Best way for Decade Resistor

[zlymex]

I've to find a place to ask for a quote of:
Vishay 101 for 100 Ohm, 1K, 10K, 100K and VHP202Z for 1 Ohm, 10 Ohm.
For 1M, 10M and 100M, I'm thinking about Caddock  TF020R/N or TF050R/N.
........

The smallest value Vishay provides for VHP202Z is 5 Ohm according to the datasheet.
I once try to order 5 Ohm(in the hope to use 5 to make 1 Ohm) and they rejected saying that the actual smallest available was 10 Ohm, so I ordered 20 10-Ohm.

Vishay provides 1 Ohm hermetic Z-foil as VHP4Z and VPR247Z.

AFAIK, Z-foil is better than regular foil only in TCR aspect. However, VHP202Z only guarantee 4ppm/K TCR for 10 Ohm, far more worse than required by a decent resistor standard. In this respect, regular hermetic foil resistors are equally good, since temperature compensation of some kind should be used in order to DIY a good resistance standard anyway.

[zlymex]

........
You mentioned how you might compensate a negative TCR in another thread [with a copper-wire "resistor", which is what I thought of too], but how do you compensate a positive TCR?  NTC thermistors are not very linear-- do you know of a more linear negative compensation material?

I have developed a quick and efficient way to compensate alpha(of both positive and negative) and beta TCR to virtually zero by using hermetic precision grade NTC(and with copper resistor).
Although the value of a NTC is exponential with temperature, the curve is concave, opposite of most of metal-based resistors(such as WW and foil, most of them with negative beta with convex shape). By adding a resistor in series with the NTC and possible another resistor in parallel, I can control the curvature, making the final complementary resistance a 3rd order, with very small resistance variation of less than 0.1ppm in normal lab temperature range(18 to 28 degree C). 
Due to the very large variation of NTC with temperature, usually very small 'amount' of compensation is needed, making the NTC and associated resistor very insignificant and easy to choose.

I haven't publish the compensation in English yet(waiting for an actual test result), but available in Chinese(with many charts and tables): http://bbs.38hot.net/forum.php?mod=viewthread&tid=167995

[Nuno_pt]

The smallest value Vishay provides for VHP202Z is 5 Ohm according to the datasheet.
I once try to order 5 Ohm(in the hope to use 5 to make 1 Ohm) and they rejected saying that the actual smallest available was 10 Ohm, so I ordered 20 10-Ohm.

Vishay provides 1 Ohm hermetic Z-foil as VHP4Z and VPR247Z.

AFAIK, Z-foil is better than regular foil only in TCR aspect. However, VHP202Z only guarantee 4ppm/K TCR for 10 Ohm, far more worse than required by a decent resistor standard. In this respect, regular hermetic foil resistors are equally good, since temperature compensation of some kind should be used in order to DIY a good resistance standard anyway.

Thanks for the heads up zlymex, at the time I must have been looking at other datasheet, and writing this at same time, so the confusion.
You're right it only goes down to 5 Ohm.

I've send a email yesterday to Rhopoint to quote some Caddock USF - 240, 271, and 371 series.

[Alex Nikitin]

Here is my first attempt to get a half-decent 10K reference. I've used this well aged LT450/C (3ppm/C max) resistor and trimmed it to read close to 10K exactly on the HP3458A by adding a 300M shunt (the resistor on its own is +35ppm). So far it looks quite good, with an overnight variation in the lab (not temperature controlled) under 2ppm (including obviously the HP3458A drift).

Cheers

Alex

[zlymex]

Here is my first attempt to get a half-decent 10K reference. I've used this well aged LT450/C (3ppm/C max) resistor and trimmed it to read close to 10K exactly on the HP3458A by adding a 300M shunt (the resistor on its own is +35ppm). So far it looks quite good, with an overnight variation in the lab (not temperature controlled) under 2ppm (including obviously the HP3458A drift).

Cheers

Alex

Good job!
I got some of those MC wire-wound( and 100M) too that often show upwards drift.

[Alex Nikitin]

I got some of those MC wire-wound( and 100M) too that often show upwards drift.

Yes, wire-wound resistors do apparently drift up in time. However in this case it is about +70ppm (maximum, taking in the uncertainty of the meter, and could be below +15ppm ) drift over 27 years, or +2.5ppm/year . I can live with that .

I've bought a set of these resistors, new old stock, from 1 Ohm to 1M (x1,x2,x4,x8 values for six decades). I will make the rest of the decades with these - 1, 10, 100 Ohm, 1K (these with a 4-way connection), 100K and 1M. I also have 10M 0.01% 5ppm Caddock as well as a couple of 1% 1G and 100G resistors, so only 100M and 10G are missing at the moment for a full 12 decades range.

Cheers

Alex

[Mickle T.]

Here is my first attempt to get a half-decent 10K reference. I've used this well aged LT450/C (3ppm/C max) resistor ...

Why do you think it's 3ppm/C max ? I has tons of Mann Components PWW resistors (LT, UP, DUP etc) and have never met the official datasheets. The same problem with the Kelvin PWW resistors, widely used in Datron equipment.

[Alex Nikitin]

Here is my first attempt to get a half-decent 10K reference. I've used this well aged LT450/C (3ppm/C max) resistor ...

Why do you think it's 3ppm/C max ? I has tons of Mann Components PWW resistors (LT, UP, DUP etc) and have never met the official datasheets. The same problem with the Kelvin PWW resistors, widely used in Datron equipment.

That is what the datasheet says. From my initial measurements it looks like it is better than 1ppm/C around the 22-25C range. I will measure the R(t) curve soon and will know for sure.

Cheers

Alex

[Mickle T.]

That is what the datasheet says. From my initial measurements it looks like it is better than 1ppm/C around the 22-25C range. I will measure the R(t) curve soon and will know for sure.

All of my measurements says the same - TC is less than 1 ppm/C. But can you give a link to a datasheet?

[Alex Nikitin]

That is what the datasheet says. From my initial measurements it looks like it is better than 1ppm/C around the 22-25C range. I will measure the R(t) curve soon and will know for sure.

All of my measurements says the same - TC is less than 1 ppm/C. But can you give a link to a datasheet?

Here it is. You should bear in mind that the tempco is defined for the full temperature range, which is up to 135C for these resistors, and should be considerately lower around 25C.

Cheers

Alex

[Kleinstein]

For a reference the TC is not that important. It should be reasonably low, but temperature measurement / stabilization is not unreasonable. If really good there are also influences from humidity and maybe magnetic fields that get important.

The more important factor is long term stability.

[lars]

It is also my conclusion that long-time stability and humidity effects are more critical than temperature sensitivity.

Has anyone some figures to share for Wire Wounds? I have only tested General Resistance 8E16 and Ultrohm and in both cases I have been disappointed by humidity sensitivity. For the old 8E16 I have, long-term stability is far better than the humidity sensitivity. For the Ultrohm I can´t determine the long-term drift as the humidity sensitivity is so high and I bought them last year.

Lars

[zlymex]

Long term stability is the most important factor in my regard too.
Humidity is an very annoying factor for non-hermetic resistors that it not only has delayed effect but I suspect there are long term effect too.
When I DIYed an 10k standard resistor by using 8 Fluke 19.999k wire-wound 9 years ago, It was very difficult for me to characterize it for some years. I gave up it and decided to use hermetic resistors since for all my later DIY on less than 100 Meg resistance standard.

[Gyro]

Long term stability is the most important factor in my regard too.
Humidity is an very annoying factor for non-hermetic resistors that it not only has delayed effect but I suspect there are long term effect too.

Why not solder up some hermetic enclosures then? Obviously fine trim would have to be external, but you could seal the main resistors in for good.

[zlymex]

Long term stability is the most important factor in my regard too.
Humidity is an very annoying factor for non-hermetic resistors that it not only has delayed effect but I suspect there are long term effect too.

Why not solder up some hermetic enclosures then? Obviously fine trim would have to be external, but you could seal the main resistors in for good.

I tried, but I cannot find a good and true hermetic enclosure. 

[Gyro]

Tin plate with soldered seams and ceramic feedthrough caps or glass feedthroughs?

Edit: even thick copper or brass foil (or thin sheet) at a pinch

[zlymex]

Tin plate with soldered seams and ceramic feedthrough caps or glass feedthroughs?

Edit: even thick copper or brass foil (or thin sheet) at a pinch

Let's say I was lazy. I once teardown an tin and ceramic sealed cap and found out it was not a true hermetic seal(see photo).
I did buy some big oil filled caps(like the 2nd photo) that I may use for sealing 100 Meg+ resistors.
I have already got all the hermetic resistor elements(decade only, with redundancy) necessary to build standard resistors from 0.1 Ohm to 10 Meg.

[Gyro]

Well you could do, but it looks a lot messier than soldering something up from thin sheet. After all, all a hermetic resistor is is a standard resistor in a solder sealed can with glass to metal seals.

I think solder-in ceramic feedthrough caps are hermetic and someone found a source of glass to metal seals on ebay a while back.

[zlymex]

Well you could do, but it looks a lot messier than soldering something up from thin sheet. After all, all a hermetic resistor is is a standard resistor in a solder sealed can with glass to metal seals.

I think solder-in ceramic feedthrough caps are hermetic and someone found a source of glass to metal seals on ebay a while back.

True, I always looking for containers with two glass to metal seals. Another thing, it must have a large cap sealed by tin in order for the content to put inside in the first place.

[Gyro]

I can certainly relate to the 'laziness factor' of having something like that already available. I was just thinking of the effort of cleaning the sticky mess out. 

I guess there are two other possible factors that might be relevant:

1. A thicker can might be more resistant (but certainly not immune!) to the effects of varying atmospheric pressure, assuming this might be a possible factor affecting drift.

2. The thicker the walls, the greater the internal temperature rise during the final sealing. It would be nice to be able to solder this very quickly to avoid drifting the resistors.

Just random thoughts anyway.


Edit: Ah, found some seals: http://www.ebay.co.uk/itm/QTY-25-HSC-HERMETIC-SEAL-CORPORATION-2709-4-EP40-1-TERMINAL-BOARD-04820-/152026811217?hash=item2365810b51:g:rMoAAOSwPhdVFzYr

[zlymex]

I can certainly relate to the 'laziness factor' of having something like that already available. I was just thinking of the effort of cleaning the sticky mess out. 

I guess there are two other possible factors that might be relevant:

1. A thicker can might be more resistant (but certainly not immune!) to the effects of varying atmospheric pressure, assuming this might be a possible factor affecting drift.

2. The thicker the walls, the greater the internal temperature rise during the final sealing. It would be nice to be able to solder this very quickly to avoid drifting the resistors.

Just random thoughts anyway.


Edit: Ah, found some seals: http://www.ebay.co.uk/itm/QTY-25-HSC-HERMETIC-SEAL-CORPORATION-2709-4-EP40-1-TERMINAL-BOARD-04820-/152026811217?hash=item2365810b51:g:rMoAAOSwPhdVFzYr

Agreed with the 2nd completely. For the 1st, if there is vacuum inside, there would be no pressure effect. Most of hermetic are filled with oil or inert gas that will transfer the atmospheric pressure inside, and the thicker the wall the better. However, modern wires is not suffer from pressure effect very much. The old double-wall standard do suffer main owning to the fact that the wire is tightly wrapped around the inner wall which deform with pressure change.

As for the ebay seals, I don't think they are very good because:
- either the conductor is Kovar, which has very large thermal EMF,
- or the conductor is copper, which gradually build up small cracks because the difference in thermal expansion.
The correct way to build a good glass to metal sealing is to use Kovar tubes, allowing copper wire go thru, thus solve both problems.

[TiN]

Those on ebay are Kovar, I got some of those while ago.

[splin]

These are probably what you want - and they're cheaper:

http://www.ebay.co.uk/itm/Russian-military-miniature-glass-Feedthrough-insulators-lot-of-100-/251041737116?hash=item3a7340e99c

[Gyro]

Ah yes! Those were the ones that came up in that previous thread (someone trying to do something with a vacuum chamber iirc) they allow you to run copper right the way to the resistors.

Thanks splin, they didn't come up in my ebay search. Damn I'll probably have to order some now... just in case.

[splin]

Ah yes! Those were the ones that came up in that previous thread (someone trying to do something with a vacuum chamber iirc) they allow you to run copper right the way to the resistors.

Thanks splin, they didn't come up in my ebay search. Damn I'll probably have to order some now... just in case.

This was the thread - it was me wanting to hermetically seal some resistors:

https://www.eevblog.com/forum/projects/low-cost-hermetic-seals/

Naturally, having bought those seals I haven't got round to using them yet due to not being able to make up my mind as to exactly which values and configurations of resistors to can. There are some interesting replies, especially those about epoxy seals, so worth a quick scan for those with an interest in the subject.