steps. The result was to reduce the error to under 10uV. The code below is being tested now, more results later . . .Code:input("unlock")DAQ6510.write('cal.unlock("KI000CAL")')input("setup temp")DAQ6510.write('cal.adjust.step.setup("TC_EN")')input("execute temp")DAQ6510.write('cal.adjust.step.execute("TC_EN", 0)')input("Connect 10VDC source . . . ")print ("Now calibrating 10Volts pos")for i in range(1, 11):DAQ6510.write('cal.adjust.step.setup("cal_DCV_10V_fs_pos")')time.sleep(120)DAQ6510.write('cal.adjust.step.execute("cal_DCV_10V_fs_pos")')print(i)input("setup 10V done")input("execute 10V done")input("setup temp")DAQ6510.write('cal.adjust.step.setup("TC_EN")')input("execute temp")DAQ6510.write('cal.adjust.step.execute("TC_EN", 1)')input("CAL Save?")DAQ6510.write('cal.save()')input("CAL SAVED, Lock?")DAQ6510.write('cal.lock()')print('CAL SAVED')print (DAQ6510.query("*IDN?"))

author: The Soulman
author_rank: Super Contributor
timestamp: October 13, 2024, 10:20:06 pm
content: I don't have experience with the calibration of this meter but I did have a read thru that manual.Did you see on page 3-7:QuoteMaybe there is still some (now wrong) temperature compensation going on?After adjustment, did you check with:Reverse polarity?Input short?

author: View[+]Finder
author_rank: Unknown
timestamp: October 14, 2024, 04:30:25 am
content: QuoteI followed the instructions to disable, see code listing above. I have two 6510 meters adjusted, however the 6500 does not incorporate the 10v reference like the other meters. There is very little information about the exact sequence between the setup and execute steps. In my script, the setup is called, then the reference is measured, then a pause for settling, finally the execute step to commit the adjustment to memory.

author: View[+]Finder
author_rank: Unknown
timestamp: October 14, 2024, 01:33:11 pm
content: QuoteOooops! From the CAL manual:"You must make sure that the correct signal is connected and fully settled before sending the associated cal.adjust command. Failing to wait for a signal to settle completely may result in a poor-quality adjustment that could cause the DAQ6510 to fail later performance verification.Once the reference signal is stable, sending the calibration adjustment command initiates internal measurement operations in the DAQ6510. These steps can take from a few seconds to 30 seconds to complete."So . . .Connect referenceWait to settle (2 min)Run setupWait (30 sec)Run executeWait (30 sec){enable temp, save and lock}We'll see . . .

author: View[+]Finder
author_rank: Unknown
timestamp: October 14, 2024, 03:40:58 pm
content: NO LUCK!The code below did NOT result in an acceptable adjustment on the KY6500 meter 10VDC range. Unless one considers 10.00080 acceptable. NOTE: the two DAQ6510 meters adjusted to 10.00008.The attached trace is from NI MAX as the python script below is running on a NI controller.Code:input("unlock")DMM6500.write('cal.unlock("KI000CAL")')time.sleep(3)input("setup temp")DMM6500.write('cal.adjust.step.setup("TC_EN")')time.sleep(3)input("execute temp")DMM6500.write('cal.adjust.step.execute("TC_EN", 0)')time.sleep(3)input("Connect 10VDC source . . . ")time.sleep(3)print ("Now calibrating 10Volts pos")for i in range(1, 2):time.sleep(300)DMM6500.write('cal.adjust.step.setup("cal_DCV_10V_fs_pos")')time.sleep(35)print("setup 10V done")DMM6500.write('cal.adjust.step.execute("cal_DCV_10V_fs_pos")')time.sleep(35)print("execute 10V done")print(i)input("setup temp")DMM6500.write('cal.adjust.step.setup("TC_EN")')time.sleep(3)input("execute temp")DMM6500.write('cal.adjust.step.execute("TC_EN", 1)')time.sleep(3)input("CAL Save?")time.sleep(3)DMM6500.write('cal.save()')time.sleep(35)input("CAL SAVED, Lock?")DMM6500.write('cal.lock()')time.sleep(3)print('CAL locked')print (DMM6500.query("*IDN?"))

author: Sensorcat
author_rank: Regular Contributor
timestamp: October 15, 2024, 12:49:40 am
content: What if the firmware of the meter has a bug, such that the adjustment of only one range does not (completely) work as described? If the sequence of adjusting all ranges works properly, such a bug could remain unnoticed for a long time, since both Keithley and calibration labs would not notice, as sending a meter for adjustment naturally covers all ranges. Would that explain what you see?

author: aronake
author_rank: Frequent Contributor
timestamp: October 15, 2024, 03:51:32 am
content: I have a DMM6500 for which i am considering to do a adjustment myself.Its quite surprising and bad that the voltage calibration only allow for exactly fixed voltages, and not allow input for some range around the supposed to be input value. Even more strange since current and resistance allow it... Even a pretty basic 6.5 digit meter like 34401a allow this.

author: View[+]Finder
author_rank: Unknown
timestamp: October 15, 2024, 05:35:30 pm
content: Quote from: Sensorcat on October 15, 2024, 12:49:40 amI tried 3 firmware versions: 1.7.8 (that came with the meter, 1.7.14 (latest), 1.7.12 and back to 1.7.14. All resulted in 10.0008 from the CAL cycle. Tried different settling times from 2 to 10 minutes. No real difference. Both 6510 meters are happy at 10.00008(3) and that verified by Datron 1271 to 8.5 digits.The other thing that doesn't work in the Keithley tech-support; it throws an error. What bugs me most is that Keithley 196 manuals support (and explain) "calibration to a value."

author: HighVoltage
author_rank: Super Contributor
timestamp: October 16, 2024, 08:46:33 am
content: A few years ago, I had a very similar case with a Keysight 34470A on the 10V range.Only when I calibrated and adjusted every DCV value that was listed (including plus and minus polarity) did it work and the calibrated value was spot on. In your case I would just give this full procedure a try.

author: View[+]Finder
author_rank: Unknown
timestamp: October 16, 2024, 01:33:18 pm
content: First the GOOD news . . .The Keithley 6500 meter now correctly represents a 10VDC reference (photo attached).The BAD news was the journey to a time in my life when "tweaking" was the norm. What should have been a straightforward adjustment of a voltage reading on the 10-volt range, became a mystery story. Fortunately (??) I now have the requisite "gray-beard, etc." as suggested by Dave.The problem with the 6500 is likely deeper than can be fixed by running more CAL, given that the "by the book" calibration procedure did not yield the expected result. The steps that led to the "correct" display are cringe-worthy.Since the presenting problem was "too low voltage display" I tried the old-school trick of "fool the meter" by using a CAL reference setlowerthan the nominal 10V to see if that would edge the meter back to more familiar territory. It worked! {insert here the sound of gnashing teeth for full effect}Hello KeithleyWhy not provide the DCV calibration routine with a "CAL to value" option as in the other modes? OK, you want me to send the meter in for factory CAL? Please do an adjustment to nominal, not just a verification that "the meter meets specs." Anything from 9.9997 to 10.00030 is not good enough for a 6.5 digit meter on 10VDC range.

author: aronake
author_rank: Frequent Contributor
timestamp: October 17, 2024, 03:32:41 am
content: Quote from: View[+]Finder on October 16, 2024, 01:33:18 pmYes, the lack of CAL to value on DCV for such quite high grade DMM is really really bad! Particularly odd as other functions have this feature. And if not avilable when first released, at least should be added in some later firmware. I can not see that it would be very complicated to do.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 17, 2024, 07:55:43 am
content: Quote from: View[+]Finder on October 16, 2024, 01:33:18 pmThe 10.0003 reading is still just 30 ppm off and thus just within specs. Still a a better adjustment should be possible.If an adjustment to nominal value, or just a verification is more suitable depends on the use case.As the tweaking / fool the meter way worked, it was not the need to do the full calibration.A possible issue could be a FW Bug, like getting mixed up the default and last scaling. They may not notice as the initial adjustment would be from the default settings and only later adjustments would be effected. With a rather new meter there may not be many that have drifted enough to warrant a new adjustment.It is odd not not allow for an adjustment to a read values instead of exact 10 V.

author: View[+]Finder
author_rank: Unknown
timestamp: October 17, 2024, 03:47:59 pm
content: QuoteEven more odd is that the 6510 meter did not have any trouble arriving at an adjusted value close to the nominal 10VDC. Both the 6500 and 6510 can accept modules for measurement, however the 6510 is far more sophisticated in the range of modules. The firmware is not the same for both meters, but it is likely that the DMM and graphics aspects are similar if not identical. Calibration seems to be unique to each model though the commands are the same at least of the DMM side. Some of the modules have their own calibration routines.The graphics and computational abilities were foremost in my decision to buy; the ease of ethernet access to download data files for analysis was an unexpected bonus.

author: Krampmeier
author_rank: Regular Contributor
timestamp: October 25, 2024, 05:41:12 pm
content: I also think this is very odd and sounds like a bug. A new firmware will be released in less than 4 weeks, and it will contain several bugfixes, but I don't know if this calibration issue is covered as well.My experiences with the Keithley application engineers and their service team have been very good (the new firmware fixes 2 esoteric bugs which were found by my colleagues). One Keithley application engineer is even active on this forum, Brad Odhner,https://www.eevblog.com/forum/profile/?u=195829.I believe it would make sense if you get in touch with him, or the official Keithley service, and explain your findings. At least they'll verify them internally and give you feedback.Let me know in case you don't get a response - I have a collected a couple of direct email addresses over the last years

author: IanJ
author_rank: Unknown
timestamp: October 25, 2024, 10:08:25 pm
content: Quote from: View[+]Finder on October 16, 2024, 01:33:18 pmInteresting!30 years ago I used to develop systems for drilling rigs, and one particular part was a proximity sensor on the rotary table. Previous method of calibration was to adjust a software multiplier, either by guesswork or calculation to get a readout to display 300rpm if it was running at 300rpm. 2 or 3 attempts got ballpark.When I came in I gave the software the option to just tell it what the known speed was and let the software do the rest. I.e. if the Driller said it was running at 285rpm then we just typed 285 into the software and let y=mx do the rest.Ian.

author: View[+]Finder
author_rank: Unknown
timestamp: October 27, 2024, 10:32:44 pm
content: Hello Ian,I have s/n 88 of the PDVS2 model and once had one of the originals, that has gone missing. You did a fantastic job on the design and build. Thanks for your work on that project.So, from your drilling rig experience, the route to calibration relies on the slope from 'zero' counts to 'full-cale" counts as a linear formula? I have some Signametrics PXI DMM's to adjust and the CAL routine for them works like that. Any advise on the process would be appreciated . . .