PID Loop Performance Guidelines for LabVIEW Real-Time on a PXI-8176 Target

Primary Software: LabVIEW Modules>>Real-Time Module
Primary Software Version: 6.1
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
Where can I find PID loop performance guidelines for LabVIEW Real-Time (RT) on a PXI RT system?

Solution:

The following table lists some performance estimates. Remember that performance results vary, depending on the particular system and the specific computations that occur within a given PID control loop; the table below provides estimated upper limit performance bounds.

The system used in this case was a PXI-8176 with a 1.2 GHz processor and 128 MB of DRAM. The tests were performed with LabVIEW RT 6.1 and NI-DAQ 6.9.2. The tests were run with the VI set for "time-critical" priority. Note: Adding host PC communication into these applications would lower the numbers in the table. See the attached VI for an example of such a test.

The PID Control Toolset was used in these calculations. For more information on the PID Control Toolset, see the Related Link (below).

Number of PID Loops	(PID Control Toolset 6) Rate in Hz
1	40000
2	27000
4	18000
8	10000
16	5000
32	2400

If you are having trouble achieving these rates, it may be due to particular configuration settings of your system. Most often, slower than expected performance is observed when the USB port is not disabled. Make sure that USB is disabled in the BIOS of your controller. See the link below for more information on general performance improvements.

- PID1.llb

Report Date: 01/11/2002
Last Updated: 07/27/2007
Document ID: 2HADGKZ8

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