17.5 MODIFICATIONS TO TUNING CRITERIA
During EASY-TUNE sequence execution, each of the three algorithm variables: Time Constant
(T
P
), Process Gain (K
P
),
and Dead-Time (W
P
) are altered by 10% in the
conservative
direction
(controller operating characteristics would be slower response, but less chance of oscillation and
instability) before the tuning parameters are computed using the ITAE equations listed in Table
17-5. (Figure 17-2 illustrates the equation variables with respect to the response curve.) The
three variables
T
p
, K
P
, and W
P
can be increased numerically to compute tuning parameters that
are more conservative or decreased for
less conservative
tuning parameter calculations (controller
operating characteristics would be faster response and greater chance of instability or oscillation).
Parameters used to alter the variables are the EASY-TUNE Modifiers, datapoints C382 (T
P
Modi-
fier), C383 (D
P
Modifier), and C384 (W
P
Modifier). It is recommended that the values entered in
C382, C383, and C384 be between -0.5 and 0.5. The effect on the equation variables is as follows:
T
P
modified = T
P
(1 - C382)
K
P
modified = K
P
(1+ C383)
W
P
modified = W
P
(1+ C384)
Table 17-5. EASY-TUNE Equations
Mode PB in % TR (Minutes) TD* (Minutes)
P204K
P
(W
P
/T
P
)
1.084
00
PI 116.4K
P
(W
P
/T
P
)
0.977
(T
P
/40.44)(W
P
/T
P
)
0.68
0
PID 73.69K
P
(W
P
/T
P
)
0.947
(T
P
/51.02)(W
P
/T
P
)
0.738
(T
P
/157.5)(W
P
/T
P
)
0.995
PD** 54.02K
P
(W
P
/T
P
)
0.947
0(T
P
/157.5)(W
P
/T
P
)
0.995
I** 0 T
P
[(K
P
/25)(W
P
/T
P
)
0.15
]0
Note: Process characteristics T
P
, K
P
, and W
P
are used to compute the ideal tuning parameters
aDOrding to the Minimum Integral of Absolute Error Multiplied by Time Criterion (ITAE) for P, PI,
and PID modes.
*If computed to be < B003/50, then T
D
= 0.
**Empirical estimates, not based on ITAE method.
Section 17. EASY-TUNE
17-5
To Next Page
Loading...
Need help?
General
