User manual

PID Loop Operation
(DL450 Only)
Maintenance
8--35
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
Setup the PID Alarms
Although the setup of the PID alarms is optional, you surely would not want to
operate a process without monitoring it. The performance of a process control loop
may generally be measured by how closely the process variable matches the
setpoint. Most process control loops in industry operate continuously, and will
eventually lose control of the PV due to an error condition. Process alarms are vital in
early discovery of a loop error condition and can alert plant personnel to manually
control a loop or take other measures until the error condition has been repaired.
The alarm thresholds are fully programmable, and each type of alarm may be
independently enabled and monitored. The following diagram shows the Alarm
dialog in the PID setup which simplifies the alarm setup.
Monitor Limit Alarms
Checking this box will allow all of the PV limit alarms to be monitored once the limits
are entered. The PV absolute value alarms are organized as two upper and two
lower alarms. The alarm status is false as long as the PV value remains in the region
between the upper and lower alarms, as shown below. The alarms nearest the safe
zone are named High Alarm and Low Alarm. If the loop loses control, the PV will
cross one of these thresholds first. Therefore, you can program the appropriate
alarm threshold values in the loop table locations shown below to the right. The data
format is the same as the PV and SP (12--bit or 15--bit). The threshold values for
these alarms s hould be set to give an operator an early warning if the process loses
control.
PV
High--high Alarm
High Alarm
Low Alarm
Low--low Alarm
Loop Table
V+16 High-high AlarmXXXX
V+15 High AlarmXXXX
V+14 Low AlarmXXXX
V+13 Low-low AlarmXXXX
NOTE: The Alarm dialog can be left as it first appears, without alarm entries. The
alarms can then be setup in the DirectSOFT PID View.