Re: [time-nuts] Rb Oscillator - rather fundamental question
Quoth Kasper Pedersen at 24/02/10 17:44... It will. Set the fuses as you would have for a 10MHz crystal, and capacitively couple the source to XTAL1. Leave XTAL2 open. Do not set the fuses for 'external clock mode'. Do put something like 100pF+1k Ohm in series with the input. While they won't promise anything, I have deliberately run 1A into the protection diodes of an ATMega16 for many seconds and still had a functional part. Many thanks. I was wondering about doing this; Chris Keuthe quoted the figures from the datasheet but then I thought that this would be the ratings for an external oscillator, as surely an actual crystal would be putting out a much smaller voltage than those quoted. A few days ago, on another list, David had suggested something similar with faking a crystal for an AT90S8535 RTC. I also wondered how an AVR could not work when PICs are reported to. I will certainly use the series R+C as you and David have suggested, but will not worry about further protection - the AVR is one of the cheapest components in the whole system - I am far more concerned about damaging the Rb module than the AVR! Thanks to all who have answered on this. I will post a link to details when I get this project up and running. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Blog/personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy Skype: msmiffy Twitter: @smiffy ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
In message 4b83a33c.1010...@smiffytech.com, Matthew Smith writes: Simple and rather fundamental question: does the common or garden rubidium oscillator constitute an atomic clock? Yes. It is classified as a secondary atomic clock, because it does not have an intrinsic physical frequency, like the cesium standards, but it is an atomic frequency, and it is an atomic clock (if you attach a display or a pair of hands :-) -- 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. ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
Cough - the rubidium clock or oscillator does have an intrinsic frequency, which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's just that the frequency generated by the transition in question isn't used to DEFINE the second, so by definition, it must be secondary. Only a Caesium clock is a primary standard, as the second is DEFINED to be the time taken for 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[1]. Unless of course they changed the rules recently ... [1] http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html Dave -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: 23 February 2010 09:53 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question In message 4b83a33c.1010...@smiffytech.com, Matthew Smith writes: Simple and rather fundamental question: does the common or garden rubidium oscillator constitute an atomic clock? Yes. It is classified as a secondary atomic clock, because it does not have an intrinsic physical frequency, like the cesium standards, but it is an atomic frequency, and it is an atomic clock (if you attach a display or a pair of hands :-) -- 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. ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
David C. Partridge wrote: Cough - the rubidium clock or oscillator does have an intrinsic frequency, which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's just that the frequency generated by the transition in question isn't used to DEFINE the second, so by definition, it must be secondary. Only a Caesium clock is a primary standard, as the second is DEFINED to be the time taken for 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[1]. Unless of course they changed the rules recently ... [1] http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html Dave Well, what you said is true as far as it goes, but not the whole story. The fact that a clock is based on cesium does not necessarily mean it is a primary standard. For example the chip scale atomic clock uses cesium and is a secondary standard. OTOH, certain experimental clocks based on atoms such as rubidium, mercury, etc could be considered primary standards in spite of the definition of the second. It's not the type of atom, but the type of clock that is crucial. Cesium usually refers to an atomic beam clock and Rubidium usually refer to a gas cell device. In an atomic beam, the atoms are, on the average, unperturbed, and will transition at exactly the 9192... frequency in the definition of the second. Except that they are offset from this frequency by a known amount due to the C-field. In a gas cell device, the atoms are perturbed by the buffer gas which results in a unknown frequency shift from the 6834... frequency. You have to remove this offset by comparing to a primary standard. We used to say that in theory you could build a cesium beam standard from a kit of parts on a desert island having no other clocks, and when you turned it on, it would be on the correct frequency (within a tolerance) guaranteed by design/physics. There is no way you could do this with a rubidium or cesium gas cell standard to any kind of accuracy associated with atomic clocks (it would only be in the general neighborhood of 6834...) That is the difference between primary and secondary standards. Another difference is that secondary standard have aging and primary standards don't. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
Sorry - I should have written a longer response - but you've put it all straight anyway. I wonder how long it will be before the definition of the second is changed to use the newer types of clocks using strontium, ytterbium, mercury, or aluminium (which I believe is the current front runner)? Cheers Dave -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Richard (Rick) Karlquist Sent: 23 February 2010 17:13 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question snip Well, what you said is true as far as it goes, but not the whole story. snip Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
All very informative and useful information for sure and good to know, But I'm thinking the real difference between a primary and secondary standard, Has More to do with if there is anything else more accurate and repeatable available. I'd guess a Rb would of made a great cave man Primary standard. And sounds like it will NOT be long before the Freq and drift of a CS Primary will be consider just another secondary standard that will have to be calibrated. (to get the 1e-16 + or whatever accuracy/repeatability it is they are now working on.) ws [time-nuts] Rb Oscillator - rather fundamental question Sorry - I should have written a longer response - but you've put it all straight anyway. I wonder how long it will be before the definition of the second is changed to use the newer types of clocks using strontium, ytterbium, mercury, or aluminium (which I believe is the current front runner)? Cheers Dave -Original Message- From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Richard (Rick) Karlquist Sent: 23 February 2010 17:13 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question snip Well, what you said is true as far as it goes, but not the whole story. snip Rick Karlquist N6RK David C. Partridge wrote: Cough - the rubidium clock or oscillator does have an intrinsic frequency, which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's just that the frequency generated by the transition in question isn't used to DEFINE the second, so by definition, it must be secondary. Only a Caesium clock is a primary standard, as the second is DEFINED to be the time taken for 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[1]. Unless of course they changed the rules recently ... [1] http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html Dave Well, what you said is true as far as it goes, but not the whole story. The fact that a clock is based on cesium does not necessarily mean it is a primary standard. For example the chip scale atomic clock uses cesium and is a secondary standard. OTOH, certain experimental clocks based on atoms such as rubidium, mercury, etc could be considered primary standards in spite of the definition of the second. It's not the type of atom, but the type of clock that is crucial. Cesium usually refers to an atomic beam clock and Rubidium usually refer to a gas cell device. In an atomic beam, the atoms are, on the average, unperturbed, and will transition at exactly the 9192... frequency in the definition of the second. Except that they are offset from this frequency by a known amount due to the C-field. In a gas cell device, the atoms are perturbed by the buffer gas which results in a unknown frequency shift from the 6834... frequency. You have to remove this offset by comparing to a primary standard. We used to say that in theory you could build a cesium beam standard from a kit of parts on a desert island having no other clocks, and when you turned it on, it would be on the correct frequency (within a tolerance) guaranteed by design/physics. There is no way you could do this with a rubidium or cesium gas cell standard to any kind of accuracy associated with atomic clocks (it would only be in the general neighborhood of 6834...) That is the difference between primary and secondary standards. Another difference is that secondary standard have aging and primary standards don't. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
I don't think I agree with that, Warren. I'd view a primary standard as an intrinsic one -- that is accurate by definition and doesn't need calibration against another, higher level, source. A cesium beam standard is based on the same physical phenomenon that defines the second, so if it's working, it's right within some degree of tolerance. As others have pointed out, a gas cell standard is subject to pulling and needs to be set to a correct value (and also has drift over time). And standards based on other ions may actually be more accurate and stable than cesium, but they still need to be related to the official definition of the second through a measurement. In either case, they need to be referred to the cesium transition, so they are not primary standards. Make sense? John WarrenS wrote: All very informative and useful information for sure and good to know, But I'm thinking the real difference between a primary and secondary standard, Has More to do with if there is anything else more accurate and repeatable available. I'd guess a Rb would of made a great cave man Primary standard. And sounds like it will NOT be long before the Freq and drift of a CS Primary will be consider just another secondary standard that will have to be calibrated. (to get the 1e-16 + or whatever accuracy/repeatability it is they are now working on.) ws [time-nuts] Rb Oscillator - rather fundamental question Sorry - I should have written a longer response - but you've put it all straight anyway. I wonder how long it will be before the definition of the second is changed to use the newer types of clocks using strontium, ytterbium, mercury, or aluminium (which I believe is the current front runner)? Cheers Dave -Original Message- From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Richard (Rick) Karlquist Sent: 23 February 2010 17:13 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question snip Well, what you said is true as far as it goes, but not the whole story. snip Rick Karlquist N6RK David C. Partridge wrote: Cough - the rubidium clock or oscillator does have an intrinsic frequency, which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's just that the frequency generated by the transition in question isn't used to DEFINE the second, so by definition, it must be secondary. Only a Caesium clock is a primary standard, as the second is DEFINED to be the time taken for 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[1]. Unless of course they changed the rules recently ... [1] http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html Dave Well, what you said is true as far as it goes, but not the whole story. The fact that a clock is based on cesium does not necessarily mean it is a primary standard. For example the chip scale atomic clock uses cesium and is a secondary standard. OTOH, certain experimental clocks based on atoms such as rubidium, mercury, etc could be considered primary standards in spite of the definition of the second. It's not the type of atom, but the type of clock that is crucial. Cesium usually refers to an atomic beam clock and Rubidium usually refer to a gas cell device. In an atomic beam, the atoms are, on the average, unperturbed, and will transition at exactly the 9192... frequency in the definition of the second. Except that they are offset from this frequency by a known amount due to the C-field. In a gas cell device, the atoms are perturbed by the buffer gas which results in a unknown frequency shift from the 6834... frequency. You have to remove this offset by comparing to a primary standard. We used to say that in theory you could build a cesium beam standard from a kit of parts on a desert island having no other clocks, and when you turned it on, it would be on the correct frequency (within a tolerance) guaranteed by design/physics. There is no way you could do this with a rubidium or cesium gas cell standard to any kind of accuracy associated with atomic clocks (it would only be in the general neighborhood of 6834...) That is the difference between primary and secondary standards. Another difference is that secondary standard have aging and primary standards don't. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
WarrenS wrote: All very informative and useful information for sure and good to know, But I'm thinking the real difference between a primary and secondary standard, Has More to do with if there is anything else more accurate and repeatable available. I'd guess a Rb would of made a great cave man Primary standard. And sounds like it will NOT be long before the Freq and drift of a CS Primary will be consider just another secondary standard that will have to be calibrated. (to get the 1e-16 + or whatever accuracy/repeatability it is they are now working on.) Sorry but you have completely misunderstood the concept. It is admittedly a difficult concept to grasp; I know it took me a long time. A hydrogen maser with the wall shift servo'ed out will run rings around a compact Cs beam clock like the HP5062, used on submarines. (An interesting trivia item is that I don't believe the 5061 can fit through a submarine hatch). The 5062 is still a primary frequency standard and the hydrogen maser is still a secondary frequency standard. Regarding drift of primary cesium beam standards: the 5071A has unmeasurable drift, aging and tempco, down to a measurement limit of at least 1E-15. It has a typical *random* error of a few parts in 1E-13. The systematic error (average error of all 5071A's built) has been established to be below 1E-14. It will always be a primary standard even in the presence of longer reversible optically pumped laboratory Cs beam standards of higher accuracy and better short term stability, or cesium fountains, etc. Even the 5061A/B is considered a primary standard, albeit with reduced accuracy, even though it has a measurable tempco. We were very proud of the E1938A crystal oscillator when it was able to meet the 5061 tempco spec. It is in no way a primary frequency standard regardless of that or any other accomplishment. Primary means that the clock will meet its spec without being calibrated against a better clock. Secondary means that calibration against a primary standard is necessary. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
Rick Thanks, Interesting but maybe you have missed my too subtle of a point. Example: Lets say the second is redefined in the future to some new super duper thing that is good to 1 part in e20 (Which will happen if (when) the super duper thing becomes more available and proven) (Maybe based on the time it takes to count all the atoms in the new purposed 1 Kg sphere OR something like that.) Then the CS Osc would not be the BEST primary standard anymore, at least NOT at the new improved spec it could then be given. Not because it has changed or is less accurate, but because there is now something better. If it is not the primary standard, it does not make it worse, but it does mean it will now be a second standard at the new higher performance spec, by definition and need to be then calibrated and checked against the new primary standard IF one wanted to use it to it's maximum capability as a cost effective substitute for the supper duper. Same with RB, One can not do something to it to make it more than say 1 part in e6 (or whatever) that the cave man needed, so it could of been their Primary repeatable Intrinsic standard that was repeatable Good Enough without cal for them. Primary means that the clock will meet its spec without being calibrated against a better clock. From your definition a Rb can be a primary standard for a 1e-6 world and a crystal as well as my wrist watch can be a primary standard in a 1e-3 spec or whatever they can repeat without Calibration. BUT I have not hear anyone argue that any of the above are primary standards, even at some reduced spec. (maybe just because not cost effective?) The existing Cs oscillators can not be primary standard at the new 1e-16 + accurate word, but they would be useful just the same in that word as a secondary standard. There is always progress and change in the time world ws ** ws Sorry but you have completely misunderstood the concept. It is admittedly a difficult concept to grasp; I know it took me a long time. A hydrogen maser with the wall shift servo'ed out will run rings around a compact Cs beam clock like the HP5062, used on submarines. (An interesting trivia item is that I don't believe the 5061 can fit through a submarine hatch). The 5062 is still a primary frequency standard and the hydrogen maser is still a secondary frequency standard. Regarding drift of primary cesium beam standards: the 5071A has unmeasurable drift, aging and tempco, down to a measurement limit of at least 1E-15. It has a typical *random* error of a few parts in 1E-13. The systematic error (average error of all 5071A's built) has been established to be below 1E-14. It will always be a primary standard even in the presence of longer reversible optically pumped laboratory Cs beam standards of higher accuracy and better short term stability, or cesium fountains, etc. Even the 5061A/B is considered a primary standard, albeit with reduced accuracy, even though it has a measurable tempco. We were very proud of the E1938A crystal oscillator when it was able to meet the 5061 tempco spec. It is in no way a primary frequency standard regardless of that or any other accomplishment. Primary means that the clock will meet its spec without being calibrated against a better clock. Secondary means that calibration against a primary standard is necessary. Rick Karlquist N6RK ** WarrenS wrote: All very informative and useful information for sure and good to know, But I'm thinking the real difference between a primary and secondary standard, Has More to do with if there is anything else more accurate and repeatable available. I'd guess a Rb would of made a great cave man Primary standard. And sounds like it will NOT be long before the Freq and drift of a CS Primary will be consider just another secondary standard that will have to be calibrated. (to get the 1e-16 + or whatever accuracy/repeatability it is they are now working on.) ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
My two cents: A primary standard is one that is directly compared with the accepted or defined standard. In years past, an oscillator could only be called a primary time or frequency standard if it had a clock in order to make comparisons with the Earth's rotation. Note, there are no limits on the accuracy or stability. A standard that is compared to a primary standard is a secondary standard even if it is more stable. Since 1967, the second has been defined to be the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Therefore, any standard which is compared directly with the transition is a primary standard. Any standard compared to a primary standard is a secondary standard. A standard more stable than a caesium standard is still a secondary standard until the process the new standard is directly compared to is designated the accepted or defined standard. A rubidium standard compared to a caesium standard is still a secondary standard because it is not directly compared the the caesium transition. To summarize from the 1933 Bulletin 10 from General Radio on Frequency Measurements at Radio Frequencies, all frequency standards are compared either directly or indirectly with a standard time interval derived from the earth's rotation...It should be noted, however, that the accuracy depends on how direct a comparison is made with the standard time interval. Replace derived from the earth's rotation with accepted or defined. Direct comparison's yield primary standards and indirect yield secondary standards. John WA4WDL -- From: Rick Karlquist rich...@karlquist.com Sent: Tuesday, February 23, 2010 3:00 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question WarrenS wrote: All very informative and useful information for sure and good to know, But I'm thinking the real difference between a primary and secondary standard, Has More to do with if there is anything else more accurate and repeatable available. I'd guess a Rb would of made a great cave man Primary standard. And sounds like it will NOT be long before the Freq and drift of a CS Primary will be consider just another secondary standard that will have to be calibrated. (to get the 1e-16 + or whatever accuracy/repeatability it is they are now working on.) Sorry but you have completely misunderstood the concept. It is admittedly a difficult concept to grasp; I know it took me a long time. A hydrogen maser with the wall shift servo'ed out will run rings around a compact Cs beam clock like the HP5062, used on submarines. (An interesting trivia item is that I don't believe the 5061 can fit through a submarine hatch). The 5062 is still a primary frequency standard and the hydrogen maser is still a secondary frequency standard. Regarding drift of primary cesium beam standards: the 5071A has unmeasurable drift, aging and tempco, down to a measurement limit of at least 1E-15. It has a typical *random* error of a few parts in 1E-13. The systematic error (average error of all 5071A's built) has been established to be below 1E-14. It will always be a primary standard even in the presence of longer reversible optically pumped laboratory Cs beam standards of higher accuracy and better short term stability, or cesium fountains, etc. Even the 5061A/B is considered a primary standard, albeit with reduced accuracy, even though it has a measurable tempco. We were very proud of the E1938A crystal oscillator when it was able to meet the 5061 tempco spec. It is in no way a primary frequency standard regardless of that or any other accomplishment. Primary means that the clock will meet its spec without being calibrated against a better clock. Secondary means that calibration against a primary standard is necessary. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
Quoth Poul-Henning Kamp at 2010-02-23 20:22... In message 4b83a33c.1010...@smiffytech.com, Matthew Smith writes: Simple and rather fundamental question: does the common or garden rubidium oscillator constitute an atomic clock? Yes. ... Many thanks for the responses and ensuing discussion that has considerably value-added to the yes/no nature of my original question ;-) Now I know a lot more about primary/secondary standards than I did a (9,192,631,770 Cs wobbles * 86400) ago. I can now proceed with my unconventional calendar design (a cascade of dekatrons) knowing that it will be driven by an atomic ticker. BTW: does anyone know if a 0.55V p-t-p sine wave from an Rb source would be enough to clock an Atmel AVR microcontroller? The crystal/clock input *is* an amplifier, but didn't know if I'd need to do anything to the signal first, to get it closer to the 5V logic level. Cheers M -- Matthew Smith Smiffytech - Technology Consulting Web Application Development Business: http://www.smiffytech.com/ Blog/personal: http://www.smiffysplace.com/ LinkedIn: http://www.linkedin.com/in/smiffy Skype: msmiffy Twitter: @smiffy ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
jmfranke wrote: Therefore, any standard which is compared directly with the transition is a primary standard. Any standard compared to a primary standard is a I don't agree. By your definition the chip scale atomic clock, which uses cesium, would be a primary standard. I don't know of anyone who believes that. Rick Karlquist N6RK ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
In message 4b845267.8080...@smiffytech.com, Matthew Smith writes: BTW: does anyone know if a 0.55V p-t-p sine wave from an Rb source would be enough to clock an Atmel AVR microcontroller? The crystal/clock input *is* an amplifier, but didn't know if I'd need to do anything to the signal first, to get it closer to the 5V logic level. No experience with Atmels, but Microchip's PIC18 work OK, but you may have to AC-couple the signal and bias it to 1.mumble volts with a couple of resistors. -- 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. ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
On Tue, Feb 23, 2010 at 2:10 PM, Matthew Smith m...@smiffytech.com wrote: BTW: does anyone know if a 0.55V p-t-p sine wave from an Rb source would be enough to clock an Atmel AVR microcontroller? The crystal/clock input *is* an amplifier, but didn't know if I'd need to do anything to the signal first, to get it closer to the 5V logic level. AVR's define 0.8*Vcc as V[IH1] and 0.1*Vcc as V[IL1], and you can get AVR's rated down to 1.8V. Your 0.55V signal won't work. Source: page 316 and 322 of the ATmega48/88/168/328 datasheet (http://atmel.com/dyn/resources/prod_documents/8271.pdf), likely any other AVR will have these requirements. -- GDB has a 'break' feature; why doesn't it have 'fix' too? ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
Richard (Rick) Karlquist wrote: David C. Partridge wrote: Cough - the rubidium clock or oscillator does have an intrinsic frequency, which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's just that the frequency generated by the transition in question isn't used to DEFINE the second, so by definition, it must be secondary. Only a Caesium clock is a primary standard, as the second is DEFINED to be the time taken for 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[1]. Unless of course they changed the rules recently ... [1] http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html Dave Well, what you said is true as far as it goes, but not the whole story. The fact that a clock is based on cesium does not necessarily mean it is a primary standard. For example the chip scale atomic clock uses cesium and is a secondary standard. OTOH, certain experimental clocks based on atoms such as rubidium, mercury, etc could be considered primary standards in spite of the definition of the second. Indeed. It's not the type of atom, but the type of clock that is crucial. Cesium usually refers to an atomic beam clock and Rubidium usually refer to a gas cell device. In an atomic beam, the atoms are, on the average, unperturbed, and will transition at exactly the 9192... frequency in the definition of the second. Except that they are offset from this frequency by a known amount due to the C-field. In a gas cell device, the atoms are perturbed by the buffer gas which results in a unknown frequency shift from the 6834... frequency. You have to remove this offset by comparing to a primary standard. We used to say that in theory you could build a cesium beam standard from a kit of parts on a desert island having no other clocks, and when you turned it on, it would be on the correct frequency (within a tolerance) guaranteed by design/physics. There is no way you could do this with a rubidium or cesium gas cell standard to any kind of accuracy associated with atomic clocks (it would only be in the general neighborhood of 6834...) That is the difference between primary and secondary standards. Another difference is that secondary standard have aging and primary standards don't. It should be pointed out that just because you have a caesium beam clock, or lately caesium fointain clock, means that you achieve the full definition of primary standard as give above. A beam standard has many different flaws. Older beam standards will age since the C-field is not being maintained. Modern digital clocks has a servo-loop to ensure that. RF-amplitude, phase-difference betweeen the interaction fields, temperature/average speed of beam provides doppler shifts etc. The repeatability brings many issues in. Caesium beams have excellent repeatability compared to rubidium gas-cells. Any gas-cell standard has wall-shifts, buffer-gas shifts, temperature shift, excitation signal strength and polarisation etc. etc. etc. Rubidium cells forms nice gas-cell standards even if the gas cell technology is limited. Price/performance is usually very good. So... beyond the atom being used, the clock type and the details of its operation needs to be overviewed before a well-founded judgement of it's stability and repeatability... and thus primary standard ability, can be given. Cheers, Magnus ___ 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.
Re: [time-nuts] Rb Oscillator - rather fundamental question
On 02/23/2010 11:10 PM, Matthew Smith wrote: BTW: does anyone know if a 0.55V p-t-p sine wave from an Rb source would be enough to clock an Atmel AVR microcontroller? The crystal/clock input *is* an amplifier, but didn't know if I'd need to do anything to the signal first, to get it closer to the 5V logic level. It will. Set the fuses as you would have for a 10MHz crystal, and capacitively couple the source to XTAL1. Leave XTAL2 open. Do not set the fuses for 'external clock mode'. Do put something like 100pF+1k Ohm in series with the input. While they won't promise anything, I have deliberately run 1A into the protection diodes of an ATMega16 for many seconds and still had a functional part. /Kasper Pedersen ___ 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.
