User manual

PID Loop Operation
(DL450 Only)
Maintenance
and Troubleshooting
8--54
PID Loop Operation (DL450 only)
DL405 User Manual, 4th Edition, Rev. A
For those who are using DirectSOFT 5, you have the opportunity to use the Analog
Helper Intelligent Boxes (IBox) instructions. Following is one example which is
available. IBox instruction IB--402, Filter Over Time in Binary (decimal) will perform a
first--order filter on the Raw Data on a defined time interval. The equation is,
New = Old + [(Raw -- Old)
/
FDC
]
where,
New = New Filtered Value
Old = Old Filtered Value
FDC = Filter Divisor Constant
Raw = Raw Data
The Filter Divisor Constant is an inte-
ger in the range K1 to K100, such that
if it equaled K1, then no filtering is per-
formed.
The rate at which the calculation is performed is specified by time in hundredths of a
second (0.01 seconds) as the Filter Freq Time parameter. Note that this Timer
instruction is embedded in the IBox and must NOT be used any other place in your
program. Power flow controls whether the calculation is enabled. If it is disabled, the
Filter Value is not updated. On the first scan from Program to Run mode, the Filter
Value is initialized to 0 to give the calculation a consistent starting point.
Since the following binary filter example does not write directly to the PID PV
location, the BCD filter could be used with BCD values and then converted to BIN.
Following is an example of how the FilterB IBox is used in a ladder program. The
instruction is used to filter a binary value that is in V2000. Timer (T1) is set to 0.5
seconds, the rate at which the filter calculation will be performed. The filter constant
is set to 3.0. A larger value will increase the smoothing effect of the filter. A value of 1
results with no filtering. The filtered value will be placed in V2100.
See DL405 IBox Instructions PLC User Manual Supplement for more detailed
information.
NOTE: In order to use the IBox instructions found in DirectSOFT 5, the D4--450
CPU must have firmware version 3.30 or higher installed.
Use the
DirectSOFT5Filter
Intelligent Box
Instruction
FilterB Example