Performance; Fieldbus Cycle Time - Omron C200HW-PRM21 Operation Manuals

Performance

3-2

Performance

3-2-1 Fieldbus cycle time

20
This section gives a simplified method of fieldbus cycle time calculations.
Refer to EN 50170 for a more detailed calculation of the fieldbus cycle time.
The fieldbus cycle time with only one master is approximately:
t = (ns + nr) x t
BC
where: ns
nr
t
MC
t
GAP_REQ
t
TC
The calculation of the fieldbus cycle time for multiple master networks is more
complex. For simplicity, extra time needed by each additional master can be
said to equal the time it holds the token and passes the token to the next
station, plus the time to check for live stations. In this case the fieldbus cycle
is approximately:
t = (ns + nr) x t
BC
where: ns
nr
t
MC
nm
t
GAP_REQ
t
TC
For each master station it is possible to specify the target rotation time using
the configurator software. If the actual fieldbus cycle time is less than the
target rotation time, all messages will be transmitted. If not, the master
stations will retain the low priority messages and transmit them at the next or
the following token receptions.
Note The fieldbus cycle time depends on many variables, not only those
mentioned in the formulas above. Therefore the formulas above only
give an approximation of the fieldbus cycle time.
The minimum possible fieldbus cycle time equals approximately 1 ms
(even if the formula gives a lower value).
The message cycle time, the live list check time, and the token cycle time are
explained below.
+ t + t
MC GAP_REQ TC
= number of slave stations
= number of message retry cycles
= message cycle time
= live list check time
= token cycle time
+ nm x (t + t
MC GAP_REQ
= number of slave stations
= number of message retry cycles
= message cycle time
= number of master stations
= live list check time
= token cycle time
Section 3-2
)
TC