Timing problem using simulation loop and DAQ

[Seh]

Hi,

I am currently working on PID controller using labview. When I execute the controller on the plant by using the DAQ assistant, the time displayed on the x-axis of the chart is not the real time. How do I make the time displayed on the chart the same as the real time in seconds? (Since I would like to see how long that the measured temperature converges to the set temperature) 

I have set the generation mode for both my input and output of DAQ assistant to 1 sample(On demand) while the sampling rate is determined by the simulation loop. Is that correct? Can anyone give a brief explaintaion on how to configure the parameters of the simulation loop?

[Stephen_S.]

Hi Seh,

You can edit the display format of the X-axis by right-clicking your graph, and going to Properties>>Display Format, and Selecting Time (X-Axis). If you select Absolute time, the graph should display the time the data was taken, in the format you choose, on your graph.

As for the general timing parameters that you are asking about, how are you doing you PID control? There is a PID Toolkit that is set up for this type of application, as well as a Real-Time Module for deterministic programming. In general, the DAQ assistant is a good way to read simple pieces of data, but it is relatively slow and inefficient compared with the DAQmx VIs if you want to do finely tuned PID control, for example.

Regards,

Stephen S.