480
FX
3G
/FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
16 External FX Device – FNC 80 to FNC 89
16.9 FNC 88 – PID / PID Control Loop
Cautions
1. When using two or more PID instructions
Two or more PID instructions can be executed at the same time. (There is no limitation in the number of loops.)
However, make sure that
,
and other operands specified in each instruction are different to each other.
2. Number of devices occupied for parameters starting from
1) In the limit cycle method
- Twenty-nine devices are occupied from the head device specified in
.
2) In the step response method
- Operation setting (ACT): When bits 1, 2 and 5 are not all "0"
Twenty-five devices are occupied from the head device specified in
.
- Operation setting (ACT): When bits 1, 2 and 5 are all "0"
Twenty devices are occupied from the head device specified in
.
3. When specifying a device in the latched area backed up against power failure
For the output value (MV) in the PID instruction, specify a data register (D) outside the latched area.
Program example
When specifying a data register in the latched area, make sure to clear the latched (backed up) contents when the
PLC mode is set to RUN using the following program.
Error
When an operation error occurs, the special auxiliary relay M8067 turns ON, and the error code is stored in the special
data register D8067.
→
For the error code, refer to Section 38.4.
S
3
D
S
3
S
3
S
3
S
3
M8002
Initial pulse
RST
D***
Program example
Data register number in the latched area specified in
D
