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@quackers.net password: <none> or via a browser: ftp://ftp@quackers.net:ftp@ftp.quackers.net/ Enjoy. -- Bill Ezell ---------- They said 'Windows or better' so I used Linux.

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: ftp@quackers.net > password: <none> > > or via a browser: > > ftp://ftp@quackers.net:ftp@ftp.quackers.net/ > > Enjoy. > >