[volt-nuts] Fluke 732B

[Bill Gold]

Joe:

    That was a very interesting teardown of the 732B on eevblog.  The one thing that this answered for me was if Fluke was using their "Reference Amplifier" in all of the 732B production and Fluke did.

    If you look at a paper by David Deaver called "Predictability of Solid State References" which he wrote, and you can download from the Fluke website http://us.fluke.com/. you will see on page three of the paper that he talks about the reference drifts of a number of 732Bs that were checked over a period of time.  Deaver talks about Motorola References and Linear Technology References and that the Motorola's drift upwards while the Linear Tech's drift downwards over time.  Also look at Fig. 10.  I was assuming (wrongly of course as I see now) that Fluke had switched from the "Reference Amplifier" to the LTZ1000 in the production of the 732B.  Now I see that it is just what company made the "Reference Amplifiers" for Fluke.  Of course the 4 legged device is a "Reference Amplifier" that they have used for a least 25 years or more as the voltage reference in a lot of their instruments.

    I have never seen a schematic of the super secret "oven assembly" but you can probably bet that it looks a lot like the 732A but with a lot more "black magic" built into it.  I don't think that Fluke would ever expect someone to fix this beyond the unit replacement level as I am sure that this would require factory precedures far beyond anything that we could muster in the field.  Part of the black magic is adjusting the collector current of the reference amplifier to obtain a zero TC around a very limited range of operating temperatures.  The digital adjustments also add something inside the oven assembly, probably a DAC, and it would be interesting what they are doing there, so a schematic would be interesting to see.

    Anyway I will quit rambling.  So many things to do, so little time.

Bill