User manual

PID Loop Operation
(DL450 Only)
Maintenance
8--13
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
The DL450 loop controller provides for bumpless mode changes. A bumpless
transfer from manual mode to automatic mode is achieved by preventing the control
output from changing immediately after the mode change.
When a loop is switched from Manual mode to Automatic mode, the setpoint and
Bias are initialized as follows:
Position PID Algorithm Velocity PID Algorithm
SP = PV SP = PV
Mx = Control Ouput
The bumpless transfer feature of the DL450 is available in two types: Bumpless I and
Bumpless II (see page 8--27). The transfer type is selected when the loop is set up.
The DL450 allows the user to specify alarm conditions that are to be monitored for
each loop. Alarm conditions are reported to the CPU by s etting up the alarms in
DirectSOFT using the PID setup alarm dialog when the loop is setup. The alarm
features for each loop are:
S PV Limit y Specify up to four PV alarm points.
High--High PV rises above the programmed High--High
Alarm Limit.
High PV rises above the programmed High Alarm
Limit.
Low PV fails below the Low Alarm Limit.
Low--Low PV fails below the Low--Low Limit.
S PV Deviation Alarm y Specify an alarm for High and Low PV deviation
from the setpoint (Yellow Deviation). An alarm for High High and Low
Low PV deviation from the setpoint (Orange Deviation) may also be
specified. When the PV is further from the setpoint than the
programmed Yellow or Orange Deviation Limit the corresponding alarm
bit is activated.
S Rate--of--Change y This alarm is set when the PV changes faster than
a specified rate--of--change limit.
S PV Alarm Hysteresis y The PV Limit Alarms and PV Deviation Alarms
are programmed using threshold values. When the absolute value or
deviation exceeds the threshold, the alarm status becomes true.
Real--world PV signals have some noise on them, which can cause
some fluctuation in the PV value in the CPU. As the PV value crosses
an alarm threshold, its fluctuations will cause the alarm to be intermittent
and annoy process operators. The solution is to use the PV Alarm
Hysteresis feature.
Bumpless Transfer
Loop Alarms