Question:
How can I determine the required FSoE watchdog time of my slave modules and the resulting reaction time of my safety function?
Answer:
FSoE watchdog time
The recommended FSoE watchdog time T_WD can be calculated according to the formula in chap. 9.3.2 of the ETG FSoE protocol specification. The processing times in the individual subsystems (T_InputFilter / T_Input / T_SafetyPLC / T_Output) and the processing time of the communication (T_FSoE) are included in this calculation. In addition, a reserve of 20% (Delta T) is added.
Depending on the input and output module used, different values may result from the calculation. If one and the same module is used as input and output module of a safety function, the higher value must be used. This can be activated via a checkbox in the attached Excel table.
Response time
The calculated watchdog times are part of the formulas for calculating the maximum reaction time in the event of an error (ETG chap. 9.3.3), which are also described in the c250-S manual (chap. 4.5.4). These formulas can be used to calculate the reaction time of a safety function during error-free operation and when an error occurs in the input or output module.
Note: In the manual of the c250-S the processing time of the communication (T_FSoE) is described with max. 3x of the EtherCAT cycle time, while in the protocol specification of the ETG only a factor of 2x is applied. In the attached Excel table both variants can be calculated by switching a radio button.
