At each call, the VI measures the time since the last call and uses that difference in its calculations. If dt is less than or equal to zero, the VI calculates new timing information each time LabVIEW calls it. A VI can acquire timing information either from a value you supply to the cycle time control, dt, or from a time keeper such as those built into the PID VIs. The PID VI and the PID Lead-Lag VI are time-dependent. Potential polling rates are limited only by your hardware and by the number and graphical complexity of your VIs. You can adjust polling rates in real time. You can handle the inputs and outputs through DAQ devices, FieldPoint I/O modules, GPIB instruments, or serial I/O ports. The only elements missing from this simplified VI are the loop-tuning parameters and the automatic-to-manual switching. In the previous images, FT is the flow transmitter, LT is the level transmitter, LC is the level of control, and SP is the setpoint. The following image shows the equivalent LabVIEW block diagram: The following image shows a sample control flowchart: You then can use the PID VIs, combined with the math and logic VIs and functions in LabVIEW, to translate the flowchart into a LabVIEW block diagram. Also include feedback from the process and any required computations. You can design a control strategy by sketching a flowchart that includes the physical process and control elements such as valves and measurements.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |