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 <[email protected]> > 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&D, 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
