Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 12:43 PM
Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
To: "Donald E. Pauly" trojancowboy@gmail.com
Hi
Which statement is not true:
-
That there is a tolerance on the cut angle of a crystal?
-
That true zero temperature coefficient only happens at the turn?
-
That heater based controllers are impossible to build?
Bob
On Jun 2, 2017, at 3:40 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
That is not true. I say that thermal coolers have made ovens
obsolete. A zero temperature coefficient at room temperature is
easier to hit than a zero temperature at the upper turnover point when
such a thing exists. See
curve 0 in Figure 6 at https://coloradocrystal.com/applications/ .
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
Hi
How many OCXO’s have you actually built?
Bob
On Jun 2, 2017, at 5:51 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 12:43 PM
Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
To: "Donald E. Pauly" trojancowboy@gmail.com
Hi
Which statement is not true:
-
That there is a tolerance on the cut angle of a crystal?
-
That true zero temperature coefficient only happens at the turn?
-
That heater based controllers are impossible to build?
Bob
On Jun 2, 2017, at 3:40 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
That is not true. I say that thermal coolers have made ovens
obsolete. A zero temperature coefficient at room temperature is
easier to hit than a zero temperature at the upper turnover point when
such a thing exists. See
curve 0 in Figure 6 at https://coloradocrystal.com/applications/ .
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
Have you checked out the papers from the 1950 and `1960’s where they actually tried what you
propose with essentially the same parts you are looking at using?
Bob
On Jun 2, 2017, at 5:51 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 12:43 PM
Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
To: "Donald E. Pauly" trojancowboy@gmail.com
Hi
Which statement is not true:
-
That there is a tolerance on the cut angle of a crystal?
-
That true zero temperature coefficient only happens at the turn?
-
That heater based controllers are impossible to build?
Bob
On Jun 2, 2017, at 3:40 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
That is not true. I say that thermal coolers have made ovens
obsolete. A zero temperature coefficient at room temperature is
easier to hit than a zero temperature at the upper turnover point when
such a thing exists. See
curve 0 in Figure 6 at https://coloradocrystal.com/applications/ .
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 6/2/17 2:51 PM, Donald E. Pauly wrote:
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
without getting into the whole crystal issue, one of the advantages of a
heater is that it can be VERY simple (and hence reliable, just on a
parts count basis). With a decent package, once it's hot, the power
required to keep it hot can be quite low.
With a heat/cool, you need to be able to have a bipolar supply to the
peltier device, and they're not particularly efficient (that is, to
extract 1 Watt of heat, you're putting in significantly more than 1 watt
of DC, and rejecting 1+X watts to the outside world.
And then, if you use a linear power supply/amplifier to drive the
device, that is probably a class A device, and somewhat lossy. A
switcher would be more efficient, but then you have the problem of
switching noise, in close proximity to the crystal. You could put a big
low pass filter in, but now you're adding even more components.
There are undoubtedly some cases where the thermoelectric scheme would
work better - for instance, you have a system with a TCXO and it's
really set up for the TCXO to be at 25C, and you want to regulate that.
Thermomechanical fatigue can significantly reduce the lifetime of Peltier devices if the ripple current flowing in the Peltier device is too high. This can become an issue with switchmode drive to a Peltier cooler.
Bruce
On 03 June 2017 at 11:02 jimlux <jimlux@earthlink.net> wrote:
On 6/2/17 2:51 PM, Donald E. Pauly wrote:
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
without getting into the whole crystal issue, one of the advantages of a
heater is that it can be VERY simple (and hence reliable, just on a
parts count basis). With a decent package, once it's hot, the power
required to keep it hot can be quite low.
With a heat/cool, you need to be able to have a bipolar supply to the
peltier device, and they're not particularly efficient (that is, to
extract 1 Watt of heat, you're putting in significantly more than 1 watt
of DC, and rejecting 1+X watts to the outside world.
And then, if you use a linear power supply/amplifier to drive the
device, that is probably a class A device, and somewhat lossy. A
switcher would be more efficient, but then you have the problem of
switching noise, in close proximity to the crystal. You could put a big
low pass filter in, but now you're adding even more components.
There are undoubtedly some cases where the thermoelectric scheme would
work better - for instance, you have a system with a TCXO and it's
really set up for the TCXO to be at 25C, and you want to regulate that.
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
https://www.febo.com/pipermail/time-nuts/2017-May/105566.html
Electronic thermal coolers did not exist then so it could not be done.
Electronic temperature sensors did not exist either. That crystal cut
has been known since the 1940's at least. It has been neglected
because of limited temperature range. It yields ±1 ppm over a range of
±20° C from 25° C. A slightly different angle of cut can yield ±250
ppb over that range. (4:1 improvement) Contrast that with a normal AT
cut which yields ±9 ppm over that range.
I built an oven with an Analog Devices temperature sensor 20 years
ago. I did not have time to incorporate foam insulation. The heater
power was not available to run it at 65° C without insulation. It had
to run at 40° C and it would hold about 1 ppb over a few hours. It
would hold the crystal within 0.01° or so but it was far away from the
turnover temperature. Convection currents cause problems. It
convinced me that ovens were headaches. Thermal coolers remove most
of these.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 3:50 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Cc: "rward0@aol.com" rward0@aol.com, "Donald E. Pauly"
trojancowboy@gmail.com
Hi
Have you checked out the papers from the 1950 and `1960’s where they
actually tried what you
propose with essentially the same parts you are looking at using?
Bob
On Jun 2, 2017, at 5:51 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
With an AT crystal, manufacturing tolerances will likely ensure that the inflection point slope is non zero whereas the same manufacturing tolerances will merely change the turnover temperature. Its likely that a more manufacturable design will result if one operates at a turnover point (with the oven temperature adjusted to the actual turnover) than trying to achieve a sufficiently low slope at an inflection point. Even for a one off design one the selection process required to achieve a sufficiently low slope at the inflection point may prove expensive.
Bruce
On 03 June 2017 at 09:51 "Donald E. Pauly" <trojancowboy@gmail.com> wrote:
# 2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq <kb8tq@n1k.org>
Date: Fri, Jun 2, 2017 at 12:43 PM
Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
To: "Donald E. Pauly" <trojancowboy@gmail.com>
Hi
Which statement is not true:
1) That there is a tolerance on the cut angle of a crystal?
2) That true zero temperature coefficient only happens at the turn?
3) That heater based controllers are impossible to build?
Bob
On Jun 2, 2017, at 3:40 PM, Donald E. Pauly <trojancowboy@gmail.com> wrote:
That is not true. I say that thermal coolers have made ovens
obsolete. A zero temperature coefficient at room temperature is
easier to hit than a zero temperature at the upper turnover point when
such a thing exists. See
curve 0 in Figure 6 at https://coloradocrystal.com/applications/ .
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq <kb8tq@n1k.org> wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Jun 2, 2017, at 7:45 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
https://www.febo.com/pipermail/time-nuts/2017-May/105566.html
Electronic thermal coolers did not exist then so it could not be done.
Electronic temperature sensors did not exist either. That crystal cut
has been known since the 1940's at least. It has been neglected
because of limited temperature range. It yields ±1 ppm over a range of
±20° C from 25° C. A slightly different angle of cut can yield ±250
ppb over that range. (4:1 improvement) Contrast that with a normal AT
cut which yields ±9 ppm over that range.
I built an oven with an Analog Devices temperature sensor 20 years
ago. I did not have time to incorporate foam insulation. The heater
power was not available to run it at 65° C without insulation. It had
to run at 40° C and it would hold about 1 ppb over a few hours. It
would hold the crystal within 0.01° or so but it was far away from the
turnover temperature. Convection currents cause problems. It
convinced me that ovens were headaches. Thermal coolers remove most
of these.
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 3:50 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Cc: "rward0@aol.com" rward0@aol.com, "Donald E. Pauly"
trojancowboy@gmail.com
Hi
Have you checked out the papers from the 1950 and `1960’s where they
actually tried what you
propose with essentially the same parts you are looking at using?
Bob
On Jun 2, 2017, at 5:51 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
On Jun 2, 2017, at 7:45 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
https://www.febo.com/pipermail/time-nuts/2017-May/105566.html https://www.febo.com/pipermail/time-nuts/2017-May/105566.html
Ok, so yet again a reference to the start of this thread … why?
Electronic thermal coolers did not exist then so it could not be done.
Electronic temperature sensors did not exist either.
I guess they must have just dreamed up the pelter devices they used. FYI, they have
been around since 1834 (no that’s not a typo).
That crystal cut
has been known since the 1940's at least.
And once you get away from an AT or SC, how much is known about the mode spectra of
the cut ….
It has been neglected
because of limited temperature range. It yields ±1 ppm over a range of
±20° C from 25° C. A slightly different angle of cut can yield ±250
ppb over that range. (4:1 improvement) Contrast that with a normal AT
cut which yields ±9 ppm over that range.
Umm …. errr … it’s quite easy to get a +/- 2 ppm 0-50C AT cut including the tolerance
on the cut angle.
I built an oven with an Analog Devices temperature sensor 20 years
ago. I did not have time to incorporate foam insulation. The heater
power was not available to run it at 65° C without insulation. It had
to run at 40° C and it would hold about 1 ppb over a few hours. It
would hold the crystal within 0.01° or so but it was far away from the
turnover temperature. Convection currents cause problems. It
convinced me that ovens were headaches. Thermal coolers remove most
of these.
I’d suggest you try a few more experiments with real crystals in real applications.
Bob
πθ°μΩω±√·Γ
WB0KVV
---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 3:50 PM
Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Cc: "rward0@aol.com" rward0@aol.com, "Donald E. Pauly"
trojancowboy@gmail.com
Hi
Have you checked out the papers from the 1950 and `1960’s where they
actually tried what you
propose with essentially the same parts you are looking at using?
Bob
On Jun 2, 2017, at 5:51 PM, Donald E. Pauly trojancowboy@gmail.com wrote:
2 is not true. A cut has either two turning points or zero. Where
both turning points exist there are two temperatures at which the
temperature coefficient of frequency is zero. Cut 0 on figure 6 at
https://coloradocrystal.com/applications has no turnover point. It is
neither fish nor fowl. Cut 6 is the normal AT curve with extremes of
±16 ppm for -55° C thru +105° C. All curves normally intersect at 25°
C rather than the 27° C shown. 25° C is half way between -55° C thru
+105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0
is y=4x^3.
Consider the standard AT cut which has turnover points at -15° C and
65° C. The lower turnover would ordinarily not be used in ovens. A
set point error of ±1° C in the upper turnover point at 65° C results
in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error
in room temperature results in a frequency error of ±31.25·10^-12.
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
πθ°μΩω±√·Γ
WB0KVV
On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:
Hi
Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.
Bob
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
https://www.febo.com/pipermail/time-nuts/2017-June/date.html
I am familiar with this effect. My specialty is switching amplifiers
and I wrote the classic paper for Motorola on the subject, see
http://gonascent.com/papers/an1042.pdf . Ripple in the dc from a
switching amplifier is less than a part per thousand. These thermal
coolers have about a 10% efficiency which means it takes 10 Watts to
pump a Watt. That is a tiny switching amplifier. Ovens also require
several Watts if operated at -55° C. Thermo coolers/heaters require
little power when operated close to room temperature. Highest power
is required at high ambient temperatures.
πθ°μΩω±√·Γ
WB0KVV
https://www.febo.com/pipermail/time-nuts/2017-June/date.html
---------- Forwarded message ----------
From: Bruce Griffiths bruce.griffiths@xtra.co.nz
Date: Fri, Jun 2, 2017 at 4:34 PM
Subject: Re: [time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
To: jimlux jimlux@earthlink.net, Discussion of precise time and
frequency measurement time-nuts@febo.com
Thermomechanical fatigue can significantly reduce the lifetime of
Peltier devices if the ripple current flowing in the Peltier device is
too high. This can become an issue with switchmode drive to a Peltier
cooler.
Bruce
On 03 June 2017 at 11:02 jimlux <jimlux@earthlink.net> wrote:
On 6/2/17 2:51 PM, Donald E. Pauly wrote:
This is an improvement of 476 to 1. You apparently have not thought
thru what improvements are possible with thermal coolers/heaters.
Among these is near instant warm up and greatly reduced power for
thermal management.
without getting into the whole crystal issue, one of the advantages of a
heater is that it can be VERY simple (and hence reliable, just on a
parts count basis). With a decent package, once it's hot, the power
required to keep it hot can be quite low.
With a heat/cool, you need to be able to have a bipolar supply to the
peltier device, and they're not particularly efficient (that is, to
extract 1 Watt of heat, you're putting in significantly more than 1 watt
of DC, and rejecting 1+X watts to the outside world.
And then, if you use a linear power supply/amplifier to drive the
device, that is probably a class A device, and somewhat lossy. A
switcher would be more efficient, but then you have the problem of
switching noise, in close proximity to the crystal. You could put a big
low pass filter in, but now you're adding even more components.
There are undoubtedly some cases where the thermoelectric scheme would
work better - for instance, you have a system with a TCXO and it's
really set up for the TCXO to be at 25C, and you want to regulate that.
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