Chapter 10 Built-in PID Functions
10 - 17
(12) _PIDn_PV (PID Process Variable)
- Input/Output Area
K DEVICE AREA : K1038+32n
Unit : INT [ -32768 ~ 32767 ]
This displays the PV of the corresponding loop.
PV is an indicator of the current state of the system. In general, the input from the sensor is stored on the U
device of the CPU via an input device such as A/D conversion module: At each scan, this value should be
transferred to _PIDn_PV using a instruction such as MOV. Please refer to the program examples in the
latter part of this manual.
(13) _PIDn_PV_old (PID previous PV)
-
Setting
Prohibited
K DEVICE AREA : K1039+32n
Unit : INT [ -32768 ~ 32767 ]
This is used internally for derivative and integral operations at a step prior to the PV state of the
corresponding loop. This can be referred to when necessary. Input of a random value will lead to a
malfunction.
(14) _PIDn_MV (PID Manipulated output Variable)
- Input/Output Area
K DEVICE AREA : K1040+32n
Unit : INT [ -32768 ~ 32767 ]
This displays the MV of the corresponding loop.
MV is a signal source for system startup. Contrary to the description of _PID_PV in (12), this values is
transferred at each scan to the U device using a instruction such as MOV and then used as a system
startup input via an output device such as D/A conversion module. Please refer to the program examples
in the latter part of this manual.
(15) _PIDn_MV_BMPL_val (PID MV BuMPLess changeover VALue)
- Setting Prohibited
K DEVICE AREA : K1041+32n
Unit : WORD [ 0 ~ 65535 ]
This stores the information necessary for the Bumpless changeover operation of the corresponding loop.
The corresponding memory is automatically set and input by PID-internal operation and this value should
not be set by the user.
Note
Bumpless Change Over
When the PID controller is converted to manual output mode and back again to auto output
mode, the output is increased again from 0 as in a freshly started control system. This causes
a mode conversion impact to the system. To avoid this, the MV_BMPL function is used;
when the current system is converted to auto mode with the corresponding bit authorized, this
senses the system’s last state in manual mode and lets the control output continue smoothly
from that point. Furthermore, with the master loop MV_BMPL in cascade control authorized,
the master loop senses the state of the slave loop and generates a smoothly continuing control
output.
