Flowserve 3400IQ Digital Positioner - Manual (Page 61)


Logix 3400IQ Digital Positioner FCD LGENIM3402-00 – 0/07
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3. RATE is the tuning constant of the Derivative term. RATE is usually modified by a lag, which is set
at some fixed ratio higher than the rate time to create a rate gain. No lag occurs with the rate in
this implementation.
4. OUT_LAG is the fourth tuning constant used in the robust PID, it adds roll off to the output
response. The action is similar to PID with rate gain.
PID Ideal and PID Robust
The ideal equation is a parallel or non-interacting implementation of PID control using three tuning
constants. It automatically fixes OUT_LAG to 16 times the RATE time constant. This produces
response characteristics equivalent to the algorithms used in TPS products.
The robust equation is the same parallel implementation of ideal PID control but allows the engineer
to set the OUT_LAG and effectively change the rate gain.
ALGO_TYPE is a configuration parameter that contains one of three selected algorithm types, A, B, or
C.
Where:
A - RATE, GAIN and RESET all act on the error between set point and measured variable.
B - RATE acts on the measured variable only, GAIN and RESET use the error.
C - RATE and GAIN act on the measured variable only, and RESET uses the error.
PID Tuning Parameters
Table 8.10 lists the valid ranges for the tuning parameters for the PID block. Note that OUT_LAG
parameter is cannot be configured when ideal PID is selected (PID_FORM = 1) and can be configured
when robust PID is selected (PID_FORM = 2).
The values given for these tuning parameters are valid under the following conditions:
The values assume that the minimum configured PID function block execution period (Ts) is 0.125
seconds.
Algorithm type setting (i.e. A, B, or C) has no effect on the validation of these tuning parameters.
The PID function block will reject all values outside these ranges.
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