[volt-nuts] LTZ1000 project build

[Lars Walenius]

Hi,

Do you have any idea of the aging and humidity sensitivity of these 2ppm/C resistors?

I have tested many resistors during the years and my opinion is that tempco is not the biggest problem for normal nuts use but of course may be if you sell a product. For a nut it is quite easy to check the tempco but not aging and humidity sensitivity.

Of the resistors I have tested it is only hermetical sealed resistors that I don´t see a humidity sensitivity on. Even if they are bulk metal foil, wire wounds or metal films with low tempco´s they seem to have very varying humidity sensitivity if not sealed. Lower values of resistance (100-1k) normally seems to be better than 10-100kohm values that in all families may have up to 1-2ppm/%RH.
Last year I bought wire wounds, to be used in a LTZ1000 based design, that were supposed to be insensitive to humidity but they were not. They were even worse than other brands of WW and had several months of time constant. After a while the manufacturer admitted that it was a problem in the manufacturing and they were humidity sensitive. So far I haven´t received a replacement.

Of course if you have a resistor with 2ppm/%RH and a seasonal variation of 50%RH it is only maximum 1ppm seasonal variation on the output on the LTZ. That is not easy to measure for most of us nuts.

Lars

Från: ian at ianjohnston.com<mailto:ian at ianjohnston.com>
Skickat: den 26 maj 2016 13:35
Till: illya at xdevs.com<mailto:illya at xdevs.com>; volt-nuts at febo.com<mailto:volt-nuts at febo.com>
Ämne: Re: [volt-nuts] LTZ1000 project build

Hi all,

TiN, out of interest I spent ages fishing for low ppm/degC resistors for my own reference......ended up with 2ppm units from DigiKey. Yes, they are expensive and send the BOM into the clouds!..............so I know how you feel!

Ian.


----- Original Message -----
 From: Illya Tsemenko [mailto:illya at xdevs.com]
 To: volt-nuts at febo.com
 Sent: Thu, 26 May 2016 18:42:54 +0800
 Subject: [volt-nuts] LTZ1000 project build

 I'm glad my little project got so much attention. Worth to mention few
points regarding my (or any other LTZ1000) unit:

A. One should consider cost of whole BOM, not only LTZ chip. In my case
resistors from VPG exceed cost of LTZ1000 by far.
B. PCB I designed was targeted best to my own application need, where
compact size and direct output (whatever is coming out of LTZ) were key
importance. Since modules are part of bigger system with DAC synth,
specific value, like 7.1500000 was not important for me.
C. If there is large enough group to have this project going, I can
actually modify original design (e.g. for easier hand soldering, or
added buffer or ratio circuits, onboard LDO, you name it) and get PCBs
made for interested nuts, at small cost.

You can also find lot of temco/stability data with
temperature/environment logs with mentioned LTZ modules on my site here:
https://xdevs.com/services/ in LTZ1000 voltage reference tests section.
RAW DSV data are available. I still have 3 modules at hand for any
testing/checks (one was sold while ago, one was installed in HP 3245A
source to replace LM399).

Illya "TiN" Tsemenko

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