With an AT crystal, manufacturing tolerances will likely ensure that the inflection point slope is non zero whereas the same manufacturing tolerances will merely change the turnover temperature. Its likely that a more manufacturable design will result if one operates at a turnover point (with the oven temperature adjusted to the actual turnover) than trying to achieve a sufficiently low slope at an inflection point. Even for a one off design one the selection process required to achieve a sufficiently low slope at the inflection point may prove expensive.
Bruce > > On 03 June 2017 at 09:51 "Donald E. Pauly" <trojancow...@gmail.com> wrote: > > # 2 is not true. A cut has either two turning points or zero. Where > both turning points exist there are two temperatures at which the > temperature coefficient of frequency is zero. Cut 0 on figure 6 at > https://coloradocrystal.com/applications has no turnover point. It is > neither fish nor fowl. Cut 6 is the normal AT curve with extremes of > ±16 ppm for -55° C thru +105° C. All curves normally intersect at 25° > C rather than the 27° C shown. 25° C is half way between -55° C thru > +105° C. Curve 6 is the Tchebychev polynomial y=4x^3-3x and curve 0 > is y=4x^3. > > Consider the standard AT cut which has turnover points at -15° C and > 65° C. The lower turnover would ordinarily not be used in ovens. A > set point error of ±1° C in the upper turnover point at 65° C results > in a frequency error of +14.875·10^-9. For cut 0, that same ±1° error > in room temperature results in a frequency error of ±31.25·10^-12. > This is an improvement of 476 to 1. You apparently have not thought > thru what improvements are possible with thermal coolers/heaters. > Among these is near instant warm up and greatly reduced power for > thermal management. > > πθ°μΩω±√·Γ > WB0KVV > > ---------- Forwarded message ---------- > From: Bob kb8tq <kb...@n1k.org> > Date: Fri, Jun 2, 2017 at 12:43 PM > Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies > To: "Donald E. Pauly" <trojancow...@gmail.com> > > Hi > > Which statement is not true: > > 1) That there is a tolerance on the cut angle of a crystal? > > 2) That true zero temperature coefficient only happens at the turn? > > 3) That heater based controllers are impossible to build? > > Bob > > On Jun 2, 2017, at 3:40 PM, Donald E. Pauly <trojancow...@gmail.com> > wrote: > > That is not true. I say that thermal coolers have made ovens > obsolete. A zero temperature coefficient at room temperature is > easier to hit than a zero temperature at the upper turnover point when > such a thing exists. See > curve 0 in Figure 6 at https://coloradocrystal.com/applications/ . > > πθ°μΩω±√·Γ > WB0KVV > > On Friday, June 2, 2017, Bob kb8tq <kb...@n1k.org> wrote: > > > > > > > > Hi > > > > Any real crystal you buy will have a tolerance on the angle. In the > > case of a crystal cut for turn > > the temperature will be a bit different and you will match your > > oven to it. If you attempt a zero > > angle cut, you will never really hit it and there is no way to > > compensate for the problem. > > > > Bob > > > > _______________________________________________ > > 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.
