DL205 Analog Manual, 7th Edition Rev. D
7-23
Chapter 7: F2-04THM, 4-Channel Thermocouple Input
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Filtering Input Noise (DL250-1 and DL260 CPUs Only)
Add the following logic to filter and smooth analog input noise in DL250-1 and DL260 CPUs.
This is especially useful when using PID loops. Noise can be generated by the field device and/
or induced by field wiring.
The analog value in BCD is first converted to a binary number. Memory location V1400 is the
designated workspace in this example. The MULR instruction is the filter factor, which can be
from 0.1–0.9. The example uses 0.2. Using a smaller filter factor increases filtering. A higher
precision value can be used, but it is not generally needed. The filtered value is then converted
back to binary and then to BCD. The filtered value is stored in location V1402 for use in the
application program or a PID loop.
NOTE:
Be careful not to do a multiple number conversion on a value. For example, if the pointer method is used to get
the analog value, it is in BCD and must be converted to binary. However, if the conventional method of reading analog is
used and the first 15 bits are masked, the value is already in binary and no conversion is needed. Also, if the conventional
method is used, change the LLD V2000 instruction to LD V2000.
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LDD
V2000
SUBR
V1400
BTOR
SP1
BIN
Loads the analog signal, which is a BCD value
and has been loaded from V-memory location
V2000, into the accumulator. Contact SP1 is
always on.
Converts the BCD value in the accumulator to
binary. Remember, this instruction is not
needed if the analog value is originally
brought in as a binary number.
Converts the binary value in the accumulator
to a real number.
Subtracts the real number stored in location
V1400 from the real number in the accumulator,
and stores the result in the accumulator. V1400
is the designated workspace in this example.
Multiplies the real number in the
accumulator by 0.2 (the filter factor),
and stores the result in the
accumulator. This is the filtered value.
OUTD
V1400
ADDR
V1400
MULR
R0.2
OUTD
V1402
BCD
RTOB
Adds the real number stored in
location V1400 to the real number
filtered value in the accumulator, and
stores the result in the accumulator.
Copies the value in the accumulator to
location V1400.
Converts the real number in the
accumulator to a binary value, and
stores the result in the accumulator.
Converts the binary value in the accumulator
to a BCD number.
NOTE:
The BCD instruction is not needed for
PID loop PV (loop PV is a binary number).
Loads the BCD number filtered value from
the accumulator into location V1402 to use in
your application or PID loop.
Содержание DL205
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