Most of the manufacturers that are using the LTZ1000A are building it onto a module, and then "burning-in" the whole module-- not just the LTZ.
According to the "rumors"-- yes. And their outputs are monitored as well. The module for the 3458A has a cheap resistor on it that doesn't appear to be used for anything [R419, 2K67]-- not even on the main board that you plug the reference board into. The resistor is connected from -15V to ground-- and nothing on the board uses -15V. It's my theory that they are "watching" the drift of this cheap resistor [in the "burn-in" fixture] to know how far they have come in the burn-in process. I could be wrong, but it's the only thing that makes sense.
I've done a high temperature storage at 120°C on my LM399 reference board for more than 300h and the color has changed clearly. I can't see such an evidence on the pictures of the reference boards or even the pcb material on the 3458A reference boards.
Whatever burn-in means for several manufactors, power the circuit up or power the circuit up driving a temperatur profil, most things discussed help keeping a myth alive.
I appreciate an offical publication that do away with all that fairy tales.
The highest performance DMM's on the market today are the HP/Agilent/Keysight 3458A and the Fluke 8508A. They both use the LTZ1000A, and they use "reference modules" that are burned-in separately from the rest of the instrument. They are *not* doing this "because it seemed to be the right idea"-- they are doing it because they have spent a ton of money and manpower on this problem, and they both reached the same conclusion.
I'm still collecting all reference types (LTZ/A, SZA, LTFLU) of the instruments, and their different stabilization temperatures.
Fluke 8508A and the Keithley 2002 are still lacking.
QuoteI'm still collecting all reference types (LTZ/A, SZA, LTFLU) of the instruments, and their different stabilization temperatures.
The pictures by TiN didn't help?
Freshly calibrated 34401A@work arrived from cal today, will measure my LTZ source soon
7) Note that for LM399-based designs, the slots in the PC board [plus a lot of insulation top and bottom] make sense-- Bob said that the less power the heater requires, then the more stable the output voltage will be. So, in this case, the slots [plus insulation] are helping with this. Oh-- and he also said that the LM399 should be run at about 1mA of Zener current for best stability. The more stable you can make the Zener current, the more stable will be the output voltage. He said that there is about 1uV of voltage change for 1uA of current change.
9) For the LM399 and both of the LTZ parts, he said a good burn-in routine would be to operate them at 125C [in an oven] for 2 weeks. After that, you can cycle the power on and off 10 to 15 times at normal operating temperature, and this will get them to settle down. This process should remove most of the initial drift that these devices exhibit. [So, my initial guess for a burn-in cycle was pretty good-- there is nothing wrong with a burn-in 10 times longer than this.]
Thank you very much to Bob Dobkin and to you DiligentMinds.com.
I have been working a lot with the SZA263-type AmpRef/RefAmp circuit, and have found that HP used the circuit/component already in 1963, while Fluke seems to use it first time around 1971. The circuits are so similar that it is imo unreasonable to argue for any originality in the Fluke 731A.
So may be it could be an idea for US based volt-nuts to contact Fluke and ask them to "free" the LTFLU-1.
Good luck with that! Fluke was purchased by the evil Danaher corporation (along with Keithley and Tektronix)-- they pretty much fire everyone over the age of 30 [thus losing the people that actually know *why* things were done in the past], then they cancel anything that isn't making huge profits, and then milk their "captive customers" for everything that they are worth. I seriously doubt if they are going to budge even one inch in giving us access to *anything*. But you can *try*... Let us know how that goes!