User manual

PID Loop Operation
(DL450 Only)
Maintenance
8--19
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
On a PROGRAM-to-RUN mode transition, the CPU reads the loop setup
parameters as pictured below. At that moment, the CPU learns the location of the
loop table and the number of loops it configures. Then during the ladder program
scan, the PID Loop task uses the loop data to perform calculations, generate alarms,
and so on. There are some loop table parameters the CPU will read or write on every
loop calculation.
READ
(at powerup)
CONFIGURE/
MONITOR
V--Memory Space
User Data
Setup Parameters
LOOP
DATA
CPU Tasks
READ/
WRITE
Ladder
Program
PID Loop
Task
DirectSOFT 5 Programming Software
V7640, V7641
NOTE: The DL450 CPU’s PID algorithm requires at least DirectSOFT32, version
3.0c, Build 58 (or later) and CPU firmware version 1.9 (H8) and 2.446 (SH) (or later),
or DirectSOFT 5, version 5.0 (or later). See our website for more information:
www.automationdirect.com.
The Loop Table contains data for only the
number of loops selected. The address for
the table is stored in V7641. Each loop
configuration occupies 32 words (0 to 37
octal) in the loop table.
For example, consider an application with
4 loops, and V2000 has been chosen as
the starting location. The Loop Parameter
will occupy V2000 -- V2037 for loop 1,
V2040 -- V2077 for loop 2 and so on. Loop
4 occupies V2140 -- V2177.
V--Memory Space
User Data
LOOP #1
V2000
32 words
LOOP #2
32 words
LOOP #3
32 words
LOOP #4
32 words
V2037
V2040
V2077
Determine the block of V--memory to be used for each PID loop. Besides being the
beginning of the PID parameter memory block, the first address will be the start of
loop 1 parameters. Remember, there are 32 words (0 to 37 octal) needed for each
loop. Once you have determined the beginning V--memory address to be used, you
can setup and store the PID parameters either directly in your RLL program or by the
using PID Setup in DirectSOFT.
NOTE: Whether one or more loops are being setup, this block of V--memory will only
be used for the PID loop parameters, do not use this block of memory for
anything else in your program.
Establishing the
Loop Table Size
and Location