Re: [time-nuts] algorithms and hardware for comparing clock pulses

2015-09-22 Thread Magnus Danielson 

Jim,

I had the intent to try this, but never got around doing it. Thanks for 
reminding me. Please share any enhancements.


I did exchange some emails with Lars, but as that project never got off 
the ground, it faded out.


Cheers,
Magnus


On 09/21/2015 10:02 PM, Jim Harman wrote:

Hi Can,

For a simple analog solution, you might try a 74HC4046 phase detector
followed by a diode and RC network as used in Lars Walenius' GPSDO,
described here in the archives:

https://www.febo.com/pipermail/time-nuts/2014-February/082820.html

The phase detector produces a pulse whose width equals the time difference
between the two pulses. The RC network converts this to a voltage
proportional to the time difference, which you then measure with the MCU's
A/D converter. Using the rising edge of the signal at pin 14 as the
interrupt source triggers the A/D converter at the end of the pulse, which
corresponds to the peak of the analog signal.. The 1 meg resistor
discharges the capacitor between pulses.

Lars' code also includes a filtering algorithm which does a nice job of
controlling one of the oscillators to match the 1-PPS generated by the GPS.
I have enhanced this if you are interested.

On Mon, Sep 21, 2015 at 1:45 PM, Can Altineller 
wrote:




I probably need a hardware to measure the time pulses more precisely. I
thought of XOR'ing the clocks, and measuring both rising and falling edges
trough interrupts, but when the pulse is close enough, it will lead to same
condition.

Are there any solutions to this problem? Maybe an analog hack? And what
are the mostly used algorithms to tune an oscillator to another? Currently
my algorithm sign corrects the result difference, and adjusts aging
register simply by adding to it, then runs a conversion command each second
to add or substract the ppms.

This looks a lot of fun,

Best Regards,
Can Altineller
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Re: [time-nuts] Z380XA The saga of the aging 10811

2015-09-22 Thread Magnus Danielson 
Analog is nice and dandy, but for longer time-constants, digital does 
have it's merits.


Wonder how good resolution one really need for sensing and how to 
achieve it.


Cheers,
Magnus


On 09/15/2015 12:58 PM, Bob Camp wrote:

Hi

To the extent that the oven controller is an integrator, it only integrates 
over a couple
of seconds.

Bob


On Sep 14, 2015, at 5:58 PM, Bob Benward  wrote:

Robert,
The drift has slowed down to something around 8xE-10, which is a bit over
the spec of <5E-10.  But this is the single oven, I have not reassembled the
double oven yet.

If the oven regulation was off, I would suspect I would see the EFC go back
and forth a bit, maybe a general trend up, but some retracing would be
expected.  The oven control is an integrator, so unless the offset is very
large compare to the output of the thermistor, a continuously changing
offset voltage will not have a large effect on setpoint.  A crystal
resonator will drift about 1-5E-8/degC, so I guess a loose temperature
control would certainly exhibit the drift I am seeing.

Bob




-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of George
Atkinson
Sent: Monday, September 14, 2015 2:42 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Z380XA The saga of the aging 10811

Well, if the batch/revision of op-amps had a doping, contamination or

similar

issue, the input offset could be drifting fairly constantly causing a
temperature channge in one direction.

Robert G8RPI.

On 9 September 2015 at 04:40, Bob Benward 
wrote:


Hi Ed,
OK, a bad oven.  I can buy that.  But then if the oscillator is
constantly drifting, would that not imply that the oven is constantly
changing temperature, in one direction?

BTW, the curve is starting to flatten out.  It might be flat before It
gets to 1000K counts.

Bob


-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
ed breya
Sent: Tuesday, September 08, 2015 10:55 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] Z380XA The saga of the aging 10811

It could be that the inner oven temperature regulation is off a
bit, or

even

failed. There was a report at one of the popular time-nuts
oriented

websites (I

forget which one, but it's the one that had extensive coverage of
the

Z3801A)

about inner oven problems a few years ago. I took mine apart and
found

that

it had an IC of a particular date code range that was prone to

failure.

I can't

recall whether I replaced it with the same type but different
date, or

an

alternative, but it worked just fine after that, with no tweaking
of

coarse EFC

needed.

The IC was a dual opamp I think, that controlled the oven
temperature according to the thermistor signal, and drove the

heater

transistor(s).

It was a fairly high performance type, but not that unusual. I
think it

was a

Linear Technology brand part.

Ed
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