Calibration capabilities (UK/Prema 6048) - Page 1
Forum section: electronics / general

author: essele
author_rank: Frequent Contributor
timestamp: September 16, 2019, 08:23:12 pm
content: I've managed to join the volt-nut club by getting my hands on a Prema 6048 -- which is superb! It's currently running on the original factory calibration constants because the NVRAM was replaced by the previous owner, the firmware has also been upgraded, but he assures me he copied the data over, and initial tests show that it's reasonably accurate on most ranges.However, clearly you don't have one of these without wanting it to be accurate, so I have been looking at calibration options here in the UK and I've been getting some responses that confuse me. I have approached three different companies for calibration quotes so far, and then more recently had a look at their UKAS certificate for their capabilities. I'll keep the names out of it for the moment ... just in case it's me being daft.Company A -- this is the company that calibrated my Datron 4000A and 4200. They said they were unable to calibrate the 6048 because they didn't believe they had the accuracy to meet the units specification. Their UKAS certificate shows 10V at 0.34ppm, resistance sub-ppm for relevant ranges. DC Current 11ppm at 1A, AC stuff also looks fine ... I don't see how you'd get much better than this?? They did say they have a subcontractor who they will get a quote from, so I do wonder if these values are for the subcontractor?Company B - this company happily quoted me £47 + shipping. Clearly that rang alarm bells. Their UKAS cert shows 10V at 6ppm and everything else much worse.Company C - they quoted £190 + shipping, which seemed more reasonable to me, however their UKAS cert shows 10V at 9.8ppm + 43uV.So it seems to me that Company A are doing themselves a disservice, but I'm pleased to see they are trying to deal with the capabilities of the 6048. Company B and C are offering services below the needed level and shouldn't really be quoting, or at the very least they should be specific about what they can do.Or am I just completely missing something?

author: branadic
author_rank: Super Contributor
timestamp: September 16, 2019, 09:06:35 pm
content: So it was you who scored it on ebay? Nice. Have you asked Keysight to calibrate this unit? The also calibrate third party instruments.-branadic-

author: essele
author_rank: Frequent Contributor
timestamp: September 16, 2019, 09:12:58 pm
content: Ha ha - yes, it was me! I probably paid a bit of a premium, but I have limited physical depth to put stuff so this was the only real viable good 8.5 digit option, so I knew I had to act fast when it appeared! So far it all seems to be great.I haven’t tried Keysight, interesting idea ... I’ll see if I can get a quote. I’m assuming that won’t be £47 ;-)

author: Kean
author_rank: Unknown
timestamp: September 17, 2019, 11:36:56 am
content: I bought Dave's Prema 6047, but I've been slack and not done much of anything with it.I guess I'm just not made to be a volt nut

author: borghese
author_rank: Regular Contributor
timestamp: September 17, 2019, 11:38:27 am
content: At Prema in Germany adjustment, certificate, and calibration report is 414€

author: branadic
author_rank: Super Contributor
timestamp: September 17, 2019, 11:53:51 am
content: Quote from: Kean on September 17, 2019, 11:36:56 amAh, I once asked Dave but never got an answer on that. I suggest that you send your 6047 to essele for direct comparison, so we can see what is different. Just some firmware + different voltage reference?-branadic-

author: Kean
author_rank: Unknown
timestamp: September 17, 2019, 12:02:09 pm
content: Quote from: branadic on September 17, 2019, 11:53:51 amHmmm... not sure I want to part with it, but I guess I'm open to offersI think Dave did a pretty comprehensive teardown, but I'd be happy to verify any info.

author: essele
author_rank: Frequent Contributor
timestamp: September 17, 2019, 01:35:44 pm
content: Actually the schematics for both models are in the manual ... at a quick glance there seems to be some extra stuff on the microprocessor schematic (U18 and associated OP07's), then the different reference and reference-supporting circuitry for the LTZ1000. The pre-amp and display are the same schematic for both.I've put a request in to Keysight for a calibration quote - I notice that their UKAS capabilities are 2.8ppm for 11V-110V.I've also had a further reply from Company A above (when I asked why they thought they couldn't do it given the data on the UKAS cert), they said that those specs were using their standard cells and would take a significant amount of time for each reading therefore would cost thousands to do. So they would use a 5720 which doesn't meet the Prema 6048 spec for anything other than AC voltage.

author: branadic
author_rank: Super Contributor
timestamp: September 17, 2019, 02:08:04 pm
content: Maybe essele can share some high resolution teardown pictures and both of you guys could readout the firmware containing chips? A comparison could prove whether a 6047 could be upgraded to 6048 with small effort.-branadic-

author: e61_phil
author_rank: Frequent Contributor
timestamp: September 19, 2019, 07:43:29 am
content: Quote from: essele on September 17, 2019, 01:35:44 pmAlmost every lab will use a calibrator like that, if you are able to pay for the calibration. The Prema 6048 seems to between the 3458A with 8ppm ref and the 3458A with 4ppm ref (for DCV). There are papers how to calibrate such high precision instruments with a 5720A.Our local cal lab here uses their standards to bring the 5720A to 24h specifications before they calibrate a 3458A.

author: Kean
author_rank: Unknown
timestamp: September 19, 2019, 11:16:40 am
content: Quote from: branadic on September 17, 2019, 02:08:04 pmHappy to do that.I want to make a backup of the ROM and NVRAM anyway. I believe it may have lost the NVRAM data at some point.Kean

author: essele
author_rank: Frequent Contributor
timestamp: September 19, 2019, 11:17:01 am
content: Thanks e61_phil.It's actually the lab that have said they didn't feel able to do it! They have subsequently sent me a quote using their subcontractor, and that's £793 for non UKAS, and £906 for UKAS ... and that will be plus VAT and shipping costs. Gulp.I'm still waiting for a quote from Keithley, and I've also asked another couple of places with good UKAS capabilities.

author: TiN
author_rank: Super Contributor
timestamp: September 19, 2019, 12:23:43 pm
content: Better idea is to receive 6048 and perform own tests first for few months, checking stability and noise performance. Replace all electrolytic capacitors, check all power supply rails for noise/spec. Clean connectors, reseat cables.Once you are confident that unit behaves good and no drifts or jumps observed in datalogs - then think about calibration.It is not uncommon that old instruments have hidden issues, that would invalidate expensive calibration, if not taken care before.

author: essele
author_rank: Frequent Contributor
timestamp: September 21, 2019, 01:36:26 pm
content: Hi TiN - yes, that’s a good suggestion, although I have a bit of a catch 22 problem in terms of accurate references, but I’ll figure something out.

author: tggzzz
author_rank: Super Contributor
timestamp: September 21, 2019, 04:26:18 pm
content: Quote from: essele on September 21, 2019, 01:36:26 pmStability is more important than accuracy.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 21, 2019, 05:23:07 pm
content: For testing the main requirement is a known stable reference. The main part would be some 10 V and at least 1 better a few different range resistors, or a know very stable meter like a well aged 3458. Just for testing the stability of the meter no accurate value is needed - so some +-2% for an LTZ1000 would be good enough (still need some burn in and confidence in the resistors).One may also do a budget calibration to slightly larger tolerances first, to get all the ranges checked at least to a good level. To really trust a "new" meter may need some historic data for maybe 6 month or 1 year.While still in the EU, the 415 EUR option from Prema may still be an option.