[volt-nuts] Experiment: tilting LTZ reference
brooke95482 at att.net
Sat Sep 18 14:43:08 UTC 2010
I have a friend who does equipment calibration and the orientation is
very important to him, although not to all calibration people. He told
me about the case of a crystal oscillator where the access was by
removing the bottom cover. In that case he needed to mount the
instrument into an empty rack and lay on a jury rigged mechanics creeper
to get to the bottom. An easier way would be to put the instrument on
the bench on it's side, but the cal would not be a cal.
Andreas Jahn wrote:
>> For Andreas - never did such a crazy experiment before.
> Thanks for doing the experiment.
> For me its just a missing spec in the datasheet which
> seems to be important for heated references.
> Others could be the relative humidity for plastic cases
> or power-on hysteresis on low power devices.
> I found this effect by accident when I missed 30uV
> between calibration location and home between the
> two LM399 references. Unfortunately I had not
> payed attention to the orientation of the devices
> at the calibration.
> The most weird thing I observed is the fact
> that the two Keithleys show exact the same
> reading of my 7V references when the one
> instrument is orientated in 0 degrees and the
> other in 90 degrees. So I am wondering what
> the guys at the calibration lab are doing when
> they have not much space on the table or if this result is by luck.
> When I have built my reference and pre-aged
> I will compare your LTZ1000 with 12K/1K
> setpoint to my LTZ1000A which will have
> 12K5/1K (UPW50) setpoint. If the effect
> depends on the difference between environment
> and setpoint temperature I should be worse.
> If it depends on heater power I could have
> had luck.
> By the way: can you estimate the room temperature which was during the
>> From your description of thermal shielding I got
> the impression that on the 0 degrees orientation
> is with the legs of the LTZ above the metal can.
> Or did I mis-interpret the description?
> On the other side the PCB could be mounted
> vertically in the case.
> So how is the orientation of the LTZ with respect
> to the 0 degrees?
> best regards
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