What structure/type of resistors would be best for purest R resistors to
make up and be measured with an accurate calibrated measurement bridge.
Normal off the shelf resistors that is, secondary standard level of accuracy
is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values known
accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On May 18, 7:19 am, "N Cook" wrote:
What structure/type of resistors would be best for purest R resistors to
make up and be measured with an accurate calibrated measurement bridge.
Normal off the shelf resistors that is, secondary standard level of accuracy
is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values known
accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

You can buy 0.01% resistors, but they're not cheap!

Alternatively, there used to be a guy on eBay that sold resistor
kits-- He'd measure some wirewound resistors with a GOOD ohmmeter, and
mark them with their measured values, to 0.01% or so IIRC.

Ancient_Hacker wrote in
ps.com:

On May 18, 7:19 am, "N Cook" wrote:
What structure/type of resistors would be best for purest R resistors
to make up and be measured with an accurate calibrated measurement
bridge. Normal off the shelf resistors that is, secondary standard
level of accuracy is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values
known accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list
onhttp://home.graffiti.net/diverse:graffiti.net/

You can buy 0.01% resistors, but they're not cheap!

Alternatively, there used to be a guy on eBay that sold resistor
kits-- He'd measure some wirewound resistors with a GOOD ohmmeter, and
mark them with their measured values, to 0.01% or so IIRC.




I'd want to know what "good ohmmeter" he was using before I spent any money
on his "precision" resistors.

--
Jim Yanik
jyanik
at
kua.net

On 18 May, 15:37, Ancient_Hacker wrote:
On May 18, 7:19 am, "N Cook" wrote:

What structure/type of resistors would be best for purest R resistors to
make up and be measured with an accurate calibrated measurement bridge.
Normal off the shelf resistors that is, secondary standard level of accuracy
is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values known
accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

You can buy 0.01% resistors, but they're not cheap!

Alternatively, there used to be a guy on eBay that sold resistor
kits-- He'd measure some wirewound resistors with a GOOD ohmmeter, and
mark them with their measured values, to 0.01% or so IIRC.

The worst R type for drift is carbon, so forget about those. Picking
cheap Rs using a meter isnt really effective: you may know its value
when measured, but theyre sold as rough tolerance precisely because
they cant be relied on to stay that value. Temperature and time cause
wander.

As already mentioned, metal film are routinely spiral cut, so are no
use for hf, but should be good for 10kHz, and are relatively stable.

The main thing is to pick an R with a very small tolerance - not only
does this tell you what value you're getting, but also that the R
should remain within that small tolerance.


NT

wrote in
oups.com:

On 18 May, 15:37, Ancient_Hacker wrote:
On May 18, 7:19 am, "N Cook" wrote:

What structure/type of resistors would be best for purest R resistors
to make up and be measured with an accurate calibrated measurement
bridge. Normal off the shelf resistors that is, secondary standard
level of accuracy is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values
known accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list
onhttp://home.graffiti.net/diverse:graffiti.net/

You can buy 0.01% resistors, but they're not cheap!

Alternatively, there used to be a guy on eBay that sold resistor
kits-- He'd measure some wirewound resistors with a GOOD ohmmeter, and
mark them with their measured values, to 0.01% or so IIRC.

The worst R type for drift is carbon, so forget about those. Picking
cheap Rs using a meter isnt really effective: you may know its value
when measured, but theyre sold as rough tolerance precisely because
they cant be relied on to stay that value. Temperature and time cause
wander.

Resistors used for calibration purposes should NOT be used for ANY other
purposes.

NEVER subject them to any current other than that of your ohm meter.

In such a case, long term chemical stability would be your main concern.

Even most carbon resistors would probably be ok provided you store them
under normal 'comfort level' conditions (0-80 percent RH, 65-85 degrees F).

Ceramic encapsulated metal film or wire resistors should be more resistant
to environmental factors than composite body carbon resistors.



As already mentioned, metal film are routinely spiral cut, so are no
use for hf, but should be good for 10kHz, and are relatively stable.

The main thing is to pick an R with a very small tolerance - not only
does this tell you what value you're getting, but also that the R
should remain within that small tolerance.

When used within certain environmental and power limits that may or may not
be apparent to the user.

HIGH REL or MIL SPEC resistors usually have tighter limits and longer
lifetimes under load than 'ordinary resistors'.





--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

"N Cook" wrote in :

What structure/type of resistors would be best for purest R resistors to
make up and be measured with an accurate calibrated measurement bridge.

Over what frequency range will the bridge be used? Over what range of
resistances?

If you are only working with audio frequencies, you can use carbon
resistors, wire wound resistors and metal film resistors.

If you are working at higher frequencies, in the RF region, you must make
sure your resistors are non inductive. Even some metal film resistors have
spiral patterns cut in the metal film, making the resistor into an RF choke
at some frequencies.

For ultra low resistance readings, 4 wire kelvin connections are necessary
to reduce the error due to the resistance of the leads.

What is the temperature range under which you will be doing calibrations?
All resistive devices have some kind of temperature coefficient of
resistance.

What is your application?

Normal off the shelf resistors that is, secondary standard level of
accuracy is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values
known accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/









--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

bz wrote in message
98.139...
"N Cook" wrote in :

What structure/type of resistors would be best for purest R resistors to
make up and be measured with an accurate calibrated measurement bridge.

Over what frequency range will the bridge be used? Over what range of
resistances?

If you are only working with audio frequencies, you can use carbon
resistors, wire wound resistors and metal film resistors.

If you are working at higher frequencies, in the RF region, you must make
sure your resistors are non inductive. Even some metal film resistors have
spiral patterns cut in the metal film, making the resistor into an RF
choke
at some frequencies.

For ultra low resistance readings, 4 wire kelvin connections are necessary
to reduce the error due to the resistance of the leads.

What is the temperature range under which you will be doing calibrations?
All resistive devices have some kind of temperature coefficient of
resistance.

What is your application?

Normal off the shelf resistors that is, secondary standard level of
accuracy is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values
known accurately to +/- 0.01%, in the range 20 ohm to 100K

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/









--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap

only 100Hz to 10K and 15 to 25 degree C

"N Cook" wrote in :

bz wrote in message
98.139...
"N Cook" wrote in
:

What structure/type of resistors would be best for purest R resistors
to make up and be measured with an accurate calibrated measurement
bridge.

Over what frequency range will the bridge be used? Over what range of
resistances?

If you are only working with audio frequencies, you can use carbon
resistors, wire wound resistors and metal film resistors.

If you are working at higher frequencies, in the RF region, you must
make sure your resistors are non inductive. Even some metal film
resistors have spiral patterns cut in the metal film, making the
resistor into an RF
choke
at some frequencies.

For ultra low resistance readings, 4 wire kelvin connections are
necessary to reduce the error due to the resistance of the leads.

What is the temperature range under which you will be doing
calibrations? All resistive devices have some kind of temperature
coefficient of resistance.

What is your application?

Normal off the shelf resistors that is, secondary standard level of
accuracy is not required.
Required a few, odd values like 374 ohm +/- 2 ohm , butactual values
known accurately to +/- 0.01%, in the range 20 ohm to 100K

.....

only 100Hz to 10K and 15 to 25 degree C

Go to radio shack and buy some resistors with the necessary precision. For
your application, the construction will not matter.


If you need odd values, make them from series/parallel combinations of
standard values.







--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap