12-22-2006 08:18 AM
01-03-2007 07:14 AM
Hi zermelo,
You just have to build a kind of selector (case selector could be button on front panel) where you choose either one or two inputs for the PID control. But you have to keep in mind, the PID VIs needs the setpoint and also the process variable as input. So for the case of two inputs you can wire them through, but for the case with only one input, so the error or differntial signal you have to build your setpoint and process variable to route them to the PID VI (e.g. by adding a constant: 1+error=process variable, setpoint=1).
BR, Christian
01-31-2007 10:15 AM
Hi zermelo:
The PID algorithm requires that you provide the process variable as well as the setpoint. It is true that an error signal is calculated from the process variable and setpoint, which will be used subsequently in the algorithm. However, the algorithm still uses the process variable signal. In order to have a PID VI that takes the error signal as an input without providing the setpoint and the process variable, you need to modify the PID code yourself. The following link should give you a brief introduction to PID controllers
http://zone.ni.com/devzone/cda/tut/p/id/3782
Also, I would recommend that you look at the book by Karl Astrom on control system design (try google for that). This should give you more in-depth ideas about the different PID algorithms.
Please let me know if you have more questions.
Cheers...
05-02-2014 01:31 AM
Or you could simpy set the setpoint input on the PID to be your error signal and the process variable to be zero.