Empathy List Archives

RK

Rob Klein

Mon, Dec 14, 2009 10:01 PM

My first post to the group, and it's Ohm-nut, rather than Volt-nut, but
I hope you'll forgive me for that :-).
The nutty idea is this: To build a Volt-nuts grade resistance standard.
Or, actually, two, perhaps three.
The first one is quite simple, but rather pricey: I have ordered four
Vishay VHP202Z's, at $ 96 each (ouch!). Expected to be delivered late
february/early march. They will be placed in a series/parallel
configuration to deliver a 10kOhm resistor that should easily rival a
Fluke 742A,
probably be even better. When finished, I intend to have it calibrated
at regular intervals and use it as my house standard.
The other two are a bit more involved, but it will be interesting to
see the results.
For these two, I will use 9 each Z201's from Vishay. These use the same
chip as the VHP202, but are molded, rather than hermetically sealed.
Also, I will use 0.01% types, rather than the 0.001% VHP's. These are
much cheaper (the 18 I need to make two standards cost less than the
four VHP's!), but also less stable over time.
To overcome the stability problem, I am looking at two ways to make
them hermetically sealed. The first is to house the 9 (three in series,
three
sets in parallel) in an RF shielding can, fill this up with oil and
solder it shut.
The can I have in mind is a PCB mounted type, for which I shall have to
design a board. The PCB area inside the can will be solid copper,
extending
some way beyond the outside, so I can make a proper seal. Connections
to the outside world will be through glass-sealed, solder mounted
feedthrough capacitors of low capacitance. After mounting the resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight
to get rid of any moisture, then filled with oil and soldered shut.
This assembly will be placed inside a sturdy metal box (Hammond model
[1]1457K1201), which will hold four low EMF binding posts (Pomona
3770).
For the second solution, I want to use much the same method, but rather
than filling the can with oil, I want to fill it with epoxy or maybe
polyurethane resin.
This is a much simpler solution, because there will be no need for the
feedthrough caps and no need to solder the can shut.
However, of course, I am aware that neither of these resins will
provide an actual hermetic seal, since they will absorb some
moisture. I am curious
though, as to how much of a positive effect can be gained from this
method, as the shear volume of the resin, as compared to the quantity
use to mold the
actual resistors, should at least greatly diminish any effects of
moisture.
So, if you're still with me after this, I would very much like the
knowledgeables of this group to comment on these ideas. Are they
feasible? What potential
pitfalls might I have overlooked? What oil to use (as an avid cook, I
know my olive- from my sesame oil, but I haven't a clue what type of
mineral oil to
look for :-( ).
Thanks,
Rob Klein.

References

http://www.hammondmfg.com/pdf/1457K1201.pdf

My first post to the group, and it's Ohm-nut, rather than Volt-nut, but I hope you'll forgive me for that :-). The nutty idea is this: To build a Volt-nuts grade resistance standard. Or, actually, two, perhaps three. The first one is quite simple, but rather pricey: I have ordered four Vishay VHP202Z's, at $ 96 each (ouch!). Expected to be delivered late february/early march. They will be placed in a series/parallel configuration to deliver a 10kOhm resistor that should easily rival a Fluke 742A, probably be even better. When finished, I intend to have it calibrated at regular intervals and use it as my house standard. The other two are a bit more involved, but it will be interesting to see the results. For these two, I will use 9 each Z201's from Vishay. These use the same chip as the VHP202, but are molded, rather than hermetically sealed. Also, I will use 0.01% types, rather than the 0.001% VHP's. These are much cheaper (the 18 I need to make two standards cost less than the four VHP's!), but also less stable over time. To overcome the stability problem, I am looking at two ways to *make* them hermetically sealed. The first is to house the 9 (three in series, three sets in parallel) in an RF shielding can, fill this up with oil and solder it shut. The can I have in mind is a PCB mounted type, for which I shall have to design a board. The PCB area inside the can will be solid copper, extending some way beyond the outside, so I can make a proper seal. Connections to the outside world will be through glass-sealed, solder mounted feedthrough capacitors of low capacitance. After mounting the resistors and a thorough cleaning, the whole thing will be baked at ~85°C overnight to get rid of any moisture, then filled with oil and soldered shut. This assembly will be placed inside a sturdy metal box (Hammond model [1]1457K1201), which will hold four low EMF binding posts (Pomona 3770). For the second solution, I want to use much the same method, but rather than filling the can with oil, I want to fill it with epoxy or maybe polyurethane resin. This is a much simpler solution, because there will be no need for the feedthrough caps and no need to solder the can shut. However, of course, I am aware that neither of these resins will provide an actual hermetic seal, since they *will* absorb some moisture. I am curious though, as to how much of a positive effect can be gained from this method, as the shear volume of the resin, as compared to the quantity use to mold the actual resistors, should at least greatly diminish any effects of moisture. So, if you're still with me after this, I would very much like the knowledgeables of this group to comment on these ideas. Are they feasible? What potential pitfalls might I have overlooked? What oil to use (as an avid cook, I know my olive- from my sesame oil, but I haven't a clue what type of mineral oil to look for :-( ). Thanks, Rob Klein. References 1. http://www.hammondmfg.com/pdf/1457K1201.pdf

W

WB6BNQ

Tue, Dec 15, 2009 5:40 AM

Rob,

Fluke has over 60 years of real experience correctly make highly accurate stable
resistors. Actually they figured it out in the very beginning of their
business. Without a serious metallurgic background, plus a few more disciplines,
I doubt seriously you would even come close. However, there is nothing wrong
with trying.

First off, what is your purpose for such accuracy ? What do you intend to do
with these ?

I see a number of problems that need to be addressed. First, it does no good to
have the highest possible quality resistor if you do not have the proper means to
compare it to other items. To maintain that level of quality, for that given
resistor, you would need to duplicate its measurement environment precisely,
i.e., temperature, humidity, etc.

Having a resistor, in of itself, serves no purpose without the proper equipment
to compare it against other items or to use it in a measurement process. Items
like a highly accurate voltage/current source and a very good null meter (Fluke
845A/B) are but a few things needed.

Nonetheless, some of your intended construction ideas need to be reviewed. You
talk about wanting to equal or beat Fluke, yet you only intend to buy 0.01%
instead of 0.001% resistors. Whats up with that ? Those are not considered
standards by any means. Just series/paralleling a bunch of resistors is not
going to help you unless you know, precisely, the temperature coefficients are
for each resistor. In order to play that game you would need to buy a whole lot
(like thousands) of them, not just a couple. Then you spend an inordinate amount
of time testing the temperature coefficient for each and then mixing and matching
in trying to achieve a zero temperature coefficient. Or at the least the
smallest variation of resistance verse temperature change.

The problem is these composition type resistors will be homogeneous in their make
up and most likely they will all exhibit the same or very similar temperature
coefficient. Fluke did it by making their resistors out of different types of
metal that had different temperature coefficients. Thus they were able to
compensate over a wider temperature range by mixing the different metal wires
that made up the resistor. Your only choice with a homogeneous composition is to
provide a constant temperature chamber.

On the one hand you talk about buying expensive resistors then decide to get the
non-hermetically sealed models because they are cheaper. Using an oil filled
container is not going to help if the resistor is not hermetically sealed. The
same goes for using any other kind of fill material. It is going to impact the
non-hermetically sealed resistor and its going to impact the leakage.

LEAKAGE is going to be your other big problem. The best environment is going
to be dry clean AIR. Very hard to get ! Besides inside a container, it is also
important outside of the container. ERGO, not going to happen. Things used to
POT the inside of a container is only going to make matters worse. The biggest
point for leakage is the connection post insulation material; most are junk !
The second biggest point will be dirt between the connection posts.

You mention oil as a filler. Even the oil is going to cause LEAKAGE issues.
The only reason you would use a carefully selected OIL is to provide a thermal
time constant. Yes, even Fluke used OIL in some of their arrangements.
However, it is not so simple as just pouring in some oil. Oil has a multitude of
properties and the selection is not going to be an easy one. The oil that I
would use is Johnson & Johnsons BABY oil. For a hobbyist it is more then good
enough as other environmental effects would most likely mask any ill effects from
the BABY oil.

You talk of baking the resistor/can combination. What are the limits of the
resistors relative to heat ? Heating it to 85c is going to change its
characteristics and would require you to re-test the resistor all over again.
What about that low emf connector ? You need to consider what that material
(insulation) will do when you bake it at 85c. Most likely will ruin it.

Dont mean to come on so hard, but some of your comments tell me you are way out
of your class at the moment with no experience. So before you spend large
amounts of money I would suggest looking at sites like http://www.nist.gov and a
number of top of the line companies who make resistor standards and see what
publications, app notes, and other engineering papers might be available for
study. It would not hurt to look around for reference books, tables, etc., that
show the properties for various metals and insulation materials to grasp their
contribution the final product.

Bill....WB6BNQ

Rob Klein wrote:

My first post to the group, and it's Ohm-nut, rather than Volt-nut, but
I hope you'll forgive me for that :-).
The nutty idea is this: To build a Volt-nuts grade resistance standard.
Or, actually, two, perhaps three.
The first one is quite simple, but rather pricey: I have ordered four
Vishay VHP202Z's, at $ 96 each (ouch!). Expected to be delivered late
february/early march. They will be placed in a series/parallel
configuration to deliver a 10kOhm resistor that should easily rival a
Fluke 742A,
probably be even better. When finished, I intend to have it calibrated
at regular intervals and use it as my house standard.
The other two are a bit more involved, but it will be interesting to
see the results.
For these two, I will use 9 each Z201's from Vishay. These use the same
chip as the VHP202, but are molded, rather than hermetically sealed.
Also, I will use 0.01% types, rather than the 0.001% VHP's. These are
much cheaper (the 18 I need to make two standards cost less than the
four VHP's!), but also less stable over time.
To overcome the stability problem, I am looking at two ways to *make*
them hermetically sealed. The first is to house the 9 (three in series,
three
sets in parallel) in an RF shielding can, fill this up with oil and
solder it shut.
The can I have in mind is a PCB mounted type, for which I shall have to
design a board. The PCB area inside the can will be solid copper,
extending
some way beyond the outside, so I can make a proper seal. Connections
to the outside world will be through glass-sealed, solder mounted
feedthrough capacitors of low capacitance. After mounting the resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight
to get rid of any moisture, then filled with oil and soldered shut.
This assembly will be placed inside a sturdy metal box (Hammond model
[1]1457K1201), which will hold four low EMF binding posts (Pomona
3770).
For the second solution, I want to use much the same method, but rather
than filling the can with oil, I want to fill it with epoxy or maybe
polyurethane resin.
This is a much simpler solution, because there will be no need for the
feedthrough caps and no need to solder the can shut.
However, of course, I am aware that neither of these resins will
provide an actual hermetic seal, since they *will* absorb some
moisture. I am curious
though, as to how much of a positive effect can be gained from this
method, as the shear volume of the resin, as compared to the quantity
use to mold the
actual resistors, should at least greatly diminish any effects of
moisture.
So, if you're still with me after this, I would very much like the
knowledgeables of this group to comment on these ideas. Are they
feasible? What potential
pitfalls might I have overlooked? What oil to use (as an avid cook, I
know my olive- from my sesame oil, but I haven't a clue what type of
mineral oil to
look for :-( ).
Thanks,
Rob Klein.

References

1. http://www.hammondmfg.com/pdf/1457K1201.pdf

volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

Rob, Fluke has over 60 years of real experience correctly make highly accurate stable resistors. Actually they figured it out in the very beginning of their business. Without a serious metallurgic background, plus a few more disciplines, I doubt seriously you would even come close. However, there is nothing wrong with trying. First off, what is your purpose for such accuracy ? What do you intend to do with these ? I see a number of problems that need to be addressed. First, it does no good to have the highest possible quality resistor if you do not have the proper means to compare it to other items. To maintain that level of quality, for that given resistor, you would need to duplicate its measurement environment precisely, i.e., temperature, humidity, etc. Having a resistor, in of itself, serves no purpose without the proper equipment to compare it against other items or to use it in a measurement process. Items like a highly accurate voltage/current source and a very good null meter (Fluke 845A/B) are but a few things needed. Nonetheless, some of your intended construction ideas need to be reviewed. You talk about wanting to equal or beat Fluke, yet you only intend to buy 0.01% instead of 0.001% resistors. Whats up with that ? Those are not considered standards by any means. Just series/paralleling a bunch of resistors is not going to help you unless you know, precisely, the temperature coefficients are for each resistor. In order to play that game you would need to buy a whole lot (like thousands) of them, not just a couple. Then you spend an inordinate amount of time testing the temperature coefficient for each and then mixing and matching in trying to achieve a zero temperature coefficient. Or at the least the smallest variation of resistance verse temperature change. The problem is these composition type resistors will be homogeneous in their make up and most likely they will all exhibit the same or very similar temperature coefficient. Fluke did it by making their resistors out of different types of metal that had different temperature coefficients. Thus they were able to compensate over a wider temperature range by mixing the different metal wires that made up the resistor. Your only choice with a homogeneous composition is to provide a constant temperature chamber. On the one hand you talk about buying expensive resistors then decide to get the non-hermetically sealed models because they are cheaper. Using an oil filled container is not going to help if the resistor is not hermetically sealed. The same goes for using any other kind of fill material. It is going to impact the non-hermetically sealed resistor and its going to impact the leakage. LEAKAGE is going to be your other big problem. The best environment is going to be dry clean AIR. Very hard to get ! Besides inside a container, it is also important outside of the container. ERGO, not going to happen. Things used to POT the inside of a container is only going to make matters worse. The biggest point for leakage is the connection post insulation material; most are junk ! The second biggest point will be dirt between the connection posts. You mention oil as a filler. Even the oil is going to cause LEAKAGE issues. The only reason you would use a carefully selected OIL is to provide a thermal time constant. Yes, even Fluke used OIL in some of their arrangements. However, it is not so simple as just pouring in some oil. Oil has a multitude of properties and the selection is not going to be an easy one. The oil that I would use is Johnson & Johnsons BABY oil. For a hobbyist it is more then good enough as other environmental effects would most likely mask any ill effects from the BABY oil. You talk of baking the resistor/can combination. What are the limits of the resistors relative to heat ? Heating it to 85c is going to change its characteristics and would require you to re-test the resistor all over again. What about that low emf connector ? You need to consider what that material (insulation) will do when you bake it at 85c. Most likely will ruin it. Dont mean to come on so hard, but some of your comments tell me you are way out of your class at the moment with no experience. So before you spend large amounts of money I would suggest looking at sites like http://www.nist.gov and a number of top of the line companies who make resistor standards and see what publications, app notes, and other engineering papers might be available for study. It would not hurt to look around for reference books, tables, etc., that show the properties for various metals and insulation materials to grasp their contribution the final product. Bill....WB6BNQ Rob Klein wrote: > My first post to the group, and it's Ohm-nut, rather than Volt-nut, but > I hope you'll forgive me for that :-). > The nutty idea is this: To build a Volt-nuts grade resistance standard. > Or, actually, two, perhaps three. > The first one is quite simple, but rather pricey: I have ordered four > Vishay VHP202Z's, at $ 96 each (ouch!). Expected to be delivered late > february/early march. They will be placed in a series/parallel > configuration to deliver a 10kOhm resistor that should easily rival a > Fluke 742A, > probably be even better. When finished, I intend to have it calibrated > at regular intervals and use it as my house standard. > The other two are a bit more involved, but it will be interesting to > see the results. > For these two, I will use 9 each Z201's from Vishay. These use the same > chip as the VHP202, but are molded, rather than hermetically sealed. > Also, I will use 0.01% types, rather than the 0.001% VHP's. These are > much cheaper (the 18 I need to make two standards cost less than the > four VHP's!), but also less stable over time. > To overcome the stability problem, I am looking at two ways to *make* > them hermetically sealed. The first is to house the 9 (three in series, > three > sets in parallel) in an RF shielding can, fill this up with oil and > solder it shut. > The can I have in mind is a PCB mounted type, for which I shall have to > design a board. The PCB area inside the can will be solid copper, > extending > some way beyond the outside, so I can make a proper seal. Connections > to the outside world will be through glass-sealed, solder mounted > feedthrough capacitors of low capacitance. After mounting the resistors > and a thorough cleaning, the whole thing will be baked at ~85°C > overnight > to get rid of any moisture, then filled with oil and soldered shut. > This assembly will be placed inside a sturdy metal box (Hammond model > [1]1457K1201), which will hold four low EMF binding posts (Pomona > 3770). > For the second solution, I want to use much the same method, but rather > than filling the can with oil, I want to fill it with epoxy or maybe > polyurethane resin. > This is a much simpler solution, because there will be no need for the > feedthrough caps and no need to solder the can shut. > However, of course, I am aware that neither of these resins will > provide an actual hermetic seal, since they *will* absorb some > moisture. I am curious > though, as to how much of a positive effect can be gained from this > method, as the shear volume of the resin, as compared to the quantity > use to mold the > actual resistors, should at least greatly diminish any effects of > moisture. > So, if you're still with me after this, I would very much like the > knowledgeables of this group to comment on these ideas. Are they > feasible? What potential > pitfalls might I have overlooked? What oil to use (as an avid cook, I > know my olive- from my sesame oil, but I haven't a clue what type of > mineral oil to > look for :-( ). > Thanks, > Rob Klein. > > References > > 1. http://www.hammondmfg.com/pdf/1457K1201.pdf > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

GB

Greg Burnett

Tue, Dec 15, 2009 6:47 AM

Bill wrote:

...You talk about wanting to equal or beat Fluke, yet you only intend to
buy 0.01%
instead of 0.001% resistors.

--------clip----------

Bill, please re-read Rob's post. For his main resistance standard he ordered
Vishay VHP202Z's (0.2ppm/degC; shelf life stability 2ppm / 6 years).
Datasheet at: http://www.vishay.com/docs/63120/hzseries.pdf

Rob, welcome to the group with your first post! Judging from the datasheet,
the VHP202Z does look interesting and suitable for use as a secondary
standard. Thanks for your post - I'll add a VHP202Z to the list of items
I'll order in the future, for use as a secondary standard in some of my
metrology projects. Let us know how your project goes. ...And hopefully some
more group members will offer their technical advice/experience regarding
your other questions.
Best, Greg

Bill wrote: >...You talk about wanting to equal or beat Fluke, yet you only intend to >buy 0.01% >instead of 0.001% resistors. --------clip---------- Bill, please re-read Rob's post. For his main resistance standard he ordered Vishay VHP202Z's (0.2ppm/degC; shelf life stability 2ppm / 6 years). Datasheet at: http://www.vishay.com/docs/63120/hzseries.pdf --------------------------------------- Rob, welcome to the group with your first post! Judging from the datasheet, the VHP202Z does look interesting and suitable for use as a secondary standard. Thanks for your post - I'll add a VHP202Z to the list of items I'll order in the future, for use as a secondary standard in some of my metrology projects. Let us know how your project goes. ...And hopefully some more group members will offer their technical advice/experience regarding your other questions. Best, Greg

BG

Brent Gordon

Tue, Dec 15, 2009 7:53 AM

Rob Klein wrote:

feedthrough capacitors of low capacitance. After mounting the resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight to get rid of any moisture, then filled with oil and soldered shut.

I tried something similar to this about 15 years ago. I needed a 10 KW
dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed
the resistors, and connected them together in a series-parallel
combination to get 50 Ohms. I measured the value just to make sure. I
then got a small drum and filled it with baby oil and put the resistor
assembly in. The next day the resistance had changed by more than 50% (
I don't remember if it increased or decreased.). The value continued to
drift and every time the resistor heated up the value changed even
more. Tried cleaning, washing in solvent, and baking at high
temperatures in various combinations but I could never get the value of
any of the resistors even close to 50 Ohms. Ended up throwing the whole
mess away.

The resistors were uncoated, tubular types so this warning probably does
not apply to your molded resistors.

Another post in this topic mentions baby oil. Even though I had
problems with my dummy load, it wasn't because of the baby oil. I also
tried some lab-grade mineral oil and had the same problem. I recall
reading on a mailing list somewhere (probably Time Nuts) that at Los
Alamos National Lab a group had to buy baby oil because mineral oil was
considered a hazardous material.

Brent

Rob Klein wrote: > feedthrough capacitors of low capacitance. After mounting the resistors > and a thorough cleaning, the whole thing will be baked at ~85°C > overnight to get rid of any moisture, then filled with oil and soldered shut. I tried something similar to this about 15 years ago. I needed a 10 KW dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed the resistors, and connected them together in a series-parallel combination to get 50 Ohms. I measured the value just to make sure. I then got a small drum and filled it with baby oil and put the resistor assembly in. The next day the resistance had changed by more than 50% ( I don't remember if it increased or decreased.). The value continued to drift and every time the resistor heated up the value changed even more. Tried cleaning, washing in solvent, and baking at high temperatures in various combinations but I could never get the value of any of the resistors even close to 50 Ohms. Ended up throwing the whole mess away. The resistors were uncoated, tubular types so this warning probably does not apply to your molded resistors. Another post in this topic mentions baby oil. Even though I had problems with my dummy load, it wasn't because of the baby oil. I also tried some lab-grade mineral oil and had the same problem. I recall reading on a mailing list somewhere (probably Time Nuts) that at Los Alamos National Lab a group had to buy baby oil because mineral oil was considered a hazardous material. Brent

EA

Electronics and Books

Tue, Dec 15, 2009 3:25 PM

Look at :
www.metrology.pg.gda.pl/full/2009/M&MS_2009_183.pdf

These are temperature regulated resistor compared to a standard.

Met vriendelijke groeten
Regards

ElectronicsAndBooks@Yahoo.com
http://www.ElectronicsAndBooks.tk
TEL +31-(0)6-36024590

--- On Mon, 12/14/09, Rob Klein rob.klein@smalldesign.nl wrote:

From: Rob Klein rob.klein@smalldesign.nl
Subject: [volt-nuts] Resistance standard
To: volt-nuts@febo.com
Date: Monday, December 14, 2009, 5:01 PM
   My first post to
the group, and it's Ohm-nut, rather than Volt-nut, but
   I hope you'll forgive me for that :-).
   The nutty idea is this: To build a
Volt-nuts grade resistance standard.
   Or, actually, two, perhaps three.
   The first one is quite simple, but rather
pricey: I have ordered four
   Vishay VHP202Z's, at $ 96 each (ouch!).
Expected to be delivered late
   february/early march. They will be placed
in a series/parallel
   configuration to deliver a 10kOhm
resistor that should easily rival a
   Fluke 742A,
   probably be even better. When finished, I
intend to have it calibrated
   at regular intervals and use it as my
house standard.
   The other two are a bit more involved,
but it will be interesting to
   see the results.
   For these two, I will use 9 each Z201's
from Vishay. These use the same
   chip as the VHP202, but are molded,
rather than hermetically sealed.
   Also, I will use 0.01% types, rather than
the 0.001% VHP's. These are
   much cheaper (the 18 I need to make two
standards cost less than the
   four VHP's!), but also less stable over
time.
   To overcome the stability problem, I am
looking at two ways to make
   them hermetically sealed. The first is to
house the 9 (three in series,
   three
   sets in parallel) in an RF shielding can,
fill this up with oil and
   solder it shut.
   The can I have in mind is a PCB mounted
type, for which I shall have to
   design a board. The PCB area inside the
can will be solid copper,
   extending
   some way beyond the outside, so I can
make a proper seal. Connections
   to the outside world will be through
glass-sealed, solder mounted
   feedthrough capacitors of low
capacitance. After mounting the resistors
   and a thorough cleaning, the whole thing
will be baked at ~85°C
   overnight
   to get rid of any moisture, then filled
with oil and soldered shut.
   This assembly will be placed inside a
sturdy metal box (Hammond model
   [1]1457K1201), which will hold four low
EMF binding posts (Pomona
   3770).
   For the second solution, I want to use
much the same method, but rather
   than filling the can with oil, I want to
fill it with epoxy or maybe
   polyurethane resin.
   This is a much simpler solution, because
there will be no need for the
   feedthrough caps and no need to solder
the can shut.
   However, of course, I am aware that
neither of these resins will
   provide an actual hermetic seal, since
they will absorb some
   moisture. I am curious
   though, as to how much of a positive
effect can be gained from this
   method, as the shear volume of the resin,
as compared to the quantity
   use to mold the
   actual resistors, should at least greatly
diminish any effects of
   moisture.
   So, if you're still with me after this, I
would very much like the
   knowledgeables of this group to comment
on these ideas. Are they
   feasible? What potential
   pitfalls might I have overlooked? What
oil to use (as an avid cook, I
   know my olive- from my sesame oil, but I
haven't a clue what type of
   mineral oil to
   look for :-( ).
   Thanks,
   Rob Klein.

References

1. http://www.hammondmfg.com/pdf/1457K1201.pdf

volt-nuts mailing list -- volt-nuts@febo.com
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Look at : www.metrology.pg.gda.pl/full/2009/M&MS_2009_183.pdf These are temperature regulated resistor compared to a standard. Met vriendelijke groeten Regards ElectronicsAndBooks@Yahoo.com http://www.ElectronicsAndBooks.tk TEL +31-(0)6-36024590 --- On Mon, 12/14/09, Rob Klein <rob.klein@smalldesign.nl> wrote: > From: Rob Klein <rob.klein@smalldesign.nl> > Subject: [volt-nuts] Resistance standard > To: volt-nuts@febo.com > Date: Monday, December 14, 2009, 5:01 PM > My first post to > the group, and it's Ohm-nut, rather than Volt-nut, but > I hope you'll forgive me for that :-). > The nutty idea is this: To build a > Volt-nuts grade resistance standard. > Or, actually, two, perhaps three. > The first one is quite simple, but rather > pricey: I have ordered four > Vishay VHP202Z's, at $ 96 each (ouch!). > Expected to be delivered late > february/early march. They will be placed > in a series/parallel > configuration to deliver a 10kOhm > resistor that should easily rival a > Fluke 742A, > probably be even better. When finished, I > intend to have it calibrated > at regular intervals and use it as my > house standard. > The other two are a bit more involved, > but it will be interesting to > see the results. > For these two, I will use 9 each Z201's > from Vishay. These use the same > chip as the VHP202, but are molded, > rather than hermetically sealed. > Also, I will use 0.01% types, rather than > the 0.001% VHP's. These are > much cheaper (the 18 I need to make two > standards cost less than the > four VHP's!), but also less stable over > time. > To overcome the stability problem, I am > looking at two ways to *make* > them hermetically sealed. The first is to > house the 9 (three in series, > three > sets in parallel) in an RF shielding can, > fill this up with oil and > solder it shut. > The can I have in mind is a PCB mounted > type, for which I shall have to > design a board. The PCB area inside the > can will be solid copper, > extending > some way beyond the outside, so I can > make a proper seal. Connections > to the outside world will be through > glass-sealed, solder mounted > feedthrough capacitors of low > capacitance. After mounting the resistors > and a thorough cleaning, the whole thing > will be baked at ~85°C > overnight > to get rid of any moisture, then filled > with oil and soldered shut. > This assembly will be placed inside a > sturdy metal box (Hammond model > [1]1457K1201), which will hold four low > EMF binding posts (Pomona > 3770). > For the second solution, I want to use > much the same method, but rather > than filling the can with oil, I want to > fill it with epoxy or maybe > polyurethane resin. > This is a much simpler solution, because > there will be no need for the > feedthrough caps and no need to solder > the can shut. > However, of course, I am aware that > neither of these resins will > provide an actual hermetic seal, since > they *will* absorb some > moisture. I am curious > though, as to how much of a positive > effect can be gained from this > method, as the shear volume of the resin, > as compared to the quantity > use to mold the > actual resistors, should at least greatly > diminish any effects of > moisture. > So, if you're still with me after this, I > would very much like the > knowledgeables of this group to comment > on these ideas. Are they > feasible? What potential > pitfalls might I have overlooked? What > oil to use (as an avid cook, I > know my olive- from my sesame oil, but I > haven't a clue what type of > mineral oil to > look for :-( ). > Thanks, > Rob Klein. > > References > > 1. http://www.hammondmfg.com/pdf/1457K1201.pdf > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

JF

J. Forster

Tue, Dec 15, 2009 5:46 PM

A good, pure mineral oil is Nujol. Look in the Laxative section.

-John

=============

Rob Klein wrote:

feedthrough capacitors of low capacitance. After mounting the

resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight to get rid of any moisture, then filled with oil and
soldered shut.

I tried something similar to this about 15 years ago. I needed a 10 KW
dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed
the resistors, and connected them together in a series-parallel
combination to get 50 Ohms. I measured the value just to make sure. I
then got a small drum and filled it with baby oil and put the resistor
assembly in. The next day the resistance had changed by more than 50% (
I don't remember if it increased or decreased.). The value continued to
drift and every time the resistor heated up the value changed even
more. Tried cleaning, washing in solvent, and baking at high
temperatures in various combinations but I could never get the value of
any of the resistors even close to 50 Ohms. Ended up throwing the whole
mess away.

The resistors were uncoated, tubular types so this warning probably does
not apply to your molded resistors.

Another post in this topic mentions baby oil. Even though I had
problems with my dummy load, it wasn't because of the baby oil. I also
tried some lab-grade mineral oil and had the same problem. I recall
reading on a mailing list somewhere (probably Time Nuts) that at Los
Alamos National Lab a group had to buy baby oil because mineral oil was
considered a hazardous material.

Brent

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A good, pure mineral oil is Nujol. Look in the Laxative section. -John ============= > Rob Klein wrote: >> feedthrough capacitors of low capacitance. After mounting the >> resistors >> and a thorough cleaning, the whole thing will be baked at ~85°C >> overnight to get rid of any moisture, then filled with oil and >> soldered shut. > > I tried something similar to this about 15 years ago. I needed a 10 KW > dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed > the resistors, and connected them together in a series-parallel > combination to get 50 Ohms. I measured the value just to make sure. I > then got a small drum and filled it with baby oil and put the resistor > assembly in. The next day the resistance had changed by more than 50% ( > I don't remember if it increased or decreased.). The value continued to > drift and every time the resistor heated up the value changed even > more. Tried cleaning, washing in solvent, and baking at high > temperatures in various combinations but I could never get the value of > any of the resistors even close to 50 Ohms. Ended up throwing the whole > mess away. > > The resistors were uncoated, tubular types so this warning probably does > not apply to your molded resistors. > > Another post in this topic mentions baby oil. Even though I had > problems with my dummy load, it wasn't because of the baby oil. I also > tried some lab-grade mineral oil and had the same problem. I recall > reading on a mailing list somewhere (probably Time Nuts) that at Los > Alamos National Lab a group had to buy baby oil because mineral oil was > considered a hazardous material. > > Brent > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > >

CH

Chuck Harris

Tue, Dec 15, 2009 7:41 PM

Brent Gordon wrote:

Rob Klein wrote:

feedthrough capacitors of low capacitance. After mounting the

resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight to get rid of any moisture, then filled with oil and
soldered shut.

I tried something similar to this about 15 years ago. I needed a 10 KW
dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed
the resistors, and connected them together in a series-parallel
combination to get 50 Ohms. I measured the value just to make sure. I
then got a small drum and filled it with baby oil and put the resistor
assembly in. The next day the resistance had changed by more than 50% (
I don't remember if it increased or decreased.). The value continued to
drift and every time the resistor heated up the value changed even
more. Tried cleaning, washing in solvent, and baking at high
temperatures in various combinations but I could never get the value of
any of the resistors even close to 50 Ohms. Ended up throwing the whole
mess away.

The resistors were uncoated, tubular types so this warning probably does
not apply to your molded resistors.

Another post in this topic mentions baby oil. Even though I had
problems with my dummy load, it wasn't because of the baby oil. I also
tried some lab-grade mineral oil and had the same problem. I recall
reading on a mailing list somewhere (probably Time Nuts) that at Los
Alamos National Lab a group had to buy baby oil because mineral oil was
considered a hazardous material.

+/- some suggestive perfume, they are the same thing

-Chuck

Brent Gordon wrote: > Rob Klein wrote: >> feedthrough capacitors of low capacitance. After mounting the >> resistors >> and a thorough cleaning, the whole thing will be baked at ~85°C >> overnight to get rid of any moisture, then filled with oil and >> soldered shut. > > I tried something similar to this about 15 years ago. I needed a 10 KW > dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed > the resistors, and connected them together in a series-parallel > combination to get 50 Ohms. I measured the value just to make sure. I > then got a small drum and filled it with baby oil and put the resistor > assembly in. The next day the resistance had changed by more than 50% ( > I don't remember if it increased or decreased.). The value continued to > drift and every time the resistor heated up the value changed even > more. Tried cleaning, washing in solvent, and baking at high > temperatures in various combinations but I could never get the value of > any of the resistors even close to 50 Ohms. Ended up throwing the whole > mess away. > > The resistors were uncoated, tubular types so this warning probably does > not apply to your molded resistors. > > Another post in this topic mentions baby oil. Even though I had > problems with my dummy load, it wasn't because of the baby oil. I also > tried some lab-grade mineral oil and had the same problem. I recall > reading on a mailing list somewhere (probably Time Nuts) that at Los > Alamos National Lab a group had to buy baby oil because mineral oil was > considered a hazardous material. +/- some suggestive perfume, they are the same thing -Chuck

RA

Robert Atkinson

Tue, Dec 15, 2009 8:00 PM

Hi,
As Chuck mentioned, Baby oil is mostly refined mineral oil, liquid paraffin in fact, which is also a laxative. So "generic" pharmaceutical grade liquid paraffin is a good refined oil. Had a problem in a biotech lab once, customer sent a sample of lab grade (GPR) liquid paraffin complete with MSDS that said to use a full face shield and mask. The safety officer would not let us use it. They were quite happy with some locally purchased baby oil though!
Don't know why it affected your resistors unless they were some kind of unfired ceramic and it was getting between the particles.

Robert G8RPI.

--- On Tue, 15/12/09, Brent Gordon volt-nuts@adobe-labs.com wrote:

From: Brent Gordon volt-nuts@adobe-labs.com
Subject: Re: [volt-nuts] Resistance standard
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Date: Tuesday, 15 December, 2009, 7:53

Rob Klein wrote:

feedthrough capacitors of low capacitance. After mounting the resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight to get rid of any moisture, then filled with oil and soldered shut.

I tried something similar to this about 15 years ago. I needed a 10 KW dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed the resistors, and connected them together in a series-parallel combination to get 50 Ohms. I measured the value just to make sure. I then got a small drum and filled it with baby oil and put the resistor assembly in. The next day the resistance had changed by more than 50% ( I don't remember if it increased or decreased.). The value continued to drift and every time the resistor heated up the value changed even more. Tried cleaning, washing in solvent, and baking at high temperatures in various combinations but I could never get the value of any of the resistors even close to 50 Ohms. Ended up throwing the whole mess away.

The resistors were uncoated, tubular types so this warning probably does not apply to your molded resistors.

Another post in this topic mentions baby oil. Even though I had problems with my dummy load, it wasn't because of the baby oil. I also tried some lab-grade mineral oil and had the same problem. I recall reading on a mailing list somewhere (probably Time Nuts) that at Los Alamos National Lab a group had to buy baby oil because mineral oil was considered a hazardous material.

Brent

volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.

Hi, As Chuck mentioned, Baby oil is mostly refined mineral oil, liquid paraffin in fact, which is also a laxative. So "generic" pharmaceutical grade liquid paraffin is a good refined oil. Had a problem in a biotech lab once, customer sent a sample of lab grade (GPR) liquid paraffin complete with MSDS that said to use a full face shield and mask. The safety officer would not let us use it. They were quite happy with some locally purchased baby oil though! Don't know why it affected your resistors unless they were some kind of unfired ceramic and it was getting between the particles. Robert G8RPI. --- On Tue, 15/12/09, Brent Gordon <volt-nuts@adobe-labs.com> wrote: From: Brent Gordon <volt-nuts@adobe-labs.com> Subject: Re: [volt-nuts] Resistance standard To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Date: Tuesday, 15 December, 2009, 7:53 Rob Klein wrote: > feedthrough capacitors of low capacitance. After mounting the resistors > and a thorough cleaning, the whole thing will be baked at ~85°C > overnight to get rid of any moisture, then filled with oil and soldered shut. I tried something similar to this about 15 years ago. I needed a 10 KW dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed the resistors, and connected them together in a series-parallel combination to get 50 Ohms. I measured the value just to make sure. I then got a small drum and filled it with baby oil and put the resistor assembly in. The next day the resistance had changed by more than 50% ( I don't remember if it increased or decreased.). The value continued to drift and every time the resistor heated up the value changed even more. Tried cleaning, washing in solvent, and baking at high temperatures in various combinations but I could never get the value of any of the resistors even close to 50 Ohms. Ended up throwing the whole mess away. The resistors were uncoated, tubular types so this warning probably does not apply to your molded resistors. Another post in this topic mentions baby oil. Even though I had problems with my dummy load, it wasn't because of the baby oil. I also tried some lab-grade mineral oil and had the same problem. I recall reading on a mailing list somewhere (probably Time Nuts) that at Los Alamos National Lab a group had to buy baby oil because mineral oil was considered a hazardous material. Brent _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

RK

Rob Klein

Tue, Dec 15, 2009 8:14 PM

Bill,

Thanks for your comments, they are appreciated.

WB6BNQ schreef:

Rob,

Fluke has over 60 years of real experience correctly make highly accurate stable
resistors. Actually they figured it out in the very beginning of their
business. Without a serious metallurgic background, plus a few more disciplines,
I doubt seriously you would even come close. However, there is nothing wrong
with trying.

But I am not going to try to actually make a resistor, I 'merely' want
to build several resistance standards, out of
commercially available ones. And I certainly do not have any intention
of beating Fluke at their own game.

First off, what is your purpose for such accuracy ? What do you intend to do
with these ?

Purpose? This is the volt-nuts group, isn't it? :-)
I'm a self-employed electronics engineer with 'a thing' for precision
measurements. I have, over the years, built
up a nice collection of multimeters, calibrators, etc. and a resistance
standard is going to make a welcome
addition to that.

I see a number of problems that need to be addressed. First, it does no good to
have the highest possible quality resistor if you do not have the proper means to
compare it to other items. To maintain that level of quality, for that given
resistor, you would need to duplicate its’ measurement environment precisely,
i.e., temperature, humidity, etc.

While my workshop isn't a cal-lab, it is nonetheless pretty stable,
environmentally. It has to be, in order to keep
my pick-and-place machine happy.
As I'm not aiming for sub-ppm precision, it will more than likely suffice.

Having a resistor, in of itself, serves no purpose without the proper equipment
to compare it against other items or to use it in a measurement process. Items
like a highly accurate voltage/current source and a very good null meter (Fluke
845A/B) are but a few things needed.

Let's see:

Fluke 720 KVD, check
Fluke 845, check
Various high stability voltage sources, check
Add a recently aquired lead compensator (bought "as is" and not yet
tested, so maybe not) and I think I'm
reasonably well set-up.

Nonetheless, some of your intended construction ideas need to be reviewed. You
talk about wanting to equal or beat Fluke, yet you only intend to buy 0.01%
instead of 0.001% resistors. What’s up with that ?

The VHP202's I'm buying are 0.001%, as I stated.

Those are not considered standards by any means.

Really? Then kindly explain how the metrological world was able to
succesfully maintain the Volt for decades,
using standards that deviated almost 2%.
As long as the value is known and stable to within the required
uncertainty limits, I'd almost say that anything
could be considered a "standard".

Just series/paralleling a bunch of resistors is not
going to help you unless you know, precisely, the temperature coefficients are
for each resistor. In order to play that game you would need to buy a whole lot
(like thousands) of them, not just a couple. Then you spend an inordinate amount
of time testing the temperature coefficient for each and then mixing and matching
in trying to achieve a zero temperature coefficient. Or at the least the
smallest variation of resistance verse temperature change.

The RTC of Vishay's Z-foil resistors is as low as it gets, not by
selection, but by design! The series/paralleling
is mainly to increase the long term stability

On the one hand you talk about buying expensive resistors then decide to get the
non-hermetically sealed models because they are cheaper.

I intend to use both, so that I can build several different types, in
order to compare their long term behaviour.
It will be interesting to see just how good these non-hermetic types
behave over time.

Using an oil filled container is not going to help if the resistor is not hermetically sealed.

But the point is to use an oil filled hermetically sealed container to
hold the non-sealed resistors. Fluke did this for the
main resistors of the first decade of their 720 KVD, Tegam, formerly
ESI, do it for their SR104, widely considered to be one
of the best, if not the best, standard resistor there is. So it appears
this idea might not be as daft as you make it seem.

The
same goes for using any other kind of fill material. It is going to impact the
non-hermetically sealed resistor and its going to impact the leakage.

How, exactly, is it going to impact the resistor?

The biggest
point for leakage is the connection post insulation material; most are junk !

Hmm, this got me curious enough to dig out my insulation resistance
tester. Unfortunately it seems the batteries
are flat :-( To be continued ...

The second biggest point will be dirt between the connection posts.

I am well aware of the neccesity of keeping a clean shop.

However, it is not so simple as just pouring in some oil. Oil has a multitude of
properties and the selection is not going to be an easy one.

Eh, yeah, that's one of the main reasons I came here for advice :-)

You talk of baking the resistor/can combination. What are the limits of the
resistors relative to heat ? Heating it to 85c is going to change its
characteristics and would require you to re-test the resistor all over again.

I have already 'pre-cooked' the first batch of 9 Z201's for three weeks
at around 60 °C and found a
downward shift of maybe a few ppm, as compared to a 1kOhm reference; a
20 year old VHA412, from Vishay.
The TCR of this older resistor is, at around 2 ppm/°C, a lot higher than
that of the resistors under test and
may have had a considerable influence on the measurement.

I have not been able to find any references to changes in TCR, caused by
temperature cycling, in these devices.

The baking may also help relieving some of the stresses that might built
up during soldering.

What about that low emf connector ? You need to consider what that material
(insulation) will do when you “bake” it at 85c. Most likely will ruin it.

The binding posts are rated at 115 °C max. operating temperature and are
not going to be baked anyway.

Best regards,
Rob.

Bill, Thanks for your comments, they are appreciated. WB6BNQ schreef: > Rob, > > Fluke has over 60 years of real experience correctly make highly accurate stable > resistors. Actually they figured it out in the very beginning of their > business. Without a serious metallurgic background, plus a few more disciplines, > I doubt seriously you would even come close. However, there is nothing wrong > with trying. > But I am not going to try to actually make a resistor, I 'merely' want to build several resistance standards, out of commercially available ones. And I certainly do not have any intention of beating Fluke at their own game. > First off, what is your purpose for such accuracy ? What do you intend to do > with these ? > Purpose? This is the volt-nuts group, isn't it? :-) I'm a self-employed electronics engineer with 'a thing' for precision measurements. I have, over the years, built up a nice collection of multimeters, calibrators, etc. and a resistance standard is going to make a welcome addition to that. > I see a number of problems that need to be addressed. First, it does no good to > have the highest possible quality resistor if you do not have the proper means to > compare it to other items. To maintain that level of quality, for that given > resistor, you would need to duplicate its’ measurement environment precisely, > i.e., temperature, humidity, etc. > While my workshop isn't a cal-lab, it is nonetheless pretty stable, environmentally. It has to be, in order to keep my pick-and-place machine happy. As I'm not aiming for sub-ppm precision, it will more than likely suffice. > Having a resistor, in of itself, serves no purpose without the proper equipment > to compare it against other items or to use it in a measurement process. Items > like a highly accurate voltage/current source and a very good null meter (Fluke > 845A/B) are but a few things needed. > Let's see: - Fluke 720 KVD, check - Fluke 845, check - Various high stability voltage sources, check Add a recently aquired lead compensator (bought "as is" and not yet tested, so maybe not) and I think I'm reasonably well set-up. > Nonetheless, some of your intended construction ideas need to be reviewed. You > talk about wanting to equal or beat Fluke, yet you only intend to buy 0.01% > instead of 0.001% resistors. What’s up with that ? The VHP202's I'm buying *are* 0.001%, as I stated. > Those are not considered standards by any means. Really? Then kindly explain how the metrological world was able to succesfully maintain the Volt for decades, using standards that deviated almost 2%. As long as the value is known and stable to within the required uncertainty limits, I'd almost say that anything could be considered a "standard". > Just series/paralleling a bunch of resistors is not > going to help you unless you know, precisely, the temperature coefficients are > for each resistor. In order to play that game you would need to buy a whole lot > (like thousands) of them, not just a couple. Then you spend an inordinate amount > of time testing the temperature coefficient for each and then mixing and matching > in trying to achieve a zero temperature coefficient. Or at the least the > smallest variation of resistance verse temperature change. > The RTC of Vishay's Z-foil resistors is as low as it gets, not by selection, but by design! The series/paralleling is mainly to increase the long term stability > On the one hand you talk about buying expensive resistors then decide to get the > non-hermetically sealed models because they are cheaper. I intend to use *both*, so that I can build several different types, in order to compare their long term behaviour. It will be interesting to see just how good these non-hermetic types behave over time. > Using an oil filled container is not going to help if the resistor is not hermetically sealed. But the point is to use an oil filled *hermetically sealed* container to hold the non-sealed resistors. Fluke did this for the main resistors of the first decade of their 720 KVD, Tegam, formerly ESI, do it for their SR104, widely considered to be one of the best, if not the best, standard resistor there is. So it appears this idea might not be as daft as you make it seem. > The > same goes for using any other kind of fill material. It is going to impact the > non-hermetically sealed resistor and its going to impact the leakage. > How, exactly, is it going to impact the resistor? > The biggest > point for leakage is the connection post insulation material; most are junk ! > Hmm, this got me curious enough to dig out my insulation resistance tester. Unfortunately it seems the batteries are flat :-( To be continued ... > The second biggest point will be dirt between the connection posts. > I am well aware of the neccesity of keeping a clean shop. > However, it is not so simple as just pouring in some oil. Oil has a multitude of > properties and the selection is not going to be an easy one. Eh, yeah, that's one of the main reasons I came here for advice :-) > You talk of baking the resistor/can combination. What are the limits of the > resistors relative to heat ? Heating it to 85c is going to change its > characteristics and would require you to re-test the resistor all over again. > I have already 'pre-cooked' the first batch of 9 Z201's for three weeks at around 60 °C and found a downward shift of maybe a few ppm, as compared to a 1kOhm reference; a 20 year old VHA412, from Vishay. The TCR of this older resistor is, at around 2 ppm/°C, a lot higher than that of the resistors under test and may have had a considerable influence on the measurement. I have not been able to find any references to changes in TCR, caused by temperature cycling, in these devices. The baking may also help relieving some of the stresses that might built up during soldering. > What about that low emf connector ? You need to consider what that material > (insulation) will do when you “bake” it at 85c. Most likely will ruin it. > The binding posts are rated at 115 °C max. operating temperature and are not going to be baked anyway. Best regards, Rob.

RK

Rob Klein

Tue, Dec 15, 2009 8:27 PM

Greg Burnett schreef:

Rob, welcome to the group with your first post!

Thanks Greg.

Judging from the datasheet,
the VHP202Z does look interesting and suitable for use as a secondary
standard.

The VHP202 (or maybe it's the closely related VHP100) is at the heart of
the HP3458, that should say something.
And that's probably with the older 'K' foil. The Z foil is a lot better
still.

Let us know how your project goes.

I certainly will

...And hopefully some
more group members will offer their technical advice/experience regarding
your other questions.

They are going at it even as I write ;-)

Best regards,
Rob.

Greg Burnett schreef: > Rob, welcome to the group with your first post! Thanks Greg. > Judging from the datasheet, > the VHP202Z does look interesting and suitable for use as a secondary > standard. The VHP202 (or maybe it's the closely related VHP100) is at the heart of the HP3458, that should say something. And that's probably with the older 'K' foil. The Z foil is a lot better still. > Let us know how your project goes. I certainly will > ...And hopefully some > more group members will offer their technical advice/experience regarding > your other questions. > They are going at it even as I write ;-) Best regards, Rob.

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Resistance standard