What Kind of Data Throughput Should I Expect from an FP-3000? Hardware: FieldPoint>>Controllers/Network Modules>>FP-3000
Problem: I would like to know what the data throughput of an FP-3000 is. Solution: There are two factors affecting the throughput of the FP-3000:
If you are running a PID control loop that is entirely contained on the FP-3000 (i.e., the AI, PID, and AO blocks are all instantiated on the FP-3000) with no interaction with an HMI (Human-Machine Interface) software package (such as Lookout or BridgeVIEW), then you can expect a minimum 50 Hz control loop. Add the worst-case function block execution time for each function block in the loop to this minimum. A PID control loop has one AI, one PID, and one AO block. Together they take 20 ms. (The maximum execution time of a function block is a function block parameter you can find in the Configurator under the Block Information tab for the individual function block.) For example, if you want to run 10 PID control loops, then at 20 ms each, this will be a total of 200 ms of execution time (one-fifth of a second). You could run 10 loops as fast as 5 times per second. Be aware that the Expression block takes significantly longer to execute than other function blocks and is dependent of the downloaded expression. See KnowledgeBase 1KIED0B7 (linked to below) for more specific information on the rate at which function blocks can execute entirely within one FP-3000. Bandwidth 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 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:
Rule of Thumb: The best results are obtained by making sure that 30-40% of the total schedule (macrocycle) is available for unscheduled communications. With slow devices (this does NOT include the FP-3000) you can often include a large part of the time that function blocks are executing in your calculation of this percentage. This is because, on slow devices, only a small part of the execution time involves broadcasting information over the bus. During the rest of the execution time, there is no scheduled communication on the bus. With the FP-3000, the function block execution times are so short that there is usually not enough time to send an unscheduled message between the scheduled broadcasts of the function blocks. In this case, you need to include extra time in your macrocycle for unscheduled communication. Rules of Thumb concerning interaction with the host:
Related Links: KnowledgeBase 1KIED0B7: How Many PID Loop Iterations per Second Can the FP-3000 Run? KnowledgeBase 1O3CJ7US: Sampling Speed of FieldPoint Modules Attachments:
Report Date: 12/16/1999 Last Updated: 09/15/2008 Document ID: 1SFE93QV |
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