Project box for DIY resistor standard - Page 1
Forum section: electronics / projects

author: JBaughb
author_rank: Regular Contributor
timestamp: April 26, 2015, 04:40:24 am
content: So i've got some low temperature drift, extremely accurate resistors coming that I'd like to place in a project box for multimeter calibration and accuracy checking. I'm thinking something similar to Daves homemade resistor box, the single value one, not that decade box. I'm aware that some would consider them overkill for a home lab but when I build something, I try to "over-engineer" it as much as possible. I mean, if its worth doing, its worth overdoing, right?So in an ideal setup, would these be placed in a shielded box of some sort or would a standard plastic box be suficcient? Would anyone have a specific recommendation for a suitable box (5 resistor values, each should have space for their own banana terminals. Since some of my gear has 4 wire resistance measurement, should I include four terminals for each resistor value?Also, as far as terminals go, I figured I should get some beefy case mountable ones, similar to the PCB mount ones available on Daves uCurrent. Any recommendations?Last, but not least, are there any other considerations for this thing? Anything that I should build into it, to enhance its accuracy or functionality (built in thermometer, I dunno, that might be stupid?) Just seeing what people have run into in the past so I can potentially learn from others experiences.Thanks guys, everyone in here is always so helpful.

author: Andreas
author_rank: Super Contributor
timestamp: April 26, 2015, 05:22:12 am
content: Hello,of course it all depends on your accuracy needs.A box like that from Frank (for each resistor) would be a good starting point.https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg617211/#msg617211Mandatory:4 wire measurementtemperature sensorshielded housing which you can connect to your "guard" pin of your measurement instrument.With best regardsAndreas

author: sync
author_rank: Frequent Contributor
timestamp: April 26, 2015, 11:44:20 am
content: I salvaged some precision resistors and building a resistor box too. I'm using a small die cast aluminum enclose for shielding. Look at this video for an efficient way to connect multiple resistors for 4 wire measurement.

author: acbern
author_rank: Frequent Contributor
timestamp: May 03, 2015, 06:04:46 pm
content: Here is some other implementation I wanted to share, for your condsideration:I had a set of claibration resistors, mostly used for performance verififaction/calibration of precision multimeters. They were based on Z-foil resistors, exhibiting a very low TC, well below 1ppm/K. However, since my environment is not temperature controlled (and varies between about 18C to 25C), the overall drift of a resistor can easily exceed 1ppm. Now this may sound low, but given the 10k resistor I have as the main calibrated resistance standard item (used to derive all others) is accurate to about 0.3ppm, and errors multiply when doing a ladder calibration, my goal was to have a set of resistor that are preferably independend of temperature.So I used a set of hermetic Z-foil resistors that also have very good aging characteristics (well below 0.5ppm/a). These were integrated in a block of aluminum, which is heated by a temperature controller, see pictures. The Keithley 2002 on the left is used to measure the resistr standard's (top right) temperature internally (by a 4-wire PT100 sensor, class B). I measure with a resolution (not accuracy) of 0.001K, so one can very well see how the temerature stabilzies and oszillates until it reaches the set temperature (arround 32 C). Stability is better than 0.05K once settled (the reguator actually has a much tighter spec).

author: Vgkid
author_rank: Super Contributor
timestamp: May 03, 2015, 07:45:10 pm
content: Impressive lab,do you schematics for the temp controller?

author: acbern
author_rank: Frequent Contributor
timestamp: May 03, 2015, 09:06:47 pm
content: I bought the controller as a used item, I did not want to spend the time to build one, an also, more importantly, buying one allows to rely on specs whcih is always good when building precision gear.It is from Wavelength Electronics.