The internal details shown for the LTZ1000 are incorrect (see the latest datasheet where it has been corrected). The parasitic diode connections are inaccurate.
Bruce 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: [email protected] > password: <none> > > or via a browser: > > ftp://[email protected]:[email protected]/ > > Enjoy. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
