Hi,So, one of my hydrogen masers have a tiny leak. The outer vacuum does not pump down as it should, and it has consumed the ion pump. This have massive effect on the thermal balance and causes heat to leak out much faster from the outer heaters to surrounding wall. This prohibits its controllers of reaching the temperature but also prohibits next layer to achieve it and finally inside that the actual resonator temperature stabilization. That is in itself 5 temperature control-loops in 3 layers. There is also passive heat-shields in it. So, it is crazy efficient heat transfer. It is so efficient method, that it's the basis for pressure gauges, such as the Pirani gauge.
Now, while it is annoying it does not work, I can say that it has significantly increased my knowledge about temperature stabilitzation of hydrogen masers and workings of vacuum systems. Not to say I am fully skilled, but at least not as ignorant as before, so there is a good start. I also learned how to write some Python to log the serial port, toss it into a InfluxDB and plots it with Graphana.
So the effect is real, very real.We are looking into bringing a masspectrometer over, pump it down and then do helium leakage tests to see if we can locate the joint that is leaking. While there is many possible joints in the vacuum system, my testing have helped to narrow it down to three. Of those, in particular one could be suspect as it could potentially take more hit than the others upon transport. Yes, I need a turbopump setup and spare parts.
Cheers, Magnus On 2022-06-13 03:30, Bob kb8tq via time-nuts wrote:
Hi Tear into some of your SC cut based OCXO’s. Take a look at the crystal package. For bonus points, open up the crystal package. If you have the gear to test it, take a look at what the gas *is* inside the package. ( Good luck with that :) :) :) ) If you had the gear and the willingness to scrap out OCXO’s you would find that a number of fast warmup OCXO’s have a *tiny* amount of He in the package. Measuring this would be tough ( it’s that small). Go through the thermal modeling and it’s *way* more conductive (thermal wise) than a *perfect* vacuum …… BobOn Jun 12, 2022, at 9:18 AM, Ross P via time-nuts <[email protected]> wrote: I have seen that manufacturers seal their crystals in a vacuum, maybe air interaction affects Q. The point that vacuum inhibits heat flow is something I have never considered in ovenized units. My ovenized crystals take about an hour to settle. I have some WW2 surplus crystals in non-sealed packages that I have not tested... something to do.rp On Sunday, June 12, 2022 at 07:26:19 AM PDT, Louis Taber via time-nuts <[email protected]> wrote: I have been of the impression for years now that most "better" crystals are in a vacuum. And the electrical and mechanical connections to the quartz itself place as little mechanical load on the crystal as possible. Thermal conductivity from the oven to the crystal itself would be both hard to model and hard to speed up. IR transmission of energy to the crystal also seems problematic considering the IR transmission of quartz and the IR reflectivity of gold contact plating. Is any of this an issue? - Louis On Fri, Jun 10, 2022 at 9:53 PM Bob kb8tq via time-nuts < [email protected]> wrote:HiOn Jun 10, 2022, at 2:38 PM, Lux, Jim via time-nuts <[email protected]> wrote:On 6/10/22 1:57 PM, Dr. David Kirkby wrote:On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <[email protected]> wrote:On the subject of rapid warm up. I suppose if you had a need, one could dump as much power as you need into the heater. Turn on oscillator, lights in room dim for a few moments. Is that not likely to damage a crystal? Different parts of the crystaland likely to be at significantly different temperatures at the same time, putting a lot of stress on the crystal due to a thermal gradient. It's probably a bit academic, as nobody is going to make an oven that heats up in fractions of a second, but if one did, I suspect it might not do the crystal a lot of good. This is only an educated guess - I don't have anything to back it up.Oh, it would be disastrous, although quartz is pretty strong, all therest of the mounting components might not be. Indeed, breaking a quartz blank via thermal stress would be very hard to do. The “rest of the parts” actually are pretty durable as well. Most of it is metal and it is quite able to handle thermal issues. The big issue in a fast warm up AT turned out to be designing the heater and the mount to get the energy to the blank quickly….. If you use a small enough package and blank, the amount of power turns out to be surprisingly small. If you want to go bonkers, you mount the heaters *inside* the crystal package. This does indeed create some issues in various areas. BobAt the other extreme, would there be any advantage in actually heatingthe crystal very slowly, over the course of an hour/day/week, so the temperature gradient across the crystal is very small? Of course, if an oven took ages to reach the correct temperature, it would be inconvenient for most applications, but for some applications, the advantages might outweigh the disadvantages. Of course, if one does this, I suspect one would have to cool the crystal slowly too to prevent a significant thermal gradient across the crystal.I know it's a bit different, but I have a 600 mm f4 Nikon camera lens.I was told that Nikon cools the front element over a period of 6 months to reduce stresses in the glass.Big glass mirrors for telescopes do the same.Dave_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected] _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]
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