Author Topic: T.C. measurements on precision resistors  (Read 271005 times)

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Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #125 on: July 15, 2014, 05:25:45 pm »
Hi Itz2000,

The 'modern' alloy IET refers to would be Zeranin, it is a slightly updated version of Manganin, the main difference is that Zeranin has a slightly 'flatter' curve around the reference temperature range than Manganin does.  There was some small improvement in long term drift and arguably TCR but the main Manganin characteristics are still there.  The TCR curve is still hyperbolic and that cannot be changed significantly.

Yes, the 242D system has always used General Radio style Manganin resistors, ESI used them and now IET uses them, they were originally developed by GR many years ago and the general design of these resistors has changed very little over the decades.  As I said, Evanohm has replaced Manganin (and Zeranin for that matter) as primary standards around the world.  By the way, the specified TCR of those ESI/IET resistors are 0±3 PPM/°C for >100 ohms in the RS925D (earlier versions were 0±5 PPM/°C), basically my standard line resistor specification as far as TCR is concerned.  In the SR1010 series of working standards, the TCR is 0±5 PPM/°C, TCR varies with value and grade of standard but the older ones were 5 PPM/°C or higher.

In the ESI 242D system, most of the resistor decades were trimmable in the 240C and RS925D to high accuracy but according to the manual the system only held 0±20 PPM/year (usually better than that).  Manganin (and its relatives) require kid glove care to maintain their values, TCR and long term drift.  They do not tolerate mishandling very well at all, there are many Manganin standards selling on eBay which are out of tolerance and drifting badly because they were mishandled.  Unfortunately it is easy to cause permanent changes in these alloys by mishandling them.  I've worked with ESI 242Ds since 1973, I am very familiar with their characteristics, probably more so than many of the people at IET.  Very good resistors indeed, but there are better ones available now.
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #126 on: July 15, 2014, 06:19:08 pm »
Hi Ken,

It would be possible to wind the finer gauge wires on these mica cards but you probably could not terminate the wire to the terminals on either side of the card, they are too soft and since they were made compatible to Manganin for soldering I'm sure they would not weld to Evanohm.  Since Evanohm is a much 'harder' alloy, it would not bend around the edge of the mica cards very well particularly with large gauges, probably <0.0063" diameter at best and that might be pushing it a bit.  Otherwise there is a little bit better heat dissipation given the open winding surface but I'd say the difficulty of winding on mica and the slow winding speed would likely negate any advantage over a bobbin style.
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #127 on: July 15, 2014, 07:22:43 pm »
Is it possible to wind Evanohm wire on an old-school mica card?  Would there be any advantages or disadvantages to this?

I would vote for advantages, because that is how the ESI SR104 is made. The thermal expansion coefficient of thin mica card is low and close enough to that of Evanohm. The final unit has several resistors of opposite TC cancelling out each other.
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #128 on: July 15, 2014, 07:55:04 pm »
Hello Itz2000,

The SR104 and its two brothers, the 1k and 100 ohm versions are very special cases, they cannot be made in production numbers by any stretch of the imagination.  They are slow to make and go through many cycles of processing, it is far more than winding a wire on a mica card (which, by the way, has absolutely nothing to do with matching thermal expansions, Evanohm is far stronger in tensile strength than mica, mica can't 'stretch' Evanohm if it tried) for long term stability and low TCR.  The SR-1010 and SR1 series are of similar make, wire on a mica card, but the manufacturing processes are not the same.  These resistors are not production line resistors, they cannot be made in large quantities, not even moderate quantities.  If you have ever checked out the quotes for these resistors, they make Vishay's hermetic resistors look like a bargain. 

I can easily beat the specifications of the SR1010 and SR1 series resistors and with 'special' processing, I can come pretty darn close to primary standard specifications too.  Mica card build resistors are obsolete now in most cases, they have been surpassed by newer technology.
 

Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #129 on: July 15, 2014, 09:29:47 pm »
You are correct.

Increasing the sweep time from 3 to 24 hours remarkably reduced the hysteresis of the RS92 resistors, but didn't much affect the Vishay. The speed of the temperature change seems to be important. Interesting...

Hello,

not totally. Some effect is also different with respect of perspective or scaling of the diagrams:

The "leading" part only looks leading when regarding unzoomed.
When you zoom in within the linear part (and rescale) it will look like 2 lines in parallel.

I made a set point jump measurement yesterday within the linear part of the rising T.C. edge.
(From around 21 deg C to 30 deg C).
The front edge is the NTC on the heat spreader of the heater.
The dotted line the resistance of S102#1
The following line the NTC near the S102.

The T.C. 6ppm resistor change for the 9 deg C temp rise is around 0.75 ppm/deg C for fast temperature changes.

I see nearly no thermal time constant at the rising edge within thermal block.
There seems to be a much slower time constant after the top edge.
The resistor value seems to fall sligthly whereas the temperature within thermal block still is rising.
I guess this time constant is some kind of plastic / bond creeping which needs time.
Would be interesting what the difference between S102 and Z201 is regarding the construction.

With best regards

Andreas

 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #130 on: July 15, 2014, 09:38:32 pm »
Do you have any photos of the insides of an SR-104 that you are allowed to post?  Also-- how many resistors are in an SR-104?  Are they in series, or parallel, or series/parallel?  I always wondered exactly how they made such a good resistor...

They are slow to make and go through many cycles of processing, it is far more than winding a wire on a mica card (which, by the way, has absolutely nothing to do with matching thermal expansions, Evanohm is far stronger in tensile strength than mica, mica can't 'stretch' Evanohm if it tried) for long term stability and low TCR.

I have never seen the internals of an SR104 and I am not an expert of this subject in any way. Long time ago I was in a seminar where an ESI engineer (or a university researcher involded in the project?) told us about the rocky road of development of these resistors. I remember seeing a diagram with four resistors in series-parallel configuration but that could have been just an example simple enough for mathematically representing the idea of the opposite temperature coefficients. The key of the whole manufacturing process was the special temperature treatment which was used to "null" the TC of the individual resistors. Like Edwin said it was not easy to control and large percent of the resistors were not usable. But if I understood correctly, it was possible to do the treatment again and again until the result was good enough. I got an impression that the thermal expansion properties of the mica card were very important and made possible that the SR104 withstands large temperature variations that would ruin all other same level standards.
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #131 on: July 15, 2014, 10:56:48 pm »
Hi Itz2000,

This is a little speculation on my part plus some theory concerning the innards of a SR-104.  While it is possible that they are using four resistors in series/parallel configuration, I think that may be more trouble than it is worth to build and match.  Theoretically, since Vishay has used it in at least one of their wiz-bang resistor types, it is possible to use two resistors in series (in this case, two 5K resistors) with matched opposing TCRs to 'cancel' out to near zero.  Out of a given batch, say a number larger than 50 resistors, there is a fair probability of finding a reasonable number of equal but opposite TCRs to build near zero TCR sets out of.  At least with Evanohm, there are no hyperbolic TCR curves to mess with.

This may or may not be how the SR-104 is built, I've never seen the insides of one either and because they are very expensive I doubt that anyone outside of the production line has seen the insides of an SR-104.  The most recent descriptions I've read of the SR-104 resistor sounds more like there is only one 10K resistor inside there as the primary, the other 10K resistor is strictly for internal temperature measurement.  It is certainly not out of the question that there is only one resistor in there instead of two.

Fortunately, since an SR-104 deals with very small temperature excursions, this makes the matching game a bit easier and if the TCRs are reasonably linear around the cardinal point, you get a very nice, near zero TCR as a result.  That is the relatively easy part of it, the other part is the conditioning of the alloy/bobbin (mica in this case) to play nice with each other.  While it is possible to get wire with zero (or near zero) TCR, when it is wound onto a bobbin (whatever the kind) things do change and only if the remaining processing does the right things to the wire/bobbin assembly does the resistors turn out with the desired end TCR.  The variables involved are many and most of them cannot be controlled real tightly so there are always variations in the end product no matter how good the total processing is.  Just about every process done to a resistor, right up until the final calibration, imparts stress or removes stress, the end product, hopefully, has had most, if not all, of the stresses removed or compensated for.

Yes, a metallurgist told me that alloys can generally be recycled as long as they are not contaminated so wire that misses the TCR mark can be cooled down and put back through the heat treatment process again to try and hit the mark.  The tighter the 'mark', the harder it is to hit.

That impression about the mica card making it possible to withstand large temperature variations was more smoke and mirrors, perhaps in their minds mica did that but I don't use mica and my resistors withstand even wider temperature swings which would likely wreck havoc on even an Evanohm standard, but yes, an Evanohm standard will certainly take more abuse than a Manganin standard with much less damage to it.
 

Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #132 on: July 16, 2014, 08:44:43 pm »
Hello,

added results for S102JT#2 on page 1:

https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg462303/#msg462303

similar hysteresis +/- 6.3 ppm like #1 (+/- 5.5 ppm) but additional T.C. of +0.55 ppm/K overlayed.

With best regards

Andreas
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #133 on: July 17, 2014, 08:03:46 am »
similar hysteresis

It would be interesting to test the audiophoolery VAR.

http://www.vishaypg.com/docs/63140/var.pdf

According to some sources it is just a naked Z201 (probably lacquered). That could give some idea how much the mechanical connection from the rigid housing to the chip affects the hysteresis, compared to a "free" chip and wire connections.

 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #134 on: July 17, 2014, 03:02:31 pm »
Hello Itz2000,

An interesting data sheet from Vishay, the supposed photo of the VAR is too small to reveal very much detail.  I doubt very much that it would be coated in something like lacquer (just as an example) but if it is coated with something, it would have to impart no significant strain to the resistor element and yet be able to endure the total temperature range.  I think that a detailed photo of the real finished VAR product would possibly be more revealing than what is shown in the data sheet.  Vishay still likes to play with its customers in the dark.

The data sheet has a fair amount of true, partially true and downright BS information in it.  Obviously it attempts to appeal to the mostly less informed crowd in the audio sector with all the non-sense piled on for audio's benefit (if you can call that a benefit).  Here again, all Vishay needed to do was tell the facts and that should be enough but no, the data sheet is drowning in buttered BS.

You are right, Itz2000, with the Z201 outside of its hermetic can, it does lay the resistor element open to external stresses that it is normally protected from.  The only question is how good is the coating in protecting the element?  It definitely is fragile being out in the open, almost any accidental contact with it is going to likely cause damage.  I wonder how much these are going for?  Perhaps Digi Key lists them.

http://media.digikey.com/Photos/Vishay%20Foil%20Resistors/Y0706.jpg

The VAR should respond pretty quickly to temperature so the temperature tails should be short, noticeably shorter than the hermetic version but these resistors will have to be physically protected  or else these could be some expensive accidents.

Nice, the actual photo of an VAR is the back side which doesn't tell much at all.  My guess is that Vishay is coating the VAR with polyester-imide rated at 180°C.  The actual connections to the element appears to be something else, almost looks like the old black dopant we used to put on high voltage connections but I know it isn't.
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #135 on: July 17, 2014, 03:36:18 pm »
I wonder how much these are going for?  Perhaps Digi Key lists them.

Digikey:

100 ohm
http://www.digikey.com/product-search/en?mpart=Y0706100R000T9L&vendor=804

1 kohm
http://www.digikey.com/product-search/en?mpart=Y07061K00000T9L&vendor=804

10 kohm
http://www.digikey.com/product-search/en?mpart=Y070610K0000T9L&vendor=804

Mouser:

71-VART100R000TB (100 ohm)
71-VART1K00000TB (1 kohm)
71-VART10K0000TB (10 kohm)

EDIT: Photo added.
« Last Edit: July 17, 2014, 03:41:04 pm by ltz2000 »
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #136 on: July 17, 2014, 04:40:10 pm »
Hi Itz2000,

Nice photo, where did you dig it up at?  There are a lot of trim points in the element, these resistors are always made at a lower resistance and trimmed 'up' in value, the photo does show some refinement in the trimming process over the years.
 

Offline Andreas

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Re: T.C. measurements on precision resistors
« Reply #137 on: July 17, 2014, 06:52:12 pm »
similar hysteresis

It would be interesting to test the audiophoolery VAR.

http://www.vishaypg.com/docs/63140/var.pdf

According to some sources it is just a naked Z201 (probably lacquered). That could give some idea how much the mechanical connection from the rigid housing to the chip affects the hysteresis, compared to a "free" chip and wire connections.

Hello,

feel free to contribute your measurements. :-)

I on my part do not think they are really devices with "long term stability".
If they are laquered: where is the benefit for audio? This will give a bad dampening factor and "nonlinearities".
The PCB (pin-stabilizer) between the pins (according to datasheet) will swell when humidity is rising.
This will also give some tension to the chip.
So I personally think that a hermetically device will be the better choice.

With best regards

Andreas
 

Offline acbern

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Re: T.C. measurements on precision resistors
« Reply #138 on: July 18, 2014, 06:29:56 am »
real long term stability (sub ppm pa) like the sr104 can only be achieved be a fully hermetic housing. conformal coating like it is used on mil and space hardware helps avoid humidity/condensation issues by passivation but does not by any means subsititute a hermetic housing. (so btw: when we are talking about high precision resistors here, to me the aging drift issue is more important than the temp. coefficient which can be controlled by measuring the temperature whenever the resistor is used, you cannot do this with the aging factor, you have to rely on the unit being stable by design and verify from time to time. what help is a <1ppm/K tempco resistor if the annual aging is 10ppm and beyond).

the only way to get hermeticity is by metal/glass/ceramic.
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #139 on: July 18, 2014, 12:53:00 pm »
real long term stability (sub ppm pa) like the sr104 can only be achieved be a fully hermetic housing.

Sorry, but I have to disagree. It depends on the technology and contruction, if the hermetic sealing is necessary or not. It helps only if remarkably reduces some of the main drift mechanisms.

For example the 1 ohm standard designed by the Australian National Measurement Laboratory, a sort of  "modern Thomas", can be as stable as 0.01 ppm/year. The construction is open, basically just a perforated metal can.

Another example could be the classic 1 ohm Thomas. A common problem with the very early units is that the hermetic seal starts leaking. That increases the pressure coefficient but the long term drift is necessarily not affected.

And don't forget my ESI SR1 mentioned earlier. It has predictable drift of approximately +0.3 ppm/year which is quite good even compared to the SR104 (0.1ppm typical and 0.5 ppm/year specified). A bare mica card in a bended aluminium box which not even dust proof.

I have never used the Evanohm resistors manufactured by Edwin. But if carefully selected I wouldn't be surprised to find sub-ppm units.

 

Offline Conrad Hoffman

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Re: T.C. measurements on precision resistors
« Reply #140 on: July 18, 2014, 08:57:18 pm »
With the talk of what's inside the ESI boxes, I have to wonder what's inside the high end Fluke calibrators? I would assume very few inherently stable standards, with everything else being compared and compensated in software. Is that how it's done, or do they use banks of near-perfect resistors for both resistance and dividers?
 

Offline acbern

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Re: T.C. measurements on precision resistors
« Reply #141 on: July 18, 2014, 10:03:47 pm »
real long term stability (sub ppm pa) like the sr104 can only be achieved be a fully hermetic housing.
Sorry, but I have to disagree. It depends on the technology and contruction, if the hermetic sealing is necessary or not. It helps only if remarkably reduces some of the main drift mechanisms.

For example the 1 ohm standard designed by the Australian National Measurement Laboratory, a sort of  "modern Thomas", can be as stable as 0.01 ppm/year. The construction is open, basically just a perforated metal can.

Another example could be the classic 1 ohm Thomas. A common problem with the very early units is that the hermetic seal starts leaking. That increases the pressure coefficient but the long term drift is necessarily not affected.

the fact that there are resitors out there that were measured stable and re not hermetic (the NML is operated in oil and thats the way to keep humidity away, this is in no way comparable with a resin encapsulated resistor) does not mean that by design they are stable. you wil also find ref01 references that are much more stabe that the data sheet. that does not mean anything. otherwise they would have been specified that way.

for critical resistors earlier fluke units used oil filled resistors, as far as I know current fluke units use hermetic metal can resistors. the 34401 network e.g. is ceramic.
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #142 on: July 19, 2014, 12:58:46 am »
Hello Acbern,

The reasons for hermetically sealing resistors are not necessarily the ones assumed.  In the case of Manganin (et al), it is very sensitive to oxide (rusting if you please), barometric pressure and also water, i.e. humidity.  In the case of a primary standard, Manganin must be sealed or its stability will significantly degrade over time, its nominal value will change as well.  In the case of a working standard where the absolute stability requirements are not so severe, enameled wire will keep humidity problems to a minimum, barometric pressure is not such an issue and keeps oxide at bay.

Evanohm (et al) is not sensitive to humidity like Manganin, is not sensitive to barometric pressure and oxide is not a significant issue if built correctly, even bare.  Evanohm has none of the sensitivities that Manganin has.  Therefore, Evanohm need only be coated in enamel and the job is done for a standard.

The main purpose of an oil bath is not to keep humidity out of the resistor but to keep the resistor at a constant temperature, it has no other function.

All primary standards require utmost processing of the wire (even multiple times through the heat treating process) to achieve the best possible stability and even then, not all of a given batch ends up as standards, the wire may be sent back for another trip through processing again.

My resistors do not need to be hermetically sealed to achieve superior stability compared to other non-hermetic resistors and can compare favorably even to hermetics under similar conditions.  My main claim to fame is that my resistors can take more of a thermal shock licking than anybody else's with much less change in resistance or long term drift under such conditions.  I do not claim that my resistors are primary standard grade, that process is too complex and demands equipment that few can afford, not to mention developing the process in the first place.  My resistors do exceed working (transfer) standard specs under military working conditions.
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #143 on: July 19, 2014, 11:22:36 am »
for critical resistors earlier fluke units used oil filled resistors, as far as I know current fluke units use hermetic metal can resistors. the 34401 network e.g. is ceramic.

Reminds me of the Datron thermal slots i.e. replicating things made by some "high authority" without thinking why. They make the best instruments you can buy, so they can't be wrong. And they aren't. If it works well and doesn't cost too much, don't change. If you own a hermetic resistor production line or stock them in large quantity, it can be economically wise to use them in all products even if not techically required. Or just in case, if the hermetic adds only a tiny fraction of the total manufacturing costs. It can even save money if you get rid of expensive and time consuming environmental testing.

Hermetic sealing obviously improves stability, but it depends on the resistor techology and construction used, how much. And if the improvement is meaningful at all in the big picture. With bulk metal foil, based on the Vishay stability figures, it seems to be important. But not with wire wound, if designed properly. But if not, hermetic sealing can help to hide the design flaws or material limitations.

the NML is operated in oil and thats the way to keep humidity away, this is in no way comparable with a resin encapsulated resistor

Oil doesn't stop humidity or oxygen. Unfortunately.
 
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Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #144 on: July 19, 2014, 11:28:00 am »
An SR-104 that is more than a few years old will only drift [typically] about -0.07ppm/yr.  This is too small of a drift to measure without some very sophisticated gear [probably, a QHR and CCC].  The drift value in the data sheet only applies to the first few years [typically the first year].A *very* old SR-104 that has an intact hermetic enclosure can drift even less than the -0.07ppm/year.

Please note that the numbers you can find in literature were determined before 1990 against the US legal ohm which also drifted to the same direction and almost the same annual rate.
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #145 on: July 19, 2014, 02:06:09 pm »
Historically, there were three reasons for hermetic sealing resistors.

1. They were going to be used in harsh environments which the resistor itself could not easily tolerate, mainly military or aerospace and resistor technology had no other solution at the time.

2. They were going to be used as primary standards and while the environment was 'friendly', the inherent resistor characteristics were not good enough to meet long term stability without hermetic sealing and resistor technology had no other solutions at the time.  Because hermetic sealing was in use for decades and was a 'proven' technology, its use remained mostly unchallenged even today.  It is also very expensive having NIST qualify a new resistor as a primary standard, it takes years and truck loads of cash, another reason to not buck the system.

3. Hermetic sealing was found to be a very effective method of covering up resistor design flaws, keeping all that unfriendly environment at bay made the resistor look better than it actually was.  This technique is still in use today and while it is not cheap for the customer, it is an excellent selling point.

Hermetic sealing is not cheap, never has been and it is labor intensive to boot.  Because hermetics have had such an illustrious and long history, its unfettered use today is mostly unchallenged and unquestioned.  The one really serious weak point of a hermetic seal is the seal itself, unless carefully tested it can and will leak, after all, it is nothing more than a soldered joint and some of them are quite large.

Not all high quality resistor standards are hermetically sealed, many are not in oil but in air and perform very well.  Primaries still tend to be in oil for all of the historical reasons and perhaps because the hermetic primary standard has not been challenged, the old adage, "if it works, don't fix it" is a favorite of the resistor industry even when it is broken and can be fixed, they still don't want to change things.

Getting the resistor industry to change the way they do things is more difficult than going to the Moon (and even that is still questioned.....see!).
 

Offline Edwin G. Pettis

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Re: T.C. measurements on precision resistors
« Reply #146 on: July 19, 2014, 02:35:56 pm »
To Conrad Hoffman (reply #148),

The resistors inside the Fluke 5420A / 30A and 50A units are just good quality working standard grade resistors, no hermetics and the resistor specs are not all that special, either TCR or tolerance.  When these units are calibrated by the cal lab, the actual measured values are stored in non-volatile memory, it is these values that are displayed on the unit.  They are reasonably stable resistors but again, they do not have to be exceptional.  If best accuracy is needed, a cal cycle is done just before use, otherwise, it is roughly a working grade standard.
 

Offline quarks

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Re: T.C. measurements on precision resistors
« Reply #147 on: July 19, 2014, 03:56:35 pm »
With the talk of what's inside the ESI boxes, I have to wonder what's inside the high end Fluke calibrators? I would assume very few inherently stable standards, with everything else being compared and compensated in software. Is that how it's done, or do they use banks of near-perfect resistors for both resistance and dividers?

Hello Conrad,

unfortunately I do not have a Fluke Multifunction Calibrator, but from my Wavetek calibrators I know, hermetically sealed Vishay Z-Foils (mainly 0.005% and 1ppm/K TCR) and Caddock (0.1% 15ppm/K TCR for 100MOhm) are used as internal references.  Additionally some trimming resistors are there in every range.

My guess is, Fluke is very similar, but maybe with their own Fluke Resistors.

bye
quarks
« Last Edit: July 19, 2014, 04:48:28 pm by quarks »
 

Offline ltz2000

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Re: T.C. measurements on precision resistors
« Reply #148 on: July 19, 2014, 03:59:52 pm »
If we throw out the data on the SRX which has nothing to do with the SR-104, and throw out John Lion's self-calibrated value, then we are left with an average of +0.07ppm/year drift.

Yes, I noticed the sign mistake, non stressed Evanohm drifts upwards. But that was not my point.

First, the drift of the US legal ohm prior to 1990 makes the simple calculated drift look much better than the actual drift.

Second, the calibration uncertainties are not low enough for determining the drift of an SR104 from just a few data points. Not even in the high level labs and especially not in the 70s or early 80s.

 

Offline Conrad Hoffman

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Re: T.C. measurements on precision resistors
« Reply #149 on: July 19, 2014, 08:15:55 pm »
By a stroke of surplus luck, I actually have a 5450A. It gets "calibrated" simply by storing the measured values in memory.

Though I like the historical aspects of manganin, I've also read it get used as a pressure sensor for high force shock waves like nuclear blasts! It doesn't seem like something that can be used as a pressure sensor is ideal for something that should be immune to the external environment, though I try to keep the number of nuclear blasts in my lab at a minimum.
 


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