Hello colleagues,
I am about to get a few precision resistors (vishay s104, 0,01%, 2ppm) from a local gentleman. They are removed from an old equipment and measured using calibrated HP3458A in 4wire configuration (30 minutes to stabilize them) in an air conditioned lab.
I want to use these as a resistor reference for my home lab. Is it worth to think about some oven ? There are a lot of topics regarding the voltage or current reference but not a much about the resistor counterpart.
Thanks
It all depends on your requirements..
The 3458A may determine the value of your resistors to about 10ppm (0.001%) uncertainty, so the temperature of the resistor during that measurement would also have to be measured exactly.. due its T.C., which may be as high as +/- 4.5ppm/K.. see datasheet: +/-2ppm/K typ. +/- 2.5ppm/K max. spread!!
Intended as a reference of that uncertainty level , you would have to attach properly a precise thermometer to the resistor.
Then your colleague, owning that 3458A, would have to determine the R(T) curve of your S104, so that you could later correct for temperature deviations.
What's the alloy technology used? C-alloy or K-alloy? (i.e. S104C or S104K?)
How to solidly attach the resistor and the thermometer is discussed in Andreas' thread. (iso-thermal mass required)
Depending on the case type of your S104?, i.e. plastic (as shown in the spec:
http://www.vishaypg.com/docs/63001/63001.pdf) or metal can, you also have to take care about heat flow, over the case or over the leads.
These metal foil resistors may drift over time if they are NOT hermetically sealed AND oil filled (VHP case). This annual drift may be as high as 20ppm/yr., shelf life, disregarding that these are aged resistor. See longterm ageing curve in spec, also!
Therefore, regular recalibration , i.e. annual monitoring of its value is required.
Also take care for proper 4W jacks, especially if its value is equal or below 10k.
My construction of such a resistance reference, involving all of the mentioned features, can be seen here:
https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/30/I achieve < 1ppm/K, correction to <0.2ppm by measuring temperature, and < 0.5ppm/ 4yr. ageing with VHP202Z.
Your S104? may achieve about 10 fold worse stability figures, which still would be quite good.
Frank