Interpreting plots for TSC Clock comparisons

Allan Variance

These are the allan variance graphs of the clock in cubin lab and in the machine room.

Cubin Lab

Machine Room

The reason for such graphs can be explained by looking closely towards their offset graphs. The offset graph of the machine room has small cycles in addition to the larger variations of the daily cycle.So the first bend in the graph is due to the these cycles and the second one is due to the actual daily variation.

Offset

Cubin Lab

Machine Room

On a similar time scale the offset of the machine room looks as follows

But if we look much closer, it looks as below

So, the smaller cycles cause the allan variance to bend once before the actual bend caused by the daily variation.

Fake

We can also understand the reason by using the following fake data For off = 1e-8*cumsum(1:2^15) + 0.002 * rand(1,2^15) + 0.005*sin(2*pi*(1:2^15)/256), we get the following graph.

If we remove the "0.005*sin(2*pi*(1:2^15)/256)" (third term in the off), we get