Re: [time-nuts] E1938 oven design
Hi I certainly saw the “positive gain at this setting” going to “negative gain at that setting” result on a lot of OCXO designs. I never had the patience (or a stable enough system) to get into the millions or even 100K’s on a single oven. As a practical result, a gain of -500 is not really any better or worse than a gain of +500. It *can* be a bit confusing to set up though …. Bob > On Jun 11, 2017, at 1:43 PM, Richard (Rick) Karlquist> wrote: > > > > On 6/11/2017 8:59 AM, Attila Kinali wrote: > >>> The exact insulation is relatively unimportant. >>> We even tried still air using a knife edge >>> cradle. Didn't make much difference. > > >> What is a knife edge cradle? > > We wanted to test still air as insulation. > We couldn't just replace the insulation with > "nothing". There had to be some kind of mechanical > support to keep the oven mass suspended inside the > outer case. Our ME built a skeleton framework > made of plastic to support it. In order to minimize > conduction thru the plastic, he designed in knife > edges where the plastic came into contact with the > oven mass. > > >> One big question remains: How did you set the ratio >> between face and rim heater? Was it determined at design >> time and then just set the same for all units or was >> it part of the production test? > > During proof of concept phase in R, I peaked up the > thermal gain on each unit by trial and error. I could > usually get a run with positive thermal gain, then > increment the ratio, and get a run with negative > thermal gain. I could then interpolate to get the > ratio that should give "infinite" gain. Maybe one > or two more runs after that would get me to where > the gain passed through infinity at some ambient > temperature, and was well into the millions over the > whole range. At extremely high thermal gain, the > gain is not constant over ambient temperature. > > I collected data on a number of units and then used > the average ratio as the production setting. I > checked production units from time to time and they > typically ran well in the 100's of thousands for gain. > > This compromise was workable because we individually > programmed the oven set point to the exact turnover > temperature. This is a lot easier because it doesn't > require environmental chamber runs. The E1983A software that > I "leaked" to the time-nuts community I believe has a > command that can be used to search for the turnover. > > > Rick N6RK > >> Attila Kinali > ___ > 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] E1938 oven design
On 6/11/2017 8:59 AM, Attila Kinali wrote: The exact insulation is relatively unimportant. We even tried still air using a knife edge cradle. Didn't make much difference. What is a knife edge cradle? We wanted to test still air as insulation. We couldn't just replace the insulation with "nothing". There had to be some kind of mechanical support to keep the oven mass suspended inside the outer case. Our ME built a skeleton framework made of plastic to support it. In order to minimize conduction thru the plastic, he designed in knife edges where the plastic came into contact with the oven mass. One big question remains: How did you set the ratio between face and rim heater? Was it determined at design time and then just set the same for all units or was it part of the production test? During proof of concept phase in R, I peaked up the thermal gain on each unit by trial and error. I could usually get a run with positive thermal gain, then increment the ratio, and get a run with negative thermal gain. I could then interpolate to get the ratio that should give "infinite" gain. Maybe one or two more runs after that would get me to where the gain passed through infinity at some ambient temperature, and was well into the millions over the whole range. At extremely high thermal gain, the gain is not constant over ambient temperature. I collected data on a number of units and then used the average ratio as the production setting. I checked production units from time to time and they typically ran well in the 100's of thousands for gain. This compromise was workable because we individually programmed the oven set point to the exact turnover temperature. This is a lot easier because it doesn't require environmental chamber runs. The E1983A software that I "leaked" to the time-nuts community I believe has a command that can be used to search for the turnover. Rick N6RK Attila Kinali ___ 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] E1938 oven design
On Thu, 8 Jun 2017 16:17:20 -0700 "Richard (Rick) Karlquist"wrote: > We were stuck under 1,000 for a long time > using only face heaters. I still remember the > day that I rigged up the first crude rim header > by winding a piece of magnet wire around the rim > and holding it in place with 5 min epoxy. I > didn't know what else to try. This seemed like > a Hail Mary play at the time, until I > measured the gain. We instantly went to gains > above 20,000. It seemed high at the time but > it was only the beginning. > > The exact insulation is relatively unimportant. > We even tried still air using a knife edge > cradle. Didn't make much difference. What is a knife edge cradle? One big question remains: How did you set the ratio between face and rim heater? Was it determined at design time and then just set the same for all units or was it part of the production test? Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] E1938 oven design
Yes, that's right. The copper oven mass has two pieces: a main piece and a lid. The main piece has a wall around the outside into which the cover fits, using an O-ring. In the center, there is a cylindrical cavity into which the crystal mounts. It is like a 10811 crystal, except the height is reduced. In retrospect, there is no reason why the 10811 crystal shouldn't have been that size. It is potted into the cavity, therefore, it doesn't use the famous flat head 4-40 screw welded to the can as in the 10811. Thermistors are potted into holes drilled in the cavity wall. The lid has screws that screw into the cavity wall. The main piece holds a circular PC board containing the bridge oscillator circuit. It has a big hole in the middle for the crystal cavity. The production people immediately named it the "donut board." And the finished oscillator is the "hockey puck". Summarizing, the crystal is very well thermally connected to the copper oven mass. There are 3 flex circuit heaters. One for the lid, one for the other face of the main piece, and one that goes around the outside. The two face heaters are operated together as one heater. The ratio of heat to the faces vs the outside rim is adjusted for maximum thermal gain. The rim heater is the difference between under 1,000 gain and over 1,000,000 gain. We were stuck under 1,000 for a long time using only face heaters. I still remember the day that I rigged up the first crude rim header by winding a piece of magnet wire around the rim and holding it in place with 5 min epoxy. I didn't know what else to try. This seemed like a Hail Mary play at the time, until I measured the gain. We instantly went to gains above 20,000. It seemed high at the time but it was only the beginning. The exact insulation is relatively unimportant. We even tried still air using a knife edge cradle. Didn't make much difference. Rick N6RK On 6/8/2017 1:27 PM, Attila Kinali wrote: On Wed, 7 Jun 2017 14:21:52 -0700 "Richard (Rick) Karlquist"wrote: The crystal case is well connected to the oven mass and gets heated by conduction. I don't think radiation is a player. Do I interpret the papers correctly, that the oven mass is a closed can, with the crystal holder "molded" into it? Then wrapped around it are the face and the rim heaters, and outside those comes the insulation and the outer can? Attila Kinali ___ 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] E1938 oven design (was: Poor man's oven)
On Wed, 7 Jun 2017 14:21:52 -0700 "Richard (Rick) Karlquist"wrote: > The crystal case is well connected to the oven mass and gets > heated by conduction. I don't think radiation is a player. Do I interpret the papers correctly, that the oven mass is a closed can, with the crystal holder "molded" into it? Then wrapped around it are the face and the rim heaters, and outside those comes the insulation and the outer can? 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.