National Instruments FP-3000 - Manual (Page 70)

Chapter 4 Block Reference
FieldPoint FP-3000 User Manual 4-18 www.ni.com
milliseconds). The NI-FBUS Configurator does not allow function blocks
to be scheduled any closer together than these maximum execution times.
PID: 8 ms
AI: 6 ms
AO: 6 ms
For one PID loop:
Total time scheduled for function block execution = 20 ms (8 ms +
6 ms + 6 ms). Multiplying this number by 1.5 will allow 30%
unscheduled time = 30 ms
No unscheduled time = 1/0.020 s = 50 iterations per second (for one
loop)
30% unscheduled time = 1/0.030 s = about 33 iterations per second
(for one loop)
For 49 PID loops:
Total time scheduled for function block execution = 980 ms
(49*(8 ms + 6 ms + 6 ms)). Multiplying this number by 1.5 will allow
30% unscheduled time = 1470 ms
No unscheduled time = 1/0.980 s = about one iteration per second
(for each of 49 loops)
30% unscheduled time = 1/1.470 s = about one iteration per
1.5 seconds (for each of 49 loops)
Alarming
The Fieldbus network supports event notification messages from field
devices like the FP-3000. Fieldbus function blocks use event notification
messages to implement alarms and events. Alarms are used to report
conditions that can either be active or inactive. An example of an alarm is
when the measured value of an AI block exceeds the user-defined alarm
limit. The function block sends an event notification alarm to the host each
time conditions transition between active and inactive. Events are
notifications of one-time events as they are detected by the field device. An
example of an event is the update event that is reported as a host application
or operator modifies configuration parameters of the device.