User manual

PID Loop Operation
(DL450 Only)
Maintenance
and Troubleshooting
8--28
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
Process Variable V+03
Loop
Calculation
Σ
+
--
Control Output V+05Setpoint V+02
013456789101112131415 2Bit
12 bit unipolar
12 bit bipolar
15 bit bipolar
15 bit unipolar
0 to 0FFF (0 to 4095)
0 to 0FFF, 8FFF to 8001
(0 to 4095, --4095 to --1)
0 to 32767
0 to 7FFF, FFF to 8001
(0 to 32767, --32767 to --1)
Data formats
013456789101112131415 2Bit
PID Mode 2 Setting V+01
00
01
10
11
Select data
format using
bits 0 and 1.
= sign bit
LSB
The data format determines the numerical interface between the PID loop and the
PV sensor and the control output device. This selects the data format for both the SP
and the PV.
Loop Mode
The feature called Independent of CPU mode in the dialog is not available in the
DL450. However, the DL450 does provide the three standard control modes:
Manual, Automatic, and Cascade . The sources of the three basic variables SP, PV
and control output are different for each mode.
In Manual Mode, the loop is not executing PID calculations (however, loop alarms
are still active). With regard to the loop table, the CPU stops writing values to location
V+05 (control output) for that loop. It is expected that an operator or other intelligent
source is manually controlling the output by observing the PV and writing data to the
control output as necessary to keep the process under control. The drawing below
shows the equivalent schematic diagram of manual mode operation.
Loop
Calculation
Control Output V+05
Input from Operator
Manual
Auto
In Automatic Mode, the loop operates normally and generates new control output
values. It calculates the PID equation and writes the result in location V+05 every
sample period of that loop. The equivalent schematic diagram is shown below.
Loop
Calculation
Control Output V+05
Input from Operator
Manual
Auto