General, Example application, Application example 1, continuous block transfer – Rockwell Automation 1771-PD PID MODULE (+DU) User Manual
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Appendix
B
BĆ1
Application Example 1, Continuous Block Transfer
The example described in this appendix is a single closed loop
temperature control application. Standard and/or expanded control
features can be selected as required by the application. The program uses
block transfer to maintain continuous communication between the PID
module and the PC processor.
Following the program description, typical values of selected standard
control features are introduced using a worksheet for the dynamic block
and loop 1 block. Worksheets simplify record keeping associated with
writing the program. Worksheet forms in appendix A should be
reproduced and used as needed.
A fluid or material is passed through a heat exchanger where its
temperature is maintained at set point. A temperature transmitter, which
outputs a +1 to +5V DC signal to the PID module, monitors the
temperature of the fluid or material as it leaves the heat exchanger. The
temperature is controlled by regulating the amount of thermal energy
permitted into the heat exchanger. An manual control station is connected
to provide manual backup to the control system (Figure B.1).
Program for PLC-2 Family Processors
A ladder diagram program that can be used to control the single loop is
presented in Figure B.2. The program is written for a Mini-PLC-2/15 or
PLC-2/30 controller.
NOTE: The same program could be used if a second loop is required by
the application. If used, loop 2 parameters would have to be entered into
appropriate files. Bit W01 B15 would have to be set to zero in the master
control word W01 to set the module for 2-loop operation.
This general ladder diagram program uses alternating read/write block
transfers. During normal operation, dynamic block and status block data
is continuously exchanged between the PID module and PC processor.
This allows the latest process status to be read into the data table. This
also allows data in the dynamic block to be written to the module
General
Example Application