Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies
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" trojancowboy@gmail.com 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit he used in a satellite. Not to your circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation
over temperature range (-30°C to 60°C). Also, to hold the temperature
stable to 0.001K in a room temperature environment (let's say 10K variation),
you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%20RTD%20Measurement.pdf
--
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
Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
fit into this ?
On Mon, Jun 5, 2017 at 12:59 AM, Attila Kinali attila@kinali.ch wrote:
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" trojancowboy@gmail.com 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit he used in a satellite. Not to your
circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation
over temperature range (-30°C to 60°C). Also, to hold the temperature
stable to 0.001K in a room temperature environment (let's say 10K
variation),
you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%
20RTD%20Measurement.pdf
--
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
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.
The other issue that needs to be considered is the drift in temperature sensor characteristics when operated at a constant temperature (as is typical in a continuously operated crystal oven). High quality thermistors can achieve drifts of around 1mK/month. Its unlikely that something as complex as an AD590 will achieve a similar drift (1nA/month in a operating current of 300uA or so at 25C). High quality PRT sensors drift even less than thermistors when operating at constant temperature.
Bruce
.On 05 June 2017 at 11:59 Attila Kinali <attila@kinali.ch> wrote:
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" <trojancowboy@gmail.com> 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit _he_ used in a satellite. Not to your circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation over temperature range (-30°C to 60°C). Also, to hold the temperature stable to 0.001K in a room temperature environment (let's say 10K variation), you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%20RTD%20Measurement.pdf
--
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
_______________________________________________
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 6/4/17 4:59 PM, Attila Kinali wrote:
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit he used in a satellite. Not to your circuit.
We've also used 3k. It's more about supply voltage, expected
temperature range, and the ADC you're using (if any). 1k is handy if
you're running off 5V and are feeding a 1 volt full scale ADC - room
temp is 0.3 V. Note that the minimum voltage across an AD590 is 4V,
so if you've got a 3V supply, you're out of luck.
10k gives you 3V at room temp, and is quite ok into a 5V ADC, as long as
your supply is at least 7-8 volts.
There is self heating to worry about if you have a high supply voltage
(12V @ 0.3 mA is 3.6 mW), but realistically, all sensors have that
problem (unless you are using a PRT in some sort of bridge that nulls
the current)
Hi
If your objective is a resolution of < 0.001 C at something < 1 second, the current crop of
digital sensors don’t quite do what you need to do. They are a terrific way to do wide range
measurements that might feed into some sort of correction algorithm. A conventional
thermistor bridge falls apart if you try to run it -55 to +125. The range of resistances
involved results in significantly lowered resolution at the end(s) of the range.
Bob
On Jun 4, 2017, at 8:18 PM, Adrian Godwin artgodwin@gmail.com wrote:
Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
fit into this ?
On Mon, Jun 5, 2017 at 12:59 AM, Attila Kinali attila@kinali.ch wrote:
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" trojancowboy@gmail.com 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit he used in a satellite. Not to your
circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation
over temperature range (-30°C to 60°C). Also, to hold the temperature
stable to 0.001K in a room temperature environment (let's say 10K
variation),
you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%
20RTD%20Measurement.pdf
--
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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
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On Mon, 5 Jun 2017 01:18:59 +0100
Adrian Godwin artgodwin@gmail.com wrote:
Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
fit into this ?
AFAIK, these are all band-gap temperature sensors. But unlike a discrete
sensor, you have the problem that they only contain a low resolution
ADC on die (somewhere between 8 and 14 bit). If your goal is to measure
temperature and report it with an accuracy of about 1°C, then these are
the easiest to use sensors you can buy. Sensor noise doesn't really matter
with them, as it is dominated by the low ADC resolution. I don't have any
long term stability data on those, but given their use-case I do not think
that they are very stable. Although long term stability might not be an
issue at all, again due to low ADC resolution.
If you need better precision, accuracy, or stability, then choosing one
of the modern delta-sigma ADCs that directly support thermistors
(e.g. like AD7124) is not much more difficult, though a bit more expensive
(around 10USD instead of 5USD like for an TMP107). Additionally you need
to calbirate the system, which means you need a reference temperature sensor
and a setup with which you can produce different temperatures. Though for
an oven kind of temperature control, one can live without calibration.
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
Hi
On Jun 5, 2017, at 7:30 AM, Attila Kinali attila@kinali.ch wrote:
On Mon, 5 Jun 2017 01:18:59 +0100
Adrian Godwin artgodwin@gmail.com wrote:
Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
fit into this ?
AFAIK, these are all band-gap temperature sensors. But unlike a discrete
sensor, you have the problem that they only contain a low resolution
ADC on die (somewhere between 8 and 14 bit). If your goal is to measure
temperature and report it with an accuracy of about 1°C, then these are
the easiest to use sensors you can buy. Sensor noise doesn't really matter
with them, as it is dominated by the low ADC resolution. I don't have any
long term stability data on those, but given their use-case I do not think
that they are very stable.
Based on using them in a lot of designs, they are indeed quite stable. They are not
going to rival a thermistor or an RTD, but compared to their resolution they are stable.
Put another way, if they read out at the (say) 0.5 C level, you can come back a year later
and the temperature repeats at < the 0.5 C level.
None of this is simple or straightforward. All temperature sensors have a sensitivity
to strain. They all exhibit some level of hysteresis. That can make aging measurements
a bit challenging.
Bob
Although long term stability might not be an
issue at all, again due to low ADC resolution.
If you need better precision, accuracy, or stability, then choosing one
of the modern delta-sigma ADCs that directly support thermistors
(e.g. like AD7124) is not much more difficult, though a bit more expensive
(around 10USD instead of 5USD like for an TMP107). Additionally you need
to calbirate the system, which means you need a reference temperature sensor
and a setup with which you can produce different temperatures. Though for
an oven kind of temperature control, one can live without calibration.
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
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, guys
I have been following time nuts and volt nuts for some time out of interest and fascination. Although my personal backyard hobby is more along a volt nuts line, the two worlds often collide - like in this discussion of temperature sensors, and in particular their long term stability. NTC thermistors appear to be very commonly used in ovens used to stabilize voltage references (solid state as well as chemical) . I have long wondered about their stability. If, as Bruce asserts, "high quality thermistors can achieve drifts of around 1mK/month" then it appears that this level of drift is a significant factor in the "apparent" aging of, say, a bank of Weston cells (which is still my best backyard shot at a voltage reference).
I have had no luck with Google; Bruce's statement is the first quantified allusion that I have seen to this subject. Is there any actual data available on the long term performance of NTC sensors?
Roman
On 5 Jun 2017, at 9:53 AM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
The other issue that needs to be considered is the drift in temperature sensor characteristics when operated at a constant temperature (as is typical in a continuously operated crystal oven). High quality thermistors can achieve drifts of around 1mK/month. Its unlikely that something as complex as an AD590 will achieve a similar drift (1nA/month in a operating current of 300uA or so at 25C). High quality PRT sensors drift even less than thermistors when operating at constant temperature.
Bruce
.On 05 June 2017 at 11:59 Attila Kinali <attila@kinali.ch> wrote:
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" <trojancowboy@gmail.com> 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit _he_ used in a satellite. Not to your circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation over temperature range (-30°C to 60°C). Also, to hold the temperature stable to 0.001K in a room temperature environment (let's say 10K variation), you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%20RTD%20Measurement.pdf
--
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
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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and follow the instructions there.
Hi
Well, as part of the process of designing them into OCXO’s you do indeed check their long term stability.
The test is done in an indirect fashion so you only come up with a “it’s below the limit” sort of number. The
typical process involves running a group of OCXO’s on turn to check the frequency and then shifting them
off turn to make a sort of thermometer. After a few months of frequency readings you take them back to turn
for a while. Relative frequency shift math gives you a stability number for the thermistor and the rest of the
circuitry. You may repeat the run for months / shift process a couple of times. If the answer isn’t “I can’t see
a difference” you look for a new thermistor. Since it’s a long drawn out test, the tendency is to stick with a
vendor’s part for quite a while. The parts also tend to be design specific so what works in my (say SMT)
design may not work well in your (say chip and wire) design.
Bob
On Jun 5, 2017, at 9:20 AM, romeo987 romeo987@westnet.com.au wrote:
Hi, guys
I have been following time nuts and volt nuts for some time out of interest and fascination. Although my personal backyard hobby is more along a volt nuts line, the two worlds often collide - like in this discussion of temperature sensors, and in particular their long term stability. NTC thermistors appear to be very commonly used in ovens used to stabilize voltage references (solid state as well as chemical) . I have long wondered about their stability. If, as Bruce asserts, "high quality thermistors can achieve drifts of around 1mK/month" then it appears that this level of drift is a significant factor in the "apparent" aging of, say, a bank of Weston cells (which is still my best backyard shot at a voltage reference).
I have had no luck with Google; Bruce's statement is the first quantified allusion that I have seen to this subject. Is there any actual data available on the long term performance of NTC sensors?
Roman
On 5 Jun 2017, at 9:53 AM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
The other issue that needs to be considered is the drift in temperature sensor characteristics when operated at a constant temperature (as is typical in a continuously operated crystal oven). High quality thermistors can achieve drifts of around 1mK/month. Its unlikely that something as complex as an AD590 will achieve a similar drift (1nA/month in a operating current of 300uA or so at 25C). High quality PRT sensors drift even less than thermistors when operating at constant temperature.
Bruce
.On 05 June 2017 at 11:59 Attila Kinali attila@kinali.ch wrote:
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" trojancowboy@gmail.com 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 precision application.
With a 3 point calibration, better than 0.5°C accuracy can be achieved
(modulo aging) within their operating temperature range, which is
rather limited, compared to the other sensor types.
I don't know enough about thermocouples to say much about them, beside
that they are cumbersome to work with (e.g. the cold contact) and
produce a low voltage (several µV) output with quite high impedance,
which makes the analog electronics difficult to design as well.
With todays electronics, the easiest sensors to work with are NTC and
PT100/PT1000 as most high resolution delta-sigma ADCs have direct support
for 3 and/or 4 wire measurement of those, including compensation for
reference voltage/current variation. Using a uC as control element
also opens up the possibility to linearize the curve of NTCs without
loss of accuracy. Usually measurement precision, with a state-of-the-art
circuit, is limited by noise coupling into the leads of the sensor
and noise in and around the ADC. (see [3-5])
Where did you get the idea to use a 1 k load for an AD590?
Jim was refering to a circuit he used in a satellite. Not to your circuit.
The room temperature coefficient of an AT crystal is -cd 100 ppb per
reference cut angle in minutes. (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°. If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.
It has been heard of. The 8607 was spec'ed to <2e-10 p-p deviation over temperature range (-30°C to 60°C). Also, to hold the temperature stable to 0.001K in a room temperature environment (let's say 10K variation), you need a thermal gain of >10k. That's quite a bit and needs considerable
design effort. Most OCXO design's I am aware of are in the order of 100
(the DIL14 designs) to a few 1000 for single ovens, to a few 10k for
double ovens. The only exception is the E1938 which achieves >1M.
But that design is not for the faint hearted. I don't remember seeing
any number, but i would guess the 8607 has a thermal gain in the
order of 100k to 1M as well, considering it being a double oven in
a dewar flask.
Also, what do you mean by atomic standard and feed forward?
If you have an atomic standard you don't need to temperature
stabilize your quartz. You can just simply use a PLL to lock
it to your reference and achieve higher stability than any oven
design.
Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior. It does no good to have a perfect crystal if the
oscillator components drift.
Beyond tau=100s, the temperature and moisture sensitivity of the
electronics, combined with the aging of the electronics and the
crystal will be the limit of stability. Of course, this is under
the assumption that you achieved a thermal noise limited design
and thus the 1/f^a noise of the oscillator is negligible in the
time range considered.
Attila Kinali
[1] "Traceable Temperatures - An Introduction to Temperature Measurement
and Calibration", 2nd edition, by Nicholas and White, 2001
[2] "Thin-film platinum resistance thermometer for use at low temperatures
and in high magnetic fields", Haruyama, Yoshizaki, 1986
[3] "Completely Integrated 4-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0381
http://www.analog.com/CN0381
[4] "Completely Integrated 3-Wire RTD Measurement System Using a Low Power,
Precision, 24-Bit, Sigma-Delta ADC", Analog Circuit Note CN-0383
http://www.analog.com/CN0383
[5] "2- 3- 4- Wire RDT (Pt100 to PT1000)Temperature Measurement"
Ti Presentation
http://www.ti.com/europe/downloads/2-%203-%204-Wire%20RTD%20Measurement.pdf
--
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
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.
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and follow the instructions there.
In message 20170605133013.526e8505158e68b6a8091e05@kinali.ch, Attila Kinali w
rites:
Where do digital sensors (e.g. ds1820 and some more recent parts from TI)
fit into this ?
AFAIK, these are all band-gap temperature sensors.
The Ds1820 is based on the frequency difference between two
free-running silicon oscillators with different physical design.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@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.