traceable calibration of AD587LW#02 and AD587LWB#04
On our Volt Nut meeting on 27.10.2018 I was also calibrating (not adjusting) 2 of the 10 V references.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1921490/#msg1921490The adjustment against my LTZ#4 reference has been several kHrs before.
Method:
- climated room (room temperature was 23.5 deg C humidity 30% rH).
- connect reference to HP3458A + K2002
- wait 1 minute for temperature egalisation
- measure values on HP3458A with 100 NPLC over 5 minutes and calculate average
- manually read the values on K2002
- reverse connect the reference connectors
- wait 1 minute
- 5 minutes measurement reverse connected.
Uncertainity of calibration:
- out of HP3458A protocol +/-2.7 ppm (27 uV for 10 V) unceratinity for calibration.
Since calibration has been recently we can add the 3458A (option 02)
90 day specs for error propagation of the reference calibration measurements.
so we have 2.6 ppm of reading + 0.05 ppm of range resulting in another 26.5 uV uncertainity
of the instrument within 90 days.
As both errors (calibrator + 3458A) are uncorrelated I add them per square law.
so 27 + 26.5 uV give +/- 38uV uncertainity for this calibration for a 10V reference.
- from K2002 protocol I have to use the 1 year specs (since calibration was more than 90 days ago)
+ the uncertainity of the 5720 calibrator which has been used.
so 10ppm + 0.15ppm in 20V range give together with the 1.45ppm of calibrator 104uV uncertainity
Evaluation:
- calculate a correction factor for positive readings out of the calibration protocol
on HP positive values at 10V were reading 0.55 ppm too low and negative values 0.21 ppm
So correction factor 1.00000055 for positive and 1.00000021 for negative readings
similarly the readings of K2002 were corrected by 0.99999753 / 0.99999532 for readings in 20V range
- AD587LW#2 3458A 5 minute averaged readings:
9999.992163 corrected 9999.997663
-9999.994063 corrected -9999.996163
final value (average of pos and negative reading)
value 27.10.2018: 9999.996913 mV +/- 0.038
- AD587LW#2 K2002 (plausibility check) with manual readings:
10000.0251 corrected 10000.0004
-10000.0428 corrected -9999.996
final value (average of pos and negative reading)
value 27.10.2018: 9999.9982 mV +/- 0.104
- similarly AD587LW#4 on K2002 result in
3458A 27.10.2018: 10000.00212 mV +/- 0.038
K2002 27.10.2018: 10000.00395 mV +/- 0.104
The K2002 and 3458A results are very close (within 0.2 ppm).
So I guess the actual uncertainity is much less than the 38 uV from calculation.
Error estimation for further transfers:
- noise: around 1 ppm
AD587LW#02 0.6-0.7 ppm typical observed
- temperature: around 2 ppm within 18-33 deg C
AD587LW#02 measured 1.4 ppm (box)
AD587LW#04 measured 1.8 ppm (box)
- ageing 1-2 ppm/year typical for selected AD587
AD587LW#02 measured ~ +0.4 ppm against my LTZs during the last 6 months.
AD587LW#04 still to be evaluated
so all in all around 5 ppm additional to the 3.8 ppm from calibration.
with best regards
Andreas