[time-nuts] Datron 4910/11/12 LTZ1000 Reference Board (finally)

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Feb 8 19:25:22 UTC 2009

The internal details shown for the LTZ1000 are incorrect (see the latest
datasheet where it has been corrected).
The parasitic diode connections are inaccurate.


wje wrote:
> I've finished retracing the LTZ ref board I promised months ago. While 
> it somewhat resembles the LTZ1000 data sheet example, it differs 
> significantly in a number of details. The heater control is far more 
> complex, using a PWM scheme. Take the schematic with a bit of a grain of 
> salt... tracing it is difficult because there is no access to the back 
> of the board, at least not without more surgery than I'm willing to do 
> on my secondary reference! In particular, the internal resistor 
> connections in the Vishay precision resistor network are just guesses. 
> If anyone has any info about Vishay TO5 canned precision networks from 
> the 80's, please share. I'm confident about the heater side circuitry, 
> but less so about the output side. You will also need to refer to the 
> Datron cell schematics already posted, since significant portions of the 
> heater control as well as the output buffer amp are on that board. If 
> anyone notices any highly questionable topology, let me know and I'll 
> try to confirm it. I haven't spent the time to do much of a sanity check 
> myself.
> One final note - although not apparent from the schematic, the ref board 
> itself makes extensive use of guarding. This is critical for 
> ultra-precision refs, since even picoamps of leakage in the wrong place 
> can easily lead to multi-PPM errors. I would estimate that fully 50% of 
> the total trace length on the board is guard traces.
> As a bonus, I've also scanned the 10V reference from my Solartron 7081 
> 8.5 digit voltmeter. This is an HP 3458 class voltmeter. The interesting 
> (and amazing) thing about this reference is that it does NOT use an 
> LTZ1000, or even an ovenized reference. It uses a 1N829 Zener with some 
> clever linear and non-linear temp compensation. My meter routinely 
> achieves a 1-year drift of less than 1ppm compared against my 
> (calibrated, NIST-traceable) Datron ref.
> They are all on my FTP site. Look for DatronRef.PDF, 
> SolartronReadme.txt, SolartronRef-1.PDF, and SolartronRef-2.PDF.
> FTP:
> ftp ftp.quackers.net
> login: ftp at quackers.net
> password: <none>
> or via a browser:
> ftp://ftp@quackers.net:ftp@ftp.quackers.net/
> Enjoy.

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