Dr. Frank Stellmach
drfrank.stellmach at freenet.de
Thu Sep 16 16:13:01 UTC 2010
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
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.:
They are distributed by Rhopoint, which now have a German sales
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
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,
What about the price and delivery time?
I'm looking for the hermetically encapsulated/oil filled types as a
And did you order the LTZs at Linear in USA directly, or via distributor?
regards - Frank
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