Safety Function Response Time Calculation
Basic values, process safety time (PST)
|
Abbreviation |
Process |
PST |
Note |
|---|---|---|---|
|
SIN_PST |
Single Input / Dual Input |
2.8 ms |
|
|
Func_PST |
Safety function computation |
1 ms |
|
|
STO_Out_PST |
STO output change |
2.2 ms |
|
|
FSoE_PST |
Minimum FSoE cycle time |
5 ms |
|
|
Pos_Change_PST |
Max time to propagate a position change on the encoder to the safety function in the SMM |
2.4 ms |
|
|
Brake_Out_PST |
Brake output change |
4 ms |
|
|
SOUT_PST |
Safe Output change |
4 ms |
|
|
SIN_Fault_Reaction_Time |
Safe Input Fault Reaction |
5.1 ms |
Calculation examples
Time to be set with safety parameters:
- t1 (brake time delay) see AXIS#.SAFEPARAM.SBC.BRAKETIMEDELAY
- t2 (time to STO) see AXIS#.SAFEPARAM.SS1_#.TIMETOSTO
|
Functions |
Calculation |
Response Time |
|---|---|---|
|
STO without SBC |
SIN_PST + Func_PST + STO_Out_PST |
6 ms |
|
STO with SBC (1 or 2 brakes) without SDB |
SIN_PST + Func_PST + STO_Out_PST + Brake_Out_PST + t1 |
9 ms + t1 |
|
STO with SBC with SDB |
SIN_PST + Func_PST + STO_Out_PST |
6 ms |
|
SS1-t with STO (time to activate STO) |
SIN_PST + Func_PST + t2 |
3.8 ms + t2 |
|
SS1-t with STO with SBC without SDB (time to change brake output) |
SIN_PST + Func_PST(SS1-t) + t2 + |
8.8 ms + t2 |
|
Functions |
Calculation |
Response Time |
|---|---|---|
|
STO without SBC |
FSoE_PST + Func_PST + STO_Out_PST |
8.2 ms |
|
STO with SBC (1 or 2 brakes) without SDB |
FSoE_PST + Func_PST + Brake_Out_PST |
10 ms |
|
STO with SBC without SDB |
FSoE_PST + Func_PST + STO_Out_PST + t1 |
8.2 ms + t1 |
|
STO with SBC with SDB |
FSoE_PST + Func_PST + STO_Out_PST |
8.2 ms |
|
Functions |
Calculation |
Response Time |
|---|---|---|
|
Position change to STO |
Pos_Change_PST + Func_PST + STO_Out_PST + t3 |
5.6ms + t3 |
|
Position change to safe output |
Pos_Change_PST + Func_PST + SOUT_PST + t3 |
7.4ms + t3 |
The SMM is using moving average filters to compute both the velocity and the acceleration. This filtering impacts the response time of the safety functions using speed and/or acceleration and must be considered. When computing the response time, the length of the filter (Speed Computation Time Interval/Acceleration Computation Time Interval) must be added to the numbers of the tables above (t3). The size of these filters is configurable (see AXIS#.SAFEPARAM.SPEEDCOMPUTATIONINTERVAL and AXIS#.SAFEPARAM.ACCCOMPUTATIONINTERVAL).
|
In the highly unlikely event that the safe encoder develops an internal fault simultaneously to a feedback reliant safety function being demanded, Pos_Change_PST increases by 5 ms. |
