Honeywell SmartLine RMA800 User Manual page 72

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.
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:
1. GAIN is the tuning constant of the Proportional term.
2. RESET is the tuning constant of the Integral.
3. RATE is the tuning constant of the Derivative. RATE is usually modified by a lag, which 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.
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 lists the valid ranges for the tuning parameters for the PID block. Note that OUT_LAG
parameter is not configurable when Ideal PID is selected (PID_FORM = 1) and can be configured
when Robust PID is selected (PID_FORM = 2).
Page 56 Foundation Fieldbus RMA803 Remote Indicator User's Guide Revision 4