Andreas_-_Jahn at t-online.de
Wed Sep 15 22:14:02 UTC 2010
>I would like to emphasize, what Bill wrote, i.e. use a 2nd inner shield,
>completely around the LTZ circuitry.
>This also helps to thermally stabilize the circuitry, just put some foamed
>polstyrene inside the inner box
Thats what I have already planned but with the polystyrene around the inner
within the box will be difficult since there isnt much room left.
>Use separate grounds for supply and analogue signal.
>More compact metal foil resistors, (<1ppm/K typ.) as in the HP 3458A
>design, would be preferred.
Thats what I have planned for the 2nd build. I have already the 120R and the
1K resistor as Z201. But its difficult for me to get some Z201 resistors
with 70K or 12K4.
If I can't get them, I will have to build them from 25K and 20K resistors.
>I replaced the diode at the output of the OpAmp (OP07) of the Linear Device
>schematic by an ordinary npn, to reduce the load on the OpAmp and to have a
>low impedance output stage.
I have planned a J-FET since the negative gate voltage will help to get a
better stabilisation of the Zener current even with low battery voltage.
>If you did not yet order the LTZ, I suggest to get the LTZ1000, not the A
Too late: it took me around 12 weeks to get the A-Type.
But since my design is battery powered I thougt the A-Type could
help me to save some energy. I want to have at least about 40 hours
without recharging. My power supply voltage is only 14V so I fear
that the non A-Type may get to some heater limit.
>This allows to use the lowest stabilization temperature, around 45..50°C
>for lowest drift, see Pickering patent and description of the Fluke 7000
Is this not possible with the A-type? I wanted to replace the 13K-Resistor
by a 12K4 to 12K5 resistor to get a lower temperature just shure
above 40 degrees celsius.
>So, please design a separate PCB for this, so that this could be shielded
>separately, and can be updated later, if you encounter instabilities also.
By the way. Is the LTZ1000 more immune to mechanical stress
than references in plastic housings. Otherwise I fear that the
weight of the batteries which I have planned to fix on the
same PCB as the reference will get some influence on the
reference voltage. I have at least the possibility to put
a slot between the battery area and the LTZ-area.
>Anyhow, after 3/4 year of permanent operation of both LTZs, if I run them
>against the 5442 and the 3458A (pimped to 65°C operation), all 4 standards
>are within 1ppm or less. That gives me confidence that the LTZs really have
>a drift of around 1ppm/year as stated in the data sheet. So I ignore the
>glitches at the moment.
The most interesting question for me is wether the LTZ-based
references have a output voltage change when changing the
(see my tilt-effect post for the LM399 based Keitley 2000 instrument)
How do your references and the LTZ1000-based HP 3458A behave?
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