National Instruments FP-3000 - Manual (Page 127)

Appendix F Troubleshooting
© National Instruments Corporation F-9 FieldPoint FP-3000 User Manual
How Many PID Loop Iterations per Second Can the FP-3000 Run?
The FP-3000 can run approximately 50-60 PID loop iterations per second.
You can choose how to distribute these iterations—running one PID loop
50 times per second or 49 PID loops once per second (one loop belongs to
the mandatory resource block). You can also choose a point between these
two extremes.
Note When deciding how fast to run PID loops, keep in mind the update rate of the I/O
modules. For example, the AI-100 has an update rate of 2.8 ms, but the AI-110 has an
update rate of 170 ms to 1500 ms. It does not make sense to run a PID loop at a faster rate
than the update rate. The update rate of the individual I/O modules is documented in the
National Instruments catalog and in the operating instructions of each module.
How Many Channels Per Second Can I Read?
Using OPC with NI-FBUS version 2.3.5—Expect (as a best case) to be able
to read 400 analog or 1000 discrete FP-3000 channels per second. Note that
this is divided among all the devices on the bus. Performing regular reads
with NI-FBUS version 2.3.5 are the same as version 2.3.
NI-FBUS version 2.3—Expect roughly four reads per second from typical
third-party transmitters. Expect (as a best case) to be able to read 30
FP-3000 channels per second. (The FP-3000 is a very fast Fieldbus device.)
How Can I Determine Bandwidth of the Bus?
The bandwidth of the bus affects communications between devices,
including the interface board on the host machine. This is important if you
are running a loop with function blocks from different devices. For
example, a PID loop with the AI block on one device and the PID and AO
blocks on another will not run as fast as a PID control loop contained
entirely within one device. This is due to the time necessary for the data
from the AI to cross the bus. The scheduler in the NI-FBUS Configurator
software will take bus traffic into account when scheduling function block
execution. The amount of information that can cross the bus in a given
period of time depends on several factors including:
• Whether you have adjusted the bus timing parameters to accommodate
slower devices
• How many devices are connected to the bus
• Whether you are using OPC or traditional reads and writes and how
often you have host communications