Re: [time-nuts] HP5065A C-field mods and optical unit mods
Hi One interesting claim made “back in the good old days” was that certain pots had near zero TC when used as radiometric devices. Essentially the metal on one side “always” had the same characteristics as the metal on the other side of the wiper. People would go to great extremes to exploit this “well known fact”. Oddly enough I never really saw much proof that this was true ….You still see people doing things this way though. It was a major “design item” with a certain company that made both potentiometers and OCXO’s …. === At some point, the magnetic field of the car in the garage gets into the act on your Rb standard. There *is* a point where all sorts of things start to be questioned. Shielding is only just so good. That’s true if it’s heat shielding, magnetic shielding or whatever …. Once you get into the “part in 10^-15” range on an Rb, you are well past the “show me” level of effects. You can (correctly) calculate that this or that is the impact. Demonstrating that it works that way at that level … not so much. Why worry about demonstrating this or that? Often second or third order effects pop up as you “null out” the first order stuff. Hysteresis in the TC of a “compensated” standard is one very common example. At this point it’s not a big surprise when it shows up. That was not always the case …. None of this is easy, there always is a lot more work involved that one might think. Bob > On Nov 22, 2017, at 12:04 PM, cdel...@juno.com wrote: > > HP5065A C-field mods and optical unit mods > > The contribution of the temperature coefficients of the fixed resistors > and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up > as frequency errors as shown for several combinations. > > Note that the pot does not cover the entire 2X10-9 frequency range. > There is a high, mid, and low switch setting that shorts both 1k, > one 1k, or neither 1k resistor that in conjunction with the pot allows > the entire range to be covered. This allows the pot to have a finer > frequency resolution > > A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C > change > will cause a 2.8X10-15 frequency change. > > B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will > cause a 8.55X10-15 frequency change. > > C- With the 2.4K in combination with the pot at 1K and both 1K resistors > in > circuit a 1 Deg C change will cause a 3.99X10-15 frequency change. > > If in example C you replace the pot with a 100PPM pot a 1 Deg C change > will equate to a 2.45X10-14 frequency change. > > As you can see this circuit will work quite well in eliminating any power > supply related C-field changes. > > Now the C-field coil is only partially temperature regulated by the > ovens in the optical unit as they regulate the lamp and cell > temperatures > and the C-field is not co-located. > > That is why I'm going to use the PC liquid cooler to actively regulate > the > temperature of the sealed enclosure I have placed the optical unit into. > > Cheers, > > Corby > > ___ > 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.
[time-nuts] HP5065A C-field mods and optical unit mods
HP5065A C-field mods and optical unit mods The contribution of the temperature coefficients of the fixed resistors and the pot (which is a 21 turn bulk metal foil 10PPM/Deg C pot) show up as frequency errors as shown for several combinations. Note that the pot does not cover the entire 2X10-9 frequency range. There is a high, mid, and low switch setting that shorts both 1k, one 1k, or neither 1k resistor that in conjunction with the pot allows the entire range to be covered. This allows the pot to have a finer frequency resolution A- With only the 2.4K in circuit with the pot at zero Ohms a 1 Deg C change will cause a 2.8X10-15 frequency change. B- With the 2.4K in combination with the pot at 1K a 1 Deg C change will cause a 8.55X10-15 frequency change. C- With the 2.4K in combination with the pot at 1K and both 1K resistors in circuit a 1 Deg C change will cause a 3.99X10-15 frequency change. If in example C you replace the pot with a 100PPM pot a 1 Deg C change will equate to a 2.45X10-14 frequency change. As you can see this circuit will work quite well in eliminating any power supply related C-field changes. Now the C-field coil is only partially temperature regulated by the ovens in the optical unit as they regulate the lamp and cell temperatures and the C-field is not co-located. That is why I'm going to use the PC liquid cooler to actively regulate the temperature of the sealed enclosure I have placed the optical unit into. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
Charles, Imagine having a source and fixed resistors with TC equal to zero. The current variation of the coil varies between 2.5 and 6 mA. In addition, the relationship between current and frequency variation of the HP5065A is not linear. If the pot is short-circuit, the current is 6 mA and the overall TC is that of the imaginary generator ie zero, in our real case 1ppm / C (source+fixed resistors). So the pot TC is completely irrelevant. When the pot is fully inserted the current will be 2.5mA, so the total current variation is 3.5mA. The whole thefull range of pot resistance generates a 3.5mA current variation. This variation generates a frequency fine adjustment of 2E-9. As a result, the influence of the pot TC is directly correlated to the current stability with a nonlinear frequency variation between zero and X in the range of 6- 2.5mA. Or not? best regards, Luciano timeok Da "time-nuts" time-nuts-boun...@febo.com A "Discussion of precise time and frequency measurement" time-nuts@febo.com Cc Data Tue, 21 Nov 2017 15:16:36 -0500 Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods Luciano wrote: > what you refer is the resistance relation referred to the LM299 source around 14VDc but you have to consider > the tuning range of the pot, in the original HP5065A is 2E10-9. > Of course, it depends on the setting value of the variable resistance, but you have to consider a possible variation of 20PPM/c on 2E10-9. No, you don't. The tempco that matters is the aggregate tempco of the series string. Only a very small portion of the string voltage appears across the pot, so a 20ppm tempco of that small part will cause a much smaller change in overall tempco of the series string. Perhaps Corby will tell us what value the pot is, and then you can calculate the aggregate tempco of the string at various pot settings and see for yourself. Charles ___ 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] HP5065A C-field mods and optical unit mods
In message <1159987519.5777361.1511296831...@webmail.xtra.co.nz>, Bruce Griffit hs writes: >What is the effect of the C-field coil dimension tempco? I have not been able to measure it. The C-coil is located thermally close to the temperature controlled parts of the physics package. -- 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] HP5065A C-field mods and optical unit mods
What is the effect of the C-field coil dimension tempco? At some point this will surely dominate overthe coil current tempco. Bruce > > On 22 November 2017 at 09:16 Charles Steinmetz > wrote: > > Luciano wrote: > > > > > > what you refer is the resistance relation referred to the LM299 > > source around 14VDc but you have to consider > > the tuning range of the pot, in the original HP5065A is 2E10-9. > > Of course, it depends on the setting value of the variable > > resistance, but you have to consider a possible variation of 20PPM/c on > > 2E10-9. > > > > > > No, you don't. The tempco that matters is the aggregate tempco of the > series string. Only a very small portion of the string voltage appears > across the pot, so a 20ppm tempco of that small part will cause a much > smaller change in overall tempco of the series string. > > Perhaps Corby will tell us what value the pot is, and then you can > calculate the aggregate tempco of the string at various pot settings and > see for yourself. > > Charles > > ___ > 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] HP5065A C-field mods and optical unit mods
Luciano wrote: what you refer is the resistance relation referred to the LM299 source around 14VDc but you have to consider the tuning range of the pot, in the original HP5065A is 2E10-9. Of course, it depends on the setting value of the variable resistance, but you have to consider a possible variation of 20PPM/c on 2E10-9. No, you don't. The tempco that matters is the aggregate tempco of the series string. Only a very small portion of the string voltage appears across the pot, so a 20ppm tempco of that small part will cause a much smaller change in overall tempco of the series string. Perhaps Corby will tell us what value the pot is, and then you can calculate the aggregate tempco of the string at various pot settings and see for yourself. Charles ___ 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] HP5065A C-field mods and optical unit mods
Hi Charles, what you refer is the resistance relation referred to the LM299 source around 14VDc but you have to consider the tuning range of the pot, in the original HP5065A is 2E10-9. Of course, it depends on the setting value of the variable resistance, but you have to consider a possible variation of 20PPM/c on 2E10-9. Regards Luciano timeok Da "time-nuts" time-nuts-boun...@febo.com A time-nuts@febo.com Cc Data Tue, 21 Nov 2017 06:31:25 -0500 Oggetto Re: [time-nuts] HP5065A C-field mods and optical unit mods Luciano wrote: > about the C field ten turn pot you write is a low TC pot. Normally a good Vishay pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage reference. In the schematic Corby posted, the potentiometer (used as a variable resistor) makes up a very small part of the total resistance of the series string, so the overall tempco is dominated by the tempcos of the fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim). The pot will increase the overall tempco a little bit, but not anywhere near 20ppm. Best regards, Charles ___ 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] HP5065A C-field mods and optical unit mods
Luciano wrote: about the C field ten turn pot you write is a low TC pot. Normally a good Vishay pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage reference. In the schematic Corby posted, the potentiometer (used as a variable resistor) makes up a very small part of the total resistance of the series string, so the overall tempco is dominated by the tempcos of the fixed resistors (2.4k to 4.4k 1ppm/ C, depending on trim). The pot will increase the overall tempco a little bit, but not anywhere near 20ppm. Best regards, Charles ___ 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] HP5065A C-field mods and optical unit mods
Hi Corby, about the C field ten turn pot you write is a low TC pot. Normally a good Vishay pot is 20 PPM/C, This is in conflict with the 1PPM resistors ad voltage reference. What kind of pot do you have used? http://www.mouser.com/ds/2/427/533534-768216.pdf Luciano timeok Da "time-nuts" time-nuts-boun...@febo.com A time-nuts@febo.com Cc Data Fri, 17 Nov 2017 12:37:57 -0800 Oggetto [time-nuts] HP5065A C-field mods and optical unit mods Luciano, The TX and choke and filter caps were removed as I had envisioned I would have to re-mount the A1 and A7 in their location. However with some judicious movement of the mounting holes I was able to squeeze them in close to their original spots. The 5065 chassis was removed and inserted into a chassis from an HP 8405A. (just used the side panels and the rear panel.) I'll post a schematic of the new C-field supply next week. It consists of two LM299AH in series feeding a string consisting of a 2.4K, 1k, 1K and a 1K low TC pot. A switch allows you to short out one or both of the 1K resistors as a coarse adjustment. All resistor are 1PPM. Fixing the 20Volt and the C-field temperature contributions allowed me to isolate the optical units changes due to temp. The resistor thermistor combo I mentioned would be taped to the optical unit and compensate it only. It would be in series with the C-field coil. Not needed in my unit but thought that others might want to try it rather than getting as complex as I have. Yes the active baro and temp circuit would be an alternative for a unit without my mods. attached are PIX of the enclosed optical unit and the front panel. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
In message <5AC3D7F0C1F14BAB8B7BE4A552034FCC@dell370>, ws at Yahoo via time-nuts writes: >C-fields are current sensitive, so if they are wound with copper wire, any >small change in their temperature, even when temperature controlled, could >have a effect much greater than 1PPM on that current when driven from a >fixed voltage thru a resistor. > >Does anyone use current drive? The standard circuit is current drive... -- 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] HP5065A C-field mods and optical unit mods
Warren, Most all Rubidium standards do not have active current drive. The HP 5065A is the exception. However the mod I installed is not active. The C-field coils are roughly temperature compensated as they are near the cell oven that is regulated. If you check out Poul-Hennings "hacking the 5065a" you will see that the C-field coil does exhibit some temperature effect even with active current regulation, and the stock C-field circuit also introduces some effects. Now these amount to a small coefficient but we are Time Nuts here so we can do better! My circuit gives a precise current into the coil (for a fixed temperature of the coil), and with the active temperature stabilization I am adding to the outside of the sealed optical unit enclosure those effects will be eliminated. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
Corby Just a 1 cent thought that may not apply or be accurate. C-fields are current sensitive, so if they are wound with copper wire, any small change in their temperature, even when temperature controlled, could have a effect much greater than 1PPM on that current when driven from a fixed voltage thru a resistor. Does anyone use current drive? ws * Corby posted: Attached is the schematic of the C-field supply. Cheers, Corby ___ 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] HP5065A C-field mods and optical unit mods
Attached is the schematic of the C-field supply. Cheers, Corby___ 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] HP5065A C-field mods and optical unit mods
Hi Corby, I would first like to thank you for sharing your precious studies with us. I love the HP5065A because it's an extremely interesting project and I'm convinced like you we have a lot of room for improving its performance. * In addition to the power supply mods: -removed AC components -power now supplied with an external DC lab grade low noise highly regulated supply. -temperature coefficient of +20 Volt supply adjusted to be below 1PPM/deg C See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html ** My approach to modifying some equipment is to try to keep it as good as possible under original conditions unless the modification leads to a substantial increase in specifications. For this reason I do not understand why you have removed the power transformer and its filter inductance. You could power it from the DC input and leave disconnected the AC power supply or have I missed a reason to do this? ** I've now installed the improved C-field circuit that has less than +- 1PPM variation per degree C. ** It would be very interesting to see the schematic of your solution. I have tested a simple ssolution replacing the R12 (333Ohms) with parallel of a 470 Ohms and a 5k Ohms NTC, this mounted in the middle of the chassis. I must admit, however, that I do not have a suitable instrumentation and a Maser reference to make appropriate measures. ** The optical unit has been installed into a sealed enclosure that has been purged with dry Nitrogen. This eliminates any Barometric pressure effects and also eliminates drift caused by Helium permeation. Tests at this point show a very nice long term stability. Last mod will use a small PC closed loop liquid cooler to keep the outside of the sealed enclosure at a constant temperature essentially making it a double oven. *** Do you have any more detailed photographs? *** I'm also working on: An active temp compensation scheme to add to the active barometric compensation I outlined earlier. See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html And a passive optical unit temperature compensation using a thermistor/resistor arrangement. * [C:\Users\PRINCI~1\AppData\Local\Temp\msohtml1\01\clip_image001.gif] As you have previously written , boxing the 5065A physical module solve the problem of barometric pressure variation, making an active compensation is an alternative are you studying? Hope to read you soon, Luciano Timeok Da "time-nuts" time-nuts-boun...@febo.com A time-nuts@febo.com Cc Data Thu, 16 Nov 2017 12:58:13 -0800 Oggetto [time-nuts] HP5065A C-field mods and optical unit mods HP5065A C-field mods and optical unit mods In addition to the power supply mods: -removed AC components -power now supplied with an external DC lab grade low noise highly regulated supply. -temperature coefficient of +20 Volt supply adjusted to be below 1PPM/deg C See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html I've now installed the improved C-field circuit that has less than +- 1PPM variation per degree C. The optical unit has been installed into a sealed enclosure that has been purged with dry Nitrogen. This eliminates any Barometric pressure effects and also eliminates drift caused by Helium permeation. Tests at this point show a very nice long term stability. Last mod will use a small PC closed loop liquid cooler to keep the outside of the sealed enclosure at a constant temperature essentially making it a double oven. I'm also working on: An active temp compensation scheme to add to the active barometric compensation I outlined earlier. See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html And a passive optical unit temperature compensation using a thermistor/resistor arrangement. PIX shows the sealed optical unit installed into a slightly taller chassis. (The 5065C ?) Cheers! Corby ___ 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] HP5065A C-field mods and optical unit mods --> OFF LIST !!!
Hi So, when do they go up for sale? :) ( = If and when they do, I’m still shopping for one) Bob > On Nov 16, 2017, at 3:58 PM, wrote: > > HP5065A C-field mods and optical unit mods > > In addition to the power supply mods: > -removed AC components > -power now supplied with an external DC lab grade low noise > highly regulated supply. > -temperature coefficient of +20 Volt supply adjusted to be > below 1PPM/deg C > See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html > > > I've now installed the improved C-field circuit that has > less than +- 1PPM variation per degree C. > > The optical unit has been installed into a sealed enclosure > that has been purged with dry Nitrogen. This eliminates > any Barometric pressure effects and also eliminates > drift caused by Helium permeation. > > Tests at this point show a very nice long term stability. > > Last mod will use a small PC closed loop liquid cooler to > keep the outside of the sealed enclosure at a constant temperature > essentially making it a double oven. > > > I'm also working on: > > An active temp compensation scheme to add to the > active barometric compensation I outlined earlier. > See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html > > And a passive optical unit temperature compensation using a > thermistor/resistor > arrangement. > > PIX shows the sealed optical unit installed into a slightly taller > chassis. (The 5065C ?) > > Cheers! > > Corby<5065crs.jpg>___ > 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.
[time-nuts] HP5065A C-field mods and optical unit mods
HP5065A C-field mods and optical unit mods In addition to the power supply mods: -removed AC components -power now supplied with an external DC lab grade low noise highly regulated supply. -temperature coefficient of +20 Volt supply adjusted to be below 1PPM/deg C See: https://www.febo.com/pipermail/time-nuts/2017-August/106634.html I've now installed the improved C-field circuit that has less than +- 1PPM variation per degree C. The optical unit has been installed into a sealed enclosure that has been purged with dry Nitrogen. This eliminates any Barometric pressure effects and also eliminates drift caused by Helium permeation. Tests at this point show a very nice long term stability. Last mod will use a small PC closed loop liquid cooler to keep the outside of the sealed enclosure at a constant temperature essentially making it a double oven. I'm also working on: An active temp compensation scheme to add to the active barometric compensation I outlined earlier. See: https://www.febo.com/pipermail/time-nuts/2016-May/097829.html And a passive optical unit temperature compensation using a thermistor/resistor arrangement. PIX shows the sealed optical unit installed into a slightly taller chassis. (The 5065C ?) Cheers! Corby___ 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.