Re: [time-nuts] PRS10 rubidium lamp module failure

[Stewart Cobb]

Follow-up: as several time-nuts noted, there was a lot of corrosion on
parts of the lamp module. Oddly, there was no corrosion on the rest of the
PRS10, or on the TS2500 which it came out of.  The resistor lead was
severely oxidized and partly melted. It's possible that the inductance of
the wire-wound resistor helped sustain an arc. Alternatively, the grounded
lead may have arced to the hot end of the lamp drive coil, although the
coil itself showed very little damage. Perhaps ozone from an arc
accelerated the corrosion. Dunno, it's a mystery.

The resistor is specified at 2W, but it's much smaller than a typical 2W
resistor. I removed the damaged lead and replaced it with a bit of 16 AWG
magnet wire. This gave mechanical support as well as an electrical
connection. Buttoned it all back up and applied power, and the lamp lit
almost immediately (it wasn't lit before) and it locked quickly.  Tuned it
to match a GPSDO, and it seems to be working fine.

A note on tuning: the documentation says that the "SF" tuning command has a
resolution of 1E-12. That's true, but the actual available tuning
resolution seems to be more like 1E-11.

The actual tuning is done by adjusting the C-field with a 12-bit DAC. The
"MR?" command gives the present value of that DAC.  Unfortunately, the full
range of the SF command (4000 counts) only moves the DAC about 600 counts.
You can increment the SF command several times before seeing a response.
Anyone planning to use a PRS10 inside a control loop should be aware of
this quirk.

Cheers!
--Stu
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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Gerhard Hoffmann]

Am 09.05.2016 um 10:08 schrieb Magnus Danielson:

Hi,

On 05/08/2016 09:53 PM, Attila Kinali wrote:


True and not true. Yes, there are many ADCs that do high conversion
rates, but these are optimized for piplined applications where 
conversion

happens at a constant rate. Ie they expect a constant conversion clock
with a constant rate. If you want to trigger conversion at an 
arbitrary time,

you either have to build your own sampler or need to  use one of the
non-pipelined ADCs whic are much slower (IIRC they stop around 5-10Msps
aka >100ns conversion time). Flash ADCs with direct access to the 
sampling

circuitry are basically extinct.


You can let the ADC convert as a continuous process as long as you 
filter out the samples you are interested in.




And, at least for the LTC2165, you could really use the encode clock to 
read the result
of the capacitor immediately. All one would have to do is to flush the 
pipeline with
5 or 6 clocks after the encode, with a cycle time not much faster than 
10 ns and

not slower than 1 usec.
That seems not too hard to do but costs a differential mux in the encode 
lines.



We then would not need to switch the current source, it could degenerate 
to a
20V source with a resistor & safety clamps; that would be as linear as 
it gets.
The reset level could be clamped by a Sky or Avago phemt, they can 
swallow the
current easily, are blinding fast and do not drop a voltage for the base 
current

over Re (from Gummel-Poon model). And an inverse transistor may have less
Re, but also less beta and therefore more base current.


I have already built a time stretcher and was restricted to spaceworthy 
components;
those Intersil transistor arrays had the only acceptable PNPs. These 
flatpacks are

huge, and the legs are endless; anything more complicated than a simple
current mirror would oscillate or would at least lurch to its 
destination, and you

cannot simply damp it to death. Not funny.


Minimizing the E-E-inductance: The next best thing to an onchip-connection
might be abusing 2 Infineon SiGETs on the 2 sides of a thin board; they 
are optimized
for low emitter inductance and have 2 emitter legs each. And their Early 
voltage

is huge, so they are not impressed by the VCE changes of the current source.
(SiGe BFP650, 750 etc, available in a tiny package)

regards, Gerhard


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[time-nuts] Microchip PIC CTMU

[David]

I ran a search through the time-nuts archives and found only one
mention of this a couple years ago asking the same question which is,
has anybody explored the capabilities of the Microchip PIC CTMU for
use as a time to digital converter or programmable delay?

The Microchip datasheets lack detailed performance specifications but
my conservative estimate is that resolution down to 500ps over 200ns
using the built in 10 bit ADC should be possible without complex
calibration.  (The PIC series ADCs with more than 10 bits are pretty
horrible.)

See What You Can Do with the CTMU:
http://ww1.microchip.com/downloads/en/AppNotes/CTMU%2001375a.pdf

Overview of Charge Time Measurement Unit (CTMU):
http://www.microchip.com/stellent/groups/SiteComm_sg/documents/DeviceDoc/en542792.pdf

PIC18(L)F2X/4XK22 w/10 Bit ADC:
http://ww1.microchip.com/downloads/en/DeviceDoc/39977f.pdf

PIC18F66K80 w/12 Bit ADC:
http://ww1.microchip.com/downloads/en/DeviceDoc/39977f.pdf

I prefer more discrete implementations but this might be useful for
its higher integration, lower cost, and simplicity in less demanding
applications.
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Re: [time-nuts] HP 105B oscillator

[Tom Van Baak]

Perry,

There are several op/svc manuals for the HP 105B. Original models used the 
00105 brick oscillator; newer models the 10811. Check the S/N of your manual 
against the S/N of your hp 105B.

Yes, the 105B makes a good test bed. For years I used one to measure lots of 
10811's.

/tvb

- Original Message - 
From: "Perry Sandeen via time-nuts" 
To: 
Sent: Tuesday, May 10, 2016 12:10 AM
Subject: [time-nuts] HP 105B oscillator


List,
I purchased a HP 105B oscillator on ebay and it arrived today. Previous to 
getting it I D/L the manual and brief;y perused it.

So when I popped open the top cover to see the internal parts, what to my 
wondering eyes appeared Not the A1 module shown in the manual but a 10811 
lookalike.
The only information on the oscillator is S/N 3010A59493 and R11215k.
So what do I have? The next question that comes to mind is the plug in base the 
same electrical configuration of the 10811? (Being a TN You can see where this 
is going.)
Leaving out the divide issue for the moment, this would seem to be an ideal 
test bed for my 10811 oscillators as the 3 in my 5370B's have no EFC adjustment 
installed and I have another 10811 spare.
I have enough 5370B's and 5335's in which I could put all my 10811's in to 
*incubate* for months before attempting to tune them.
Also are there upgrades that are practical to add to the present PS for greater 
stability. I am going to replace the original screw cap capacitor with a new 
Nichicon 105C cap.
Thoughts? 
Regards,
Perrier

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Re: [time-nuts] PRS10 rubidium lamp module failure

[Vasco Soares]

I agree with Arthur. It's not possible that such temperature had happened. 
My unit had a severe board and components electrochemical corrosion probably 
caused by a mix of factors as flux residues action and the pcb coating that 
simple dissapear. I think that all together under hot conditions in a small 
enclosure is the most probably reason to that failure. Also, in picture it 
can be seen clearly many spots with electrochemical corrosion.




- Original Message - 
From: "Arthur Dent" 

To: 
Sent: Tuesday, May 10, 2016 1:06 AM
Subject: [time-nuts] PRS10 rubidium lamp module failure



..."apparently got hot enough to create a localized thermal runaway in
its lead wire."

I don't think that explanation is correct. There are no signs of
discoloration
caused by overheating anywhere else in the photo and yet the lead wire
has apparently melted as you say. That would probably require at least a
2000 degree temp which would cause lots of damage. Are there any signs
of chemical contamination that could have caused this? Not the same but
In older equipment that had leaky Hg batteries I've seen similar damage.

-Arthur
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Re: [time-nuts] PRS10 rubidium lamp module failure

[Attila Kinali]

On Mon, 9 May 2016 15:47:06 -0700
Stewart Cobb  wrote:

>  A half-melted bit of wire fell
> away before I could take the picture.  Without that heater working, the
> lamp is apparently too cold to start.

This looks more like it corroded away than melted.
Though, it's a bit hard to judge with that angle
and only one picture.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Attila Kinali]

Hoi Bruce,

On Mon, 9 May 2016 23:34:24 + (UTC)
Bruce Griffiths  wrote:

> Its probably easier/cheaper to construct a suitable filter for a GSPS ADC
> than to construct a TAC that is fast enough to suit an ADC with a GHz clock.

Probably. 

> Minimising the emitter to emitter inductance of a longtailed pair or
> equivalent is key to achieving a fast enough switching time for a suitable
> TAC. 

How does one minimize this inductance? The only way I am aware of is
to use a package with a pair of transistors with common emiter pin.

> The somewhat heroic measures employed in the Wavecrest counters is
> perhaps the limit of discrete construction techniques.

Are these heroic measures documented somewhere?
So far I have not even seen a block diagram of a Wavecrest counter,
much less a schematic.

Attila kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] High rate, high precision/accuracy time interval counter methods

[Bruce Griffiths]

Hoi Attila
Yes, the only way to reduce emitter-emitter inductance is indeed to connect 
them on the die. Its even better if the current source transistor collector is 
also connected to the common emitter node of the long tailed pair on the die as 
this minimises the capacitance at this node. 

Alternatively one can add a small series resistance to reduce the associated 
emitter circuit time constant as Wavecrest do.

The Wavecrest patent is somewhat detailed and complete with reasonably detailed 
circuit diagrams and explanatory text.
US6185509
US6194925 ***
US6226231US4908784
Bruce 

On Tuesday, 10 May 2016 9:17 PM, Attila Kinali  wrote:
 

 Hoi Bruce,

On Mon, 9 May 2016 23:34:24 + (UTC)
Bruce Griffiths  wrote:

> Its probably easier/cheaper to construct a suitable filter for a GSPS ADC
> than to construct a TAC that is fast enough to suit an ADC with a GHz clock.

Probably. 

> Minimising the emitter to emitter inductance of a longtailed pair or
> equivalent is key to achieving a fast enough switching time for a suitable
> TAC. 

How does one minimize this inductance? The only way I am aware of is
to use a package with a pair of transistors with common emiter pin.

> The somewhat heroic measures employed in the Wavecrest counters is
> perhaps the limit of discrete construction techniques.

Are these heroic measures documented somewhere?
So far I have not even seen a block diagram of a Wavecrest counter,
much less a schematic.

            Attila kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                -- Miss Matheson, The Diamond Age, Neil Stephenson


  
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[time-nuts] HP 105B oscillator

[Perry Sandeen via time-nuts]

List,
I purchased a HP 105B oscillator on ebay and it arrived today.  Previous to 
getting it I D/L the manual and brief;y perused it.

So when I popped open the top cover to see the internal parts, what to my 
wondering eyes appeared Not the A1 module shown in the manual but a 10811 
lookalike.
The only information on the oscillator is S/N 3010A59493 and R11215k.
So what do I have?  The next question that comes to mind is the plug in base 
the same electrical configuration of the 10811? (Being a TN You can see where 
this is going.)
Leaving out the divide issue for the moment, this would seem to be an ideal 
test bed for my 10811 oscillators as the 3 in my 5370B's have no EFC adjustment 
installed and I have another 10811 spare.
I have enough 5370B's and 5335's in which I could put all my 10811's in to 
*incubate* for months before attempting to tune them.
Also are there upgrades that are practical to add to the present PS for greater 
stability.  I am going to replace the original screw cap capacitor with a new 
Nichicon 105C cap.
Thoughts?  
Regards,
Perrier




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