Reference/standard resistance DIY project (?...)

[Rax]

[...] if you don't have a known accurate way of getting the absolute value you still don't know the actual resistance any closer than your meter will already tell you.

These AB-Precision resistors apparently come with calibrated measured absolute values (I'd assume by 8.5 digit or so lab standard ohmmeter).

I have confirmed this. The kit comes with documentation where each R section presents actual 8.5 digit measured resistance value. Thank you, Adrian!

[Rax]

I'm getting a Z201 this week and can't wait to check it out a bit.

I promised to get back here with some impressions after playing with the Z foil. This is a .005% 100 ohms resistor.

If I use this in 4 wire measurement with offset with my 8840A, I get essentially dead on 100.000 ohms readings. I assume using an offset dialed in with all 4 wires shorted to each other is the correct way of doing this.

Just going 4 wire w/out an offset was getting me somewhere around 99.98X ohms or so. There's a bit of a wobble in any case scenario.

I have a pretty eclectic mix of meters here, from 3.5 to 6.5 digits. My 8840A is the one I currently have here and trust the most, but they're all in very good shape.

If anyone's wondering, my bench is in my garage and the wall thermometer (not a precision instrument) says 74F. Geographically, this is in Southern California near the coast, where the weather is typically relatively stable and mild, both temperature and humidity-wise. The garage is not tightly air conditioned (I do have both heating and cooling portable units in here but can't probably reach a very stable temperature as I would if my workspace would have a central AC type of environment).

[Villain]

I'm getting a Z201 this week and can't wait to check it out a bit.

I promised to get back here with some impressions after playing with the Z foil. This is a .005% 100 ohms resistor.

If I use this in 4 wire measurement with offset with my 8840A, I get essentially dead on 100.000 ohms readings. I assume using an offset dialed in with all 4 wires shorted to each other is the correct way of doing this.

Just going 4 wire w/out an offset was getting me somewhere around 99.98X ohms or so. There's a bit of a wobble in any case scenario.

I have a pretty eclectic mix of meters here, from 3.5 to 6.5 digits. My 8840A is the one I currently have here and trust the most, but they're all in very good shape.

If anyone's wondering, my bench is in my garage and the wall thermometer (not a precision instrument) says 74F. Geographically, this is in Southern California near the coast, where the weather is typically relatively stable and mild, both temperature and humidity-wise. The garage is not tightly air conditioned (I do have both heating and cooling portable units in here but can't probably reach a very stable temperature as I would if my workspace would have a central AC type of environment).

4 wire ohms verification is done without offset math correction, this is also what 8840A cal manual says.

[bdunham7]

4 wire ohms verification is done without offset math correction, this is also what 8840A cal manual says.

Calibration adjustment of the meter is a separate issue.  The measurement in the 20/200R resistance ranges on the 8840A/AF/8842A series are essentially just a measurement of low voltages in the 20mV and 200mV ranges with additional gain stages.  The specified accuracy for those ranges--both voltage and resistance--is only acheived using the offset control for zeroing. That is right in the specifications.  Using 4-wire doesn't change this, that only eliminates the need to compensate for lead resistance. 

[bdunham7]

If I use this in 4 wire measurement with offset with my 8840A, I get essentially dead on 100.000 ohms readings. I assume using an offset dialed in with all 4 wires shorted to each other is the correct way of doing this.

That would be the correct way to do it.  If you put your  4-wire short on and then switch to the 200mVDC range (without offset) do you get a small negative voltage, about -.020mV?

[Villain]

If I use this in 4 wire measurement with offset with my 8840A, I get essentially dead on 100.000 ohms readings. I assume using an offset dialed in with all 4 wires shorted to each other is the correct way of doing this.

That would be the correct way to do it.  If you put your  4-wire short on and then switch to the 200mVDC range (without offset) do you get a small negative voltage, about -.020mV?

Indeed fluke mentions that all  resistance specs are using offset control. I am a bit surprised they do not specifically tell the user to do that during the verification procedure after adjustment.

[bdunham7]

Indeed fluke mentions that all  resistance specs are using offset control. I am a bit surprised they do not specifically tell the user to do that during the verification procedure after adjustment.

The specs require you to do a zeroing with the offset control within one hour of the reading.  During the calibration adjustment, you are setting new zero and gain constants in the calibration memory, so as long as you do your performance check within the hour, no additional zeroing should be needed to meet the specification.  The specs are what they are guaranteeing, the calibration process is what they want you do to to make sure that happens.  Also the calibration and performance check are done at 23 +/-1 C, the specs are guaranteed to 23 +/- 5C.  You expect better results when you control the temperature more closely.

[jhoffman]

To get a better understanding, here is an example of an individual passport for one of my resistance standards. The true resistance value, alpha-beta coefficients for each standard are given in its individual data sheet. In the absence of an individual passport, all of these values will need to be measured by yourself.
P.S. I do not use these standards in any exact measurements, so I have not measured the true value of their resistance to date. I have these resistance standards more as a collection.

I thought it might help the audience to translate your "individual passport for one of my resistance standards" into English.
I used Google Translate to do this, so please don't shoot the messenger if there are any mistakes. Much easier now to understand what is going on for the English speaking audience.

[gamalot]

This is for my 1 milliohm resistor, and it just so happens that I made a digital backup of it the other day.

[Nanitamuscen]

I will add information about the stability of the resistance coils produced by the USSR models p321 and p331. I am attaching a screenshot from a document containing data on the stability of several coils of different denominations. Stability data is the penultimate column.

[MiDi]

Translation

[alligatorblues]

The VPG HZ Series are most accurate in the world. 0.001% 0.2ppm/C. Vishay even touts them as resistance stamdards..

[Mickle T.]

0.2 ppm/°C 

[alm]

The VPG HZ Series are most accurate in the world. 0.001% 0.2ppm/C. Vishay even touts them as resistance stamdards..

Why do you consider accuracy important? Accuracy is just about the value the day it was manufactured, not the value it may have a year later. Accuracy is pretty much irrelevant for a resistance standard which would have regular calibrations. I'd say drift and tempco are way more important (and humidity coefficient, pressure coefficient, etc). Regarding tempco, don't count on "typical" specs from a Vishay datasheet. Those are should be called "exceptional specs that you may never encounter". See this previous post of mine where I give links to real data and experience from multiple members of the community. They are certainly good resistors, probably the best you can readily buy, but if you expect "typical" performance you'll be sorely disappointed.

Regarding their use in standard resistors. Wekomm started off using off-the-shelf VPG resistors (we've probably all seen the pictures), but had problems reaching performance targets and yield, so in the end moved to a custom process. IET is also using a number of (no doubt selected from a large pool) VPG resistors and is having worse performance than back when ESI were using their own custom precision wirewound process. So don't count on off-the-shelf VPG resistors rivaling a good commercial resistance standard, though depending on your requirements you could make a standard out of any resistor if the goal is to calibrate a 3.5 digit multimeter.

[alligatorblues]

Vishay Precision does have some stipulations in the HZ series datasheet. They are not end all to be all. The TCR is shown on a chart, and it is different for a number of temp. ranges.