Micromod Micro-DCI: 53SL5100B Single Loop Controller - Manual (Page 85)

53SL5100B Single-Loop Controller
INSTRUCTION MANUAL
79
11.5 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, (instrument 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 11-4. (Figure 11-2 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 (instrument 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 Modifier), 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 11-3. EASY-TUNE Equations
Mode PB in % TR (Minutes) TR* (Minutes)
P 204K
P
(W
P
/T
P
) 1.084 0 0
PI 116.4K
P
(W
P
/T
P
) 0.977 (T
P
/40.44)(W
P
/T
P
) 0.68 0
PID 3.69K
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 TP, KP, and WP are used to compute the ideal tuning parameters
according 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.
 NOTE: The approximation of a process step response curve by a first order time lag plus dead-
time model is done by equating their values at 0.2835 and 0.6321 fraction of the total excursion.