103
SC-F70
SC-F70
PID Operation Operating Instructions
8. PID Constants Manual Tuning Method
Among various Auto-tuning or manual method for determining proper PID
constants, this section introduces two manual methods. The manual
methods are effective when Auto-tuning does not provide the proper values.
If you still cannot obtain satisfactory control results even if you use the
methods described here, refer to "3.6 PID Constants Fine Tuning Method" on
page52.
8.1 Step Response Method
In this method, you change the control output values in steps, and you
measure and analyze a value for each step to attain the best PID values.
You need a recorder to trace the measured value change. This method is
done in MAN/LOC mode.
1. Set the controller in the MAN/LOC mode. See page 25.
2. Adjust the control output with the or key until the
measured value almost reaches the target setting value.
3. Wait until the value stabilizes a little below the target measurement
value.
4. Start a recorder to record the variation of the measured value.
5. Quickly increase the control output 5 to 15% over the value set in step
3. Write the variance (
D
MV) of this increase.
6. The recorder should show a graph like
that shown at the lower right. Draw a
tangent crossing the inflection point
of the S curve. The intersection point
of the tangent and old equilibrium
value gives L and T (sec).
7. Specify the value variation as
D
PV,
and define the process gain Kp using
the following equation:
Kp =
D
PV
¥
100
¥
1
(Measurement range)
D
MV
<
<
△MV
control output
the point to
change the
control output
infrection
point
measured value
L
T
△PV
time
time