Definitions of Jitter and Latency

In the “Task Configuration” object, on the “Watchdog” tab, you can monitor the periodic jitter values of the individual tasks at runtime. The periodic jitter is differentiated from latency-based release jitter. See the following definitions:

Periodic jitter

Periodic jitter (J_per) is the deviation of the cycle time of a task (T_per) from the desired task cycle time (T₀).

J_per = T_per - T₀

The desired (ideal) cycle time T₀ is specified in the configuration of the task as “Interval”.

You can monitor the current value, as well as the maximum and minimum value of the periodic jitter, on the “Watchdog” tab of the “Task Configuration”.

If the sum of all negative J_per values and the sum of all positive J_per values do not balance each other, then a drift results.

Latency

Latency is the delay between the invocation of a task and the actual start of its release.

Release jitter

The release jitter J_r is the difference between the maximum and the minimum latency (L) that has ever occurred.

J_r = L_max - L_min

In the case that L_max = L_min, a release jitter J_r of 0. results. This corresponds to a plain offset shift.