On 28/01/2013 22:47, Andreas Jahn wrote:
After a run in phase of nearly 1 year the ageing of ADC #13 stabilized.
Currently I compare ADC13 nearly every day with 3 heated references (1
LM399 = LM_2 and 2 LTZ1000A = LTZ_1/2).
The last half year the ageing is about 0.5 to 1.5 ppm for 6 months
compared to the heated references.
See picture ADC13_longterm:
X-Axis is day
Y-Axis left is drift in ppm with red = LM399#2, green = LTZ1000A #1,
blue = LTZ1000A #2
Y-axis right is temperature in degree celsius of the temperature
sensor near ADC13 reference.
By the way: up to now I could not measure any effect which is related
to thermocouples.
Ok my temperature step noise is still too high. And probably I am
using the wrong connectors in my tests:
cheap D-Sub connectors where a metal shield is equalizing the
temperature of 2 relative close neighboured contacts.
With best regards
Andreas
Andreas,
Very interesting results - thanks for sharing your painstaking work.
Hope you don't mind me asking a few questions though:
How are you dealing with the issue of drift in the thermocouple
measurements (including the cold junction compensation)? Do you
calibrate it periodically? Thermocouples aren't noted for high stability
- but presumably at room temperature its perhaps not much of an issue.
Do you know what temperature the LTZ1000 references are operating at,
and how long have they been operated for - ie. have they been aged prior
to starting the long term test? (Presumably the answer to that is the
fact that you are showing results from day 460 onwards?)
Have you any insight into how stable the ADC's reference (AD586LJ) is?
I.E. Have you made any occasional or periodic measurements with other
calibrated instruments during the long term test or is it the long term
test results themselves which leads you to state: "After a run in phase
of nearly 1 year the ageing of ADC #13 stabilized."?
Thanks, Tony H
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