Reference Calibration Options - Solartron 7081 and Fluke 731B and 335A
Fred wrote:
How do you know the standards drift and not the meters?
Josephson Array
Yesterday i turned on the 7061 again and it showed 1.000,006,2 V after
three hours it was 1.000,000,1 V and stayed there, so keeping it powered on
seems to work better.
Yes, effectively you were characterizing the warm-up characteristics of your
7061. Obviously don't depend on it for the best accuracy and stability right
after
power-up.
have last week adjusted to 1.000,000 V on the keithley 2000.
After a week it was 1.000,046 but I adjusted it to 1 V again. But the
reference in that has only about 150 hours burn in time total. The Short
time drift is now allmost gone. It flips + 1 uV now and then, but it could
be it is adjusted to 1.000,000,8 or so.
Yeah, I would definitely leave your Keithley 2000 running 24/7 for the
foreseeable future, while you're running these kinds of experiments.
Keep up the good work and experimenting, Fred!
-Greg
Fred wrote:
How do you know the standards drift and not the meters ? In worst
case they could drift the same amount in the same direction.
One needs to be able to trust something to be within a known
tolerance band, based on either historical calibration data or a
reliable manufacturer's guarantee (i.e., you bought it brand new and
it is guaranteed to be within +/- x right now, within +/- y after a
month, and within +/- z within one year).
Lacking either of these, one is feeling his or her way in the
dark. Even a used item, purchased and then calibrated, cannot really
be trusted until it has been through several calibration cycles in
one's own hands, because one never knows what indignities it may have
suffered in its earlier life. (The same applies to a
newly-constructed reference, which has not been burned in to reach
operating stability and also has just been through soldering trauma.)
Best regards,
Charles
Charles wrote:
... the actual expected stability of a properly operating
731B (particularly one that has been operating 24/7 for several years
or more) is significantly better than the specified performance of a
7081 (or 3458A), and in addition its drift can be characterized
reasonably accurately and subtracted (not so much with meters, with
their several different error mechanisms).
Hi Charles - I'll trade you a 731B for your 732A! :-)
The beauty of the 3458A is that the drift/aging of its DC circuitry
(everything except its LTZ-1000 Reference) can
effectively be cancelled anytime the user invokes its "ACAL DC" feature. In
other words, immediately after each "ACAL DC", the meter's DC aging is
solely a function of the aging/drift of its 7V Zener Reference. This feature
plus the meter's state-of-art linearity give you a meter whose actual low DC
error is difficult to characterize unless you have a trended 732A
(trending based on its history as measured via a Josephson Array).
Cheers,
Greg
Within a week or so i am going to order parts for the 1-2000MHz signal
generator i m building, and then i want to order some better voltage
references. The LM399 is not vailable. What would be the best choise ? ( I
will order from Farnell) i like a reference with low tempco, so with build
in heather because my lab is on the addict and temp changes can be big.
From 16 to 35 dergees as extremes.
Hello Fred,
the LM399 or LM399A are both available at Digikey.
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=de&site=DE&KeyWords=lm399&x=0&y=0
the only references with heater from Farnell would be the LT1019.
But the heater is no longer specified in the current data sheet.
(so look for a old one or for a old application note).
And I have heard of reference voltage output shifts in the order of 1mV
due to heater current.
With best regards
Andreas
Is it better to leave my keithly on for a few weeks to burn in ? Or just 24/7/365.
I left the references on, but not the meter, that stabelizes after about an hour and the shift is only a few ppm. I bought it new and do not want to wear it down quick, but reading all this i think it will be shift the most when new and if the Vref in the 2000 is burned in it will stablize. So after a certain time ( howlong ? ) you adjust it, or do a software calibration and then the meter will stay better within specs ? Is that correct.
The 7061 does not stay on, it gets so hot I do not dare to leave it on unattended until I find a Service manual and be able to check everything inside.
Fred PA4TIM
Op 10 sep. 2011 om 10:32 heeft "gbusg" gbusg@comcast.net het volgende geschreven:
Fred wrote:
How do you know the standards drift and not the meters?
Josephson Array
Yesterday i turned on the 7061 again and it showed 1.000,006,2 V after
three hours it was 1.000,000,1 V and stayed there, so keeping it powered on
seems to work better.
Yes, effectively you were characterizing the warm-up characteristics of your
7061. Obviously don't depend on it for the best accuracy and stability right
after
power-up.
have last week adjusted to 1.000,000 V on the keithley 2000.
After a week it was 1.000,046 but I adjusted it to 1 V again. But the
reference in that has only about 150 hours burn in time total. The Short
time drift is now allmost gone. It flips + 1 uV now and then, but it could
be it is adjusted to 1.000,000,8 or so.
Yeah, I would definitely leave your Keithley 2000 running 24/7 for the
foreseeable future, while you're running these kinds of experiments.
Keep up the good work and experimenting, Fred!
-Greg
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I want to buy a writing voltmeter to connect to my 845 so I can monitor the deviation between a Vref i made and a fluke calibrator.
I can buy a philips PM 8252 or a BBC Goerz Servogor 120.
The BBC is including new pens and a few rolls of paper in mind condition and 125 euro. The philips is in unknown condition but 65 euro.
But these things are new for me. A friend told me some are for process monitoring and have terrible slow slewrates. He thinks the philips is a lab instrument, the bbc he does not know.
Fred