Micromod Micro-DCI: 53SL6000 Single Loop Controller - Manual (Page 105)

process control element would be moved until tem-
perature increased an additional 9
° from 410 ° to
419
°
. Integral action would continue at each repe-
tition interval until setpoint was reached. In this
way integral action sneaks-up on setpoint. The
time between repetition intervals can be set from
0.02 minutes/repeat (maximum integral action) to
200 minutes/repeat (minimum integral action); 0 is
off.
9.4 Derivative Action (td)
Derivative action (conF-cn.1[cn.2]-td) is used for
quick attainment of stability after sudden process
disturbances. It augments proportional action by
responding to the rate of change of the process
variable. If the error does not change, the output is
proportional only. The rate of change is the incre-
mental difference in the error with respect to an
incremental amount of time, which is the slope (rise
over run) of the error. Derivative action is entered
as time from a minimum value of 0.01 minutes to a
maximum value of 8 minutes; 0 is off.
9.5 Trial and Error Tuning Method
The trial and error tuning method is usually pre-
ferred for process loops that respond quickly, re-
quiring no waiting to determine steady cycling
process conditions. The steps to perform the trial
and error tuning method are as follows:
1. Set the process to approximately normal condi-
tions with the controller in manual mode.
2. Set the integral parameter conF-cn.1(cn.2)-tr
first to 0.02 for several moments, then set it to
200 to lock in a fixed reset value.
3. Set the proportional band parameter conF-
cn.1(cn.2)-Pb to 1000.
4. Set the derivative parameter conF-cn.1(cn.2)-
td to 0.01.
5. Switch to auto mode.
6. Slowly reduce the proportional band parameter
conF-cn.1(cn.2)-Pb from 1000 until process cy-
cling starts.
7. I n c r e a s e t he de r iv at iv e p ar a me te r co nF -
cn.1(cn.2)-td slowly from 0.01 until process cy-
cling stops.
8. Reduce the proportional band parameter conF-
cn.1( cn.2)-Pb until process cycling starts
again.
9. I n c r e a s e t he de r iv at iv e p ar a me te r co nF -
cn.1(cn.2)-td again until cycling stops.
10. Repeat steps 8 and 9 until no improvement can
be made when the derivative parameeter
conF-cn.1(cn.2)-td is increased.
11. Increase the proportional band parameter
conF-cn.1(cn.2)-Pb to a safe margin approxi-
mately 1.5 times the value attained in steps 8
through 10.
12. Introduce integral action slowly by decreasing
the conF-cn.1(cn.2)-tr parameter until cycling
starts.
13. B a c k o f f t h e i n t e g r a l p a r a m e t e r c o n F -
cn.1(cn.2)-tr to a safe margin about 1.5 times
the value attained in step 12.
9.6 Proportional Cycle Tuning
Method
The proportional cycle tuning method is an expedi-
ent procedure for slow processes. The steps to
perform this method are as follows:
1. Set the process to approximately normal condi-
tions with the controller in manual mode.
2. Set the integral parameter conF-cn.1(cn.2)-tr
first to 0.02 for several moments, then set it to
200 to lock in a fixed reset value.
3. Set the proportional band parameter conF-
cn.1(cn.2)-Pb to 1000.
4. Set the derivative parameter conF-cn.1(cn.2)-
td to 0.01.
5. Switch to auto mode.
6. Slowly reduce the proportional band parameter
conF-cn.1(cn.2)-Pb from 1000 until process cy-
cling starts.
7. When a slight cycle is repeatedly established,
measure the peak-to-peak period of oscillation
and record it as T minutes.
8. Observe the proportional band parameter
conF-cn.1(cn.2)-Pb setting and record it as P.
9. Using the multipliers provided, compute the
best settings as follows:
•
Proportional and integral (PI): Pb = 2P; tr
= 0.8T.
•
Proportional and derivative (PD): Pb =
0.8P; td = 0.12T.
•
P r o p o r t i o na l, in te gr a l, an d d er i va ti ve
(PID): Pb = 1.5P; tr = 0.5T; td = 0.12T.
9.7 Step Response Tuning Method
(Ziegler-Nichols)
The step response tuning method is another expe-
dient procedure for slow processes. The step re-
sponse tuning curve is illustrated in Figure 9-1 and
the steps to perform this method are as follows:
1. Set the process to approximately normal condi-
tions with the controller in manual mode.
2. Introduce a 10% (approximate) step change to
the controller output signal. Observe the mag-
53SL6000 Instruction Manual Section 9. Commissioning
9-2