Справочник Пользователя для Mitsubishi Electronics FX2NC
FX Series Programmable Controlers
Applied Instructions 5
5-102
5.9.8
PID (FNC 88)
Operation:
This instruction takes a current value (S
2
) and
compares it to a predefined set value (S
1
). The
difference or error between the two values is then
processed through a PID loop to produce a
processed through a PID loop to produce a
correction factor which also takes into account previous iterations and trends of the calculated
error. The PID process calculates a correction factor which is applied to the current output
value and stored as a corrected output value in destination device (D). The setup parameters
for the PID control loop are stored in 25 consecutive data registers S
error. The PID process calculates a correction factor which is applied to the current output
value and stored as a corrected output value in destination device (D). The setup parameters
for the PID control loop are stored in 25 consecutive data registers S
3
+0 through S
3
+24.
Points to note:
a) Every PID application is different. There will be a certain amount of “trial and error”
necessary to set the variables at optimal levels.
b) The PID instruction is only available on FX and FX
2C
Main Processing Units fitted with CPU
versions 3.11 or greater.
c) On FX
2N
MPUs a Pre-tuning feature is available that can quickly provide initial values for the
PID process. Refer to page 10-28 for more details.
d) As 25 data register are required for the setup parameters for the PID loop, the head address
of this data stack cannot be greater than D975. The contents of this data stack are
explained later in this section. Multiple PID instructions can be programmed, however
each PID loop must not have conflicting data registers.
explained later in this section. Multiple PID instructions can be programmed, however
each PID loop must not have conflicting data registers.
e) There are control limits in the PLC intended to help the PID controlled machines operate in
a safe manner. If it becomes necessary to reset the Set Point Value (S
1
) during operation,
it is recommended to turn the PID command Off and restore the command after entering the
new Set Point Value. This will prevent the safety control limits from stopping the operation
of the PID instruction prematurely.
new Set Point Value. This will prevent the safety control limits from stopping the operation
of the PID instruction prematurely.
f) The PID instruction has a special set of error codes associated with it. Errors are identified
in the normal manner. The error codes associated with the PID loop will be flagged by
M8067 with the appropriate error code being stored in D8067. These error devices are not
exclusive to the PID instruction so care should be taken to investigate errors properly.
Please see chapter 6, ‘Diagnostic Devices’ for more information.
M8067 with the appropriate error code being stored in D8067. These error devices are not
exclusive to the PID instruction so care should be taken to investigate errors properly.
Please see chapter 6, ‘Diagnostic Devices’ for more information.
g) A full PID iteration does not have to be performed. By manipulation of the setup parameters
P (proportional), I (Integral) or D (derivative) loops may be accessed individually or in a user
defined/selected group. This is detailed later in this section.
defined/selected group. This is detailed later in this section.
Mnemonic
Function
Operands
Program steps
S
1
S
2
S
3
D
PID
FNC 88
(PID
control loop)
register each
FNC 88
(PID
control loop)
register each
Receives a data
input and
calculates a
corrective action
to a specified
level based on
PID control
input and
calculates a
corrective action
to a specified
level based on
PID control
D
Note: S
1
and S
2
use a single
data register
data register
D
Note: S
3
uses 25
consecutive
data registers
consecutive
data registers
D
Note: D
uses a single
data register
uses a single
data register
PID:
9 steps
9 steps
FX
0(S)
FX
0N
FX FX
(2C)
FX
2N(C)
FX
(2C)
FX
FX
2N(C)
FX
0N
FX
0(s)
PULSE-P
FX
(2C)
FX
FX
2N(C)
FX
0N
FX
0(s)
16 BIT OPERATION
FX
FX
0N
FX
0(s)
FX
(2C)
FX
2N(C)
32 BIT OPERATION
X10
D 19
D18
PID
[ S1 ] [ S2 ]
[ D ]
D 20 D 46
[ S3 ]