Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Bob kb8tq]

Hi

One interesting claim made “back in the good old days” was that certain 
pots had near zero TC when used as radiometric devices. Essentially the
metal on one side “always” had the same characteristics as the metal on 
the other side of the wiper. People would go to great extremes to exploit
this “well known fact”. Oddly enough I never really saw much proof that 
this was true ….You still see people doing things this way though. It was
a major “design item” with a certain company that made both potentiometers 
and OCXO’s ….

===

At some point, the magnetic field of the car in the garage gets into
the act on your Rb standard. There *is* a point where all sorts of 
things start to be questioned. Shielding is only just so good. That’s
true if it’s heat shielding, magnetic shielding or whatever ….

Once you get into the “part in 10^-15” range on an Rb, you are well past
the “show me” level of effects. You can (correctly) calculate that this or 
that is the impact. Demonstrating that it works that way at that level
… not so much. 

Why worry about demonstrating this or that? Often second or third order
effects pop up as you “null out” the first order stuff. Hysteresis in the TC
of a “compensated” standard is one very common example. At this point 
it’s not a big surprise when it shows up. That was not always the case ….

None of this is easy, there always is a lot more work involved that one might
think. 

Bob



> On Nov 22, 2017, at 12:04 PM, cdel...@juno.com wrote:
> 
> HP5065A C-field mods and optical unit mods
> 
> The contribution of the temperature coefficients of the fixed resistors
> and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up 
> as frequency errors as shown for several combinations.
> 
> Note that the pot does not cover the entire 2X10-9 frequency range.
> There is a high, mid, and low switch setting that shorts both 1k,
> one 1k, or neither 1k resistor that in conjunction with the pot allows
> the entire range to be covered. This allows the pot to have a finer
> frequency resolution
> 
> A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C
> change
> will cause a 2.8X10-15 frequency change.
> 
> B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will
> cause a 8.55X10-15 frequency change.
> 
> C- With the 2.4K in combination with the pot at 1K and both 1K resistors
> in 
> circuit a 1 Deg C change will cause a 3.99X10-15 frequency change.
> 
> If in example C you replace the pot with a 100PPM pot a 1 Deg C change
> will equate to a 2.45X10-14 frequency change.
> 
> As you can see this circuit will work quite well in eliminating any power
> supply related C-field changes.
> 
> Now the C-field coil is only partially temperature regulated by the 
> ovens in the optical unit as they  regulate the lamp and cell
> temperatures
> and the C-field is not co-located. 
> 
> That is why I'm going to use the PC liquid cooler to actively regulate
> the
> temperature of the sealed enclosure I have placed the optical unit into.
> 
> Cheers,
> 
> Corby
> 
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[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect]

HP5065A C-field mods and optical unit mods

The contribution of the temperature coefficients of the fixed resistors
and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up 
as frequency errors as shown for several combinations.

Note that the pot does not cover the entire 2X10-9 frequency range.
There is a high, mid, and low switch setting that shorts both 1k,
one 1k, or neither 1k resistor that in conjunction with the pot allows
the entire range to be covered. This allows the pot to have a finer
frequency resolution

A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C
change
will cause a 2.8X10-15 frequency change.

B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will
cause a 8.55X10-15 frequency change.

C- With the 2.4K in combination with the pot at 1K and both 1K resistors
in 
circuit a 1 Deg C change will cause a 3.99X10-15 frequency change.

If in example C you replace the pot with a 100PPM pot a 1 Deg C change
will equate to a 2.45X10-14 frequency change.

As you can see this circuit will work quite well in eliminating any power
supply related C-field changes.

Now the C-field coil is only partially temperature regulated by the 
ovens in the optical unit as they  regulate the lamp and cell
temperatures
and the C-field is not co-located. 

That is why I'm going to use the PC liquid cooler to actively regulate
the
temperature of the sealed enclosure I have placed the optical unit into.

Cheers,

Corby

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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Charles,
   Imagine having a source and fixed resistors with TC equal to zero.
   The current variation of the coil varies between 2.5 and 6 mA.
   In addition, the relationship between current and frequency variation of the 
HP5065A is not linear.
   If the pot is short-circuit, the current is 6 mA and the overall TC is that 
of the imaginary generator ie zero, in our real case 1ppm / C (source+fixed 
resistors).
   So the pot TC is completely irrelevant.
   When the pot is fully inserted the current will be 2.5mA, so the total 
current variation is 3.5mA.
   The whole thefull range of pot resistance generates a 3.5mA current 
variation. This variation generates a frequency fine adjustment of 2E-9.
As a result, the influence of the pot TC is directly correlated to the 
current stability with a nonlinear frequency variation between zero and X  in 
the range of 6- 2.5mA.
   Or not?

   best regards,
   Luciano
   timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A "Discussion of precise time and frequency measurement" time-nuts@febo.com
   Cc
   Data Tue, 21 Nov 2017 15:16:36 -0500
   Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano wrote:

   > what you refer is the resistance relation referred to the LM299 source 
around 14VDc but you have to consider
   > the tuning range of the pot, in the original HP5065A is 2E10-9.
   > Of course, it depends on the setting value of the variable resistance, but 
you have to consider a possible variation of 20PPM/c on 2E10-9.

   No, you don't. The tempco that matters is the aggregate tempco of the
   series string. Only a very small portion of the string voltage appears
   across the pot, so a 20ppm tempco of that small part will cause a much
   smaller change in overall tempco of the series string.

   Perhaps Corby will tell us what value the pot is, and then you can
   calculate the aggregate tempco of the string at various pot settings and
   see for yourself.

   Charles


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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Poul-Henning Kamp]

In message <1159987519.5777361.1511296831...@webmail.xtra.co.nz>, Bruce Griffit
hs writes:

>What is the effect of the C-field coil dimension tempco?

I have not been able to measure it.

The C-coil is located thermally close to the temperature controlled
parts of the physics package.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Bruce Griffiths]

What is the effect of the C-field coil dimension tempco?

At some point this will surely dominate overthe coil current tempco.

Bruce

> 
> On 22 November 2017 at 09:16 Charles Steinmetz  
> wrote:
> 
> Luciano wrote:
> 
> > > 
> > what you refer is the resistance relation referred to the LM299 
> > source around 14VDc but you have to consider
> > the tuning range of the pot, in the original HP5065A is 2E10-9.
> > Of course, it depends on the setting value of the variable 
> > resistance, but you have to consider a possible variation of 20PPM/c on 
> > 2E10-9.
> > 
> > > 
> No, you don't. The tempco that matters is the aggregate tempco of the
> series string. Only a very small portion of the string voltage appears
> across the pot, so a 20ppm tempco of that small part will cause a much
> smaller change in overall tempco of the series string.
> 
> Perhaps Corby will tell us what value the pot is, and then you can
> calculate the aggregate tempco of the string at various pot settings and
> see for yourself.
> 
> Charles
> 
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Charles Steinmetz]

Luciano wrote:


what you refer is the resistance relation referred to the LM299 source 
around 14VDc but you have to consider
the tuning range of the pot, in the original HP5065A is 2E10-9.
Of course, it depends on the setting value of the variable resistance, but 
you have to consider a possible variation of 20PPM/c on 2E10-9.


No, you don't.  The tempco that matters is the aggregate tempco of the 
series string.  Only a very small portion of the string voltage appears 
across the pot, so a 20ppm tempco of that small part will cause a much 
smaller change in overall tempco of the series string.


Perhaps Corby will tell us what value the pot is, and then you can 
calculate the aggregate tempco of the string at various pot settings and 
see for yourself.


Charles


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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Hi Charles,
   what you refer is the resistance relation referred to the LM299 source 
around 14VDc but you have to consider
   the tuning range of the pot, in the original HP5065A is 2E10-9.
   Of course, it depends on the setting value of the variable resistance, but 
you have to consider a possible variation of 20PPM/c on 2E10-9.
   Regards
   Luciano
   timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A time-nuts@febo.com
   Cc
   Data Tue, 21 Nov 2017 06:31:25 -0500
   Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano wrote:

   > about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.

   In the schematic Corby posted, the potentiometer (used as a variable
   resistor) makes up a very small part of the total resistance of the
   series string, so the overall tempco is dominated by the tempcos of the
   fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim). The pot will
   increase the overall tempco a little bit, but not anywhere near 20ppm.

   Best regards,

   Charles


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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Charles Steinmetz]

Luciano wrote:


about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay  pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.


In the schematic Corby posted, the potentiometer (used as a variable 
resistor) makes up a very small part of the total resistance of the 
series string, so the overall tempco is dominated by the tempcos of the 
fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim).  The pot will 
increase the overall tempco a little bit, but not anywhere near 20ppm.


Best regards,

Charles


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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Hi Corby,
   about the C field ten turn pot you write is a low TC pot. Normally a good 
Vishay  pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage 
reference.
   What kind of pot do you have used?
   http://www.mouser.com/ds/2/427/533534-768216.pdf
   Luciano
   timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A time-nuts@febo.com
   Cc
   Data Fri, 17 Nov 2017 12:37:57 -0800
   Oggetto [time-nuts] HP5065A C-field mods and optical unit mods
   Luciano,

   The TX and choke and filter caps were removed as I had envisioned I would
   have to re-mount the A1 and A7 in their location.
   However with some judicious movement of the mounting holes I was able to
   squeeze them in close
   to their original spots.

   The 5065 chassis was removed and inserted into a chassis from an HP
   8405A. (just used the side panels
   and the rear panel.)

   I'll post a schematic of the new C-field supply next week. It consists of
   two LM299AH in series feeding
   a string consisting of a 2.4K, 1k, 1K and a 1K low TC pot. A switch
   allows you to short out one or both of the 1K resistors as a coarse
   adjustment. All resistor are 1PPM.

   Fixing the 20Volt and the C-field temperature contributions allowed me to
   isolate the optical units changes
   due to temp.

   The resistor thermistor combo I mentioned would be taped to the optical
   unit and compensate it only.
   It would be in series with the C-field coil.
   Not needed in my unit but thought that others might want to try it rather
   than getting as complex as I have.

   Yes the active baro and temp circuit would be an alternative for a unit
   without my mods.

   attached are PIX of the enclosed optical unit and the front panel.

   Cheers,

   Corby
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[Poul-Henning Kamp]

In message <5AC3D7F0C1F14BAB8B7BE4A552034FCC@dell370>, ws at Yahoo via 
time-nuts writes:

>C-fields are current sensitive, so if they are wound with copper wire, any
>small change in their temperature, even when temperature controlled, could
>have a effect much greater than 1PPM on that current when driven from a
>fixed voltage thru a resistor.
>
>Does anyone use current drive?

The standard circuit is current drive...


-- 
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[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect]

Warren,

Most all Rubidium standards do not have active current drive.  
The HP 5065A is the exception. However the mod I installed is not active.
The C-field coils are roughly temperature compensated as they are near
the cell oven that is regulated.
If you check out Poul-Hennings "hacking the 5065a" you will see that the
C-field coil does exhibit some temperature effect even with active
current regulation, and the stock C-field circuit also introduces some 
effects. Now these amount to a small coefficient but we are Time Nuts
here so we can do better!

My circuit gives a precise current into the coil (for a fixed temperature
of the coil), and with the active temperature stabilization I am adding
to the outside of the sealed optical unit enclosure  those effects will
be eliminated.

Cheers,

Corby

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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[ws at Yahoo via time-nuts]

Corby

 

Just a 1 cent thought that may not apply or be accurate.

 

C-fields are current sensitive, so if they are wound with copper wire, any
small change in their temperature, even when temperature controlled, could
have a effect much greater than 1PPM on that current when driven from a
fixed voltage thru a resistor.

Does anyone use current drive?

 

ws

*

Corby posted:

Attached is the schematic of the C-field supply.

 

Cheers,

 

Corby

 

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[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect]

Attached is the schematic of the C-field supply.

Cheers,

Corby___
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Re: [time-nuts] HP5065A C-field mods and optical unit mods

[tim...@timeok.it]

   Hi Corby,


   I would first like to thank you for sharing your precious studies with us.

   I love the HP5065A because it's an extremely interesting project and I'm 
convinced like you we have a lot of room for improving its performance.


   *
   In addition to the power supply mods:
   -removed AC components
   -power now supplied with an external DC lab grade low noise
   highly regulated supply.
   -temperature coefficient of +20 Volt supply adjusted to be
   below 1PPM/deg C
   See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html
   **


   My approach to modifying some equipment is to try to keep it as good as 
possible under original conditions unless the modification leads to a 
substantial increase in specifications.

   For this reason I do not understand why you have removed the power 
transformer and its filter inductance. You could power it from the DC input and 
leave disconnected the AC power supply or have I missed a reason to do this?

   **
   I've now installed the improved C-field circuit that has
   less than +- 1PPM variation per degree C.

   **

   It would be very interesting to see the schematic of your solution. I have 
tested a simple ssolution replacing the R12 (333Ohms) with parallel of a 470 
Ohms and a 5k Ohms NTC, this mounted in the middle of the chassis. I must 
admit, however, that I do not have a suitable instrumentation and a Maser 
reference to make appropriate measures.


   **

   The optical unit has been installed into a sealed enclosure
   that has been purged with dry Nitrogen. This eliminates
   any Barometric pressure effects and also eliminates
   drift caused by Helium permeation.
   Tests at this point show a very nice long term stability.
   Last mod will use a small PC closed loop liquid cooler to
   keep the outside of the sealed enclosure at a constant temperature
   essentially making it a double oven.

   ***

   Do you have any more detailed photographs?

   ***
   I'm also working on:
   An active temp compensation scheme to add to the
   active barometric compensation I outlined earlier.
   See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html
   And a passive optical unit temperature compensation using a
   thermistor/resistor
   arrangement.
   *

   [C:\Users\PRINCI~1\AppData\Local\Temp\msohtml1\01\clip_image001.gif]


   As you have previously written , boxing the 5065A physical module solve the 
problem of barometric pressure variation, making an active compensation is an 
alternative are you studying?


   Hope to read you soon,


   Luciano

   Timeok


   Da "time-nuts" time-nuts-boun...@febo.com
   A time-nuts@febo.com
   Cc
   Data Thu, 16 Nov 2017 12:58:13 -0800
   Oggetto [time-nuts] HP5065A C-field mods and optical unit mods
   HP5065A C-field mods and optical unit mods

   In addition to the power supply mods:
   -removed AC components
   -power now supplied with an external DC lab grade low noise
   highly regulated supply.
   -temperature coefficient of +20 Volt supply adjusted to be
   below 1PPM/deg C
   See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html


   I've now installed the improved C-field circuit that has
   less than +- 1PPM variation per degree C.

   The optical unit has been installed into a sealed enclosure
   that has been purged with dry Nitrogen. This eliminates
   any Barometric pressure effects and also eliminates
   drift caused by Helium permeation.

   Tests at this point show a very nice long term stability.

   Last mod will use a small PC closed loop liquid cooler to
   keep the outside of the sealed enclosure at a constant temperature
   essentially making it a double oven.


   I'm also working on:

   An active temp compensation scheme to add to the
   active barometric compensation I outlined earlier.
   See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html

   And a passive optical unit temperature compensation using a
   thermistor/resistor
   arrangement.

   PIX shows the sealed optical unit installed into a slightly taller
   chassis. (The 5065C ?)

   Cheers!

   Corby
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Re: [time-nuts] HP5065A C-field mods and optical unit mods --> OFF LIST !!!

[Bob kb8tq]

Hi

So, when do they go up for sale? :)

( = If and when they do, I’m still shopping for one)

Bob

> On Nov 16, 2017, at 3:58 PM,   wrote:
> 
> HP5065A C-field mods and optical unit mods
> 
> In addition to the power supply mods:
> -removed AC components
> -power now supplied with an external DC lab grade low noise 
> highly regulated supply.
> -temperature coefficient of +20 Volt supply adjusted to be 
> below 1PPM/deg C
> See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html
> 
> 
> I've now installed the improved C-field circuit that has
> less than +- 1PPM variation per degree C.
> 
> The optical unit has been installed into a sealed enclosure
> that has been purged with dry Nitrogen. This eliminates
> any Barometric pressure effects and also eliminates
> drift caused by Helium permeation.
> 
> Tests at this point show a very nice long term stability.
> 
> Last mod will use a small PC closed loop liquid cooler to
> keep the outside of the sealed enclosure at a constant temperature 
> essentially making it a double oven.
> 
> 
> I'm also working on:
> 
> An active temp compensation scheme to add to the
> active barometric compensation I outlined earlier. 
> See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html
> 
> And a passive optical unit temperature compensation using a
> thermistor/resistor
> arrangement.
> 
> PIX shows the sealed optical unit installed into a slightly taller
> chassis. (The 5065C ?)
> 
> Cheers!
> 
> Corby<5065crs.jpg>___
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[time-nuts] HP5065A C-field mods and optical unit mods

[cdelect]

HP5065A C-field mods and optical unit mods

In addition to the power supply mods:
-removed AC components
-power now supplied with an external DC lab grade low noise 
 highly regulated supply.
-temperature coefficient of +20 Volt supply adjusted to be 
 below 1PPM/deg C
See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html


I've now installed the improved C-field circuit that has
less than +- 1PPM variation per degree C.

The optical unit has been installed into a sealed enclosure
that has been purged with dry Nitrogen. This eliminates
any Barometric pressure effects and also eliminates
drift caused by Helium permeation.

Tests at this point show a very nice long term stability.

Last mod will use a small PC closed loop liquid cooler to
keep the outside of the sealed enclosure at a constant temperature 
essentially making it a double oven.


I'm also working on:

An active temp compensation scheme to add to the
active barometric compensation I outlined earlier. 
See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html

And a passive optical unit temperature compensation using a
thermistor/resistor
arrangement.

PIX shows the sealed optical unit installed into a slightly taller
chassis. (The 5065C ?)

Cheers!

Corby___
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