Honeywell SLG 700 Option Manual page 94

The output supports the feed forward algorithm. The FF_VAL input brings in an external value which
is proportional to some disturbance in the control loop. The value is converted to percent of output
span using the values of parameter FF_SCALE.
This value is multiplied by the FF_GAIN and added to the target output of the PID algorithm. If the
status of FF_VAL is Bad, the last usable value is used as this prevents bumping the output. When the
status returns to Good, the block adjusts its integral term to maintain the previous output. The output
supports the track algorithm. The block provides an option to use either the SP value after limiting or
the PV value for the BKCAL_OUT value.
3.10.1.
PID Control block is an algorithm that produces an output signal in response to the measured variable
and the setpoint. The PID block allows you to choose either a standard PID control equation (Ideal) or
a robust PID equation defined by Honeywell. This selection is defined in the PID_FORM parameter.
The output has three terms, namely Proportional, Integral, and Derivative. The output is adjusted by
tuning constants. There are three tuning constants in the ideal PID equation. The robust PID uses four
tuning constants:
GAIN is the tuning constant of the Proportional term.
1.
RESET is the tuning constant of the Integral.
2.
RATE is the tuning constant of the Derivative. RATE is usually modified by a lag, which
3.
is set at some fixed ratio higher than the rate time, to create a rate gain. There is no lag
with the rate in this implementation.
OUT_LAG is the fourth tuning constant used in the robust PID; it adds roll off to the
4.
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 setpoint 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.
Page 78
PID Control block
FOUNDATION Fieldbus Option User's Manual Rev.5