Re: [time-nuts] HP5065A environmental sensitivities

[Angus]

Hi Corby,

That was really what I was hoping for from the small Rb's too, but
there appears to be other things at work with them.

I had not really considered that they might be sealed, but it's
something to look at. I had been thinking more about how it was fixed
into the package and with what materials. As well as the normal
component and circuit issues, there are also some deliberate ones like
discrete steps in temp correction which all add to the fun and
confusion.

BTW, if anyone has or knows of any pictures of a teardown of a FRK or
LPRO physics package, I'd be very interested.

Anyway, it's good to see that the 5065A is better behaved - I'm just
more jealous now! I look forward to seeing the results of your tests.

Angus.


On Sun, 22 May 2016 08:58:16 -0700, you wrote:

>Angus,
> 
>The HP 5065A has a fairly open path from atmosphere to the cells as far a
>barometric pressure is concerned.
>Response is rapid to a change.
> 
>The mechanism is "oil-canning" of the windows on the ends of the cell.
>Depends on diameter of the cell, thickness of the windows, and stiffness
>of the particular glass used. (for a particular gas mix of course)
> 
>It is VERY repeatable, and VERY linear.
> 
>I have heard that one European observatory routinely tracks the
>barometric pressure by watching their 5065A shift.
> 
>After seeing Wulf's data I can believe it!
> 
>My circuit is eliminating that variable quite nicely. As others have
>said, temperature will be a different matter.
> 
>I'm currently doing temperature tests and plan to eliminate the major
>causes rather than compensate.
> 
>Early measurements show as-built to be better than the spec of
>1.6X10-12/degree C.
> 
>Cheers,
> 
>Corby
>
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Re: [time-nuts] HP5065A environmental sensitivities

[jimlux]

On 5/22/16 10:25 AM, Bob Camp wrote:

Hi

In 40 years of getting phone calls, the one that never seems to go away starts 
out with:

“We … errr… measured the temperature rise in our box and need to adjust the 
upper end
temperature on your part”.




Or, as a designer using an OCXO part, you have to explain to the 
reviewer that just because, after updating the thermal model,  the 
temperature at the part is now 50C instead of 40C, it probably doesn't 
matter, because inside the OCXO's oven, it's even hotter.  Or, even 
worse, that the power dissipation goes down as the outside temperature 
goes up.






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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message <5741e08b.9080...@rubidium.dyndns.org>, Magnus Danielson writes:

>The negative voltage switcher of A15 board should be replaced with a 
>suitable switcher, and some of the DC/DC switcher modules is built with 
>isolation, so it should allow for mounting two in parallel such that you 
>get both sides. PHK, have you checked this option?

Yes and no.

I think the +/- 20V *should* not matter, and the reason they currently do
is something a couple of well-chosen modern op-amps can take care of as
far as I can tell.

My hope was to design a couple of plug-in replacement boards to fix most
of these issues, while allowing A/B comparisons to the improvement can
actually be measured.

Basically:

A new integrator board, using a modern chopper/zero-drift op-amp.

A new AC amplifier, ditto.

Instead of the two diodes, put a modern "ideal diode" circuit and
two DC/DC converters on the first PSU board, producing the +24V and
a -15V rail for the rest of the instrument. (-15 instead of -20 since
it will be driving the opamps mentioned above.

On the second board, an opamp to drive the existing chassis-mounted
+20V series transistor from a _really_ good voltage reference (LM399)
and the most stable C-field drive circuit I can come up with.

But as I said, I'm just about to start building a new house, so my
time is limited for the next year or so...

If somebody else wants to take the lead, I'll happily assist as I can...

The "NextGen" project, would be to use a 48bit DDS chip to generate
the 60+MHz drive signal for the microwave, and a "geophone" ADC chip
to detect the modulation from the photo-diode, but that is even further
out...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message <02878e59-0bae-4220-8a86-5e59f0ca5...@n1k.org>, Bob Camp writes:

>'We ... errr... measured the temperature rise in our box and need to adjust
>the upper end temperature on your part'.

yeah, I know that story:

http://phk.freebsd.dk/hotsun/

That's the CPU/fan cover for a SUN Ultrasparc/60 where the fan connector
was not reattached after somebody messed with it...

What surprises me about the HP5065 is that they could quite easily have
done better than they did, but I suspect they had to make sure the specs
were meaningfully worse than the HP5061...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

In 40 years of getting phone calls, the one that never seems to go away starts 
out with:

“We … errr… measured the temperature rise in our box and need to adjust the 
upper end
temperature on your part”.

The really interesting part is that you can get multiple calls that go the same 
way from the 
same engineering team. Each time they drop in another board or check a rack in 
a customer
installation new data arrives …

A 5C rise is nothing. Some of these boxes run at 95C with what is supposed to 
be 50C inlet air. 

Bob



> On May 22, 2016, at 12:33 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message , Bob Camp writes:
> 
>> At least 5C offset relative to an external sensor. Likely more in some rack
>> installations. Past that it depends on how close the item of
>> interest is to the oven assembly.
> 
> That's only part of it.
> 
> The rather important zener diode regulating the C-field is located
> on the DC regulator board, where the temperature depends directly
> on the grid voltage...
> 
> -- 
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Hi Bob,

On 05/22/2016 05:21 PM, Bob Camp wrote:

Hi


On May 22, 2016, at 10:49 AM, Attila Kinali  wrote:

Hoi Poul-Henning,

On Fri, 20 May 2016 09:52:39 +
"Poul-Henning Kamp"  wrote:


Temperature effects are by far the largest effects we have to deal with.


Which is why you'd be much better of with 20 sensors at 16 bits,
than a single sensor at 24 bits.


Does the HP5065 have such huge temperature gradients/differentials inside?


At least 5C offset relative to an external sensor. Likely more in some rack 
installations. Past
that it depends on how close the item of interest is to the oven assembly.


To explain a little more.

The 5065A/B has a design that relies on self-convection. Depending on 
which generation, the AC rectifier is sitting on the PCB or on the 
chassi for cooling. Similarly the switcher on the A15 board can run a 
bit hot. This alone makes me recommend that the 5065 is put such that 
there is self-convection. I run mine free-standing.


Making the 5065 more temperature stable is definitely recommended, but 
that is to some degree orthogonal from handling the heat produced.
PHKs replacement of PSU details helps to reduce the heat and also 
produces more stable power-supply, which is a good step in the right 
direction on both accounts.


With a little cleanup of the PSU, thermal management have improved 
somewhat in the box.


The negative voltage switcher of A15 board should be replaced with a 
suitable switcher, and some of the DC/DC switcher modules is built with 
isolation, so it should allow for mounting two in parallel such that you 
get both sides. PHK, have you checked this option?


Cheers,
Magnus
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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

> On May 22, 2016, at 10:49 AM, Attila Kinali  wrote:
> 
> Hoi Poul-Henning,
> 
> On Fri, 20 May 2016 09:52:39 +
> "Poul-Henning Kamp"  wrote:
> 
>>> Temperature effects are by far the largest effects we have to deal with.
>> 
>> Which is why you'd be much better of with 20 sensors at 16 bits,
>> than a single sensor at 24 bits.
> 
> Does the HP5065 have such huge temperature gradients/differentials inside?

At least 5C offset relative to an external sensor. Likely more in some rack 
installations. Past
that it depends on how close the item of interest is to the oven assembly. 

Bob

> 
>   Attila Kinali
> 
> -- 
> Reading can seriously damage your ignorance.
>   -- unknown
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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message <20160522164909.9fbc6cc820403cc70904e...@kinali.ch>, Attila Kinali 
writes:
>Hoi Poul-Henning,
>
>On Fri, 20 May 2016 09:52:39 +
>"Poul-Henning Kamp"  wrote:
>
>> >Temperature effects are by far the largest effects we have to deal with.
>> 
>> Which is why you'd be much better of with 20 sensors at 16 bits,
>> than a single sensor at 24 bits.
>
>Does the HP5065 have such huge temperature gradients/differentials inside?

Yes.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] HP5065A environmental sensitivities

[Attila Kinali]

Hoi Poul-Henning,

On Fri, 20 May 2016 09:52:39 +
"Poul-Henning Kamp"  wrote:

> >Temperature effects are by far the largest effects we have to deal with.
> 
> Which is why you'd be much better of with 20 sensors at 16 bits,
> than a single sensor at 24 bits.

Does the HP5065 have such huge temperature gradients/differentials inside?

Attila Kinali

-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] HP5065A environmental sensitivities

[Bert Kehren via time-nuts]

I know Corby is working on it and he will share his results. I think he is  
right now on vacation that is most likely why he is not commenting.
Bert Kehren
 
 
In a message dated 5/21/2016 10:02:59 P.M. Eastern Daylight Time,  
mag...@rubidium.dyndns.org writes:

Hej  Poul-Henning,

On 05/20/2016 04:27 PM, Poul-Henning Kamp wrote:
>  
> In message <573edc73.9040...@rubidium.dyndns.org>,  Magnus Danielson 
writes:
>
>> Humidity and pressure play a role  with surrounding temperature in
>> cooling in that it they will shift  the thermal resistance through which
>> the cooling of the ovens  goes, [...]
>
> Once we get below 5e-13, the temperature effects  on electronic components
> should not be ignored either.

Well,  yes. Many of the older gear uses components in loops who's 
environmental  performance isn't stellar by any means.

> The C-field circuit in  particular. (Yes, I'm still working on it, just 
not
> very  fast...)

I was actually wondering how that was getting  along.

When I get the time, it would be fun to improve on  things.

Humidity, temperature, pressure, powergrid  voltage...

Cheers,
Magnus
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Re: [time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Hej Poul-Henning,

On 05/20/2016 04:27 PM, Poul-Henning Kamp wrote:


In message <573edc73.9040...@rubidium.dyndns.org>, Magnus Danielson writes:


Humidity and pressure play a role with surrounding temperature in
cooling in that it they will shift the thermal resistance through which
the cooling of the ovens goes, [...]


Once we get below 5e-13, the temperature effects on electronic components
should not be ignored either.


Well, yes. Many of the older gear uses components in loops who's 
environmental performance isn't stellar by any means.



The C-field circuit in particular. (Yes, I'm still working on it, just not
very fast...)


I was actually wondering how that was getting along.

When I get the time, it would be fun to improve on things.

Humidity, temperature, pressure, powergrid voltage...

Cheers,
Magnus
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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message <573edc73.9040...@rubidium.dyndns.org>, Magnus Danielson writes:

>Humidity and pressure play a role with surrounding temperature in 
>cooling in that it they will shift the thermal resistance through which 
>the cooling of the ovens goes, [...]

Once we get below 5e-13, the temperature effects on electronic components
should not be ignored either.

The C-field circuit in particular. (Yes, I'm still working on it, just not
very fast...)


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Wulf,

On 05/19/2016 11:04 AM, dg...@gmx.de wrote:

Some answers to comments:

Magnus,
I don’t think I have made a closed loop. It works like UTC for poor man. I 
gathered data from different master clocks and from a weather station and 
produced a new software corrected time scale for my own.  But you are right. 
The correction is the best fit for this specific data-set and will be worse if 
applied to another. The ADEV plot should be clipped to trusted values - maybe 
50 sec. I intend to apply a hardware compensation. Therefore I was happy to 
find a barometric pressure sensor 144SC0811-Baro at an auction side some weeks 
ago for less than one tenth of the normal prize. Approximate 240 kOhm should be 
needed from the output of this module to the base of Q6B for compensation.


If you have an open loop measure of your clock and pressure, then fit 
the pressure variations over the full data set and produce a corrected 
value for the full dataset, then this troublesome as you now have used 
the samples after the beginning to affect the beginning. You have 
provided feedback and correction. This is useful to show potential of 
such correction.


If you only used one dataset for match the coefficient and then use a 
new dataset to correct using the new pressure data and the coefficient, 
then that will be more representative of real-time performance even if 
you do it as batch-processing as an after the fact setup.


What you want to do is to look at the corrected curve and see if there 
is any other terms, that can be quadratic, differential or integral 
variants (just to give you some ideas) of the pressure data and that may 
be a hint about further improvements of the model that allows even 
better compensation model.



James,
when I made the correlation the best fit was obtained comparing a frequency 
difference data-set delayed 1 hour to the pressure measurements. But I have to 
dig into the data-set again – there might be an error calculating the MJD from 
Middle European Time.  As far as I understood from Corby´s measurements, the 
frequency reacts immediately to a pressure change without delay. For the 
compensation, a delay does not matter very much. Pressure changes are normally 
very slow.


The model should always be verified so that major components is found.
The proportional component seems strong thought.


Poul-Henning,
The measurement is made in normal environment. Temperature measurements of the 
Thunderbolt, which was two meter away, show daily variations of 1-2 degree C 
and an additional drop of 2 degree during the weekend. Humidity measurements 
are not made. Temperature effects as well as aging are still left in the 
residuals of my data. The aging of this specific instrument is nearly zero. The 
frequency was adjusted 6 month ago and the drift is less than 1E-12 during this 
time.


Humidity and pressure play a role with surrounding temperature in 
cooling in that it they will shift the thermal resistance through which 
the cooling of the ovens goes, either being higher increase the 
conductance, and varies the load of the oven which will not perfectly 
match the load and hence the temperature varies.



Bjørn,
I have the temperature measurements inside the Thunderbolt and temperature 
measurements from a temperature Data-logger placed inside the HP5065A. This 
datalogger has a temperature resolution of around 0.4 degC.

Attila,
I know the SHT11 from the old days when a LPT-port could be controlled by the 
user.
It is a nice device. But I bought the 144SC0811 which can be used by adding 
only one resistor.

Corby,
It would be nice to see the results with temperature compensation. There are 
lots of sources producing temperature sensitivity. All have a different time 
constant. AS Poul-Henning found out, the rate of temperature change is the 
worst problem. In my eyes temperature compensation is much more complicated 
then compensation for barometric pressure.


Pressure compensation is an interesting approach, thanks for 
illustrating it!


Cheers,
Magnus
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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message <20160519184616.39fd0ca08628b0843ce72...@kinali.ch>, Attila Kinali 
writes:

>For real temperature measurements, I would use a wirewond Pt sensor
>on a 24bit ADC with a stable reference.

And where would you put the sensor ?

Where do you find a temperature so representative, that it makes any
sense to sample it with 24 bits ?

>Temperature effects are by far the largest effects we have to deal with.

Which is why you'd be much better of with 20 sensors at 16 bits,
than a single sensor at 24 bits.

-- 
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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

> On May 19, 2016, at 12:46 PM, Attila Kinali  wrote:
> 
> On Thu, 19 May 2016 07:40:15 -0400
> Bob Camp  wrote:
> 
>> One advantage of doing all the compensation off of a single sensor is that 
>> *if* there are cross effects and *if* you can characterize them, you can 
>> correct them out. Put another way, if the pressure reading changes by 
>> 0.01% per C, having a reasonable idea of the temperature of the sensor lets
>> you take care of that. 
> 
> But munching everything into a single system makes the thing mathematically
> intractable. Seperating the values, compensating them for induced errors
> first and then using them is much easier and less error prone.

Having all the outputs from a single sensor or multiple sensor makes the math 
no harder or easier. If the pressure sensor moves 0.01% per C with a separate
pressure sensor and a separate temperature sensor …. the math is the same as
if it comes off a single device. You have the same effect to train out and the 
same
math to do it.


> 
> Also, composite sensors have higher uncertainties and drift
> then single sensors.

That’s often the difference between a $10,000 sensor and a $1 sensor rather
than an integrated part. 

> Even more so: the integrated temperature sensors
> are intended for use with the main sensor as a compensation tool.

Which is one of the reasons they work for that purpose. 

> The specs
> of the temperature sensor are good enough if the drift/hysteresis of the
> temperature sensor is less than the one of the main sensor. That you can
> read out the temperature sensors value is more a goody for those applications
> when a temperature sensor is needed but not high accuracy/precision required.

Again, a delta between a $10,000 sensor and a $1 sensor is indeed that you can 
likely read the Fluke / Hart setup to a lot higher level of accuracy. 

> 
> What is usually a good approach is to use the temperature sensors on
> barometric and hygrometric sensors only for their temperature compensation.
> At most, use the temperature sensor for cross checking and detecting faults.
> 
> For real temperature measurements, I would use a wirewond Pt sensor
> on a 24bit ADC with a stable reference.

I would prefer a set of at least three SPRT’s each with their own readout and 
to calibrate
them each with an independent triple point cell. That most certainly would do a 
*much* better
job of producing accurate temperature. Of course, that’s not going to fit into 
a modest $10K 
budget. 

> 
> Temperature effects are by far the largest effects we have to deal with.
> Having a stable and reliable measurement system for temperature is not
> only worthwhile, but actually a requirement before you start compensating
> anything else

But is +/- 0.0001 K  good enough or do we need +/- 0.01 K. Oddly enough, it 
turns out
that you can do a really good job compensating most frequency sources with a 
much more 
modest *relative* accuracy. It also turns out that gradients will get you 
*long* before anything 
much below 0.1C applies. 

> 
>> Things like sensor drift and sensor hysteresis … that’s not quite so easy to
>> take care of. The only hope there is that they are small enough to be
>> neglected. The same issue with hysteresis is actually a big limit on
>> humidity compensation of some devices. They adsorb water vapor at a very
>> different rate than they desorb. 
>> Modeling that can be really messy. 
> 
> Hysteresis can be properly modeled and compensated. The problem is, that
> the math behind it becomes nasty very quickly. Often just using a simple
> second order diff equation system and letting a Kalman filter estimate
> the parameters is easier than modeling a full memory system... under the
> condition that one can excite the system reliably and isolate/estimate
> the other effects well enough.

It’s generally not the math that is the issue…..Try modeling a humidity effect 
that takes < 1 minute
to adsorb and a couple of months do desorb. Hysteresis in OCXO’s can turn out 
to be dependent
on rate, range, starting point, and air flow direction. Something over a 
thousand independent 
test profiles (six directions, eight rates, ten ranges, ten starting points ..) 
 may be needed to fully train it out. 

Bob

> 
>   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] HP5065A environmental sensitivities

[Attila Kinali]

On Thu, 19 May 2016 07:40:15 -0400
Bob Camp  wrote:

> One advantage of doing all the compensation off of a single sensor is that 
> *if* there are cross effects and *if* you can characterize them, you can 
> correct them out. Put another way, if the pressure reading changes by 
> 0.01% per C, having a reasonable idea of the temperature of the sensor lets
> you take care of that. 

But munching everything into a single system makes the thing mathematically
intractable. Seperating the values, compensating them for induced errors
first and then using them is much easier and less errorprone.

Also, composite sensors have higher uncertainties and drift
then single sensors. Even more so: the integrated temperature sensors
are intended for use with the main sensor as a compensation tool. The specs
of the temperature sensor are good enough if the drift/hysteresis of the
temperature sensor is less than the one of the main sensor. That you can
read out the temperature sensors value is more a goody for those applications
when a temperature sensor is needed but not high accuracy/precision required.

What is usually a good approach is to use the temperature sensors on
barometric and hygrometric sensors only for their temperature compensation.
At most, use the temperature sensor for cross checking and detecting faults.

For real temperature measurements, I would use a wirewond Pt sensor
on a 24bit ADC with a stable reference.

Temperature effects are by far the largest effects we have to deal with.
Having a stable and reliable measurement system for temperature is not
only worthwhile, but actually a requirement before you start compensating
anything else.

> Things like sensor drift and sensor hysteresis … that’s not quite so easy to
> take care of. The only hope there is that they are small enough to be
> neglected. The same issue with hysteresis is actually a big limit on
> humidity compensation of some devices. They adsorb water vapor at a very
> different rate than they desorb. 
> Modeling that can be really messy. 

Hysteresis can be properly modeled and compensated. The problem is, that
the math behind it becomes nasty very quickly. Often just using a simple
second order diff equation system and letting a Kalman filter estimate
the parameters is easier than modeling a full memory system... under the
condition that one can excite the system reliably and isolate/estimate
the other effects well enough.

Attila Kinali

-- 
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the prosperity and technological sophistication in the world is of no 
use without that foundation.
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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

Hi

One advantage of doing all the compensation off of a single sensor is that 
*if* there are cross effects and *if* you can characterize them, you can 
correct them out. Put another way, if the pressure reading changes by 
0.01% per C, having a reasonable idea of the temperature of the sensor lets
you take care of that. 

Things like sensor drift and sensor hysteresis … that’s not quite so easy to
take care of. The only hope there is that they are small enough to be neglected.
The same issue with hysteresis is actually a big limit on humidity compensation
of some devices. They adsorb water vapor at a very different rate than they 
desorb. 
Modeling that can be really messy. 

Bob

> On May 19, 2016, at 1:49 AM, Attila Kinali  wrote:
> 
> On Thu, 19 May 2016 06:33:38 +0200
> "Björn Gabrielsson"  wrote:
> 
> 
>> What are time-nuts using for monitoring the environment?
> 
> The Sensirion SHT21 has become the gold standard silicon based
> humidity sensor over the past years. Even though it's quite old
> (IIRC close to 10 years) it has performance metrics that still
> rival modern sensors. Its rather "large" package with the 1mm
> pitch makes it one of the easier to solder sensors as well.
> It's only drawback is its relatively large price of €6
> 
> As for barometric sensors, the ones by Measurment Specialities
> are quite good. The MS5607-02BA03 for example does a resolution
> of 2.4Pa with a long term stability of 100Pa/a.
> There is also the MS5611-01BA03 which offers 1.2Pa resolution,
> but also doubles the price and I am not so sure whether that
> tiny bit more resolution is more than just noise.
> 
> A little advice: If you want to measure pressure with high precision,
> you should think about temperature stabilizing the sensor.
> 
> The same is true for humidity, but does not work as well, as temperature
> stabilization (aka heating) changes the relative humidity and thus
> the measurement value depends quite a bit on how the air around the
> sensor flows.
> 
> Also, provide good and low noise power to the sensors. These are
> precision instruments with high resolution ADCs. To work properly
> they need a clean power source.
> 
>> I have been playing a little with the Bosch BME280 - doing air pressure,
>> temp and relative humidity in a small form factor. Easy to interface to
>> Raspberry Pi or Arduino.
> 
> The only Bosch sensor i've ever used was a BMA250 acceleration sensor.
> It worked reasonably well, but i've never evaluated it for precision
> or accuracy. But at least it looks like Bosch does not exagerate
> in their datasheets.
> 
> 
>   Attila Kinali
> -- 
> Reading can seriously damage your ignorance.
>   -- unknown
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Re: [time-nuts] HP5065A environmental sensitivities

[DG2OM]

Some answers to comments:

Magnus,
I don’t think I have made a closed loop. It works like UTC for poor man. I 
gathered data from different master clocks and from a weather station and 
produced a new software corrected time scale for my own.  But you are right. 
The correction is the best fit for this specific data-set and will be worse if 
applied to another. The ADEV plot should be clipped to trusted values - maybe 
50 sec. I intend to apply a hardware compensation. Therefore I was happy to 
find a barometric pressure sensor 144SC0811-Baro at an auction side some weeks 
ago for less than one tenth of the normal prize. Approximate 240 kOhm should be 
needed from the output of this module to the base of Q6B for compensation.

James,
when I made the correlation the best fit was obtained comparing a frequency 
difference data-set delayed 1 hour to the pressure measurements. But I have to 
dig into the data-set again – there might be an error calculating the MJD from 
Middle European Time.  As far as I understood from Corby´s measurements, the 
frequency reacts immediately to a pressure change without delay. For the 
compensation, a delay does not matter very much. Pressure changes are normally 
very slow.

Poul-Henning,
The measurement is made in normal environment. Temperature measurements of the 
Thunderbolt, which was two meter away, show daily variations of 1-2 degree C 
and an additional drop of 2 degree during the weekend. Humidity measurements 
are not made. Temperature effects as well as aging are still left in the 
residuals of my data. The aging of this specific instrument is nearly zero. The 
frequency was adjusted 6 month ago and the drift is less than 1E-12 during this 
time.

Bjørn,
I have the temperature measurements inside the Thunderbolt and temperature 
measurements from a temperature Data-logger placed inside the HP5065A. This 
datalogger has a temperature resolution of around 0.4 degC. 

Attila,
I know the SHT11 from the old days when a LPT-port could be controlled by the 
user.
It is a nice device. But I bought the 144SC0811 which can be used by adding 
only one resistor.

Corby,
It would be nice to see the results with temperature compensation. There are 
lots of sources producing temperature sensitivity. All have a different time 
constant. AS Poul-Henning found out, the rate of temperature change is the 
worst problem. In my eyes temperature compensation is much more complicated 
then compensation for barometric pressure.

Best regards
Wulf Oelschlägel
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Re: [time-nuts] HP5065A environmental sensitivities

[Attila Kinali]

On Thu, 19 May 2016 06:33:38 +0200
"Björn Gabrielsson"  wrote:


> What are time-nuts using for monitoring the environment?

The Sensirion SHT21 has become the gold standard silicon based
humidity sensor over the past years. Even though it's quite old
(IIRC close to 10 years) it has performance metrics that still
rival modern sensors. Its rather "large" package with the 1mm
pitch makes it one of the easier to solder sensors as well.
It's only drawback is its relatively large price of €6

As for barometric sensors, the ones by Measurment Specialities
are quite good. The MS5607-02BA03 for example does a resolution
of 2.4Pa with a long term stability of 100Pa/a.
There is also the MS5611-01BA03 which offers 1.2Pa resolution,
but also doubles the price and I am not so sure whether that
tiny bit more resolution is more than just noise.

A little advice: If you want to measure pressure with high precision,
you should think about temperature stabilizing the sensor.

The same is true for humidity, but does not work as well, as temperature
stabilization (aka heating) changes the relative humidity and thus
the measurement value depends quite a bit on how the air around the
sensor flows.

Also, provide good and low noise power to the sensors. These are
precision instruments with high resolution ADCs. To work properly
they need a clean power source.

> I have been playing a little with the Bosch BME280 - doing air pressure,
> temp and relative humidity in a small form factor. Easy to interface to
> Raspberry Pi or Arduino.

The only Bosch sensor i've ever used was a BMA250 acceleration sensor.
It worked reasonably well, but i've never evaluated it for precision
or accuracy. But at least it looks like Bosch does not exagerate
in their datasheets.


Attila Kinali
-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] HP5065A environmental sensitivities

[Björn Gabrielsson]

>>> I got a slope of 3.86E-14/hPa frequency difference versus pressure.
>
> Did you also control for temperature ?
>
> Air pressure, in particular at high relative humidities changes the
> thermal properties of air so there is bound to be some cross coupling
> were temperature sensitivities appear as pressure sensitivity.

What are time-nuts using for monitoring the environment?

I have been playing a little with the Bosch BME280 - doing air pressure,
temp and relative humidity in a small form factor. Easy to interface to
Raspberry Pi or Arduino.


https://www.bosch-sensortec.com/bst/products/all_products/bme280

https://github.com/adafruit/Adafruit_Python_BME280

http://www.satsignal.eu/raspberry-pi/monitoring.html#BME280


--

 Björn

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Re: [time-nuts] HP5065A environmental sensitivities

[Poul-Henning Kamp]

In message , James Flynn writes:

>> I got a slope of 3.86E-14/hPa frequency difference versus pressure.

Did you also control for temperature ?

Air pressure, in particular at high relative humidities changes the
thermal properties of air so there is bound to be some cross coupling
were temperature sensitivities appear as pressure sensitivity.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] HP5065A environmental sensitivities

[James Flynn]

  writes:


> I also have a weather station at 6 km distance away, which records 
barometric pressure at time intervals of
> 10 minutes. Out from these measurements, I divided
> my phase measurements into 10 minute intervals, calculated the 10 min 
average frequencies and made a
> linear regression with the 10 minute pressure measurements.
> I got a slope of 3.86E-14/hPa frequency difference versus pressure.

Did you notice or calculate any time delay/offset in the correlation 
between your pressure data and the frequency data? That is, anything much 
larger than the 10 minute interval of your data, say, on the order of an 
hour. 

Whether there is a time delay or not may help point to the actual 
mechanism causing the frequency change. 



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Re: [time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Hi Wulf,

On 05/18/2016 08:57 AM, dg...@gmx.de wrote:

This is my first contribution to the Time-Nut list, but I am a follower for 
several years.
I have made 30 days phase difference measurements of an HP5065a versus a 
modified Thunderbolt GPSDO (got a MV180 oscillator) with a Fluke PM6681,
and recorded the results with Timelap. Starting signal of the PM6681 was the 
5MHz of the HP5065A, stop signal the 10MHz from the Thunderbolt. A single
measurement was triggered once a second from the PPS of the TB.
I also have a weather station at 6 km distance away, which records barometric 
pressure at time intervals of 10 minutes. Out from these measurements, I divided
my phase measurements into 10 minute intervals, calculated the 10 min average 
frequencies and made a linear regression with the 10 minute pressure 
measurements.
I got a slope of 3.86E-14/hPa frequency difference versus pressure.


Interesting!


Then I corrected the original 10 min average frequency measurements with the 
result from the linear regression and imported the original and the corrected
datasets into Timelap.
The influence of the barometric pressure to the ADEV for long time intervals is 
shown in the picture.
Just for fun, to render the pressure sensitivity visible for the human eye, I 
removed the noise of the GPSDO by generating a plot of overlapping 1 day
frequency averages in 10 minute time intervals. On the second picture you can 
compare it with the 10minute pressure data from the weather station. I think,
it is quite impressive. The calculated slope out of these overlapping averages 
was with 3.74e-14/hPa a little bit different compared with the non overlapping 
dataset.


Now, after the fact fitting of curve has a drawback in that you can make 
the fit as really good but there you measure the reference, hence you 
have a closed loop. The challenge now is to use a feed-forward scheme to 
take the measures from the pressure and use to adjust the C-field of the 
5065 and then measure against the Thunderbolt. I would guess it won't be 
exactly the same, not as good, but it will be then the actual performance.


Cheers,
Magnus
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Re: [time-nuts] HP5065A environmental sensitivities

[Bob Camp]

HI

Very neat !!!

Bob

> On May 18, 2016, at 2:57 AM, dg...@gmx.de wrote:
> 
> This is my first contribution to the Time-Nut list, but I am a follower for 
> several years.
> I have made 30 days phase difference measurements of an HP5065a versus a 
> modified Thunderbolt GPSDO (got a MV180 oscillator) with a Fluke PM6681,
> and recorded the results with Timelap. Starting signal of the PM6681 was the 
> 5MHz of the HP5065A, stop signal the 10MHz from the Thunderbolt. A single
> measurement was triggered once a second from the PPS of the TB.
> I also have a weather station at 6 km distance away, which records barometric 
> pressure at time intervals of 10 minutes. Out from these measurements, I 
> divided
> my phase measurements into 10 minute intervals, calculated the 10 min average 
> frequencies and made a linear regression with the 10 minute pressure 
> measurements.
> I got a slope of 3.86E-14/hPa frequency difference versus pressure.
> Then I corrected the original 10 min average frequency measurements with the 
> result from the linear regression and imported the original and the corrected
> datasets into Timelap.
> The influence of the barometric pressure to the ADEV for long time intervals 
> is shown in the picture.
> Just for fun, to render the pressure sensitivity visible for the human eye, I 
> removed the noise of the GPSDO by generating a plot of overlapping 1 day
> frequency averages in 10 minute time intervals. On the second picture you can 
> compare it with the 10minute pressure data from the weather station. I think, 
> it is quite impressive. The calculated slope out of these overlapping 
> averages was with 3.74e-14/hPa a little bit different compared with the non 
> overlapping dataset.
> 
> Best regards
> Wulf pressure.png>___
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Re: [time-nuts] HP5065A environmental sensitivities

[timeok]

Hi Corby,

very interesting. I have some questions?

1) it is difficult to read the frequency value on the plot. Can you specify?
2) how do you set the offset of the op-amp trimmer ?
3) do you think is possible to use the -20V on the HP5065A instead the -12V 
from the DC-DC converter?
4) what frequency measurement system do yo have used for?

I am curious to know how you have generate the barometric swing.


thanks ,
Luciano
www.timeok.it


On Fri 13/05/16 03:29 ,  wrote:

> HP 5065A Environmental sensitivity
> 
> First here is a comparison between the specified sensitivities of various
> 
> Rubidium units.
> 
> Barometric per mbar Temperature per degree C
> 
> HP 5065A 6.3X10-14 1.6X10-12
> M100 FRK 8.7x10-14 2.4X10-12
> LPRO 1.0X10-13 6.0X10-12
> FE5650A unspecified 1.1X10-11
> FRSC 1.0X10-13 1.1X10-11
> PRS10 unspecified 1.0X10-11
> 
> As you can see the HP specs are better than the others!
> 
> After much effort I managed to measure the actual sensitivity of a 5065A
> on my bench.
> It was much better than the spec at 1.55X10-14/mbar! I then installed
> a barometric compensation circuit consisting of a sensor and OP amp. This
> feeds the C-field circuit in the 5065A.
> After alignment the sensitivity was so low that it was below my
> measurement noise floor!
> 
> Attached is a frequency plot that illustrates the correction. On the left
> is a calibration offset from the Maser of plus/minus 1.84X10-12. The
> middle section shows the frequency with the compensation on during
> several cycles of plus/minus 35 mbar. The right is with compensation off
> and the plus/minus 35mbar excursions.
> 
> Also attached is a schematic of the compensation circuitry.
> 
> Now I'll work on the temperature sensitivity. Poul-Henning has explored
> in this area and has some good information to start with.
> 
> Cheers,
> 
> Corby
> 
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