NML 1 ohm standard resistor - Page 1
Forum section: electronics / general

author: lowimpedance
author_rank: Super Contributor
timestamp: March 14, 2016, 03:47:29 am
content: After reading Zylmex's excellent thread on a number of resistor standards I had a rummage around in some cupboards for some old parts relating to the 1 ohm standards that were produced a very long time ago. See pics.Managed to scrounge a few of the 'heat treated' coils, an outer can and inner mount, (will have to dig through some other boxes to see if I can find enough bits to assemble a complete one. Unable to really call this "bitsa" a standard though, however most likely good for the hobby lab I reckon!. (even without an oil bath!).A spec. sheet found is also posted as is a pic of the earlier style of construction with the outer can removed.Also some 'light' reading here and a mention of the NML 1 ohm, if interested.www.nist.gov/calibrations/upload/std_resistor_2009_metrologia.pdfUnfortunately I dont have access to better measuring equipment or the oil baths etc (might raise a few eye brows)

author: TiN
author_rank: Super Contributor
timestamp: March 14, 2016, 04:06:17 am
content: QuoteIndeed.Transportability = hand-carried +/-0.02 ppm/journey gives a nice smiley.

author: zlymex
author_rank: Frequent Contributor
timestamp: March 14, 2016, 05:55:05 am
content: This is great. Is it the new Thomas selling by MI? Would the coils and the supporting frame be sealed? Here are something related.Calibration Procedures For Direct-Current Resistance Apparatusdigicoll.manoa.hawaii.edu/techreports/PDF/NBS39.pdfAutomated Resistance Measurement Systems w/ Sub-PPM Accuracieswww.mintl.com/media/pdfs/tech/subppmresistancemeasurement.pdfTemperature and pressure coefficient of Resistance for Thomas 1R Resistorswww.nist.gov/calibrations/upload/coefficients-of-resistance.pdfhttp://www.mintl.com/DC/Products/Resistance/Resistors_and_Shunts

author: Vgkid
author_rank: Super Contributor
timestamp: March 14, 2016, 06:03:00 am
content: Nice job lowimpedance.Thanks for the reading materials zlymex.

author: manganin
author_rank: Regular Contributor
timestamp: March 14, 2016, 08:17:07 am
content: Quote from: lowimpedance on March 14, 2016, 03:47:29 amThere are a few major differencies compared with the Thomas type.The NML wire was Evanohm, not Manganin and the heat treatment process of the Evanohm wire allowed much lower temperature coefficient. The TC of the Thomas type was quite high even for Manganin, the process was not TC optimised.The Thomas was tightly wound on a brass cylinder, but the NML had a self supporting structure, secured with silicon rubber strips*. That solved the main problem of the Thomas type, the very high sensitivity to temperature variations. (A thermostat fault in the early 1970's resulted in abandoning five of the ten Thomas resistors in the NBS legal ohm group. The temporary rise in the oil bath tempererature was around 10 degrees, but that was enough to make the resistors unstable.)The NML was not hermetically sealed, even though a flange type sealed container was designed.* Silicon oil bath will ruin the resistor!

author: zlymex
author_rank: Frequent Contributor
timestamp: March 14, 2016, 09:10:42 am
content: Yes, the instruction sheet recommends that the resistors not be immersed in silicone fluid.http://thirdworld.nl/order/ce192d551320e48007836348d038d5610f393915

author: lowimpedance
author_rank: Super Contributor
timestamp: November 18, 2016, 12:26:54 am
content: excuse the necro.Just had to post an extra pic of the box full of 1 ohm coils that have not had the heat treatment ..........and unfortunately never will., That project is looonnng dead.

author: TiN
author_rank: Super Contributor
timestamp: November 18, 2016, 01:17:11 am
content: Toss them in Dave's dumpster

author: lowimpedance
author_rank: Super Contributor
timestamp: November 18, 2016, 01:22:26 am
content: Given he's not too far from here that may be a good place to send this 'scrap'

author: TiN
author_rank: Super Contributor
timestamp: November 18, 2016, 04:30:57 am
content: Maybe then he will have excuse to power that fancy DMM7510I'm not far too, just next door