IMO Precision Controls K7 Series User Manual page 99

Chapter 7 Usage of Various Functions
dI
dt
The digitized formula is as following;
(
I
(
I
c) D control
The continuous formula of derivative term is as following;
Td d
×
N dt
N : high frequency noise depression ration
y : the object to be controlled (PV)
The digitized formula is as following (Use Tustin approximation method)
( ) =
D n
d) Pseudo code of PID control
The pseudo code of PID control is as following;
- Step 1 : Get constants that are used for PID operation
=
Bi K
- Step 2 : Read SV and PV value
- Step 3: Calculate the proportional term.
- Step 4 : Update the derivative term. (initial value of D = 0)
- Step 5 : Calculate the MV. (initial value of I = 0)
- Step 6 : Check the actuator is saturated or not.
- Step 7 : Output the MV value to the D/A module
- Step 8 : Update the integral term.
- Step 9 : Update the PV_old value.
3) Instruction and parameter setting
For the PID operation of MK80S, following 2 instruction are included in the KGLWIN software. (version 2.0 or later)
No.
1 PID8
2 PID8AT
K
=
e
e = (SV – PV) : deviation value
Ti
+ ) 1 − ( )
n I n K
= ( )
e n
h : sampling period
h Ti
Kh
+ ) 1 = ( ) + ( )
n I n e n
Ti
dy
+ = −
D D KTd
dt
2 − 2
Td hN
( − ) 1 −
D n
2 + 2
Td hN Td
h
×
: integral gain
Ti
2 ( × − × )
Td N h
=
Ad
2 ( × + × )
Td N h
2 ( × × × )
K N Td
=
Bd
2 ( × + × )
Td N h
h
A = 0
: anti-windup gain
Tt
PV = adin(ch1)
P = K × (b × SV – PV)
D = As × D – Bd × (PV – PV_old)
MV = P + I + D
U = sat(MV, U_low, U_high)
I = I + bi × (SV – PV) + A0 × (U – MV)
PV_old = PV
Name
Perform the PID operation
Perform the auto tuning operation
KTdN [
( ) − ( − ) 1
y n y n
+
hN
: derivation gain
Description
7-
]