Using identification method in PID module to determine Kr, Tv, Tn

[AW22]

Hi all,

DASYLab 2016 full version

Setup:

I'm trying to use the PID module's built in method for determining the Kr, Tv, Tn coefficients but I'm not sure I'm setting it up right. I have a flow meter that is giving me a 0-10V input signal that I scale to determine airflow (cfm). I control airflow by using a 0-10V analog output (USB 3105) wired to a fan that I want the PID loop to drive. I have a set point and the scaled airflow as inputs to the PID module and am limiting the output of the PID module to be 0-10 to be in the required range for fan control. I set the module to one of the working modes. For the parameter determination, I have a manual slider that I can set the voltage output directly to the fan. At measurement start, I bump the output of the fan by a couple volts to get a response curve.

Problem:

I get an error after a few seconds of measurement start that says Ta/Tu < 3. Now from the DASYLab help I see this graph:

but when I look at the response that I measure when I disable the PID module and bump the output from 2 to 4V is this:

which shows that Ta/Tu is close to 13. This leads me to believe that I'm missing something in the set up of the PID module when I run the identification mode. 

Does anyone have some insight on where I might be going wrong?

Thanks,

AW