incredible PREMA current accuracy - Page 1
Forum section: electronics / general

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 13, 2017, 07:40:38 pm
content: Hi,a colleague of mine brought his private PREMA 6000 DMM (6.5 digit) to our workplace today. Nothing special in the voltage ranges (50ppm/Year), but the current range (up to 2A) is specified with 100ppm/year within 23°C+/-5°C. Which is better than the specifications of the 1281, 3458A or 8508A (1A). I also had a look at the PREMA 6048 (8.5 digits) and the specification of this meter is only 30ppm/year!There was nothing special in the schematics of the PREMA 6000. 100mR Shunt, thats it. A few pictures from google image search looks like a manganin 100mR resistor (only PREMA 5000 pictures found).The 200mV Range is specified with 60ppm/year. Therefore, there is only 40ppm left for the resistor. Without any aging, there shouldn't be more than 8ppm/K for the shunt to fulfil the specs (without selfheating). Are there any manganin resistor with such good TCs?Are these PREMA meters really that good in the current range or is it a very optimistic specifiaction?BestPhilipp

author: branadic
author_rank: Super Contributor
timestamp: February 13, 2017, 10:03:19 pm
content: Well, I had a look into the manual of my Prema 5000 and Prema 5017 SC and found:Accuracy:Prema 5000: 0,05% reading + 0,005% fullscale, 1 year 23°C +/-5°C (up to 1A)Prema 5017: 0,03% reading + 0,002% (200µA - 20mA) / 0,004% (200mA - 2A) fullscale 1 year 23°C +/-5°CPrema 6000: 0,01% reading + 0,005% fullscale, 1 year 23°C +/-5°C (up to 1A)Prema 6047/48: 0,003% reading + 0,001% fullscale, 1 year 23°C +/-5°CSo maybe this was some kind of development process they did with each new version. And probably the resistors where preaged and selected too like they did with the voltage references.

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 13, 2017, 10:08:17 pm
content: Hmm, I would think the 5017 is much newer than the 6000 (~mid 80's)?And the voltage specifications of the 6000 aren't very impressive compared to a HP 3456A with similar age (the HP is twice as stable).

author: branadic
author_rank: Super Contributor
timestamp: February 13, 2017, 10:21:39 pm
content: What I wanted to say is, the 5017 is probably the successor of the 5000, while the 6047/48 are the successor of the 6000.The 100mohm shunt in the 6047/48 seems to be a part made by Isaballenhütte (Zeranin):https://farm8.static.flickr.com/7460/14118058402_ba92d10f69_b.jpg

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 13, 2017, 10:35:41 pm
content: Very interesting! This PDF herehttp://www.isabellenhuette.de/pdf/WIDER_LEG/DE/ZERANIN%2030.pdfsays special types can have 3ppm/K. Which will fit to the TC specification from the 6048 manual.Hmm, and I thought my Vishay VCS332s are good shuntsSo, perhaps the current range is really that good. It would be interesting to give it a try and compare it to one if the 3458A..

author: Pipelie
author_rank: Regular Contributor
timestamp: February 14, 2017, 12:56:40 pm
content: interesting, I believe I have a PREMA 6000 siting in the corner, perhaps it's time to put it in the test?

author: Dr. Frank
author_rank: Super Contributor
timestamp: February 14, 2017, 01:22:15 pm
content: Quote from: e61_phil on February 13, 2017, 10:35:41 pmThe 3458A is specified 1A DCI, (110 +10) ppm @ 1 year, and the PREMA 6000 is (100+50) ppm @ 1 year.So what's the deal?And how would you like to compare both instruments, against which third 1A standard / shunt?That'll be the classic man-with-two-clocks problem.Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 14, 2017, 01:30:38 pm
content: Quote from: Dr. Frank on February 14, 2017, 01:22:15 pmThe deal is, that this "cheap" Prema has nearly the same specs as the 3458A and other 8.5 digit DMMs.I will compare it to two HP 3458A with several years of calibration reports.

author: quarks
author_rank: Frequent Contributor
timestamp: February 14, 2017, 04:36:27 pm
content: unfortunately I do not have a PREMA DMM, but I have compared most 8.5 digit DMMs and if I remember correctly the PREMA 6048 looked especially bad in DCI comparison, mainly because it seems to have only a 2A range.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 14, 2017, 04:48:18 pm
content: Just comparing 3 instruments will not tell a lot about the specs. Those specs are kind of worst case errors - so most instruments will likely be better by quite a bit. With just 3 instruments comparable accuracy (for current) it is impossible to tell which one is bad, unless one is really out of specs.The 3458 is a little different in the current specs that long term stability is set by the 40 K reference resistor and not the shunt itself. The auto-calibration to go from the 40 K to the 0.1 Ohms shunt adds a little of uncertainty, but there is not much drift in this, more like noise. In the Prema it is the drift of the shunt itself that sets the extra error for the current.Also the calibration quality could be am issue: not every cal lab might get a very good error limit for the 1 A current - the 10 V and 10 K refs needed for the 3458 tend to be lower uncertainty. With a very good calibration one might end with better short time specs (e.g. 30 days) while the 3458 would be better for something like 2 year after calibration.

author: Marcus_S
author_rank: Contributor
timestamp: February 14, 2017, 07:44:09 pm
content: Hi,it might be interesting to add the Prema 6001 to the overview above:Specs 1 year 23 °C +/- 5 °C, DC200 mV 0,002 % of rdg + 0,0007 % of full scale + 1 digit20 V 0,002 % of rdg + 0,0002 % of full scale + 1 digitand2 A 0,007 % of rdg + 0,002 % of full scale + 1 digit (up to 1A)2 mA 0,02 % of rdg + 0,005 % of full scale + 1 digitIn my 6001 I found an Isabellenhütte-Shunt 0,1R (Zeranin) and it should be calibrated with 1 A max to avoid self heating (according to the manual). I have no idea how to calibrate or adjust this meter at home...Best regardsMarcus

author: branadic
author_rank: Super Contributor
timestamp: February 14, 2017, 08:11:23 pm
content: In Prema 5000 and 5017 a 100mohm +/-1% shunt made by Bader (Manganin) is populated:http://www.mikrocontroller.net/attachment/219252/prema-5000-innen-2.jpg

author: branadic
author_rank: Super Contributor
timestamp: February 14, 2017, 08:23:53 pm
content: The german drugstore CONRAD has the PBV-Version with 30ppm/K in stock:https://www.conrad.de/de/messwiderstand-01-10-w-l-x-b-x-h-22-x-4-x-17-mm-isabellenhuette-pbv-01-1-st-447331.htmlSo maybe the version PBV-Z (5ppm/K) is at nearly the same price level? There is also a version AZ-H (3ppm/K) available:http://www.isabellenhuette.de/praezisions-und-leistungswiderstaende/produkte/uebersicht/However, element14/Farnell does have a few similar products in stock too, but at somewhat higher cost:±3ppm/Khttp://de.farnell.com/powertron/pcs-302-0r100-s-1/metallfolienwiderstand-0r1-1-sip/dp/256558330W, 300Vhttp://de.farnell.com/powertron/pcs-301-0r100-s-1/metallfolienwiderstand-0r1-1-sip/dp/256557830W, 300Vhttp://de.farnell.com/powertron/usr-4-3425-0r100-d-1/metallfolienwiderstand-0r1-1-sip/dp/256560030W, 750Vhttp://de.farnell.com/powertron/usr-4-4020-0r100-d-1/metallfolienwiderstand-0r1-1-sip/dp/256560430W, 750V±5ppm/Khttp://de.farnell.com/powertron/shr-4-2321-0r100-s-1-m/metallfolienwiderstand-0r1-1-sip/dp/256558840W, 300Vhttp://de.farnell.com/powertron/shr-4-3825-0r100-a-1-m/metallfolienwiderstand-0r1-1-sip/dp/256559150W, 500V

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 14, 2017, 09:39:40 pm
content: Quote from: Marcus_S on February 14, 2017, 07:44:09 pmI'm also thinking about creating 1A with an uncertainty below 100ppm at home. I have only "calibrated" 10k and 10V.@branadic: Very nice list!Any idea, how to measure this 100mR resistors with <100ppm uncertainty?

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 16, 2017, 04:22:53 pm
content: Today was the last chance to have a look at the Prema 6000. Inside the Prema there was this Bader Manganin Shunt.We set up a little experiment: Agilent B2902A SourceMeter sources 1A through a 3458A and the Prema connected in series. The input of the Prema was than shorten to bypass the current. We let this setup stabilize a while and then we removed the short. At this point the 1A is flowing through the Prema Shunt.The attached curve is the deviation from the current measured by the 3458A (which was quite stable). One can see, that the selfheating due to the 1A is already around 100ppm. Therefore, I think the Prema spec is very optimistic.

author: TiN
author_rank: Super Contributor
timestamp: February 16, 2017, 04:54:28 pm
content: Perhaps offtopic here, but 3458A's 1A shunt is some custom labelled HP 03458-82501-1.I measured temperature coefficient (shunt removed from board) at around-5.1ppm/Klinear, using 100mA test current and based on 20C ramp up/down span.

author: branadic
author_rank: Super Contributor
timestamp: February 16, 2017, 05:24:26 pm
content: QuoteI would have thought they used something different in the Prema 6000 than the Bader shunt. Bader seems to be only a distriburtor for such things, as you can see on their website:http://www.bader.net/

author: branadic
author_rank: Super Contributor
timestamp: February 16, 2017, 06:10:48 pm
content: QuoteWell, looking at the datasheet of POWERTRON USR 4-3425http://www.farnell.com/datasheets/2168435.pdfthey differ between- TC: max. ±5ppm/K (-55 to 155°C), typ. ±3ppm/K (-55 to 125°C), typ. ±1ppm/K (25 to 60°C)- load stability, which is given as 0.01%- shelf live stability: 25ppm / ?R after 1 year, 50ppm / ?R after 3 yearsSo what you see is a mixture of load stability plus self-heating and thus TC. So the question is, what is really given in the manuel of Prema 6000 that you are comparing to?Accuracy (1 year, 23°C ±5°C ± (%of reading (%rdg.) + % of full scale (%f.s.)) *)**)±2mA and ±2A ... 0.01 (%rdg.) + 0.005 (%f.s.)Temperature Coefficient(10°C to 18°C and 28°C to 40°C)2mA and 2A-range (up to 1A) ± (0.002%rdg. + 0.001 %f.s.)/°CTemperature Coefficient(0°C to 50°C) ... double the value at 10°C - 40°C*) Add ± 1 Digit. After autozero.**) Guard connected to "V/Ohm-LO" input socket, sinusodial signal greater then 5% of full scale.So nothing about load stability, only TC and stability after 1 year. And please don't miss the extra digit mentioned in *).

author: e61_phil
author_rank: Frequent Contributor
timestamp: February 16, 2017, 07:12:50 pm
content: Quote from: branadic on February 16, 2017, 06:10:48 pmMy interpretation of load stability is a permanent change in resistance due to the load. This is normally coupled to time. In case of the Vishay Resistor it is 1000h under load. Therefore, this isn't so important for a bench multimeter (operated only on the bench not in a system).In my opinion this 100ppm drift was almost due to the TC of the shunt (self heating).Quote from: branadic on February 16, 2017, 06:10:48 pmThe temperature was within 23+/-5°C. Therefore, the TC should be included in the spec. What I have overlooked is the second part of the spec: 50ppm of FS. This will add another 100ppm to the 100ppm of reading at 1A. So we have 200ppm uncertainty at 1A.100ppm (self-heating uncertainty) + 74ppm (uncertainty @100mV) = 174ppmThere is not much space left, but perhaps it will fit.Edit: If one adds 50ppm (10ppm/K over 5°C) then it doesn't fit into the spec even without aging of the shunt