[volt-nuts] Best reference after LTZ1000

[Andrea Baldoni]

Hello.
First of all, my greetings to the partecipants of this mailing list.
I found it very interesting and full of competent people, a rarity nowadays.
I whish to thank you all for that.


Then, let's go to my question.
I am building a precision current source (10uA/100uA) I want to use with an
Agilent 34401A and a RTD PT1000 probe to read temperature with good accuracy
(good is a relative term, actually I would be happy to be limited by the
precision of the probe, a 1/3 B DIN class).
Having already the 34401A I thought it was a good (and cheap) solution
vs. buying a complete thermometer, usually based on less accurate voltmeters
(apart some very very high price). Also, I like to experiment...

Apart the LTZ1000, that's exceeding the 34401A accuracy (and is probably
worth to be used for in-house calibration of it, but that's another matter
I want to pospone for the moment), what would you use, trying to stay in the
<20$ range?

Actually, I bought a MAX6325 of the best grade, some OP177, some good
0.1% 25PPM Vishay resistors, one 10K 0.01% 0.2PPM Z-Foil Vishay resistor for
calibration purpose of the current source...

I would also like to have your opinions about the trend of all manufacturers
who are moving away from buried zeners to go versus bandgap and XFETS, but
looking datasheets I begun to think the reason is more commercial (or
practical: high inital accuracy, low voltage, low power) than metrological...
while they publish exceptional data (the MAX6325 is declared 1PPM/C) seems that
precision instrument makers keep to use (heated) buried zeners... Where is the
truth?

Best regards,
(Mr.) Andrea Baldoni

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