Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 9)

Introduction
Chapter 1
1Ć6
Figure 1.2
System Overview
P
r
o
c
e
s
s
Tieback Input
Analog Output (V)
Man/Auto Status
Manual Request
Analog Input (PV)
Optional
User Supplied
Manual Control Station
X
1771 – P1
Supply PC Processor
or Adapter 1771 – PD
Module
Block Transfer
15V DC
100mA
+
–
1770 – P1 supply
+5V DC
1.2A
Optional
Supply
11092
Programming Description
The PID algorithm can be adapted to the particular control application by
selecting desired features. The features and parameter values are chosen
and stored in the PC processor data table. The PC processor transfers to
the PID module data table blocks which contain the feature selections and
parameter values. The module uses the values to establish its operational
characteristics. The PC processor can read the module status by
transferring information from the module into the data table.
Communication between PC processor and PID module is performed by
block transfer programming.
Levels of Fault Tolerance
The module has five levels of fault tolerance.
The first level occurs when the PID module is operating properly but a
loss of communication with the active PC processor occurs. The module
enters a mode of operation defined as soft fault. A soft fault occurs when: