User manual

PID Loop Operation
(DL450 Only)
Maintenance
and Troubleshooting
8--18
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
PID Loop Setup
Have your analog module installed and operational before beginning the loop setup
(refer to the DL405 Analog I/O Modules Manual, D4--ANLG--M). The DL450 CPU
gets its PID loop processing instructions from V--memory tables. There isn’t a PID
instruction that can be used in RLL, such as a block, to setup the PID loop control.
Instead, the CPU reads the setup parameters from system V--memory locations.
These locations are shown in the table below for reference only; they can be used in
a RLL program if needed.
Address Setup Parameter Data type Ranges Read/Write
V7640 Loop Parameter
Table Pointer
Octal V1400 -- V7340,
V10000 -- V37740
write
V7641 Number of Loops BCD 0--16 write
V7642 Loop Error Flags Binary 0or1 read
If the number of loops is “0”, the loop controller task is turned off during the ladder
program scan. The loop controller will allow use of loops in ascending order,
beginning with 1. For example, you cannot use loop 1 and 4 while skipping 2 and 3.
The loop controller attempts to control the full number of loops specified in V7641.
NOTE: The V--memory data is stored in RAM memory. If power is removed from the
CPU for an extended period of time, the PID Setup Parameters will be lost. It is
recommended to use the optional D3--D4--BAT for memory backup.
The CPU reports any programming errors of
the setup parameters in V7640 and V7641. It
does this by setting the appropriate bits in
V7642 on program-to-run mode transitions.
PID Error Flags, V7642
013456789101112131415 2Bit
If you use the DirectSOFT loop setup dialog box, i ts automatic range checking
prohibits possible setup errors. However, the setup parameters may be written using
other methods such as RLL, so the error flag register may be helpful in those cases.
The following table lists the errors reported in V7642.
Bit Error Description (0 = no error, 1 = error)
0 The starting address (in V7640) is out of the lower V-memory range.
1 The starting address (in V7640) is out of the upper V-memory range.
2 The number of loops selected (in V7641) is greater than 16.
3
The loop table extends past ( straddles) the boundary at V7377. Use an
address closer to V1400.
4
The loop table extends past ( straddles) the boundary at V37777. Use
an address closer to V10000.
As a quick check, if the CPU is in Run mode and V7642=0000, then we know there
are no programming errors.
Some Things to Do
and Know Before
Starting
PID Error Flags