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Hi all, I thought this may be worth its own thread. Definitely spun off of a "WTB" post which has its purpose, but an alternate approach would be to build something at DIY level and expected use/requirements.?
This regards putting together a little kit, or possibly a PCB with Z bulk foils and some sort of posts for the probes, in order to create a homebrew bench resistor standard.
Would love to hear thoughts on the requirements for such a kit or board. A couple of quick thoughts would be thick copper traces, short runs, and some sort of consideration for thermal mass/inertia and such for good stability (enclosure? cooling?). Maybe even a temperature sensor with some readout for monitoring.?
Thank you for pitching in your thoughts.?
Radu.?
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On Thu, 15 Dec 2022 at 20:18, Radu Bogdan Dicher < vondicher@...> wrote: Hi all,
I thought this may be worth its own thread. Definitely spun off of a "WTB" post which has its purpose, but an alternate approach would be to build something at DIY level and expected use/requirements.?
This regards putting together a little kit, or possibly a PCB with Z bulk foils and some sort of posts for the probes, in order to create a homebrew bench resistor standard.
Would love to hear thoughts on the requirements for such a kit or board. A couple of quick thoughts would be thick copper traces, short runs, and some sort of consideration for thermal mass/inertia and such for good stability (enclosure? cooling?). Maybe even a temperature sensor with some readout for monitoring.?
Thank you for pitching in your thoughts.?
Radu.?
What use are you going to put this to? You really need to think about what uncerties you can tolerate. Is it for checking 3.5 digit multimeters, or calibrating 8.5 digit ones?
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I think such a project would be useful for your typical "highly invested" hobbyists like me, for which I think a 6.5 digit DMM is pretty normative. In my case, my workhorse is a Fluke 8840A (5.5), and I also have a Fluke 8502A which gets me to 6.5 digits. I don't see myself going 7.5 any time soon unless the bug bites a good chunk of me.? Radu.?
On Thu, Dec 15, 2022 at 2:37 PM Dr. David Kirkby, Kirkby Microwave Ltd < drkirkby@...> wrote: On Thu, 15 Dec 2022 at 20:18, Radu Bogdan Dicher < vondicher@...> wrote: Hi all,
I thought this may be worth its own thread. Definitely spun off of a "WTB" post which has its purpose, but an alternate approach would be to build something at DIY level and expected use/requirements.?
This regards putting together a little kit, or possibly a PCB with Z bulk foils and some sort of posts for the probes, in order to create a homebrew bench resistor standard.
Would love to hear thoughts on the requirements for such a kit or board. A couple of quick thoughts would be thick copper traces, short runs, and some sort of consideration for thermal mass/inertia and such for good stability (enclosure? cooling?). Maybe even a temperature sensor with some readout for monitoring.?
Thank you for pitching in your thoughts.?
Radu.?
What use are you going to put this to? You really need to think about what uncerties you can tolerate. Is it for checking 3.5 digit multimeters, or calibrating 8.5 digit ones?
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I was also thinking of making a resistance "standard" for myself that would help calibrate my impedance analyzer (that I posted to this group in the past). The main reasons I want to make my own is to have a BNC 4 wire connector so the contact resistance effects are minimized (or at least consistent), and so that I can pick and choose which values to use. My initial board design is here (, schematic/board images below). With <15ppm resistors (and assuming reasonable room temperatures), I'd think this is sufficient for my application (~0.1% or so), but would happily take suggestions. Although, if you're considering thermal mass/inertia of the traces I'm guessing this is insufficient for you.? ?  
|
Jeff, Interestingly, this reminds me I have an MAX6225ACPA little kit I put together some years ago for purposes such as this. I also placed a resistive divider on there to add an 185mV output... The 2.500V shows as a 2.5002V, which is a pretty nicely trimmed reference, within the spec by an order of magnitude.? Thank you for the info above.?
Though I'd find it hard to resist using .005%+.2ppm resistors for something like?this, as David puts it, it's useful calculating exactly how much of that is really needed for a certain instrument?(vs. overkill). For instance, for the 8502A, the 100ohm accuracy is listed as?+-.002?+ 2 ("% of input?+ no. of digits"). Can anyone help decipher?this? I have a .005%+.2ppm bulk Z foil on a cart which I could have by some time next week and am wondering how that'd do with this.
Thank you, Radu.?
The Analog Devices AD584 offers 4 reference voltages, 2.500, 5.000, 7.500, 10.000V
15 ppm/¡ãC Max, 0¡ãC to 70¡ãC (AD584K)
15 ppm/¡ãC Max, -55¡ãC to +125¡ãC (AD584T)
I¡¯ve ordered products from Electronic Goldmine 5 or 6 times with no problems. I have no relationship with them other then as a customer.
Electronic Goldmine offers:
, $4.95
G20756 - Bulk Metal® Foil Technology Super Precision Calibration Resistor
$8.00 ¡À 0.05%?Rated 2¦¸ at 8Watt (if placed on heat sink).
$8.00
$4.95
?
Their stock changes daily, so check back often.
I picked up other 0.01% and 0.001% resistors and a 0.1% 0.1uF capacitor.
?
There are a plethora of ¡®precision voltage references¡¯ on Amazon and Ebay.
?
As others have said, what level of precision you need depends on what you are doing.
I suspect the DMMplus is a lot more accurate then I will ever need, but the price was right and I can now trust my meters aren¡¯t lying to me.
My brother in law has a Fluke that is way out of calibration, so quality of build is no assurance of staying within specs, he's decided it isn't worth repairing and bought a cheap DVM from Harbor Freight that wss accurate to better then 0.1%. Plenty accuracy for checking farm equipment electrical systems..
|
There is another option if the goal is to make a presicion 1/2 voltage divider or *2 multiplier.
Rather than selecting and matching 0.005% bulk metal foil resistors (which cost ~$5.00 each),
one can use a Linear Technologies (now Analog Devices) LTC1043. One device, with a few
capacitors (4 of which should be high quality) can be configured to make both a 1/2 divider
(1 ppm) and a 2* (5 ppm) multiplier per the application information on the data sheet? at the same
or lower cost.
The ultimate accuracy probably depends on the quality of the operational amplifier(s) the circuit.
Stephen Menasian?
|
I have an ESI 8 1/2 digit ohm meter. I measured my Leeds & Northrup 10K reference on a freshly calibrated 3458.
|
Hello,
This is my design for a 10k reference resistor.
It's based on a 9k9990 VHP202Z, plus a Thin Film resistor as a fixed trim. But I would recommend a 10k VHP101 instead.
It's sitting in a aluminum block, and this block is tightly attached to an aluminum case.
A precision NTC measures its temperature, so you can at first determine the R(T) curve and always precisely calculate its actual resistance at a given external temperature.
I omitted a PCB, due to leakage current, which created errors on the order of several 10 ppm.
The binding posts should be Pomona CuTe type 3770, as these have high isolation resistance, and low e.m.f..
If you use a DMMs with offset compensation, the binding posts can be of lower quality.?
4W Kelvin connection is required.
This assembly is good for 1ppm/year stability, real T.C. from 0.3 to 1 ppm/K (I got 5 of these), and a drift predictability meanwhile of < 0.2ppm.
So these can be used for calibration of a 3458A.
If you need other reference resistors, you'd need equivalent assemblies, but also transfer standards.
Frank
? ?
|
Frank, Very useful feedback. I think going P-to-P (instead of PCB) with this makes a?lot of sense. Makes the project go faster too!? I was thinking about Z201 resistors - why doesn't anyone seem to use these? They're the best combo %+ppm I can find at the typical US suppliers. They're also not quite an arm and a leg (maybe a couple of fingers...).? If/when I have a kit built, I'm thinking of sending it to a local metrology lab (being in Southern California, if there's something plentiful around is labs, instruments, and cal shops... ;)).? Thank you, Radu.?
Hello,
This is my design for a 10k reference resistor.
It's based on a 9k9990 VHP202Z, plus a Thin Film resistor as a fixed trim. But I would recommend a 10k VHP101 instead.
It's sitting in a aluminum block, and this block is tightly attached to an aluminum case.
A precision NTC measures its temperature, so you can at first determine the R(T) curve and always precisely calculate its actual resistance at a given external temperature.
I omitted a PCB, due to leakage current, which created errors on the order of several 10 ppm.
The binding posts should be Pomona CuTe type 3770, as these have high isolation resistance, and low e.m.f..
If you use a DMMs with offset compensation, the binding posts can be of lower quality.?
4W Kelvin connection is required.
This assembly is good for 1ppm/year stability, real T.C. from 0.3 to 1 ppm/K (I got 5 of these), and a drift predictability meanwhile of < 0.2ppm.
So these can be used for calibration of a 3458A.
If you need other reference resistors, you'd need equivalent assemblies, but also transfer standards.
Frank
? ?
|
Alright, so I see why the VHP101 series - both datasheet and $$$... I just only looked at my regular place - Mouser - and they have none in stock. Digikey has a 10k VHP101.? I wonder if this would be overkill for me. Maybe I only need the Z201 precision. The 3x price tag may throw my project out of range.? Radu.?
On Sat, Dec 17, 2022 at 8:05 AM Radu Bogdan Dicher via <vondicher= [email protected]> wrote: Frank, Very useful feedback. I think going P-to-P (instead of PCB) with this makes a?lot of sense. Makes the project go faster too!? I was thinking about Z201 resistors - why doesn't anyone seem to use these? They're the best combo %+ppm I can find at the typical US suppliers. They're also not quite an arm and a leg (maybe a couple of fingers...).? If/when I have a kit built, I'm thinking of sending it to a local metrology lab (being in Southern California, if there's something plentiful around is labs, instruments, and cal shops... ;)).? Thank you, Radu.?
Hello,
This is my design for a 10k reference resistor.
It's based on a 9k9990 VHP202Z, plus a Thin Film resistor as a fixed trim. But I would recommend a 10k VHP101 instead.
It's sitting in a aluminum block, and this block is tightly attached to an aluminum case.
A precision NTC measures its temperature, so you can at first determine the R(T) curve and always precisely calculate its actual resistance at a given external temperature.
I omitted a PCB, due to leakage current, which created errors on the order of several 10 ppm.
The binding posts should be Pomona CuTe type 3770, as these have high isolation resistance, and low e.m.f..
If you use a DMMs with offset compensation, the binding posts can be of lower quality.?
4W Kelvin connection is required.
This assembly is good for 1ppm/year stability, real T.C. from 0.3 to 1 ppm/K (I got 5 of these), and a drift predictability meanwhile of < 0.2ppm.
So these can be used for calibration of a 3458A.
If you need other reference resistors, you'd need equivalent assemblies, but also transfer standards.
Frank
? ?
|
Frank, I see you used Kelvin connections for this. Is that really necessary?at a value of 10 kohm? If the specific construction configuration allows for soldering the resistor legs short and directly to the posts, would that also help towards removing a pair of posts from the kit (with their cost)? As I'm going through these considerations, I'm kinda losing my own case in my head,?but would like to hear?your thinking?behind this.? Secondly, did you drill that aluminum block, and sink the precision resistor in thermal?compound? I can't really tell from the picture,?but that's how I can conceive it done.? Radu.?
On Sat, Dec 17, 2022 at 10:34 AM Radu Bogdan Dicher via <vondicher= [email protected]> wrote: Alright, so I see why the VHP101 series - both datasheet and $$$... I just only looked at my regular place - Mouser - and they have none in stock. Digikey has a 10k VHP101.? I wonder if this would be overkill for me. Maybe I only need the Z201 precision. The 3x price tag may throw my project out of range.? Radu.?
On Sat, Dec 17, 2022 at 8:05 AM Radu Bogdan Dicher via <vondicher= [email protected]> wrote: Frank, Very useful feedback. I think going P-to-P (instead of PCB) with this makes a?lot of sense. Makes the project go faster too!? I was thinking about Z201 resistors - why doesn't anyone seem to use these? They're the best combo %+ppm I can find at the typical US suppliers. They're also not quite an arm and a leg (maybe a couple of fingers...).? If/when I have a kit built, I'm thinking of sending it to a local metrology lab (being in Southern California, if there's something plentiful around is labs, instruments, and cal shops... ;)).? Thank you, Radu.?
Hello,
This is my design for a 10k reference resistor.
It's based on a 9k9990 VHP202Z, plus a Thin Film resistor as a fixed trim. But I would recommend a 10k VHP101 instead.
It's sitting in a aluminum block, and this block is tightly attached to an aluminum case.
A precision NTC measures its temperature, so you can at first determine the R(T) curve and always precisely calculate its actual resistance at a given external temperature.
I omitted a PCB, due to leakage current, which created errors on the order of several 10 ppm.
The binding posts should be Pomona CuTe type 3770, as these have high isolation resistance, and low e.m.f..
If you use a DMMs with offset compensation, the binding posts can be of lower quality.?
4W Kelvin connection is required.
This assembly is good for 1ppm/year stability, real T.C. from 0.3 to 1 ppm/K (I got 5 of these), and a drift predictability meanwhile of < 0.2ppm.
So these can be used for calibration of a 3458A.
If you need other reference resistors, you'd need equivalent assemblies, but also transfer standards.
Frank
? ?
|
Let's do a calculation. If you want to eliminate the error due to
the interconnect at the 1ppm level, you can tolerate 10mohms
(milliohms) of interconnect resistance. If your setup will have a
parasitic interconnect resistance below that level, then you don't
need a Kelvin connection.
You can, of course, re-run the calculation using whatever numbers
that apply to your goals. But the approach is hopefully clear.
-- Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
On 12/17/2022 15:39, Radu Bogdan Dicher
wrote:
toggle quoted message
Show quoted text
Frank,
I see you used Kelvin connections for this. Is that really
necessary?at a value of 10 kohm? If the specific construction
configuration allows for soldering the resistor legs short and
directly to the posts, would that also help towards removing a
pair of posts from the kit (with their cost)? As I'm going
through these considerations, I'm kinda losing my own case in
my head,?but would like to hear?your thinking?behind this.?
Secondly, did you drill that aluminum block, and sink the
precision resistor in thermal?compound? I can't really tell
from the picture,?but that's how I can conceive it done.?
Radu.?
On Sat, Dec 17, 2022 at 10:34
AM Radu Bogdan Dicher via <vondicher= [email protected]>
wrote:
Alright, so I see why the VHP101 series - both
datasheet and $$$... I just only looked at my regular place
- Mouser - and they have none in stock. Digikey has a 10k
VHP101.?
I wonder if this would be overkill for me. Maybe I only
need the Z201 precision. The 3x price tag may throw my
project out of range.?
Radu.?
On Sat, Dec 17, 2022 at
8:05 AM Radu Bogdan Dicher via
<vondicher= [email protected]>
wrote:
Frank,
Very useful feedback. I think going P-to-P (instead
of PCB) with this makes a?lot of sense. Makes the
project go faster too!?
I was thinking about Z201 resistors - why doesn't
anyone seem to use these? They're the best combo %+ppm
I can find at the typical US suppliers. They're also
not quite an arm and a leg (maybe a couple of
fingers...).?
If/when I have a kit built, I'm thinking of sending
it to a local metrology lab (being in Southern
California, if there's something plentiful around is
labs, instruments, and cal shops... ;)).?
Thank you,
Radu.?
Hello,
This is my design for a 10k reference resistor.
It's based on a 9k9990 VHP202Z, plus a Thin Film
resistor as a fixed trim. But I would recommend a 10k
VHP101 instead.
It's sitting in a aluminum block, and this block is
tightly attached to an aluminum case.
A precision NTC measures its temperature, so you can
at first determine the R(T) curve and always precisely
calculate its actual resistance at a given external
temperature.
I omitted a PCB, due to leakage current, which created
errors on the order of several 10 ppm.
The binding posts should be Pomona CuTe type 3770, as
these have high isolation resistance, and low e.m.f..
If you use a DMMs with offset compensation, the
binding posts can be of lower quality.?
4W Kelvin connection is required.
This assembly is good for 1ppm/year stability, real
T.C. from 0.3 to 1 ppm/K (I got 5 of these), and a
drift predictability meanwhile of < 0.2ppm.
So these can be used for calibration of a 3458A.
If you need other reference resistors, you'd need
equivalent assemblies, but also transfer standards.
Frank
? ?
|
Hello Radu, As solder has about 11 times the resistivity of copper, for precision work, it's best to wire-wrap the resistor leads around the terminal and to use the solder merely as 'glue'. This consideration is more important at low resistance; you can probably get away with soldering at 10 k Ohm, provided you ensure there is no air inclusion in your soldering. 73 de Brian VK2GCE
----- Original Message -----
To: <[email protected]>
Cc:
Sent: Sat, 17 Dec 2022 15:39:15 -0800
Subject: Re: [Test Equipment Design & Construction] Resistance standard/reference design / DIY
Frank, I see you used Kelvin connections for this. Is that really necessary?at a value of 10 kohm? If the specific construction configuration allows for soldering the resistor legs short and directly to the posts, would that also help towards removing a pair of posts from the kit (with their cost)? As I'm going through these considerations, I'm kinda losing my own case in my head,?but would like to hear?your thinking?behind this.? Secondly, did you drill that aluminum block, and sink the precision resistor in thermal?compound? I can't really tell from the picture,?but that's how I can conceive it done.? Radu.? _._,_._,_
Email sent using Optus Webmail
|
Hello Radu,
4W Kelvin connection is definitely necessary for a 10kOhm reference standard (as your thread title implies).
Please see any other standard resistor like the FLUKE 742A-10k, or ESI SR104. Latter has an oil bath, a thermometer and a R(T) table built in, so the Fluke is not a really good standard resistor.
How could you otherwise precisely measure this standard resistance with your DMM, if the cables from the DMM to the resistor, and the internal cabling are on the order of several 100 mOhm, or ~10ppm error?
Contact resistances come on top, and these might vary by several 10mOhm, or ~ 1ppm. If you study the schematic of the FLUKE 5450A standard resistors box, providing 2W or 4W resistances from 0 Ohm to 100 MOhm, all resistors from 0 to 10MOhm are 4W connected; only 19MOhm and 100MOhm are 2W.
If you want to use any of these as standards on 1ppm "accuracy" level, you need to be able to measure their resistances with ~ 0.1ppm resolution and repeatability.
With several additional tricks, my 3458A is able to make measurements on resistors with 0.01ppm resolution, but 0.2ppm standard deviation, which is a measure of stability of this measurement.
Both parameters are not specified in the 3458A data sheet. These parameters are also important, if you want to precisely characterize the R(T) curve for later compensation of T.C.
Those binding posts cost on the order of 10$ each, so that makes no sense to try to save money here. The VHP101 might cost 10 times of that.
You also might buy a cheaper type, with higher T.C., due to the mathematical compensation of R(T). But please chose a hermetical sealed, oil filled type for best timely stability.
The VHP202Z was promoted to be stable as 2ppm/6years, which turned out to be a false promise by Vishay Precision, again. I think, they made a mistake during production.
VHP101 might perform much better, what I heard from others. The VHP101 / 40k inside my 3458A is stable to < 2ppm over many years, see diagram.
Yes, I drilled another hole into the aluminum block, so that the head of the NTC (epcos type S863 or eq.) is a few mm near the body of the resistor. I did not drill all the way through to the cavity for the resistor.
I filled the hole with a bit of thermal compound, and I as well applied that between alu block and case.
You might use a PT100 instead, but this requires another 4W connection, using a LEMOSA connector, maybe.
This way, any external temperature variation is instantaneously transferred to thermometer and resistors (because latter is oil filled), so you get a very tight thermal coupling between NTC and resistor, and a certain thermal damping, due to the thermal mass. I always place the box on top of my 3458A, which gives sort of thermal ovenizing effect at ~ 25¡ãC, see picture.
So that looks like a very simple assembly, but it's got plenty of physics tricks included.?
I made a mistake to shorten the legs? of the VHP202Z. You should leave them long, briefly soldering a wire at 10mm distance from the body, and soldering the ends of both wires to each binding post. Wire wrapping is a good idea to make a very stable solder connection.?
Always use a heat tweezer, to avoid inducing any heat hysteresis into the resistor element. The resistor element is of the strain gauge type.
I got the uncertainty (on the order of < 1ppm) of my resistor group from Metrology Meetings or transport to other volt-nuts or the PTB at a Maker Fair, who had an uncertainty of < 0.5ppm.
I'm monitoring the drift of my group for over 10 years, meanwhile, so I can detect all kind of instabilities.
That' also what I recommend, to build at least 3 of these standard resistors to be able to compare them against each other.
You know, a man with one clock knows the time, a man with two clocks is not that sure any more..
Frank
|
Useful and interesting post; thanks.
I really ought to get off my backside and "recommission" my serried ranks of VHP202K resistors from the early 80s.?
I'd prefer to leave the assembly intact, but maybe they are worth more broken up as scrap.
Hello Radu,
4W Kelvin connection is definitely necessary for a 10kOhm reference standard (as your thread title implies).
Please see any other standard resistor like the FLUKE 742A-10k, or ESI SR104. Latter has an oil bath, a thermometer and a R(T) table built in, so the Fluke is not a really good standard resistor.
How could you otherwise precisely measure this standard resistance with your DMM, if the cables from the DMM to the resistor, and the internal cabling are on the order of several 100 mOhm, or ~10ppm error?
Contact resistances come on top, and these might vary by several 10mOhm, or ~ 1ppm. If you study the schematic of the FLUKE 5450A standard resistors box, providing 2W or 4W resistances from 0 Ohm to 100 MOhm, all resistors from 0 to 10MOhm are 4W connected; only 19MOhm and 100MOhm are 2W.
If you want to use any of these as standards on 1ppm "accuracy" level, you need to be able to measure their resistances with ~ 0.1ppm resolution and repeatability.
With several additional tricks, my 3458A is able to make measurements on resistors with 0.01ppm resolution, but 0.2ppm standard deviation, which is a measure of stability of this measurement.
Both parameters are not specified in the 3458A data sheet. These parameters are also important, if you want to precisely characterize the R(T) curve for later compensation of T.C.
Those binding posts cost on the order of 10$ each, so that makes no sense to try to save money here. The VHP101 might cost 10 times of that.
You also might buy a cheaper type, with higher T.C., due to the mathematical compensation of R(T). But please chose a hermetical sealed, oil filled type for best timely stability.
The VHP202Z was promoted to be stable as 2ppm/6years, which turned out to be a false promise by Vishay Precision, again. I think, they made a mistake during production.
VHP101 might perform much better, what I heard from others. The VHP101 / 40k inside my 3458A is stable to < 2ppm over many years, see diagram.
Yes, I drilled another hole into the aluminum block, so that the head of the NTC (epcos type S863 or eq.) is a few mm near the body of the resistor. I did not drill all the way through to the cavity for the resistor.
I filled the hole with a bit of thermal compound, and I as well applied that between alu block and case.
You might use a PT100 instead, but this requires another 4W connection, using a LEMOSA connector, maybe.
This way, any external temperature variation is instantaneously transferred to thermometer and resistors (because latter is oil filled), so you get a very tight thermal coupling between NTC and resistor, and a certain thermal damping, due to the thermal mass. I always place the box on top of my 3458A, which gives sort of thermal ovenizing effect at ~ 25¡ãC, see picture.
So that looks like a very simple assembly, but it's got plenty of physics tricks included.?
I made a mistake to shorten the legs? of the VHP202Z. You should leave them long, briefly soldering a wire at 10mm distance from the body, and soldering the ends of both wires to each binding post. Wire wrapping is a good idea to make a very stable solder connection.?
Always use a heat tweezer, to avoid inducing any heat hysteresis into the resistor element. The resistor element is of the strain gauge type.
I got the uncertainty (on the order of < 1ppm) of my resistor group from Metrology Meetings or transport to other volt-nuts or the PTB at a Maker Fair, who had an uncertainty of < 0.5ppm.
I'm monitoring the drift of my group for over 10 years, meanwhile, so I can detect all kind of instabilities.
That' also what I recommend, to build at least 3 of these standard resistors to be able to compare them against each other.
You know, a man with one clock knows the time, a man with two clocks is not that sure any more..
Frank
|
Hi all , ive been following this thread with interest.
Wouldnt it be beneficial to fill the sealed box containing the precision resistor with oil and heat it with a temperature controller?
Heating it to a temp above ambient would surely help the temperature stability.
Heating could be easily done with a large wirewould bolted to the sealed metal box and controlled with a PID digital controller that are now available cheaply.
Just my thoughts.
Regards Pete
|
Hello Pete,
The "Reichsanstalt" type resistors require a heated oil bath, and you know, how tedious this is to maintain.
The SR104 as well as the Fluke 720A first decade resistors also have an oil bath, and you as well know, how critical the design of such a sealed assembly is.
The thermometer inside the aluminum block in combination with a quite small and repeatable R(T) curve makes a cumbersome oil bath, as well as a temperature stabilization unnecessary.
In other words: The aluminum mass replaces the stabilization effect of the oil, and the in situ measurement of the temperature replaces the temperature stabilization completely.? ??
For measuring and comparing my 7 resistance standards (5 x VHP202Z, 10k; 1x VHP202, 1k; 1 x Fluke 5450A, 10k), I use a program which directly calculates all required resistance values, see screen shot from my old Turbo Pascal program. 2nd column shows the temperature as measured by a 34401A, 3rd column is the actual resistance as measured by the 3458A (afterwards, a calibration factor is applied), and the 4th column is the calculated nominal R25 value, from its previously determined T.C. Please take notice of the very low StD value!
The 5450A is always used at a constant room temperature, 22 +/- 1¡ãC over the whole year (no active Air Condition used!), and its calculated max. compensated T.C. of about 0.1ppm/K for the 10k resistor chain, similar to the 742A's, eliminates further corrections.
A regulated oil bath is over engineering in my opinion.
Frank?
|
Some thoughts on something like this:???
I'm wondering how well these would stack up against something like Leeds and Northrup references.
Hello Pete,
The "Reichsanstalt" type resistors require a heated oil bath, and you know, how tedious this is to maintain.
The SR104 as well as the Fluke 720A first decade resistors also have an oil bath, and you as well know, how critical the design of such a sealed assembly is.
The thermometer inside the aluminum block in combination with a quite small and repeatable R(T) curve makes a cumbersome oil bath, as well as a temperature stabilization unnecessary.
In other words: The aluminum mass replaces the stabilization effect of the oil, and the in situ measurement of the temperature replaces the temperature stabilization completely.? ??
For measuring and comparing my 7 resistance standards (5 x VHP202Z, 10k; 1x VHP202, 1k; 1 x Fluke 5450A, 10k), I use a program which directly calculates all required resistance values, see screen shot from my old Turbo Pascal program. 2nd column shows the temperature as measured by a 34401A, 3rd column is the actual resistance as measured by the 3458A (afterwards, a calibration factor is applied), and the 4th column is the calculated nominal R25 value, from its previously determined T.C. Please take notice of the very low StD value!
The 5450A is always used at a constant room temperature, 22 +/- 1¡ãC over the whole year (no active Air Condition used!), and its calculated max. compensated T.C. of about 0.1ppm/K for the 10k resistor chain, similar to the 742A's, eliminates further corrections.
A regulated oil bath is over engineering in my opinion.
Frank?
|
The L & N 40xx
series (4040-B=10K) has a tolerance of 0.001%, 10 times better,
but usually much more expensive <?
>
It depends on what level of accuracy you need.? If 0.01% is
sufficient, you can get by much cheaper buying precision wirewound
resistors rather than a packaged standard.? For example, a set of
five 5K 0.01% resistors could produce multiple resistor values.
?
5 in parallel = 1K, 2 in series = 10K. etc.
The seller, morrex, Spare Z Electronics,?? has other values
available in his store. Two of his 5 piece sets of 1K resistors in
series would give 1K steps from 1K to 10K.
John? KK6IL
On 12/19/2022 11:45 AM, Radu Bogdan
Dicher wrote:
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Some thoughts on something like this:???
I'm wondering how well these would stack up
against something like Leeds and Northrup references.
Hello
Pete,
The "Reichsanstalt" type resistors require a heated oil
bath, and you know, how tedious this is to maintain.
The SR104 as well as the Fluke 720A first decade resistors
also have an oil bath, and you as well know, how critical
the design of such a sealed assembly is.
The thermometer inside the aluminum block in combination
with a quite small and repeatable R(T) curve makes a
cumbersome oil bath, as well as a temperature stabilization
unnecessary.
In other words: The aluminum mass replaces the stabilization
effect of the oil, and the in situ measurement of the
temperature replaces the temperature stabilization
completely.? ??
For measuring and comparing my 7 resistance standards (5 x
VHP202Z, 10k; 1x VHP202, 1k; 1 x Fluke 5450A, 10k), I use a
program which directly calculates all required resistance
values, see screen shot from my old Turbo Pascal program.
2nd column shows the temperature as measured by a 34401A,
3rd column is the actual resistance as measured by the 3458A
(afterwards, a calibration factor is applied), and the 4th
column is the calculated nominal R25 value, from its
previously determined T.C. Please take notice of the very
low StD value!
The 5450A is always used at a constant room temperature, 22
+/- 1¡ãC over the whole year (no active Air Condition used!),
and its calculated max. compensated T.C. of about 0.1ppm/K
for the 10k resistor chain, similar to the 742A's,
eliminates further corrections.
A regulated oil bath is over engineering in my opinion.
Frank?
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On Mon, 19 Dec 2022 at 19:45, Radu Bogdan Dicher < vondicher@...> wrote: Some thoughts on something like this:???
I'm wondering how well these would stack up against something like Leeds and Northrup references.
There¡¯s no information about temperature or aging of the resistors at?
but the basic accuracy (0.01%) is worse than resistors you can get from Vishay. That said, if 0.01% is good enough and want it in an enclosure with connectors on it, by the time you spend out for a box and connectors, it might be more economical to simply buy them.?
BTW, in every case on eBay, and 99% elsewhere, you can remove the first ? in a URL, and everything after it. Hence I shorted your?
to just?
-- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Dr. David Kirkby, Kirkby Microwave Ltd
Brian
John Kolb