[volt-nuts] Poll
Dr. Frank Stellmach
drfrank.stellmach at freenet.de
Thu Sep 16 16:13:01 UTC 2010
Hello Andreas,
remember, that the LTZ circuitry attenuates all drifts of the 5 crucial
resistors by 1/100 (120, 1k, 13k) and by 1/300 (70k).
So the Z201 resistors are a little bit overkill, 1-3 ppm/K for lower
grade metal foil or wirewound ones are sufficient for a low T.C. of the
completed circuit.
All molded resistors drift around 25ppm/year, so the Z201 also does not
give any advantage over the other types.
I found a 2nd source for metal foil resistors, about the level of the
former S or K types from Vishay.
Manufacturer is alpha electronics. Here you find detailed informations
about the typical T.C.:
http://www.alpha-elec.co.jp/e_index.html
They are distributed by Rhopoint, which now have a German sales
office also:
http://www.rhopointgermany.com/
I recommend the through- hole metal foil resistors FLCY (typ. 0.3ppm/K,
+/- 0.1%), where you get all needed values, for a much lower price than
the Z201, around 6€/EA. (You have to register to see price and availability.
You may also use the wirewound econistors 8E16 / 8G16 (3ppm/K), if you
need more of special values.
I used these for my LTZ reference, as 12k was available, for setting a
stabilization temperature of around 45°C.
---
If you use the LTZ1000A, its self heating effect requires to set the
temperature 10°C higher than the LTZ1000.
Ambient temperature of 25°C gives at least 35°C chip temperature
without additional heating, and that leaves not enough headroom for a
stable temp. regulation around 45°C, especially with even higher
ambients, and with all the tolerances of the LTZ included.
So, for the LTZ1000A you should set the temperature to 55°C at least,
what you obviously intended to do.
Two 25k in parallel over the 1k will do the job, don't they?
-----
I have put more attention to thermal shielding.
I designed a single sided PCB, with the LTZ reversely assembled on the
solder side.
I built a polystyrene box, glued together from thin sheets, which
isolates the complete solder side.
I will test the stability under rotation for my LTZ box this weekend,
but the HP3458A stays where it is, sorry ;-)
In the 3458A, 2 special plastic cups on solder and component side around
the LTZ isolate it.
So I do not expect any effect by tilting, only the other components may
suffer from that effect, which can be compensated by ACAL DCV.
---
Where did you get the Z201 from, did you order custom specific values,
or off-the-shelf?
What about the price and delivery time?
I'm looking for the hermetically encapsulated/oil filled types as a
Standard Resistor.
And did you order the LTZs at Linear in USA directly, or via distributor?
regards - Frank
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