150
••••
9 - PID Loops
Simatic 505 SoftShop
9 - PID Loops
Overview
Process and batch control capability is provided using the controller’s
proportional-integral-derivative (PID) loop functions, illustrated in
Figure
9.1. When you program a loop, you can set the same eight alarm types
used by analog alarms and described in Chapter 8.
•
High-high alarm point on the process variable (PV).
•
High alarm point on the PV.
•
Low alarm point on the PV.
•
Low-low alarm point on the PV.
•
Yellow deviation alarm point referenced to the setpoint (SP).
•
Orange deviation alarm point referenced to the SP.
•
Rate of change alarm, for a PV changing too rapidly.
•
Broken transmitter, for a PV outside the designated valid range.
w Yellow
w Orange
Green
w Orange
w Yellow
Hot water
input
Product input
Product output
TIC
601
w Broken transmitter
w Rate of change
Miscellaneous alarms
Figure 9.1 Example of Loop Control
The high-high, high, low, and low-low alarms are fixed absolute alarms
and may correspond to warnings and shutdown limits for the process
equipment itself. The yellow and orange deviation alarms move up and
down with the setpoint, and may refer to specification tolerances around
the setpoint.