Re: [time-nuts] Poor man's oven

[Van Horn, David]

You can feed in an external AREF, but look at the data sheet for the particular 
AVR chip.
One thing which is commonly ignored in Arduino-Land is the I/O pin leakage 
current and the maximum source impedance specs.
You are well advised to buffer the voltage you are reading, or make sure the 
source is low enough impedance that those errors won't get you.

All uCs have these issues, I just see this error made a lot in Arduino land.  
My 3D printer is Arduino based, and uses a 100k thermistor driving the Arduino 
directly.
The community makes claims that a degree or two of temperature change is 
important, and yet the circuit isn't capable of that much accuracy.



-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Jim Harman
Sent: Tuesday, June 6, 2017 11:09 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Poor man's oven

On Tue, Jun 6, 2017 at 10:00 AM, Riley, Ian C CTR NSWC Philadelphia, 515 < 
ian.riley@navy.mil> wrote:

> Is there a practical minimum for what voltage you can feed into AREF?
>

It is hard to find on the data sheet, but the minimum voltage for an Arduino's 
AREF is the internal analog reference voltage - 1.1V for the Uno, 2.56V for the 
Leonardo or Micro. The 32U4 chip in the Leo and Micro has options for 
differential analog input and gains of 10, 40, or 200 but they are not 
supported by the Arduino IDE - you have to set the internal registers directly 
to use them. Also the input amplifier is pretty slow.


-- 

--Jim Harman
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Re: [time-nuts] MCXO and dual mode

[Hal Murray]

kb...@n1k.org said:
> Let’s say both modes are running into a 32 pf load and it is a single
> capacitor.  

I'm missing the big picture.

Can I run both modes at the same time?  Or do I switch between them?

> The beat frequency shifts since the two modes do not tune identically. 

That sounds like they are running at the same time.

What does the output look like?  I'd expect beats so the signal would drop 
out for many cycles if I looked at the right place in time.  Is that sort of 
signal good for anything other than being a thermometer?

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Re: [time-nuts] MCXO and dual mode

[Bob kb8tq]

Hi

> On Jun 6, 2017, at 10:15 PM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
> On 6/6/2017 3:16 PM, Bob kb8tq wrote:
>> Hi
>> If you do the classic MCXO with two oscillator circuits and one resonator, 
>> the issue is
>> pretty simple. You have a load capacitance on the fundamental. You have a 
>> load capacitance
>> on the third overtone. Even if it is the exact same capacitor, the tuning 
>> sensitivity on
>> the fundamental is different than the sensitivity on the third overtone. As 
>> the load impedance
>> changes (parts do drift) the delta between the two modes will show up as an 
>> offset between
>> them. If you run through the math, it gives you a delta temperature. How 
>> much? How fast? Obviously
>> that depends. When I brought this up at the time with the authors of the 
>> paper, the reply was that
>> a recalibration of the MCXO was provided for for this reason.
>> Bob
> 
> I don't understand what you are talking about here.  The tempco
> difference between modes is unrelated to load capacitance.  The
> dual mode idea would work just as well if the oscillators
> operated at series resonance.

The circuit that Stan Shadowski presented is a fundamental / third overtone 
dual. The example
below is based on that circuit. 

Let’s say both modes are running into a 32 pf load and it is a single 
capacitor. 

The capacitor changes due to aging by 1 pf, you now are at 33 pf load.

The fundamental changes frequency ~ 3X as much (in ppm) as the third overtone.

The beat frequency shifts since the two modes do not tune identically. 

Beat frequency shift = temperature error.

Yes the example is a little contrived. The real numbers would depend a bit on 
the design of
the crystal used. 

Bob


> 
> [I attended this talk in person ~25 years ago; it got a lot of
> interest].
> 
> The reason why the SC cut mode C and mode B dual mode patent
> from HP fell out of favor was the problem with activity dips
> in mode B.  Otherwise, it was a great idea.  It would still
> be fine for an OCXO, where you just avoid activity dips.
> However, the circuit design is very complicated.
> 
> Rick N6RK

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[time-nuts] TruePosition --> Skyhook!

[Gregory Beat]

On February 19, 2014, TruePosition (a Liberty Media company) of Berwyn, PA 
bought Skyhook of Boston, MA.
http://www.vcpost.com/articles/21778/20140220/us-wireless-location-firm-trueposition-buys-skyhook-wireless.htm

Combining their expertise and experience, 
they are now operating under the Skyhook brand name.
---
Regarding information on these True Position GPS / 10 MHz boards.
William Townsend worked there for 16 years, last position as Director of 
Embedded Software and Hardware Development.
https://www.linkedin.com/in/williamtownsendbsee/





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Re: [time-nuts] MCXO and dual mode

[Richard (Rick) Karlquist]

On 6/6/2017 3:16 PM, Bob kb8tq wrote:

Hi

If you do the classic MCXO with two oscillator circuits and one resonator, the 
issue is
pretty simple. You have a load capacitance on the fundamental. You have a load 
capacitance
on the third overtone. Even if it is the exact same capacitor, the tuning 
sensitivity on
the fundamental is different than the sensitivity on the third overtone. As the 
load impedance
changes (parts do drift) the delta between the two modes will show up as an 
offset between
them. If you run through the math, it gives you a delta temperature. How much? 
How fast? Obviously
that depends. When I brought this up at the time with the authors of the paper, 
the reply was that
a recalibration of the MCXO was provided for for this reason.

Bob



I don't understand what you are talking about here.  The tempco
difference between modes is unrelated to load capacitance.  The
dual mode idea would work just as well if the oscillators
operated at series resonance.

[I attended this talk in person ~25 years ago; it got a lot of
interest].

The reason why the SC cut mode C and mode B dual mode patent
from HP fell out of favor was the problem with activity dips
in mode B.  Otherwise, it was a great idea.  It would still
be fine for an OCXO, where you just avoid activity dips.
However, the circuit design is very complicated.

Rick N6RK
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Re: [time-nuts] Poor man's oven

[Richard (Rick) Karlquist]

On Jun 6, 2017, at 7:10 PM, Chris Albertson  wrote:


There are more sophisticated control loop designs that can handle this
better, eg by using two temperature sensors, one at the crystal and
one at the heater. But designing them correctly is more difficult
than the normal PID loop.



In the E1938A oscillator, we used a PIDI^2 loop.  IOW, a PID
plus a double integrator.  This was Len Cutler's idea.
Once the constants were dialed in, this worked phenomenally
well in terms of transient response.  Even dumping in liquid
nitrogen full throttle into the environmental test chamber
barely wiggled the crystal temperature/frequency.

Rick N6RK
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[time-nuts] Fwd: Temperature sensors and quartz crystals (was: HP5061B Versus HP5071 Cesium Line Frequencies)

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/105566.html

I said that thermistors have been obsolete for 40 years not
themocouples. (With a FEW rare exceptions)  I do not consider platinum
wire to be a thermistor.  I own a 100 Ω platinum wire thermometer for
the DVM in my 2236 Tekronix.  It is not worth much without a Kelvin
connection.  From 0° C to to 100° C it changes 40 Ω and uses banana
plugs.  Those are unstable by ~ 0.2Ω.  This is 0.5° C of error and
intermittent.  It is worthless for designing ovens.

I use thermocouples in my Fluke 52 stereo thermometers all the time.
They will work at nearly red heat and are stable.  They are hard to
use because they only produce 40 μV/C° and require a cold junction
comparison.  The cold junction is easily calibrated by an ice bath
however.  Thermistors depend on the cauldron in which they were
stirred by the witches at manufacture.

In the range of -55° C to 150° C, I don't think anything can match the
AD590 or equivalent for repeatability, accuracy, stability, linearity
or convenience.  They are not affected by lead resistance and can use
tiny wires. It will tolerate 3,000 Ω of lead resistance and can be
multiplexed. The chip itself is 52 mils by 42 mils or comparable to a
thermocouple bead.  I figured out that two of them can be driven back
to back by a square wave and two temperatures monitored at once with
the same pair of wires.  An Analog Devices product engineer split a
$100 prize with me for my invention.

πθ°μΩω±√·Γλ
WB0KV

-- Forwarded message --
From: Attila Kinali 
Date: Sun, Jun 4, 2017 at 4:59 PM
Subject: [time-nuts] Temperature sensors and quartz crystals (was:
HP5061B Versus HP5071 Cesium Line Frequencies)
To: Discussion of precise time and frequency measurement 

Moin,

This discussion is kind of getting heated.
Let's put some facts in, to steer it away from
opinion based discussion.

On Sun, 4 Jun 2017 08:44:33 -0700
"Donald E. Pauly"  wrote:

> I stand by my remark that thermistors have been obsolete for over 40
> years.  The only exception that I know of is cesium beam tubes that
> must withstand a 350° C bakeout.  Thermistors are unstable and
> manufactured with a witches brew straight out of MacBeth.  Their
> output voltages are tiny and are they inconvenient to use at different
> temperatures.

If you really mean thermistors, and not, as Bob suggested thermocouples,
then I have to disagree. The most stable temperature sensors are
platinum wire sensors. The standards class PRT's are the gold standard
when it comes to temperature measurement, for a quite wide range
(-260°C to +960°C) and are considered very stable. They offer (absolute)
accuracies in the order of 10mK in the temperature range below 400°C.
Even industrial grade PRT sensors give you an absolute accuracy better
than 0.1K up to 200-300°C. The "cheap" PT100 are more of the order of 1-10°C
accuracy... all numbers just using a two-point calibration.

For more information on this see [1] chapter 6 and [2] for industrial sensors.

NTC sensors have a higher variablity of their parameters in production
and are usually specified in % of temperature relative to their reference
point, which is usually 25°C. Typical values are 0.1% to 5%. Additionally
there is a deviation from the reference point, specified in °C, which
is usually in the order of 0.1°C to 1°C.

The NTC sensors are less accurate than PT sensors, but offer the advantage
of higher resistance (thus lower self-heating), higher slope (thus better
precision). Biggest disadvantage is their non-linear curve. Their price
is also a fraction of PT sensors and due to that you can have them in
many different forms, from the 0201 SMD resistor, to a large stainless
steal pipe that goes into a chemical tank. NTCs are the workhorse in
todays temperature measurement and control designs.

The next category are band-gap sensors like the AD590. Their biggest
advantage is that their 0 point is fix at 0K (and very accurately so).
Ie they can be used with single point calibration and achieve 1°C accuracy
this way. Their biggest drawback their large thermal mass and large
insulating case, because they are basically an standard, analog IC.
Ie their main use is in devices where there is a lot of convection and
slow temperature change. Due to their simple and and quite linear
characteristics, they are often used in purely analog temperature
control circuits, or where a linearization is not feasible.
But only if price isn't an issue (they cost 10-1000 times as
much as an PTC). Their biggest disadvantage, beside their slow
thermal raction time, is their large noise uncorrelated to the
supply voltage, and thus cannot be compensated by ratiometric measurement.
They are also more suceptible to mechanical stress than NTC's and PT's,
due to their construction. Similar to voltage references (which they
actually are), their aging is quite substantial and cannot be neglected
in 

Re: [time-nuts] HP8640

[KA2WEU--- via time-nuts]

yes, I need it for about 1 day.. Thanks, Ulrich 1UL
 
 
In a message dated 6/6/2017 9:37:35 P.M. Eastern Daylight Time,  
brent.ev...@gmail.com writes:

Seems a bit sacrilegious no?  


Just kidding - wish I had another myself..


Brent
KD4VMM


On Tue, Jun 6, 2017 at 9:05 PM, KA2WEU--- via time-nuts  
<_time-nuts@febo.com_ (mailto:time-nuts@febo.com) > wrote:

Hi  , I am trying to find an well working  HP 8640 to do some   measurements
like SSB  FM and AM noise.

Who can help ?   73 de Ulrich  N1UL
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Re: [time-nuts] HP8640

[Brent]

Seems a bit sacrilegious no?

Just kidding - wish I had another myself..

Brent
KD4VMM

On Tue, Jun 6, 2017 at 9:05 PM, KA2WEU--- via time-nuts 
wrote:

> Hi , I am trying to find an well working  HP 8640 to do some  measurements
> like SSB  FM and AM noise.
>
> Who can help ?  73 de Ulrich N1UL
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Re: [time-nuts] HP8640

[KA2WEU--- via time-nuts]

Hi , I am trying to find an well working  HP 8640 to do some  measurements 
like SSB  FM and AM noise.
 
Who can help ?  73 de Ulrich N1UL 
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Re: [time-nuts] TruePosition on the Arduino

[Hal Murray]

kb...@n1k.org said:
> Calibrating your GPS pulse ambiguity is one of the all time great reasons to
> get a WWVB based wall clock !!!

What makes you so sure they won't have the same sort of next/previous bug?


-- 
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Re: [time-nuts] TruePosition on the Arduino

[Bob kb8tq]

Hi

Calibrating your GPS pulse ambiguity is one of the all time great reasons to 
get a
WWVB based wall clock !!!

Bob

> On Jun 6, 2017, at 8:38 PM, Graham / KE9H  wrote:
> 
> Ben:
> 
> Be careful.
> 
> Most GPS receivers send out the serial message after the tick, that tells
> you what the time of the tick was.
> 
> Read the manual.
> 
> If you want to drive a clock display with a GPS, you pretty much have to
> have an independent time system that advances on the tick, then validate it
> when the serial message shows up.
> 
> --- Graham / KE9H
> 
> ==
> 
> On Tue, Jun 6, 2017 at 6:46 PM, Ben Hall  wrote:
> 
>> Good evening all,
>> 
>> There is a saying: "a man with one watch knows the time, a man with two is
>> never sure."  Clearly, this man wasn't a timenut and didn't have GPS.  ;)
>> 
>> I've been working on the Arduino code for the TruePosition boards that
>> quite a few of us have bought from the e-place.
>> 
>> It's my first real foray into both Arduino and the C language.  (About a
>> million years ago I was reasonably competent with FORTRAN...the 1977
>> version...)  It's mostly working - I can receive and display pretty much
>> everything that comes out of the unit minus a few parameters.  I can
>> display it all on three pages on a 4 line by 20 character I2C display.
>> Currently, the pages are selected by grounding out one of two pins, or
>> having nothing grounded.  Eventually, I'm going to change this so that it
>> changes display pages when a button is pressed.  I don't have lat/long
>> display yet, nor can I handle doing a survey, but those are coming.
>> 
>> My code probably would make a real programmer vomit, but hey, it works.  :)
>> 
>> Back to the man with multiple watches.  I was having a very frustrating
>> issue with my TruePosition and Arduino code being one second behind my
>> other sources of time.  I went round and round, trying to figure out why
>> the TruePosition thru the Arduino was a second slow.  In the end, it turns
>> out that it wasn't slow...it was correct...but that my other sources of
>> time have errors.
>> 
>> I finally proved this to myself by firing up an old Trimble Lassen LP GPS
>> board unit equipped with a 1PPS tick light and serial output...and it was
>> clear that it matched the TruePosition after correcting for the fact that
>> my TruePosition / Arduino code only updates the display when 1PPS is
>> asserted high...but that the Lassen LP displays the serial message before
>> it becomes valid at the next 1PPS tick.
>> 
>> I was slightly embarrassed...I should have known that the other sources of
>> time all had sources of error beyond my control.  I should have trusted the
>> TruePosition as being the purest, least complicated, and the path I knew
>> the most about between GPS and my eyeballs.
>> 
>> So for a while...the statement was true.  With my multiple sources of
>> time...I really didn't know the time.  But it was also untrue, as when I
>> got agreement between two very "pure" sources of time, I knew everything
>> else was wrong.  ;)
>> 
>> I'm getting to the point that once I've got the button logic working, I'll
>> send out my source to anyone who wants to take a look at it or use it.  I
>> will stipulate one condition - you can't make too much fun of how poorly
>> programmed it is.  ;)
>> 
>> thanks much and 73,
>> ben, kd5byb
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Re: [time-nuts] Poor man's oven

[Bob kb8tq]

Hi

The Freescale ADC’s are pretty good compared to a lot of other MCU ADC’s. They 
still are not as good as you might 
think from the audio ENOB numbers. Something in the 10~11 bit range is doing 
quite well at DC in a control loop, even for them. 

Bob

> On Jun 6, 2017, at 8:12 PM, jimlux  wrote:
> 
> On 6/6/17 1:37 PM, Bob kb8tq wrote:
>> Hi
>> 
>> Often when you dig into the details of MCU ADC’s they have a little note 
>> “optimized for audio” or
>> “not recommended for control loops”. It can be a bit of a head scratcher to 
>> work out what they are
>> getting at. The big issues in this case seem to be DC leakage and 1/F noise. 
>> Yes, they do sort of go hand in hand :)
>> You need to be willing to check out the ENOB at DC in order to use them 
>> effectively in a simple
>> OCXO setup. That or be willing to flip the bridge ends on demand and try to 
>> cancel out the issues.
>> Unfortunately that adds both complexity and a string of other fun and games.
>> 
> 
> This one seems to be designed specifically for this kind of DC measurement, 
> sure, it will sample at 100kHz, but not with the amplifier and averaging and 
> such.
> 
> Its based on the Freescale (now NXP, I guess..) Kinetis K20 series
> 
> It has a bewildering variety of peripherals (touch sensors, etc.), as well as 
> the usual multiple UARTs, SPI, I2C, timers, counters, etc. What's nice is 
> that PJRC (who make the teensy series) have written all the drivers and 
> libraries to integrate into the Arduino environment for those that don't live 
> for decoding the 1000 page processor family manual and 600 page package 
> specific manuals that give the specific pinouts and options on the one YOU 
> have in front of you.  Your "time to first light" is much shorter. And then 
> you can hack away.
> 
> I think this is more a chip designed for embedded controllers and the like. I 
> don't know if it has the processor and peripherals to do, say, 3 phase 
> induction motor control or Ultrasound processing, but it might.
> 
> The Atmel processors are nice (and you can actually get one of the Arduino 
> flavor ones in a rad hard version.. for those "control the device in the 
> beamline" applications), but the Kinetis are easily an order of magnitude 
> better - no bit banging to do serial protocols, USB built in, decent ADC, 
> floating point, etc.
> 
> 
> 
> 
>> Op amps are cheap ….
>> 
>> Bob
>> 
>>> On Jun 6, 2017, at 3:54 PM, jimlux  wrote:
>>> 
>>> On 6/6/17 11:47 AM, Chris Albertson wrote:
 Yes, as I wrote.  I would not mess with AREF.  At most you can only get a
 multiplication about 4.   Use an op-amp.   Signal conditioning really
 almost alway is required in the analog domain before any A/D conversion
 
 Also like the uP is not inside the oven and has a cable of some length so
 you'd want a buffered analog signal on the cable, the op-amp can do that
 to.
 
 Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12
 bits as compared to the arduino which has 10 bits
>>> 
>>> 
>>> or use a Teensy with a 16 bit differential input ADC.  Arduino compatible, 
>>> cheaper, yeah, you probably get 13 bits real performance from the ADC.  
>>> Also has a real analog output (not PWM and a LPF) if you need that.
>>> 
>>> Programmable gain, sample averaging in hardware, etc.   Not bad for <$20.
>>> 
>>> 
 
 
>>> 
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>> 
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Re: [time-nuts] TruePosition on the Arduino

[Gregory Beat]

Ben -
I assume that you never received the Arduino "C code" 
written by Bruce, WA3YUE for the original project?

Club's Powerpoint presentation indicated that source code was available.
http://www.packratvhf.com/techinal.htm

Packrat GPS Project (Gary, WA2OMY; Bruce, WA3YUE; George, KA3WXV) with 
TruePosition GPSDO and Arduino
by The Mt. Airy VHF Radio Club "Pack Rats" (Southampton, PA).
http://www.qsl.net/wa2omy/A%20Packrat%20GPS%20Receiver%20Project.pdf

greg, w9gb
==
> original message / digest <
I'm getting to the point that once I've got the button logic working, I'll send 
out my source to anyone who wants to take a look at it or use it.  
I will stipulate one condition - you can't make too much fun of how poorly 
programmed it is.  ;)
thanks much and 73,
ben, kd5byb
==
Sent from iPad Air
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Re: [time-nuts] TruePosition on the Arduino

[Graham / KE9H]

Ben:

Be careful.

Most GPS receivers send out the serial message after the tick, that tells
you what the time of the tick was.

Read the manual.

If you want to drive a clock display with a GPS, you pretty much have to
have an independent time system that advances on the tick, then validate it
when the serial message shows up.

--- Graham / KE9H

==

On Tue, Jun 6, 2017 at 6:46 PM, Ben Hall  wrote:

> Good evening all,
>
> There is a saying: "a man with one watch knows the time, a man with two is
> never sure."  Clearly, this man wasn't a timenut and didn't have GPS.  ;)
>
> I've been working on the Arduino code for the TruePosition boards that
> quite a few of us have bought from the e-place.
>
> It's my first real foray into both Arduino and the C language.  (About a
> million years ago I was reasonably competent with FORTRAN...the 1977
> version...)  It's mostly working - I can receive and display pretty much
> everything that comes out of the unit minus a few parameters.  I can
> display it all on three pages on a 4 line by 20 character I2C display.
> Currently, the pages are selected by grounding out one of two pins, or
> having nothing grounded.  Eventually, I'm going to change this so that it
> changes display pages when a button is pressed.  I don't have lat/long
> display yet, nor can I handle doing a survey, but those are coming.
>
> My code probably would make a real programmer vomit, but hey, it works.  :)
>
> Back to the man with multiple watches.  I was having a very frustrating
> issue with my TruePosition and Arduino code being one second behind my
> other sources of time.  I went round and round, trying to figure out why
> the TruePosition thru the Arduino was a second slow.  In the end, it turns
> out that it wasn't slow...it was correct...but that my other sources of
> time have errors.
>
> I finally proved this to myself by firing up an old Trimble Lassen LP GPS
> board unit equipped with a 1PPS tick light and serial output...and it was
> clear that it matched the TruePosition after correcting for the fact that
> my TruePosition / Arduino code only updates the display when 1PPS is
> asserted high...but that the Lassen LP displays the serial message before
> it becomes valid at the next 1PPS tick.
>
> I was slightly embarrassed...I should have known that the other sources of
> time all had sources of error beyond my control.  I should have trusted the
> TruePosition as being the purest, least complicated, and the path I knew
> the most about between GPS and my eyeballs.
>
> So for a while...the statement was true.  With my multiple sources of
> time...I really didn't know the time.  But it was also untrue, as when I
> got agreement between two very "pure" sources of time, I knew everything
> else was wrong.  ;)
>
> I'm getting to the point that once I've got the button logic working, I'll
> send out my source to anyone who wants to take a look at it or use it.  I
> will stipulate one condition - you can't make too much fun of how poorly
> programmed it is.  ;)
>
> thanks much and 73,
> ben, kd5byb
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Re: [time-nuts] Poor man's oven

[jimlux]

On 6/6/17 1:37 PM, Bob kb8tq wrote:

Hi

Often when you dig into the details of MCU ADC’s they have a little note 
“optimized for audio” or
“not recommended for control loops”. It can be a bit of a head scratcher to 
work out what they are
getting at. The big issues in this case seem to be DC leakage and 1/F noise. 
Yes, they do sort of go hand in hand :)
You need to be willing to check out the ENOB at DC in order to use them 
effectively in a simple
OCXO setup. That or be willing to flip the bridge ends on demand and try to 
cancel out the issues.
Unfortunately that adds both complexity and a string of other fun and games.



This one seems to be designed specifically for this kind of DC 
measurement, sure, it will sample at 100kHz, but not with the amplifier 
and averaging and such.


Its based on the Freescale (now NXP, I guess..) Kinetis K20 series

It has a bewildering variety of peripherals (touch sensors, etc.), as 
well as the usual multiple UARTs, SPI, I2C, timers, counters, etc. 
What's nice is that PJRC (who make the teensy series) have written all 
the drivers and libraries to integrate into the Arduino environment for 
those that don't live for decoding the 1000 page processor family manual 
and 600 page package specific manuals that give the specific pinouts and 
options on the one YOU have in front of you.  Your "time to first light" 
is much shorter. And then you can hack away.


I think this is more a chip designed for embedded controllers and the 
like. I don't know if it has the processor and peripherals to do, say, 3 
phase induction motor control or Ultrasound processing, but it might.


The Atmel processors are nice (and you can actually get one of the 
Arduino flavor ones in a rad hard version.. for those "control the 
device in the beamline" applications), but the Kinetis are easily an 
order of magnitude better - no bit banging to do serial protocols, USB 
built in, decent ADC, floating point, etc.






Op amps are cheap ….

Bob


On Jun 6, 2017, at 3:54 PM, jimlux  wrote:

On 6/6/17 11:47 AM, Chris Albertson wrote:

Yes, as I wrote.  I would not mess with AREF.  At most you can only get a
multiplication about 4.   Use an op-amp.   Signal conditioning really
almost alway is required in the analog domain before any A/D conversion

Also like the uP is not inside the oven and has a cable of some length so
you'd want a buffered analog signal on the cable, the op-amp can do that
to.

Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12
bits as compared to the arduino which has 10 bits



or use a Teensy with a 16 bit differential input ADC.  Arduino compatible, 
cheaper, yeah, you probably get 13 bits real performance from the ADC.  Also 
has a real analog output (not PWM and a LPF) if you need that.

Programmable gain, sample averaging in hardware, etc.   Not bad for <$20.







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[time-nuts] TruePosition on the Arduino

[Ben Hall]

Good evening all,

There is a saying: "a man with one watch knows the time, a man with two 
is never sure."  Clearly, this man wasn't a timenut and didn't have GPS.  ;)


I've been working on the Arduino code for the TruePosition boards that 
quite a few of us have bought from the e-place.


It's my first real foray into both Arduino and the C language.  (About a 
million years ago I was reasonably competent with FORTRAN...the 1977 
version...)  It's mostly working - I can receive and display pretty much 
everything that comes out of the unit minus a few parameters.  I can 
display it all on three pages on a 4 line by 20 character I2C display. 
Currently, the pages are selected by grounding out one of two pins, or 
having nothing grounded.  Eventually, I'm going to change this so that 
it changes display pages when a button is pressed.  I don't have 
lat/long display yet, nor can I handle doing a survey, but those are coming.


My code probably would make a real programmer vomit, but hey, it works.  :)

Back to the man with multiple watches.  I was having a very frustrating 
issue with my TruePosition and Arduino code being one second behind my 
other sources of time.  I went round and round, trying to figure out why 
the TruePosition thru the Arduino was a second slow.  In the end, it 
turns out that it wasn't slow...it was correct...but that my other 
sources of time have errors.


I finally proved this to myself by firing up an old Trimble Lassen LP 
GPS board unit equipped with a 1PPS tick light and serial output...and 
it was clear that it matched the TruePosition after correcting for the 
fact that my TruePosition / Arduino code only updates the display when 
1PPS is asserted high...but that the Lassen LP displays the serial 
message before it becomes valid at the next 1PPS tick.


I was slightly embarrassed...I should have known that the other sources 
of time all had sources of error beyond my control.  I should have 
trusted the TruePosition as being the purest, least complicated, and the 
path I knew the most about between GPS and my eyeballs.


So for a while...the statement was true.  With my multiple sources of 
time...I really didn't know the time.  But it was also untrue, as when I 
got agreement between two very "pure" sources of time, I knew everything 
else was wrong.  ;)


I'm getting to the point that once I've got the button logic working, 
I'll send out my source to anyone who wants to take a look at it or use 
it.  I will stipulate one condition - you can't make too much fun of how 
poorly programmed it is.  ;)


thanks much and 73,
ben, kd5byb
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Re: [time-nuts] Poor man's oven

[Bob kb8tq]

Hi

In the case of a second sensor, “at the crystal” effectively means “inside the 
crystal package”. 
That heads you into all sorts of “interesting” problems. Better to just read 
the papers and do
it the “old fashioned” way.

Bob

> On Jun 6, 2017, at 7:10 PM, Chris Albertson  wrote:
> 
>> There are more sophisticated control loop designs that can handle this
>> better, eg by using two temperature sensors, one at the crystal and
>> one at the heater. But designing them correctly is more difficult
>> than the normal PID loop.
>> 
> 
> Keeping with the thread topic, I think this is the key.For the cost of
> only one more cheap sensor you gain a lot.   Harder design as you say but
> getting help on-line seems to be free.
> 
> I have gotten PID to work myself with linear systems (motor speed) and I
> reading up on Kalman Filters as I need them for navigation using multiple
> sensors.
> 
> I guess one could use the crystal frequency as a measure of its temperature
> to tune the system.  Is there a name to Google to read up on using two
> sensors and a pid-like algorithm?
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] uC ADC resolution (was: Poor man's oven)

[Bob kb8tq]

Hi

You can only get back bits to the degree that the problems are caused by noise. 
If it is 1/F noise, averaging over long periods is going to be really tough.

Bob

> On Jun 6, 2017, at 7:43 PM, Chris Albertson  wrote:
> 
> On Tue, Jun 6, 2017 at 2:17 PM, Attila Kinali  wrote:
> 
>> On Tue, 6 Jun 2017 16:37:27 -0400
>> Bob kb8tq  wrote:
>> 
> 
> 
> 
>> . Heck, the STM32F4xx have so much internal noise that the ENOB
>> of their ADC is below 6bit... so low that they even had to write an
>> appnote on how to do averaging to get back to the 12 bits the ADC is
>> spec'ed for. (but don't mention that to an ST sales person, they will
>> hate your guts afterwards).
>> 
> 
> Can you actually get back all of those bits?   How many samples would you
> need?   My current use case for the STM32 ADC is to track battery voltage
> and maybe 6 bits is enough but if I can get to 12 with a software-only fix
> I'll take it.  Batteries volts charge slowly so I'd have time to take many
> samples.   It's a rather mundane application.  Controlling a battery
> powered motor and I can't let theLiPo battery dichange below a limit so I'm
> sampling voltage at 1Hz.   Got a link to or the name of the app note?
> 
>> 
>> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] uC ADC resolution (was: Poor man's oven)

[Chris Albertson]

On Tue, Jun 6, 2017 at 2:17 PM, Attila Kinali  wrote:

> On Tue, 6 Jun 2017 16:37:27 -0400
> Bob kb8tq  wrote:
>



> . Heck, the STM32F4xx have so much internal noise that the ENOB
> of their ADC is below 6bit... so low that they even had to write an
> appnote on how to do averaging to get back to the 12 bits the ADC is
> spec'ed for. (but don't mention that to an ST sales person, they will
> hate your guts afterwards).
>

Can you actually get back all of those bits?   How many samples would you
need?   My current use case for the STM32 ADC is to track battery voltage
and maybe 6 bits is enough but if I can get to 12 with a software-only fix
I'll take it.  Batteries volts charge slowly so I'd have time to take many
samples.   It's a rather mundane application.  Controlling a battery
powered motor and I can't let theLiPo battery dichange below a limit so I'm
sampling voltage at 1Hz.   Got a link to or the name of the app note?

>
>
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Poor man's oven

[Chris Albertson]

> There are more sophisticated control loop designs that can handle this
> better, eg by using two temperature sensors, one at the crystal and
> one at the heater. But designing them correctly is more difficult
> than the normal PID loop.
>

Keeping with the thread topic, I think this is the key.For the cost of
only one more cheap sensor you gain a lot.   Harder design as you say but
getting help on-line seems to be free.

I have gotten PID to work myself with linear systems (motor speed) and I
reading up on Kalman Filters as I need them for navigation using multiple
sensors.

I guess one could use the crystal frequency as a measure of its temperature
to tune the system.  Is there a name to Google to read up on using two
sensors and a pid-like algorithm?
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] MCXO and dual mode (was: Poor man's oven)

[Bob kb8tq]

Hi

If you do the classic MCXO with two oscillator circuits and one resonator, the 
issue is 
pretty simple. You have a load capacitance on the fundamental. You have a load 
capacitance
on the third overtone. Even if it is the exact same capacitor, the tuning 
sensitivity on
the fundamental is different than the sensitivity on the third overtone. As the 
load impedance 
changes (parts do drift) the delta between the two modes will show up as an 
offset between
them. If you run through the math, it gives you a delta temperature. How much? 
How fast? Obviously
that depends. When I brought this up at the time with the authors of the paper, 
the reply was that
a recalibration of the MCXO was provided for for this reason. 

Bob


> On Jun 6, 2017, at 5:40 PM, Attila Kinali  wrote:
> 
> On Mon, 5 Jun 2017 20:21:10 -0400
> Bob kb8tq  wrote:
> 
>> That paper is the basis for the MCXO. It is an interesting way to do a TCXO. 
>> The drift between the two modes makes it a difficult thing to master in an 
>> OCXO.
>> Plating a pair of electrodes (one pair per mode) is also an approach that 
>> has been
>> tried. 
> 
> That's the first time I hear of modes drifting respective to eachother.
> Do you have any references I could read on this?
> 
> I always wondered why the MCXO approach was not used more often.
> Or why none of the OCXOs used a dual mode approach to sense
> the temperature of the crystal directly instead of using a
> thermistor. 
> 
>   Attila Kinali
> -- 
> You know, the very powerful and the very stupid have one thing in common.
> They don't alters their views to fit the facts, they alter the facts to
> fit the views, which can be uncomfortable if you happen to be one of the
> facts that needs altering.  -- The Doctor
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[time-nuts] MCXO and dual mode (was: Poor man's oven)

[Attila Kinali]

On Mon, 5 Jun 2017 20:21:10 -0400
Bob kb8tq  wrote:

> That paper is the basis for the MCXO. It is an interesting way to do a TCXO. 
> The drift between the two modes makes it a difficult thing to master in an 
> OCXO.
> Plating a pair of electrodes (one pair per mode) is also an approach that has 
> been
> tried. 

That's the first time I hear of modes drifting respective to eachother.
Do you have any references I could read on this?

I always wondered why the MCXO approach was not used more often.
Or why none of the OCXOs used a dual mode approach to sense
the temperature of the crystal directly instead of using a
thermistor. 

Attila Kinali
-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] Poor man's oven

[Attila Kinali]

On Tue, 6 Jun 2017 11:00:57 -0700
Chris Albertson  wrote:

> >
> > 1) You want the control loop as stable as possible
> > 2) Stability is directly related to controllability
> > 3) The larger the heat flow, the better the controllability
> > 4) therefore the outside temperature should be as low as possible
> 
> 
> I think you are correct but within reason of course.   It is easy to see
> that the extremes can't work. If the internal set point is very close to
> ambient the oven is uncontrollable.  because you only use the first bit of
> the DAC to control the heater and after a few seconds you have overshoot.

You are looking at one minor issue here. Of course, if your control loop
is only of the bang-bang kind, then you will have a hard time to keep
the system parameter stable. But that is easy to deal with if one knows
the overall system.

I was talking about the control therotical "controllability":
https://en.wikipedia.org/wiki/Controllability

For a simple system like an OCXO that is mostly dependent on
thermal mass vs thermal flow (both in and out) which translates
into "delay" between the heating element and the temperature sensor.
A lot of people assume that adding more thermal mass is going to make
the control more stable. But in reality this might make it unstable
(aka cause oscillations) or make the control error larger.
What happens here is that the mass takes time to heat up. During heat
up you can describe it like a (very slow) transmission line. It will
take time until the signal (heat) reaches the other end (center of the mass).
When the heat reaches the sensor, the control electronics will dial the heater
down. But there is still a heatwave traveling inwards, ie the core will get
warmer and warmer. Thus the heater will be dialed down more and more until
it doesn't heat enough. This will cause a cold wave traveling inwards..

Having a larger thermal flow vs mass helps against this problem.
Good thermal conductivity between heater and sensor helps as well.
(that's why you will read often, that the sensor should be placed
close to the heater and not to the quartz)

> The PID algorithm needs something that is slow to change
> compared to the control loop cycle.  So you want a good size thermal mass
> compared to the amount of heat.

The control loop does not need something slow to change. You need to
factor the termal mass, its insulation etc into PID parameters so you
get a stable loop. As I have shown above, if this is not correctly done
you will get oscilations. One way to avoid them, if your physical system
is fixed, is to lower the loop bandwith and thus make the system respond
much slower to changes than the time it takes to conduct the heat from
the heater to the sensor. But this means also that the control loop will
be slow to react to changes in the environment.

There are more sophisticated control loop designs that can handle this
better, eg by using two temperature sensors, one at the crystal and
one at the heater. But designing them correctly is more difficult
than the normal PID loop. 


Attila Kinali

-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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[time-nuts] uC ADC resolution (was: Poor man's oven)

[Attila Kinali]

On Tue, 6 Jun 2017 16:37:27 -0400
Bob kb8tq  wrote:

> Often when you dig into the details of MCU ADC’s they have a little note 
> “optimized for audio” or 
> “not recommended for control loops”. It can be a bit of a head scratcher to 
> work out what they are
> getting at. The big issues in this case seem to be DC leakage and 1/F noise. 
> Yes, they do sort of go hand in hand :)
> You need to be willing to check out the ENOB at DC in order to use them 
> effectively in a simple 
> OCXO setup. That or be willing to flip the bridge ends on demand and try to 
> cancel out the issues. 
> Unfortunately that adds both complexity and a string of other fun and games.

uC ADCs are only good for low resolution, slow signals. For anything else
you need an external ADC. Even if your uC datasheet claims that you have
a 12bit ADC, the reality is quite different. For one, these ADCs are not
well specified, the surounding digital logic has a profound effect that
changes dramatically depending on what other periphery you use or not.

You can always just subtract two bits of the ADCs resolution and you
wouldn't be wrong. Losing 3 bits to internal noise isn't unehard of
either. Heck, the STM32F4xx have so much internal noise that the ENOB
of their ADC is below 6bit... so low that they even had to write an
appnote on how to do averaging to get back to the 12 bits the ADC is
spec'ed for. (but don't mention that to an ST sales person, they will
hate your guts afterwards). 

Rule of thumb: If you need your ADC DC stable, more than 8bit resolution,
or more than 10-1000 samples per second: use an external ADC.

Attila Kinali

-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] Poor man's oven

[Bob kb8tq]

Hi

Often when you dig into the details of MCU ADC’s they have a little note 
“optimized for audio” or 
“not recommended for control loops”. It can be a bit of a head scratcher to 
work out what they are
getting at. The big issues in this case seem to be DC leakage and 1/F noise. 
Yes, they do sort of go hand in hand :)
You need to be willing to check out the ENOB at DC in order to use them 
effectively in a simple 
OCXO setup. That or be willing to flip the bridge ends on demand and try to 
cancel out the issues. 
Unfortunately that adds both complexity and a string of other fun and games. 

Op amps are cheap ….

Bob

> On Jun 6, 2017, at 3:54 PM, jimlux  wrote:
> 
> On 6/6/17 11:47 AM, Chris Albertson wrote:
>> Yes, as I wrote.  I would not mess with AREF.  At most you can only get a
>> multiplication about 4.   Use an op-amp.   Signal conditioning really
>> almost alway is required in the analog domain before any A/D conversion
>> 
>> Also like the uP is not inside the oven and has a cable of some length so
>> you'd want a buffered analog signal on the cable, the op-amp can do that
>> to.
>> 
>> Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12
>> bits as compared to the arduino which has 10 bits
> 
> 
> or use a Teensy with a 16 bit differential input ADC.  Arduino compatible, 
> cheaper, yeah, you probably get 13 bits real performance from the ADC.  Also 
> has a real analog output (not PWM and a LPF) if you need that.
> 
> Programmable gain, sample averaging in hardware, etc.   Not bad for <$20.
> 
> 
>> 
>> 
> 
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Re: [time-nuts] Poor man's oven

[jimlux]

On 6/6/17 11:47 AM, Chris Albertson wrote:

Yes, as I wrote.  I would not mess with AREF.  At most you can only get a
multiplication about 4.   Use an op-amp.   Signal conditioning really
almost alway is required in the analog domain before any A/D conversion

Also like the uP is not inside the oven and has a cable of some length so
you'd want a buffered analog signal on the cable, the op-amp can do that
to.

Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12
bits as compared to the arduino which has 10 bits



or use a Teensy with a 16 bit differential input ADC.  Arduino 
compatible, cheaper, yeah, you probably get 13 bits real performance 
from the ADC.  Also has a real analog output (not PWM and a LPF) if you 
need that.


Programmable gain, sample averaging in hardware, etc.   Not bad for <$20.







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Re: [time-nuts] Poor man's oven

[Poul-Henning Kamp]

In message 
, Chris Albertson writes:

>The next step up the complexity scale would have you place an I2C
>interlaced ADC inside your oven.  These don't cost much and have several
>ADC channels.

ISOtemp made a version of their OCXO-107 which a built in DAC, but
I've been told the result was less than stellar.

When you do stuff like that, you need to pay a lot of attention to noise.

Personally I would avoid I2C, in preference for SPI to avoid the
sharp flanks required by I2C.

I would also run the SPI as slow as I possibly could and put low-pass
filter the digital signals at the boundary.

SRS uses an interesting trick in several of their instruments, where
they shut down parts or even all of the digital circuits when not
needed, see for instance their digital "all analog" lock-in amplifier.

-- 
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] Poor man's oven

[Hal Murray]

csteinm...@yandex.com said:
> It depends on what you mean by "best."  "Best" can mean "minimizes the
> wander in oven-regulated temperature at a constant (or slowly-changing)
> ambient temperature," or it can mean "fastest recovery when the ambient
> temperature changes more rapidly." 

I think it also depends on whether you are using an existing system or get to 
tweak the design to take advantage of the new rules.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Poor man's oven

[Chris Albertson]

Yes, as I wrote.  I would not mess with AREF.  At most you can only get a
multiplication about 4.   Use an op-amp.   Signal conditioning really
almost alway is required in the analog domain before any A/D conversion

Also like the uP is not inside the oven and has a cable of some length so
you'd want a buffered analog signal on the cable, the op-amp can do that
to.

Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12
bits as compared to the arduino which has 10 bits

The next step up the complexity scale would have you place an I2C
interlaced ADC inside your oven.  These don't cost much and have several
ADC channels.  then your oven has full digital interface and a much higher
quality DAC.  But this adds another 2 or 3 dollars to the design.   Maybe
worth it as now all the analog stuff is inside a temperature stable metal
tin can. But you have to watch this feature-creep as you can drive up
cost with little to show for it.

Also I'd not want the analog stuff designed to work only with ADC built
into one specific development board.  The I2C serial interface is pretty
much universal

I'm thinking something like this:
http://www.ebay.com/itm/12-Bit-I2C-4-CH-ADS1115...

Notice that the chip has programmable gain, it can scale the input over a
small range before sampling.
For $2 it's still a "poor man's part and you do NOT need to make a PCB to
use it.

On Tue, Jun 6, 2017 at 10:08 AM, Jim Harman  wrote:

> On Tue, Jun 6, 2017 at 10:00 AM, Riley, Ian C CTR NSWC Philadelphia, 515 <
> ian.riley@navy.mil> wrote:
>
> > Is there a practical minimum for what voltage you can feed into AREF?
> >
>
> It is hard to find on the data sheet, but the minimum voltage for an
> Arduino's AREF is the internal analog reference voltage - 1.1V for the Uno,
> 2.56V for the Leonardo or Micro. The 32U4 chip in the Leo and Micro has
> options for differential analog input and gains of 10, 40, or 200 but they
> are not supported by the Arduino IDE - you have to set the internal
> registers directly to use them. Also the input amplifier is pretty slow.
>
>
> --
>
> --Jim Harman
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Poor man's oven

[Bob kb8tq]

Hi

As you point out, there really is no answer that is obviously better than all 
the others. 
If you keep the outside warm (say 40C) you will reduce the strain on the heater 
devices
and likely not degrade the MTBF of anything outside the OCXO by very much. 

Bob

> On Jun 6, 2017, at 7:26 AM, Poul-Henning Kamp  wrote:
> 
> 
> In message , Bob kb8tq writes:
> 
>> In an OCXO design, the gotcha
>> is matching the PTC oven temperature to the crystal turn. You can do that if
>> you have a substantial inventory of material and custom fab the oven after
>> the crystal is built. 
> 
> Bob, you of all people must be able to answer this:
> 
> OCXO's have specified temperature ranges for instance
> -40...+70°C for the heavy duty stuff.
> 
> But I cant imagine the ovens used are so perfect that they have the
> same regulation performance at all temperatures.
> 
> I can choose the exterior temperature, which I should prefer ?
> 
> Disregard aging of electronics and materials, we all know that
> stuff, what I'm interested in is at which exterior temperature
> OCXO ovens work best ?
> 
> -- 
> 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] Poor man's oven

[Richard (Rick) Karlquist]

On 6/6/2017 4:26 AM, Poul-Henning Kamp wrote:


But I cant imagine the ovens used are so perfect that they have the
same regulation performance at all temperatures.

I can choose the exterior temperature, which I should prefer ?

Disregard aging of electronics and materials, we all know that
stuff, what I'm interested in is at which exterior temperature
OCXO ovens work best ?



My experience has been that, while ovens may not be perfect,
they are inherently linear.  So the exterior temperature is
a don't care.

I extensively characterized the E1938A oven.  By adjusting
the ratio of heat to the top/bottom vs edge, I was able to
get the thermal gain into the millions.  At that point,
finally a modicum of non-linearity showed up and the thermal
gain varied with ambient temperature.  It might be 2 million
at the ambient where I adjusted it, and drop to 1.5 million
when well away from that temperature.  Or it might change
sign at some ambient.  (Yes, you can have negative thermal
gain).  You shouldn't need to worry about this for any ordinary oven.

Rick N6RK
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Re: [time-nuts] Poor man's oven

[Bob kb8tq]

Hi

For a variety of reasons, if you go the MCU ADC route, put an op amp in between 
the
thermistor bridge and the ADC. It takes care of a whole lot of issues. 

Bob

> On Jun 6, 2017, at 12:13 PM, Adrian Godwin  wrote:
> 
> The specs for the ADC are pretty vague : most of the errors are around 2
> LSB but all are quoted with vref at 4V. If you reduce vref (there's an
> internal option of 1.1V) you'll increase gain but some of those errors are
> going to stay physically the same. In general, I'd tend expect to get more
> precision but also more noise. Averaging may help a bit.
> 
> 
> On Tue, Jun 6, 2017 at 3:00 PM, Riley, Ian C CTR NSWC Philadelphia, 515 <
> ian.riley@navy.mil> wrote:
> 
>> Chris,
>> 
>>> The trick with using a uP and it's built-in A/D converters is scale.  You
>>> want the limited 10-bits of revolution to fall over the operating range
>>> which is very narrow, like 1C.   Anything outside of that is either 
>> or
>>>  and only seen at start-up.,  So at start up the the controller is on
>>> "bang-bang" mode then later you have milli-degree resolution over your 1C
>>> range.   Basically you are measuring noise. but your $2 uP can take
>> 100,000
>>> measurments per second and putt tour a digital filter.
>> 
>> I have seen but not used the AREF pins on Arduino and similar uPs; as you
>> lower AREF, do you lose any sort of accuracy? Is there a practical minimum
>> for what voltage you can feed into AREF?
>> 
>> -Ian R.
>> ___
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Re: [time-nuts] Poor man's oven

[Charles Steinmetz]

Poul-Henning wrote:


what I'm interested in is at which exterior temperature
OCXO ovens work best ?


Jim replied:


Here's my guess...
1) you want minimal gradients across the device for a variety of reasons
2) therefore you want least amount of heat from the heater
3) therefore somewhat below the setpoint of the heater.


It depends on what you mean by "best."  "Best" can mean "minimizes the 
wander in oven-regulated temperature at a constant (or slowly-changing) 
ambient temperature," or it can mean "fastest recovery when the ambient 
temperature changes more rapidly."


Minimum heater power tends to favor the first, but be careful -- this 
means a low *available* (maximum) power, not just using a high-powered 
heater at a lower output.  This is because the rate of temperature 
change for full-scale heater swings is proportional to maximum heater 
output, not to the ambient-to-oven differential, and this "granularity" 
of the heater control function is what determines the oven wander at a 
constant (or slowly-changing) ambient temperature.


A higher differential between the set point and ambient, and higher 
maximum heater output, are necessary for fast recovery from larger 
and/or faster changes in ambient temperature (i.e., to achieve a higher 
dTemp/dTime).


Note that the above is why, for an oven controller with decent loop 
gain, it is not necessary to control the ambient temperature very 
tightly -- it is only necessary to slow down the *rate of change* in 
ambient temperature to the point that the loop can track it to the 
required tolerance.  See previous list discussions of "cast aluminum 
boxes" and "thermal capacitance."


Best regards,

Charles


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Re: [time-nuts] Poor man's oven

[Chris Albertson]

On Tue, Jun 6, 2017 at 7:34 AM, Attila Kinali  wrote:

>
> 1) You want the control loop as stable as possible
> 2) Stability is directly related to controllability
> 3) The larger the heat flow, the better the controllability
> 4) therefore the outside temperature should be as low as possible


I think you are correct but within reason of course.   It is easy to see
that the extremes can't work. If the internal set point is very close to
ambient the oven is uncontrollable.  because you only use the first bit of
the DAC to control the heater and after a few seconds you have overshoot.
Moving the set point up lets us use the full range of current on the heater
can gives us 8 or 10 bits of control and the rate of change is slow enough
that we have time take thousands of samples and see a rate of change in
temperature.  The PID algorithm needs something that is slow to change
compared to the control loop cycle.  So you want a good size thermal mass
compared to the amount of heat.


At the other extreme, where the set point to far above ambient we would
need to run the heater full time and also loose control.  So I disagree
with #4 above.   The heater would have to run full-on at 100% duty cycle.
 (In other words avoid using liquid nitrogen baths)

There is an optimum were it peaks but I don't know how to find it.Look
at the specific heat of the thermal mass (likely you are using aluminum)
and multiply that by the mass and I think you want that to be large
compared to the heat from a full-on heater so that the rate of change looks
slow compared to your control loop cycle.





-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Poor man's oven

[Jim Harman]

On Tue, Jun 6, 2017 at 10:00 AM, Riley, Ian C CTR NSWC Philadelphia, 515 <
ian.riley@navy.mil> wrote:

> Is there a practical minimum for what voltage you can feed into AREF?
>

It is hard to find on the data sheet, but the minimum voltage for an
Arduino's AREF is the internal analog reference voltage - 1.1V for the Uno,
2.56V for the Leonardo or Micro. The 32U4 chip in the Leo and Micro has
options for differential analog input and gains of 10, 40, or 200 but they
are not supported by the Arduino IDE - you have to set the internal
registers directly to use them. Also the input amplifier is pretty slow.


-- 

--Jim Harman
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Re: [time-nuts] Free to a good home: HP 100E Freq. Standard

[IEEE]

I would love to have it, but I'm afraid I would need it shipped.  What a great 
addition to my collection- no tube gear at all

I'd be happy to pay the costs- I can send you funds once we figure out cost- if 
you are game.  Shoot me an email off list and I'll provide shipping address.  

Thanks,
Dave
W8PDP

> On Jun 5, 2017, at 7:58 PM, Bob kb8tq  wrote:
> 
> Hi
> 
> If there are no takers from the rest of the list, I’ll drive down and pick it 
> up. Shipping a beast like this
> is a royal pain. Let’s wait a couple weeks and see if anybody else wants it.
> 
> Bob
> 
>> On Jun 5, 2017, at 2:48 PM, Neal MacDonald  wrote:
>> 
>> I have an HP 100E Frequency Standard that I found at a garage sale and 
>> bought on a whim a while ago. I don’t have much use for it, but it seems 
>> like a shame to toss it so I figured I’d offer it up here. It’s yours for 
>> free, just pay shipping costs from the DC area. I was told by the original 
>> owner that the vertical deflection doesn’t work, but I didn’t have the 
>> technical knowhow to attempt to diagnose the issue. I also have a scanned 
>> copy of the original manual I can pass along.
>> 
>> Some info here: http://hpmemoryproject.org/news/100e/hp100e_page_00.htm 
>> 
>> Pictures here: https://imgur.com/a/JL8h4 
>> 
>> Thanks,
>> Neal
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> 
> 
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Re: [time-nuts] Poor man's oven

[Adrian Godwin]

The specs for the ADC are pretty vague : most of the errors are around 2
LSB but all are quoted with vref at 4V. If you reduce vref (there's an
internal option of 1.1V) you'll increase gain but some of those errors are
going to stay physically the same. In general, I'd tend expect to get more
precision but also more noise. Averaging may help a bit.


On Tue, Jun 6, 2017 at 3:00 PM, Riley, Ian C CTR NSWC Philadelphia, 515 <
ian.riley@navy.mil> wrote:

> Chris,
>
> > The trick with using a uP and it's built-in A/D converters is scale.  You
> > want the limited 10-bits of revolution to fall over the operating range
> > which is very narrow, like 1C.   Anything outside of that is either 
> or
> >  and only seen at start-up.,  So at start up the the controller is on
> > "bang-bang" mode then later you have milli-degree resolution over your 1C
> > range.   Basically you are measuring noise. but your $2 uP can take
> 100,000
> > measurments per second and putt tour a digital filter.
>
> I have seen but not used the AREF pins on Arduino and similar uPs; as you
> lower AREF, do you lose any sort of accuracy? Is there a practical minimum
> for what voltage you can feed into AREF?
>
> -Ian R.
> ___
> time-nuts mailing list -- time-nuts@febo.com
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Re: [time-nuts] Poor man's oven

[Riley, Ian C CTR NSWC Philadelphia, 515]

Chris,

> The trick with using a uP and it's built-in A/D converters is scale.  You
> want the limited 10-bits of revolution to fall over the operating range
> which is very narrow, like 1C.   Anything outside of that is either  or
>  and only seen at start-up.,  So at start up the the controller is on
> "bang-bang" mode then later you have milli-degree resolution over your 1C
> range.   Basically you are measuring noise. but your $2 uP can take 100,000
> measurments per second and putt tour a digital filter.

I have seen but not used the AREF pins on Arduino and similar uPs; as you lower 
AREF, do you lose any sort of accuracy? Is there a practical minimum for what 
voltage you can feed into AREF? 

-Ian R. 
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Re: [time-nuts] Poor man's oven

[Attila Kinali]

On Tue, 6 Jun 2017 05:52:56 -0700
jimlux  wrote:

> > Disregard aging of electronics and materials, we all know that
> > stuff, what I'm interested in is at which exterior temperature
> > OCXO ovens work best ?
> 
> Here's my guess...
> 
> 1) you want minimal gradients across the device for a variety of reasons
> 2) therefore you want least amount of heat from the heater
> 3) therefore somewhat below the setpoint of the heater.
> 
> How far below? I've no idea.

I counter that guess! :-)

1) You want the control loop as stable as possible
2) Stability is directly related to controllability
3) The larger the heat flow, the better the controllability
4) therefore the outside temperature should be as low as possible

Do we have to battle now, to see who is right? :-)


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] Poor man's oven

[jimlux]

On 6/6/17 4:26 AM, Poul-Henning Kamp wrote:






OCXO's have specified temperature ranges for instance
-40...+70°C for the heavy duty stuff.

But I cant imagine the ovens used are so perfect that they have the
same regulation performance at all temperatures.

I can choose the exterior temperature, which I should prefer ?

Disregard aging of electronics and materials, we all know that
stuff, what I'm interested in is at which exterior temperature
OCXO ovens work best ?


Here's my guess...

1) you want minimal gradients across the device for a variety of reasons
2) therefore you want least amount of heat from the heater
3) therefore somewhat below the setpoint of the heater.

How far below? I've no idea.

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Re: [time-nuts] Poor man's oven

[Poul-Henning Kamp]

In message , Bob kb8tq writes:

>In an OCXO design, the gotcha
>is matching the PTC oven temperature to the crystal turn. You can do that if
>you have a substantial inventory of material and custom fab the oven after
>the crystal is built. 

Bob, you of all people must be able to answer this:

OCXO's have specified temperature ranges for instance
-40...+70°C for the heavy duty stuff.

But I cant imagine the ovens used are so perfect that they have the
same regulation performance at all temperatures.

I can choose the exterior temperature, which I should prefer ?

Disregard aging of electronics and materials, we all know that
stuff, what I'm interested in is at which exterior temperature
OCXO ovens work best ?

-- 
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] Poor man's oven

[Bob kb8tq]

Hi

For a while, a couple of outfits made TO-5 and TO-8 “cap heaters” with 
PTC material. There are still a few obscure places that people do the same
sort of thing with a mini-pcb based design. In an OCXO design, the gotcha
is matching the PTC oven temperature to the crystal turn. You can do that if you
have a substantial inventory of material and custom fab the oven after the 
crystal 
is bult. 

Bob

> On Jun 6, 2017, at 12:13 AM, David  wrote:
> 
> I have never been able to find a reference to them on the internet but
> there was a similar product intended for TO-99 packages that could be
> used with operational amplifiers.
> 
> On Mon, 5 Jun 2017 08:35:35 + (UTC), you wrote:
> 
>>   The Crystal heater clip wasa Murata "Posistor" soldered onto a clipand 
>> they were marketed by Murata.
>> I once purchased a small amount of theseand used them as "poor man's ovens".
>> Although not perfect by far, they did theirjob and kept my UHF gear stable.
>> Murata dropped that product many yearsago and I have not been able to 
>> findany similar product. The Posistors arelisted by eg. Digi-key but they do 
>> not stock them.
>> Ulf - SM6GXV
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Re: [time-nuts] Poor man's oven

[Jon Iza]

Folks,
with tongue firmly stuck in cheek, may I propose an old technique to
stabilize
xtal oscillators?You only need a "satellite" oscillator placed under your
armpit...
http://www.qsl.net/on7yd/136narro.htm#NihilNovum
jon, ea2sn
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