Electronics > Beginners

1V Reference @ 1ppm

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beanflying:
This can just go around in circles until you fall deep into the rabbit hole. When you go beyond 4 1/2 digits of resolution each extra one is 10 times the work to do it right. Until you have a traceable stable known reference to work from you will never truly know what you are reading in particular at 6 digits and greater.

So at some point failing that YOU need to create YOUR Volt preferably as close as you can to the 'true' value.

For a basic home lab this can be as simple as pick your best meter and what it says rules the others. Worst option so buy/make a Vref.

Buy one of the AD584 based references making sure it has the 'known' voltages recorded on it (most seem not to have this currently). Works well offers a range of outputs and is stable against 10M and GOhm meters. Suffers some initial drift from stated figures over time and drifts in the order of 1PPM/C. Should handle a divider to 1V and maintain ok stability and accuracy of its voltage with a small load.

Standard Cells of various sorts. See Rocking Horse Poo Requires a GOhm meter or preferably a Null Meter and several cells. Not practical but a stable over time now curio and a sanity check device for me - if you can buy one they are Cool. NIST is back from being shutdown  :horse: https://www.nist.gov/sites/default/files/documents/calibrations/mn84.pdf

LM399 and LTX1000 based devices are POINTLESS unless you have a 'known' accurate standard or meter to set them with their initial accuracy varies widely. They will only be as 'accurate' as the device YOU measure them with but generally they are more stable than other References due to Temp but can take weeks to years to settle. They are a can of worms in the Rabbit Hole with you in free fall but always just out of reach  ::)

Roll your own using the best initial accuracy Reference you can buy sensibly back to the Max series (Best Initial Accuracy) again unless someone else knows of a $10USD one that is better? I have Two in aluminum boxes running from LiPo batteries tweaked to give me an accurate 10V I am happy with for outside use. I do also own a Fluke 515A portable Calibrator which is great to 4.5 digits meters but not so good for 6.5 as it drifts more than the Max based References.

Use your best 'known' Reference to 'Null' out a separate supply with more grunt if you need it to avoid loading issues and test it's performance as you load it to see if it remains 'stable' as you load it. Feed that into a Hamon or whatever divider or op amp you like and test away being happy in the knowledge it is YOUR Volt ;)

tggzzz:

--- Quote from: spec on January 29, 2019, 07:27:53 pm ---
--- Quote from: tggzzz on January 29, 2019, 05:36:00 pm ---
--- Quote from: spec on January 29, 2019, 04:32:04 pm ---Can I ask a question of the experts in this field: When you are checking the precision of an instrument, what is the shortest time that the instrument could be connected to the reference source? I have a reason for asking. :)

--- End quote ---

I would suggest "until the reading is stable and repeatable", where you have to supply the two obvious definitions.

Are you thinking of a mechanical multimeter and a Weston standard cell?

--- End quote ---
My thought was to use a capacitor to lower the effective output impedance of  a precision voltage divider but, in view of your and K's, remarks it is clear that a fair amount of time would  be required to do the calibration so that idea goes down the tubes as only a film capacitor could be used. A supercap, which could allow sufficient time, would be too leaky, I think :)

--- End quote ---

Capacitors are crap components compared with resistors. Leakage, tempcos, non-linear voltage dependence, dielectric absorbtion, and more.

tggzzz:

--- Quote from: beanflying on January 29, 2019, 11:46:19 pm ---This can just go around in circles until you fall deep into the rabbit hole. When you go beyond 4 1/2 digits of resolution each extra one is 10 times the work to do it right. Until you have a traceable stable known reference to work from you will never truly know what you are reading in particular at 6 digits and greater.

So at some point failing that YOU need to create YOUR Volt preferably as close as you can to the 'true' value.

--- End quote ---

Getting a meter to agree with a voltage source is easy: just turn the knob.

Getting one meter to agree with another meter is a little more difficult: open one up and recalibrate it.

Getting one of your meters to agree with other people's meters is easy: just empty your wallet.


--- Quote ---Standard Cells of various sorts. See Rocking Horse Poo Requires a GOhm meter or preferably a Null Meter and several cells. Not practical but a stable over time now curio and a sanity check device for me - if you can buy one they are Cool.

--- End quote ---

Cells also have another advantage: no popcorn noise. That enables you to infer the noise in a meter's reference.

spec:

--- Quote from: tggzzz on January 30, 2019, 01:08:40 am ---
--- Quote from: spec on January 29, 2019, 07:27:53 pm ---
--- Quote from: tggzzz on January 29, 2019, 05:36:00 pm ---
--- Quote from: spec on January 29, 2019, 04:32:04 pm ---Can I ask a question of the experts in this field: When you are checking the precision of an instrument, what is the shortest time that the instrument could be connected to the reference source? I have a reason for asking. :)

--- End quote ---

I would suggest "until the reading is stable and repeatable", where you have to supply the two obvious definitions.

Are you thinking of a mechanical multimeter and a Weston standard cell?

--- End quote ---
My thought was to use a capacitor to lower the effective output impedance of  a precision voltage divider but, in view of your and K's, remarks it is clear that a fair amount of time would  be required to do the calibration so that idea goes down the tubes as only a film capacitor could be used. A supercap, which could allow sufficient time, would be too leaky, I think :)

--- End quote ---

Capacitors are crap components compared with resistors. Leakage, tempcos, non-linear voltage dependence, dielectric absorbtion, and more.

--- End quote ---
Oh yes I do know that, but there are capacitors and capacitors. Still overall you are obviously right. It was just a thought.

UPDATE: just noticed that the LTZ1000 does use a capacitor internally. :)

spec:

--- Quote from: beanflying on January 29, 2019, 11:46:19 pm ---Roll your own using the best initial accuracy Reference you can buy sensibly back to the Max series (Best Initial Accuracy) again unless someone else knows of a $10USD one that is better? I have Two in aluminum boxes running from LiPo batteries tweaked to give me an accurate 10V I am happy with for outside use. I do also own a Fluke 515A portable Calibrator which is great to 4.5 digits meters but not so good for 6.5 as it drifts more than the Max based References.
--- End quote ---
Are the electronics in the aluminum boxes in a controlled temperature?

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