Adjusting The Operating Point In P And Pd Controllers - Samson 430 Series Mounting And Operating Instructions

5. Briefly set the Tn restrictor to its minimum
setting (fully open) to allow the red con-
trolled variable pointer to move to the
green set point pointer. Close the Tn re-
strictor again.
6. Starting from a low value, increase the
proportional-action coefficient Kp until
the controlled variable pointer shows an
harmonic oscillation pattern of the con-
trolled variable (uniform oscillation am-
plitudes as shown in Fig. 4).
If oscillations do not arise with a large
Kp setting, turn the rotary knob to slight-
ly change the set point and then return it
to its former setting. It may be necessary
to increase the gain (Kp) slightly until an
harmonic oscillation pattern arises.
7. Write down the adjusted value on the Kp
scale you have just adjusted as the criti-
cal proportional-action coefficient Kp
Use a stopwatch to time the oscillation
time for one entire oscillation to find T
(PI and PID controllers only).
+
–
T
Kp
P 0.50 · Kp
crit
PI 0.45 · Kp
crit
PID 0.59 · Kp
crit
Fig. 4: Harmonic oscillation, tuning
Multiply both values with the values in the ta-
ble (Fig. 4) and set them as the favorable
settings for Kp, Tn and Tv at the controller.
EB 7030 EN
Controlled
T
crit
variable
(actual value)
crit
Tn Tv
0.85 · T
crit
0.50 · T 0.12 · T
crit
Should oscillations still occur despite these
settings, slightly reduce Kp and increase Tn.
Repeat these steps, if necessary, until the
control loop shows a satisfactory perfor-
mance.
Leave enough time in between settings to al-
low the controller to stabilize.
4.2 Adjusting the operating
point in P and PD control-
lers
Type 3433 Controller Modules only
For P and PD controllers, after setting the
proportional-action coefficient Kp, set the
operating point instead of the reset time as
described above.
When the system is in a steady-state condi-
tion, read the automatic output y
.
troller at the display (1.5) and set this value
crit
directly at the operating point adjuster (12,
Fig. 1) (setting values 0.2 to 1 bar = 0 to
crit
100 %).
Continue to correct until the system deviation
is zero. If the output pressure reading is un-
steady, find the average value.
Note
After the set point is changed, the operating
point must set again as described above.
When the set point is often changed, adjust
the operating point to 0.6 bar (e.g. 50 %,
crit
average value).
Start-up and settings
of the con-
A
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