Echelon LonPoint Application and Plug-In - Manual (Page 98)

9-14 PID Controller Functional Block
variable delta, delta PV, is the difference between the final and initial process
variable readings; the control variable step causes a process variable change of
delta PV
.
In the next part of the experiment, the dynamic properties of the process are found.
There are two time intervals that need to be measured. They are named T1 and
T2. Both intervals start when the control variable step change is made. T2 is the
time required to attain 28.8% of delta PV. T1 is the time required to reach 63.2% of
delta PV. These specific percentage values are dictated by the two-point tuning
method used in this example.
To start the LonPoint PID Tuning Calculator, open the Windows Start menu, select
the LonPoint Device Software program folder, then select PID calculator. Enter
the CV and PV data as shown below. Make a note of the PV at T2 and PV at T1
values. This says that T2 is defined as the time it takes for the process variable to
reach a value of 44.66. T1 is the time it takes to reach 51.76.
In this part, we will step the process again, watch for the process variable to reach
the PV at T2 and PV at T1 values, and record the T1 and T2 times:
1. Using the LonMaker Browser, change the Man_Value network variable to the
step value and start timing. This example uses a final step value of 60.
2. Watch the process variable, which is being monitored, to see when it reaches
the calculated T2 value; 45 in this example.
3. Record the time and keep watching PV, record the time when the T1 value is
reached; 52 in this example.