Time tags are represented as 64-bit integers in picoseconds; therefore the maximum time window of a measurement is approximately 107 days in both directions. However, the measurement accuracy for larger time intervals requires a correspondingly accurate as well as stable clock signal.
The internal clock of our Time Tagger 20 has a clock sufficiently stable to achieve jitter-limited measurements of time intervals up to about 100 ns, whereas with our Time Tagger Ultra and Time Tagger X, the internal clock is sufficiently stable to achieve measurements with a time span of up to 1-10 ms. Our Time Taggers can certainly measure larger time intervals, but users should expect increased time uncertainty beyond these referenced limits. For precise measurements over very long time intervals, users can introduce an external clock source with our Time Tagger Ultra or Time Tagger X.
The time tags are integer numbers in picoseconds relative to the creation of the Time Tagger object. After 107 days, the time tags jump to negative numbers (-107 days) and increase until they reach 0, at which point the counter restarts.