Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

On 11/24/2016 5:16 AM, Bob Camp wrote: The biggest challenge is to take out the “early stuff”. One approach is to fit the same equation twice with the time constant restricted to a range on each. For most OCXO’s (90%) the equation when fit early represents an upper limit to the drift. You

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi > On Nov 23, 2016, at 11:21 PM, Scott Stobbe wrote: > > Hi Lars, > > There are a few other pieces I have yet to fully appreciate. One of which > is that Aln(Bt+1) isn't a time-invariant model. In the most common case > (for the mfg) the time scale aligns with

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi Lars, There are a few other pieces I have yet to fully appreciate. One of which is that Aln(Bt+1) isn't a time-invariant model. In the most common case (for the mfg) the time scale aligns with infancy of the OCXO, when it's hot off the line. However after pre-aging, perhaps some service life,

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

It really means that B will be harder to get a qualitative value for. Also, you need to have "clean" data or else you will be far off. Plot the estimated variant and also plot the difference. As Jim Barnes used to teach, always check the whiteness of matching residues! Cheers, Magnus On

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi Scott. Here is a textfile with data for the 10 years (As in the graph 2001-2011). Also the ln(bt+1) fit, as Magnus said, has the derivate b/(b*t+1) that with b*t >>1 is 1/t. But my data has the aging between 1 and 10 years more like 1/sqrt(t) If I just have a brief look on the aging graph.

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Bob, I have to ask about the B-term. In the paper that Scott started this with I see that B was 4.45. But if I understand you correct Bt<1 even at 30days is normal? That would mean a B of <0.033? Lars >Bob wrote: >In a conventional fit situation, you have < 30 days worth of data and the

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi In a conventional fit situation, you have < 30 days worth of data and the “time constant” is > 30 days. Put another way bt <= 1 in the normal case. It is only when you go out to years that bt gets large. Bob > On Nov 18, 2016, at 9:58 PM, Scott Stobbe wrote: > >

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi Lars, I agree with you, that if there is data out there, it isn't easy to find, many thanks for sharing! Fitting to the full model had limited improvements, the b coefficient was quite large making it essentially equal to the ln(x) function you fitted in excel. It is attached as

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi > On Nov 18, 2016, at 4:36 PM, Magnus Danielson > wrote: > > Hi Lars, > > Now, consider f(t) = a*log(b*t+1), then the derivate is a*b/(b*t+1) and > second derivate - a * b^2 / (b*t + 1)^2. > > Forming first f'(t) and second f"(t) derivate estimates from data

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi Lars, Now, consider f(t) = a*log(b*t+1), then the derivate is a*b/(b*t+1) and second derivate - a * b^2 / (b*t + 1)^2. Forming first f'(t) and second f"(t) derivate estimates from data is trivial. Given that we can estimate a and b using a = - f('t)^2 / f"(t) b = - f'(t) / (f'(t) * t -

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Bob wrote: >As mentioned earlier in this thread. The function that has been used in >several posts >isn’t the right log function. The proper fit is to ln(bt+1) You are absolutely right. It was my mistake to use the ln(t) in the graph. As that was what I know in Excel and I don´t have Stable32

Re: [time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hi As mentioned earlier in this thread. The function that has been used in several posts isn’t the right log function. The proper fit is to ln(bt+1) Bob > On Nov 16, 2016, at 4:36 PM, Peter Vince wrote: > > Hello Lars, > > Just out of curiosity I yesterday put just

[time-nuts] Excel logarithmic function (was Thermal impact on OCXO)

Hello Lars, Just out of curiosity I yesterday put just the first thirty days (like in > the pdf mentioned below) and let Excel calculate the logarithmic function. > If I extrapolate that to 10 years it seems that the drift would be > 6E-13/day but as can be seen in the aging graph it was more