Oversampling
Basics
When operating without oversampling, process data is transferred exactly once per EtherCAT cycle. Conversely, the temporal resolution of a process record directly depends on the communication cycle time. Higher temporal resolution is only possible through a reduction in cycle time - with associated practical limits.
Oversampling enables multiple sampling of an input variable within an EtherCAT cycle and subsequent transmission of the measured values in an array. The oversampling factor describes the number of samples within an EtherCAT cycle and is therefore an integer.
Requirements
- The EtherCAT master is real-time capable.
- Distributed clocks is activated, see chapter Distributed Clocks.
- The cycle time is a maximum of 10 ms (recommended).
- The EtherCAT cycle time must be an integer multiple of the sample time (1/ODR). The integer multiple is the oversampling factor. Permissible oversampling factors are: 2, 4, 8, 10, 16, 20 and 40.
Selecting the oversampling factor
The following table shows the oversampling factors for all permissible combinations of EtherCAT cycle time and sampling rate (ODR) in accordance with the above requirements. Set the oversampling factor by selecting the corresponding Predefined PDO Assignment. See chapter Setting a Predefined PDO Assignment.
EtherCAT | Sampling-Rate (ODR) | ||||
|---|---|---|---|---|---|
4000 Hz | 2000 Hz | 1000 Hz | 200 Hz | 100 Hz | |
0.5 ms | 2 | -- | -- | -- | -- |
1 ms | 4 | 2 | -- | -- | -- |
2 ms | 8 | 4 | 2 | -- | -- |
2.5 ms | 10 | -- | -- | -- | -- |
4 ms | 16 | -- | 4 | -- | -- |
5 ms | 20 | 8 | -- | -- | -- |
8 ms | -- | 16 | 8 | -- | -- |
10 ms | 40 | 20 | 10 | 2 | -- |