Echelon LonPoint Application and Plug-In - Manual (Page 97)

The LonPoint Application and Plug-in Guide 9-13
possible step is not necessarily better than a small step; you have to wait longer for
the large step to reach its new process value. Too small of a step will make it too
hard to see when the process has settled. This example uses a 20% step size.
To perform the experiment and calculate the PID coefficients, follow these steps:
1. Open your design with the LonMaker tool, making sure to put your network
OnNet.
2. Right-click the PID controller function block and select Browse from the context
menu.
3. Use the Delete key to remove unnecessary data from the Browser window.
Leave just the rows as shown below.
4. Change the value of the Auto_Man input by entering 0.0 0 in value field.
5. Set the Man_Value network variable to the initial value for the experiment.
The example shows Man_Value as 40%. This puts the PID controller is in
manual mode, and forces its control output to 40%.
6. Right-click the PV network variable and select Monitor Value to turn on
monitoring of the process.
7. Wait for the process reading to stabilize.
8. Record the manual value and the process variable. For the example, these are
40% and 39%.
9. Change the Man_Value network variable to a new value. This example uses
60.
10. Wait for the process to stabilize and record the data. For this example the
results are 60% and 63.11%.
11. Change Man_Value back the original setting, 40% for this example. The
process will stabilize.
The LonPoint PID Tuning Calculator calculates the PID coefficients from the raw
data. Once the Man_Value step is done, the initial and final process variable
readings are known. This gives the static process gain; we know how much the
process variable changes for a given change in the control variable. The process