On 09/14/2012 07:04 PM, Fred Schneider wrote:

It is regulated to a nominal 90C.  When power is first applied heater current
spikes to typically above 120 mA.  After a few seconds it drops to a 10 - 40 mA
(depends on heater voltage level and environment).

--
Bob Smither, PhD                                  Circuit Concepts, Inc.

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"The beauty of the second amendment is that it will not be needed until
they try to take it." --Thomas Jefferson

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Smither@C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)

Hello Fred,

the heater is regulated to 90 degrees centigrade as is stated in the data
sheet.
A current source for the heater would lead to a instable regulation.
Instead it is essential to supply the heater from a well regulated voltage
source.
The output voltage of the zener changes with the heater voltage (or
current?)
by up to 2ppm/Volt at low heater voltages (around 10V).
Higher heater voltages are more stable.

The LM399 is also sensitive to orientation.
The output voltage changes if you put the LM399 up side down to the sides or
in normal orientation.
(needs 1-2 minutes for stabilization)

For the LTZ1000 try Arrow (USA) they usually have some from time to time.
(today: 13 pieces if you are fast)
http://components.arrow.com/part/search/ltz1000

with best regards

Andreas

----- Original Message -----
From: "Fred Schneider" pa4tim@gmail.com
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Saturday, September 15, 2012 2:04 AM
Subject: [volt-nuts] Lm399 heater

Fine Standard,
btw. where did you get all those hermetically sealed resistors?

best regards

Andreas

----- Original Message -----
From: "Михаил (Mickle)" timka2k@yandex.ru
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Saturday, September 15, 2012 8:52 AM
Subject: Re: [volt-nuts] Lm399 heater

Hi Mickle ( and the rest )

Thank for the answers. I only looked LM399 but looking for LM199 gives more info.
The LM399 is now running, just on its own without the buffer as test to know the excact voltage. It started after a few minutes at 7.031,321 and after an hour it was 7.031,345V. I must go on a visit now so it is turned off for now.

Allmost killed it. I'm glad I used my PM2811 psu with the max current set at 160 mA. The layout is very confusing. The plus fom the heater is at the anode side of the housing. I only looked at cathode and anode and because in all the schematics the plus and kathode are drawn on the same side i overlooked it. After this I was afraid I killed it but it looks OK. Draws around 140 mA during the first seconds and a few mA ( 30 or 40 i think, but I gave not calibrated the current reading of the psu yet) after this time.

Tommow I get in the garage and part out an old realy defect Fluke 8500. There are WW precision card types and other precision resistors in there. Maybe I'm lucky and some paralleled resitors, and one from them in series together with a 10 turn potentiometer , brings me to 10V plus/min 20 to 50 uV, so a full turn of the pot is 2 to 5  uV for finetuning. In that case the tempco and mechanical construction of the 10K or 2K pot will not give much deviation ( I think) and in that case I can skip one KV and a buffer) I can do that with the ( green vishay) resistors I have but those WW card types have lower tempco I think. I also have a few WW precision potentiometers like those used in lcr bridges. Are they a good choise ( awfull big alltough)

But I do not mind ordering resistors for this but there is so much choise I do not know what to choose and real low tempco ones are over 15 euro a piece. If I make a refrence using a LTZ1000 I will buy them.

Fred PA4TIM

Op 15 sep. 2012 om 08:52 heeft Михаил (Mickle) timka2k@yandex.ru het volgende geschreven:

On 09/15/2012 08:54 AM, Fred Schneider wrote:

Unless you want to track the first few days of stability, why not just leave it
on?  I have a Traveling Standard (see: http://www.c-c-i.com/ts ) that has made
the round trip to some of us volt nuts.  When I get it back I leave it on 24/7
to get it along towards its ultimate stability.

--
Bob Smither                                              Smither@c-c-i.com

---========
The powers not delegated to the United States by the Constitution, nor
prohibited by it to the States, are reserved to the States respectively, or
to the people.
-- Tenth amendment to the Constitution of the united States

---========
Circuit Concepts, Inc.                                        281-331-2744

Hi Bob,
It will be on 24/7 but this was the first test on a lab-psu. I have about 50 wall contacts. About 10 are 24/7 on, they feed my guildline cabinet, timestandard ect ( there is also an UPS in between). When I leave my lab all other contacts are switched off at once for safety. So if I wanted to let it powered I had to do a lot of work to put the psu on a permanent contact ( the psu is under pile of other gear and the mains wires are all behind the shelfs. The permanent contacts are not near the bench. All ovenised and other 24/7 powered stuff is in one corner.

Fred PA4TIM

Op 15 sep. 2012 om 19:08 heeft Bob Smither smither@c-c-i.com het volgende geschreven:

On 09/15/2012 01:38 PM, Fred Schneider wrote:

Hi Fred,

Sounds like a great setup.

Expanding on my first comment, it is pretty interesting looking at an LM399 when
first 'activated.'  I recently brought up a second LM199 that I have had for
decades and never powered.  I charted the difference between the new one and one
that has thousands of hours on it.  Interesting to watch it settle in over a few
days.

Best regards,

Bob Smither, PhD                                    Circuit Concepts, Inc.

---========
"I cannot undertake to lay my finger on that article of the Constitution
which granted a right to Congress of expending, on objects of benevolence,
the money of their constituents"
-James Madison, author of the Constitution

---========
Smither@C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)