[volt-nuts] Poll

[Alan Scrimgeour]

A shame they don't put all the extra LTZ1000 circuitry on the chip.
Any guesses when the LTZ1000 will be challenged?

Alan

----- Original Message ----- 
From: "Dr. Frank Stellmach" <drfrank.stellmach at freenet.de>
To: <volt-nuts at febo.com>
Sent: Thursday, September 16, 2010 5:13 PM
Subject: [volt-nuts] Poll




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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