α
2 Simple Application Controllers
Appendix 8
8 - 10
Table 8.2: List of Additional Variables used in the PID equations
Variable Description
EV
n
Deflection for current sample
EV
n-1
Deflection of previous sample
I
n
Intergration Value for current sample
K
D
Derviative Gain
K
P
Proportional Gain
MV
n
Output Value for current sample (Manipulated Value)
PV
fn
Measured Value (filtered) for current sample
PV
fn-1
Measured Value (filtered) for previous sample
PV
fn-2
Measured Value (filtered) for two samples ago
PV
n
Measured Value for current sample
SV
fn
Set Value (filtered) for current sample
SV
fn-1
Set Value (filtered) for previous sample
SV
n
Set Value for current sample
SV
n-1
Set Value for previous sample
T
D
Dervative Time
T
I
Integration Time
T
S
Sample Time
∆
MV
n
Change in Manipulated Value for the current sample
α
Proportional gain coefficient (See Control Response)
α
f
Input value filter coefficient
β
Integration time coefficient (See Control Response)
Table 8.3: Coeffiecient Values for Different Response Times
Operation
α
αα
α β
ββ
β
FAST 100% 100%
NORMAL 40% 135%
SLOW 0% 100%
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