**OPTIMUM PID CALCULATION
FOR SELF REGULATING (SR) PROCESS**

based on Zieglar-Nichols
formulation

**1. The Fundamental**

1. The white line represents
a response curve from a process.

2. The red line represent
a tangent line drawn at the steepest point.

3. The broken yellow line
with arrow shows the deadtime.

4. The broken yellow line,
making a triangle with the red line, shows how to calculate the process
rate at the steepest point.

5. Calculate the reaction
rate (RR) i.e. the process rate per change in controller input as shown
above.

6. Choose the desired mode
i.e. P or PI or PID and calculate the PIDs.

**2. Example using data
captured from a paperless recorder**

1. Td = 1.8 s

2. RR = 0.2368 / s

3. Mode = PI : P = 47.4%
and I = 6 s

**3. Example using data
captured from a chart recorder**

1. Td = 1.8 s (Notice that
Td is unmeasureable. Since I and D require Td, then estimate Td.)

2. RR = 0.231 / s (Notice
that the chart speed is in mm/hr. Convert the speed into s/mm. Then, the
time is

simply
the length in mm x the chart speed in s/mm.)

3. Mode = PI: Therefore,
P = 111.1 x 1.8 x 0.231 = 46.2% , I = 3.33 x 1.8 = 6 s
(Notice that the time unit

for Td
must be similar with RR. Else, the time unit does not cancel with each
other.)

**TEST
YOURSELF: Can you calculate the optimum PI for this process.**

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