[time-nuts] Voltage standards

WarrenS warrensjmail-one at yahoo.com
Sat Nov 29 20:05:43 UTC 2008


A Time-nut group may not be the best place top discuss Voltage references. 
Where is the Volt-Nuts site?

First thing to be aware of if you are planning to build your own reference is:
Good voltage reference parts are "SELECTED" which is just another word 
for cherry-picked. My better modified AD587LN Geller Lab voltage 
reference's are good to 0.1 PPM transfer accuracy over a 5 degree F 
temperature change and a 1 Hr time range, They also stay with in about 1PPM long term. 
I  think that  will 'qualify as a voltage standard'  to some.

The TC correction circuit I use is just two standard parts. 
A100K pot is placed between an added transistor's collector 
and ground with the pot's wiper going to the transitor's base.
What that does when current is applied to the transistor is to make  
the collector voltage vary with temperature by an adjustable amount. 
This temperature sensitive voltage is then added with the trim voltage 
to the reference's trim input to cancel the 1st order temperature drift.
The results I got was a settable 4 degF wide ZERO TC, 
turnover point at any desired room temperature.
The added parts fit on the small Geller's PCB.

The other suggestions that I have heard so far on this post take more skill 
and additional precision parts that quite frankly the average home builder 
is not going to have.

I do not mind posting my mod and results on line, if soneone will tell me a place to do it.

Some notes from my own  'make a state of the art voltage reference' efforts.
I.ve tested everything I could get my hands on, looking for simple solutions.

1) All AD587 are NOT created equal, but the 'noise' of the better ones is in 
the same general range as the 732B &/or the 3458A.
The best AD587 parts show that calibration and measurement is settable 
short term to better than 1uv (0.1 PPM).  
The poorer parts  show approx 4 uv step pulses every so often, 
but even then, If using a strip chart recorder, it is no problem to see 
their non stepped value to 1uv on most of the ones I tested.

2) The existing best references need to be kept ON to insure their calibration, 
A better low cost solution for long term stability seems to be to keep it OFF most 
of the time (using the right kind of selected zero warm up no hysteresis part).

3) My conclusion on 399's after months of long term test is,. they are great for having  a 
wide temp range low TC, but not so good for noise and long turn stability at the sub PPM levels
Holding a part at 90 degC is how you burn them in to age them 64 times faster, 
not how to hold good long term stability.

4) I personal didn't like LTZ1000's because their accuracy is very dependent on 
the stability of the external 2 terminal 100 ohm resistor that sets its zener current. 
If I remember right, it has only 10 to1 rejection so you still need a 1 PPM 
resistor to get sub PPM performance, and that's an absolute value on 
two terminals, not a tracking resistance.

BTW, I have no connection with Geller Labs other than buying some of this parts.
I must add that he was very helpful in my past quest for a good stable voltage source. 

WarrenS
**************
Re [time-nuts] time-nuts Geller 10 volt ref. modification.

Hello WarrenS,
Is it possible to have some details of your 1 transistor 1st order
temperature modification,
on the Geller 10 volt ref. ?

Helge
*****************
RE: Geller 10 volt ref.

Warren, could you or would  you share that little mod with us?

Dick Moore
*****************
RE: [time-nuts] Voltage standards

> Just to add my experiences and throw in another two cents worth.
> I live in California, and a few years back I did some experiments
> with Geller Labs which is located on the East coast by shipping back 
> and forth some of his 10V References in the regular mail.  I built  the 
> units myself on his PCBs so that I could added a simple 1 transistor 
> 1st order  Temperature compensation circuit. Using selected aged 
> AD587LN units that I also bought from him, I proved to my satisfaction 
> that better than 2PPM transfer accuracy was obtained thru the mail 
> across the country.  
> In house I can consistently get better than 1 PPM transfer with the 
> same units. Of course there are more accurate ways, but for us cheap 
> guys It sure beats the $500 I heard Fluke charges to do their underlying 
> Fluke 732B calibration.
>
> WarrenS
> *********************



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