Very special VHD200 resistor - Page 1
Forum section: electronics / general

author: SvanGool
author_rank: Regular Contributor
timestamp: March 17, 2023, 08:49:57 pm
content: I had been intrigued in the past by the clever BMF divider resistor that Alex Nikitin was using in hishttps://www.eevblog.com/forum/metrology/lt1021cmh-based-mini-reference/project.This is a resistor divider with one leg being 1k111111 and the other leg being 10k, which gives a 1:10 divider or a 10k resistor or a 1k resistor (both legs in parallel) in one very accurate package.This week I needed such a resistor again and found out that this resistor was not a Vishay VHD200 standard option. I thought let's give it a try at Texas Components. I asked for:BMF resistor (like Vishay VHD200) 1.111111k/10kTCR: +/-2 ppm/°C typical (tracking: 0.1 ppm/°C typical)Tolerance: +/-0.005% (match to 0.001%)Power rating: 0.1 WLong term stabilityToday they came back with a response:They can calibrate the resistor to 1k111111 but the resistor housing would show 1k111/10k, because of the 0.005% margin.TCR: absolute +/-3 ppm/°C, tracking +/-2 ppm/°C without additional testingTolerance: +/-0.005%, match +/- 0.005% or betterStandard long term stability for a metal/oil fill can dividerSpecial offer, because of the availability of the materials: VHD200 1K111/10K 0.005% A&M price indication $66 (62 Euro) 10 pcs minimum order quantity. Without VAT (21% for Europe), customs, shipping etc. and non-changeable and non-returnable after order, with a lead time of 4 weeks. So, I do think the cost would be, roughly, around 90 Euro per single piece.Which pleasantly surprised me (both cost and lead time), but I don't need 10 pcs.The question: who of you would also be interested in acquiring such a special resistor?Sjef.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 18, 2023, 09:03:26 am
content: Another alternative part would be LT5400-8 as a 1 K and 9 K resistor array with relative good matching specs.

author: alm
author_rank: Super Contributor
timestamp: March 18, 2023, 10:10:01 am
content: Quote from: boneDragon on March 18, 2023, 08:39:53 amI'm not convinced getting 9 resistors with the same tempco, humidity / pressure coefficient (the VHD200 is hermetic) and long term stability matching will be any cheaper. Getting 9 VHP101 or similar parts certainly won't be. But (statistical) resistor networks might be an option that can offer good matching.

author: dietert1
author_rank: Super Contributor
timestamp: March 19, 2023, 10:15:24 am
content: If you are really desperate, you could try at ebay.com looking for "1X 300190 10K/100K High Precision Voltage Divider and Network Resistors". Buy 10 of those and parallel 9 of the 10K resistors and all 100K resistors. Price of this solution will be US $ 200 or so.Another solution would be one of those SR1010 standards. We got one with 12x 1K, that was found to be within a ppm of the original calibration at the age of 60 years. They are a more expensive, yet more flexible - for other use cases.Regards, Dieter

author: SvanGool
author_rank: Regular Contributor
timestamp: March 19, 2023, 12:42:02 pm
content: I don't think that components like the LT5400 and the 300190 are comparable, on the long term, with a VHD200: they have plastic packages, in stead of a metal hermetically oil filled package, that means they will accumulate humidity at the long term and therefore deviate more.

author: alm
author_rank: Super Contributor
timestamp: March 19, 2023, 06:42:12 pm
content: If the array is arranged in a way that the two legs are distributed equally throughout the package, then I would expect the drift to track quite well. Wavetek / Fluke did it quite successfully in the 7000 series voltage standards. Remember absolute values don't matter much in a voltage divider, only the ratio does.I'm pretty sure Alex used it in his LT1021 reference just because he had one available.

author: iMo
author_rank: Super Contributor
timestamp: March 19, 2023, 07:03:55 pm
content: Quote from: alm on March 19, 2023, 06:42:12 pmSure, as it would be a total overkill with the LT1021-10..

author: Alex Nikitin
author_rank: Super Contributor
timestamp: March 20, 2023, 10:40:43 pm
content: Quote from: alm on March 19, 2023, 06:42:12 pmThe main idea was to get a resistance reference as well as a voltage one. I've purchased these resistors specifically for that reason.CheersAlex