User manual

PID Loop Operation
(DL450 Only)
Maintenance
8--15
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
Error Deadband Control
With error deadband control,no control action is takenif the PV is withinthe specified
deadband area around the setpoint. The error deadband is the same above and
below the setpoint.
Once the PV is outside of the error deadband around the s etpoint, the entire error is
used in the loop calculation.
e
n
= 0 “SP -- Deadband__Below_SP < PV < SP -- Deadband_Above_SP”
e
n
=P--PV
n
“otherwise”
The error will be squared first i f both Error Squared and Error Deadband is selected.
Derivative Gain Limiting
When the coefficient of the derivative term, Kr, is a large value, noise introduced into
the PV can result in erratic loop output. This problem is corrected by specifying a
derivative gain limiting coefficient, Kd. Derivative gain limiting is a first order filter
applied to the derivative term computation, Y
n
, as shown below.
Y
n
=Y
n--1
+
Ts + (
Td )
Kd
*
(PV
n
=Y
n--1
)
Ts__________
Position Algorithm
Mx = Ki
*
e
n
+Mx
n--1
M=Kc
*
e
n
-- K r
*
(Y
n
-- Y
n--1
)+Mx
Velocity Algorithm
nM=Kc*(e
n
-- e
n--1
)+Ki*e
n
-- K r * ( Y
n
-- 2 * Y
n--1
+Y
n--2
)