Hi The conventional MCXO uses an AT cut crystal rather than an SC. It runs on the fundamental and the third overtone. You can build one with just about any normal fundamental crystal. There are also people doing OCXO’s sort of the same way. Back when the MCXO came out, it was about the only way to get a TCXO that had < 1x10^-8 sort of stability. Now you can get that with a cheap (as in not $5,000 each) commercial IC based TCXO.
The weak point in the MCXO is the “dual frequency” oscillator. If one part in one arm ages, that “pulls” the frequency difference. Any change in the frequency difference has the potential of messing up the compensation. The whole process of making sure that the deltas are minimized is a major focus in their design and manufacture. Bob > On Mar 12, 2016, at 8:33 AM, Magnus Danielson <[email protected]> > wrote: > > Hi, > > For the 10811 you can modify it to change mode and then use that mode to > measure and trim the temperature oven. > > There exists crystal oscillators where the 10 MHz is a traditional SC-cut > mode and then a 30 MHz mode is exercised which measures the crystal > temperature. In the Microprocessor Controlled Crystal Oscillator (MCXO) one > then measure the difference in frequency and uses this to re-synthesize a > correction on the 10 MHz. The benefit is that it is the temperature of the > oscillating crystal that is being measured. > Naturally, it could be used for oven control and/or EFC control too. > > The MCXOs exists in manufacturing, but whenever you ask about them they just > wonder what military project are you working on. > > I'd love to experiment with this form of temperature sensing one day, when I > have time... if that ever happens... > > Cheers, > Magnus > > On 03/12/2016 10:21 AM, ken hartman wrote: >> Interestingly, the use of AC-cut crystals (high linear tempco of frequency) >> is found in the development of OCXOs. Using a reference AC-cut resonator - >> in place of the final AT/SC resonator - one can learn much about the >> thermal characteristics of the oven loop performance. While not a precise >> temp sensor, it is a high sensitivity indicator of temperature variations >> of the resonator. >> >> On Fri, Mar 11, 2016 at 11:44 PM, Bill Hawkins <[email protected]> wrote: >> >>> It may be that the need for that kind of resolution died out. >>> >>> The next step up from quartz thermometry is resistance thermometry. >>> The linearization equation for platinum has enough terms to make it >>> uncertain around .01 C. >>> Temperature calibration baths usually use platinum resistance sensors. >>> >>> It may be that the triple point of water does not have the certainty to >>> reach '0.0001C' >>> >>> Disclaimer: I only worked with industrial sensors from Rosemount, Inc. >>> as an employee. >>> >>> Bill Hawkins >>> >>> >>> -----Original Message----- >>> From: Alan Ambrose >>> Sent: Friday, March 11, 2016 11:42 AM >>> >>> Hi, >>> >>> I hope this is still relevant and not too off-topic...but since it >>> involves crystals and tempco... >>> >>> Quartz thermometers (e.g. the HP 2804A) with their 'linear cut' crystals >>> and '0.0001C resolution' seem to have been a thing from the mid-60's to >>> the mid-80's: >>> >>> http://www.hparchive.com/Journals/HPJ-1965-03.pdf >>> >>> There still appear to be some manufacturers making the crystals: >>> >>> http://www.statek.com/products/pdf/Temp%20Sensor%2010162%20Rev%20B.pdf >>> >>> Anyone know why they died out? Did a better technology replace them? >>> >>> TIA, Alan >>> >>> _______________________________________________ >>> 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. >> > _______________________________________________ > 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.
