User guide
Load Initial Configuration Values
Chapter 7
7-21
Type of PID Pressure Algorithm
(FCC02,
SCC02, TCC02, LPC02, INC02, PKC02, HDC02, PLC02, FOC02, SOC02,
T
OC02, OSC02, EAC02, ERC02)
When executing pressure versus position or time profiles, the QDC module
can use one of two types of PID algorithms: dependent gains (ISA) or
independent gains (Allen-Bradley).
If B07 = : Then it uses:
0 Dependent Gains (ISA)
1 Independent Gains (AB)
Dependent gains (ISA):
Output = Kc[(E) + 1/Ti
o
∫
t
(E)dt + Td*d(E)/dt]
Independent gains (AB):
Output = Kp(E) + Ki
o
∫
t
(E)dt + Kd*d(E)/dt
Comparison of Gain Constants
Compare dependent and independent gains constants as follows:
Dependent Gains Constants: Independent Gains Constants:
Controller Gain K
c
(dimensionless) Proportional Gain K
p
(dimensionless)
Reset Term 1/T
i
(minutes per repeat) Integral Gain K
i
(inverse seconds)
Rate Term T
d
(minutes) Derivative Term K
d
(seconds)
Other variables used in any algorithm choice include:
Output = Percentage of full scale
E = Error (scaled) SP-PV (Setpoint-Process Variable)
PV = Process Variable (scaled)
Convert from dependent to independent gains constants by substituting
controller gain (K
c
), reset (1/T
i
), and rate (T
d
) values in these formulas:
K
p
= K
c
unitless
K
i
=
K
c
60 T
i
inverse seconds
K
d
= K
c
(T
d
)60 seconds
We recorded bit B07 = 1 for A-B independent gains on all corresponding
worksheets.
Select the Type of
PID Algorithm