O
PEN
N
ET
C
ONTROLLER
U
SER
’
S
M
ANUAL
20-1
20: PID I
NSTRUCTION
Introduction
The PID instruction implements a PID (proportional, integral, and derivative) algorithm with built-in auto tuning to deter-
mine PID parameters, such as proportional gain, integral time, derivative time, and control action automatically. The PID
instruction is primarily designed for use with an analog I/O module to read analog input data, and turns on and off a desig-
nated output to perform PID control in applications such as temperature control described in the application example on
page 20-14. In addition, when the output manipulated variable is converted, the PID instruction can also generate an ana-
log output using an analog I/O module.
PID (PID Control)
Valid Operands
Source operand S1 (control register) uses 27 data registers starting with the operand designated by S1. Data registers D0
through D7973 can be designated by S1. For details, see the following pages.
Source operand S2 (control relay) uses 8 points of outputs or internal relays starting with the operand designated by S2.
Outputs Q0 through Q590 or internal relays M0 through M2550 can be designated by S2. For details, see page 20-10.
Source operand S3 (set point): When the linear conversion is disabled (S1+4 set to 0), the valid range of the set point (S3)
is 0 through 4000 which can be designated using a data register or constant. When the linear conversion is enabled (S1+4
set to 1), the valid range is –32768 to 32767 that is a value after linear conversion. Use a data register to designate a nega-
tive value for a set point when the linear conversion is used. For details, see page 20-12.
Source operand S4 (process variable) is designated using a data register or link register. When reading input data from an
analog input module, designate a proper link register number depending on the slot position of the analog input module
and the channel number connected to the analog input. For details, see page 20-12.
Destination operand D1 (manipulated variable) stores –32768 through 32767 that is a calculation result of the PID action.
For details, see page 20-13.
Operand
Function
I
Q
M
R
T
C
D
L
Constant
S1 (Source 1)
Control register
—
—
—
—
—
—
D0-D7973
—
—
S2 (Source 2)
Control relay
—
Q0-Q590
M0-M2550 —
—
—
—
—
—
S3 (Source 3)
Set point
—
—
—
—
—
—
D0-D7999
—
0-4000
S4 (Source 4)
Process variable
(before conversion)
—
—
—
—
—
—
D0-D7999
L100-L705
—
D1 (Destination 1)
Manipulated variable
—
—
—
—
—
—
D0-D7999
—
—
•
Special technical knowledge about the PID control is required to use the PID function of the
OpenNet Controller
. Use of the PID function without understanding the PID control may cause
the
OpenNet Controller
to perform unexpected operation, resulting in disorder of the control sys-
tem, damage, or accidents.
•
When using the PID instruction for feedback control, emergency stop and interlocking circuits
must be configured outside the
OpenNet Controller
. If such a circuit is configured inside the
OpenNet Controller
, failure of inputting the process variable may cause equipment damage or
accidents.
Warning
When input is on, auto tuning and/or PID action is exe-
cuted according to the value (0 through 2) stored in a
data register operand assigned for operation mode.
A maximum of 42 PID instructions can be used in a
user program.
D1
*****
S1
*****
PID
S2
*****
S3
*****
S4
*****
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