21st Mar 2016, 1:54 pm | #101 |
Dekatron
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Re: A precision voltage calibrator
Excellent - and it'll be good to check that the LM4040 reference survived the journey
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21st Mar 2016, 2:05 pm | #102 | |
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Re: A precision voltage calibrator
Quote:
As for the AVO readings, I understand why you have said that - and I am in agreement with the embedded thinking behind that remark. In a post of mine above, I have reported my findings using a Iso-Tech DMM. On the grounds that: 1. That instrument is the newest of the DMMs I own; 2. It has only ever been owned by me (so its history is known); 3. I note its indications when connected to the voltage calibrator √ ; 4. The calibrator is new - and I know its history; ► I am going to adjust all 3 Flukes to the voltage as indicated on the calibrator. Will I ever get to the bottom of this mystery? To be quite blunt, I've now reached the point where I care not: my mind is now totally focussed on the end result. Finally, I hope to be able to accept the offer of assistance from Oldtestgear. Once that has been done, hopefully this entire matter can finally be laid to rest. Upon review, I had no anticipation that what started out as a 'simple idea' would mushroom into such a saga. But we are talking about 'electronics' here, and now and again, strange & totally puzzling incidents do arise. Perhaps it is knowing that which keeps us so committed in this field of technology? Anyway, nuff said for now. My thanks to everyone who as contributed so far. Al. |
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22nd Mar 2016, 10:39 pm | #103 | |
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Re: A precision voltage calibrator
Quote:
Al. |
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23rd Mar 2016, 12:28 am | #104 | |
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Re: A precision voltage calibrator
Quote:
Anyway, how does it measure up? The sticker states that the unit was measured with a HP 3458A (a bit of a beast!) at a temperature of 21C. I measured with my Keithley 2015THD, and checked the temperature (20.6C). Everything had at least 3 hours to warm up and stabilise. Code:
Setting Measured Claimed Error between measurements ------- --------- -------- -------------------------- 2.5V 2.49926V 2.49917V 0.0036% 5.0V 5.00218V 5.00196V 0.0044% 7.5V 7.50171V 7.50138V 0.0044% 10.0V 10.00420V 10.00374V 0.0046% The IC (the KH variant, date code 0619) is well within spec, and the difference between my measurements and the manufacturer's measurements is pleasing - the pattern suggests that the measurements were genuinely made, rather than made up at random. The basic specification of the 2015 is 0.003%, and the 3458A is an order of magnitude better again. To apparently be that close to their 3458A is pleasing, and further increases my confidence in my Keithley. Next up, I'm expecting one like Jim's and Bill's, plus another variant that's even cheaper. I'm not sure if the latter will come with any sort of "calibration", but I'll be interested to see what the former comes with |
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23rd Mar 2016, 11:52 am | #105 |
Nonode
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Re: A precision voltage calibrator
I quite often see errors of 'many millivolts' due to 'poor' contact between differing metals on 4mm connectors, especially noticeable when using a very high impedance voltmeter (e.g. 50G ohm). I usually need to wipe the surfaces with contact cleaner to get the same voltage with the probes reversed !
dc |
4th Apr 2016, 11:33 pm | #106 | |
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Re: A precision voltage calibrator
Quote:
First up, the one already featured (see post #55). This uses the top-spec "LH" variant, as Jim's picture shows. Interestingly, mine has exactly the same date code as his (1015). I also noted that if I bring up the supply rail slowly on a bench PSU, I see the strange behaviour that was reported earlier - so I'll investigate changing that capacitor. Even more interesting is the "calibration certificate". Yes, it's identical to Jim's! And Bill said that his is also identical. Hmm. So, for these particular units the calibration appears to be false (unlike the plastic-cased versions). As before, here are my measurements. Temperature was 21C, same Keithley 2015 was used, and the supply was 15.00V, applied to the battery terminals. A minimum of 3 hours warm up time. Code:
Setting Measured Claimed Discrepancy Absolute error ------- --------- -------- ----------- ------------- 2.5V 2.49969V 2.49942V 0.0108% -0.0124% 5.0V 5.00156V 5.00037V 0.0238% 0.0312% 7.5V 7.50213V 7.50042V 0.0228% 0.0284% 10.0V 10.00333V 10.00066V 0.0267% 0.0333% Fictitious certificate aside, the IC is comfortably within the "L" specification, so I'm happy with that... Next, a type that hasn't featured yet - astonishingly cheap at just £2.89 delivered - this one uses the "JH" chip, so the least good of them. My sample has a date code of "9148". Pictures below... There is no calibration data supplied with this one. Measurement conditions exactly the same as before: Code:
Setting Measured Absolute error ------- --------- ------------- 2.5V 2.49857V -0.057% 5.0V 5.00159V 0.032% 7.5V 7.49998V -0.0003% 10.0V 10.00259V 0.026% Hope this is of interest... Mark |
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5th Apr 2016, 2:47 am | #107 |
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Re: A precision voltage calibrator
I looked at the cheapest one, and as they're both for peanuts I chose the first one for convenience. TBH for an Amateur as I am these days it's a bit of an indulgence anyway, but for Professional users it's a different matter. I trust my digital meters to stay sufficiently accurate, and it turns out they all did, at least at low voltages.
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5th Apr 2016, 1:41 pm | #108 |
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Re: A precision voltage calibrator
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8th May 2016, 11:01 am | #109 |
Nonode
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Re: A precision voltage calibrator
In late March, I decided to "join the bandwagon", so I ordered two units as shown in #106. About 2 weeks ago, I realised they had not arrived, so raised the matter (thro Ebay). I had a reply confirming despatch, but then later traced as RETURNED to their warehouse. They apologised and promised replacements which arrived after about 5 days, something of a record for far East despatch. Alas, no "Calibration certificates", and so far no time to play, but when a few minutes appear, I will be creating my own "reference centre" which should at least act as a check on my Telequipment C3 calibrator.
Les. Last edited by MotorBikeLes; 8th May 2016 at 11:02 am. Reason: Corrected #106 plus sp. |
9th May 2016, 12:34 am | #110 |
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Re: A precision voltage calibrator
Someone on the EEVBlog forum recently received one without the certificate - perhaps the seller(s) have decided to stop sending out fake certificates now that it's public knowledge?
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9th May 2016, 5:48 pm | #111 |
Octode
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Re: A precision voltage calibrator
In my earlier post #32 mine only came with a label no certificate, but the label was pretty accurate. So no fake certificate in my case.
Chris |
9th May 2016, 6:00 pm | #112 |
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Re: A precision voltage calibrator
Yes, all the hand-written labels I've seen have been pretty plausible. It's the printed "certificate" for the type with the 15V battery (unit #2 in my article) that appears to be fake
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