DIY calibration resistor / reference resistor 0.01 Ohm and 0.001 Ohm  - Page 1
Forum section: electronics / general

author: Overspeed
author_rank: Frequent Contributor
timestamp: January 15, 2023, 01:18:13 pm
content: HelloI have as need and project to built a resistor in 0.01 and 0.001 Ohm value base on coaxial Haddad design ( a clever simple design ) . my purpose is to reach the best possible accuracy but not metrology lab accuracy and a ppm/K under 10I have selected manganin wire in 2 mm diameter because I have located a supplier with wire at acceptable price , I am open to other alloy solution / shape as some lab resistor are made by using foils .My question : the connection block will be each side , I plan to use copper bloc or brass block machined by milling and EDM ( half round hole for the wire ) to make split jaw and avoid soldering but also a possible of adjustment by sliding .1 ) What is the best setup to measure the resistance ? a bridge measurement need 3 other resistor or more if that a Kelvin Bridge and equipment as Burster is costly up to very costly and make the adjustment of the length ?2) Can I silver plated them so both manganin and my connection blocs ?I have calibration equipment for strain gage 120 / 350 Ohms / 1000 Ohms with 0.01% resistors but nothing in low valueRegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 16, 2023, 05:24:29 pm
content: I've never seen a shunt that wasn't soldered. A sliding/clamped contact would probably be unreliable due to oxidation and lack of precision in exactly where the contact was over time and temperature. Most shunts are soldered at a slightly low value, then filed in the middle to raise the value to the desired reading. Low values are best done by forcing a known current and measuring the drop, rather than a bridge. Primary labs use bridges (maybe not anymore) but those bridges are very expensive to make.

author: Overspeed
author_rank: Frequent Contributor
timestamp: January 18, 2023, 07:34:11 am
content: HelloMy goal / need is to built an update design of this resistor ( see oictures ) , but in sealed tube filled with Argon or Nitrogen to avoid oxidationThe sliding connectors allow to adjust the resistance value and try to reach acceptable accuracy as trial , the contact force is a major concern in any contacts for resistivity measurements and more if that linked to surface roughness , I work on a special 4 points resistivity measurement for alloy and that a very long list of uncertainity and problem .I will compare crimped ( with own design ) and soldered as the picture linked , crimped is more easier for first samplesActually my main concern is the calibration or more exactly a metrology quality measurement of the low value resistor I have or I will built . I don t need 0.010000 value I need to know what value I have with high level of confidence as resistor value measurement at 100 or over is well know and quite easy by for low value that far less easy.Other question : How metrology labs built a bridge for 0.01 Ohm under lower value ?RegardsOS

author: Vgkid
author_rank: Super Contributor
timestamp: January 18, 2023, 07:59:53 am
content: The bridges used to measure below 1 ohm are the kelvin bridge. That is the historical way to measure low ohmic values.Next(and current) is the direct current comparator.You can also create a precise current, and measure the voltage potential. That is the easiest.

author: Overspeed
author_rank: Frequent Contributor
timestamp: January 18, 2023, 08:37:43 am
content: HelloThanksFor Kelvin bridge I have already use one but to reach a high level of accuracy that request a lot of investment , I think that better to use comparison method base on a already calibrated resistor . I will ask to our French National Lab how much cost a 0.01 Ohm calibration .I have a 1 amp accurate current source , I will make some test with 1 Amp and post result , but with 1 amp the output voltage will be low but measurable .A French laboratory have designed a new type of shunt see picture , I link the complete study which included a detailed comparison of metrology shuntThe thesis link :https://theses.hal.science/tel-02035347RegardsOS