DL205 Analog Manual, 7th Edition Rev. D
15-22
Chapter 15: F2-8AD4DA-1, 8-Ch. In / 4-Ch. Out Analog Current Combination
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B
C
D
Scaling the Input Data
Most applications require measurements in engineering units, which provide more meaningful
data. This can be accomplished by using the conversion formulas shown below.
EU = (A - A
offset
)(EU
H
- EU
L
) / (A
max
- A
offset
)
EU = (D - D
offset
)(EU
H
- EU
L
) / (D
max
- D
offset
)
• A = analog value from current transmitter
• A
offset
= 4mA offset when using 4-20 mA current transmitter
• D = digital value of input provided to PLC CPU
• D
offset
= digital value of 4mA offset with 4-20 mA current transmitter
• EU = engineering units
• EU
H
= engineering units high value
• EU
L
= engineering units low value
The following examples show a 16 bit measurement of pressure (PSI) from 0.0–140.0. The
the analog value needs to be multiplied by 10 in order to imply a decimal place when the
value is viewed with the programming software. Notice how the calculations differ when the
multiplier is used.
Scaling Example
NOTE: Binary data format is recommended for 14 or 16 bit resolution input data, especially if the input data is to
be used in any math instructions (DL205 User Manual, ch.5). There is only one V-memory word (16 bits) available for the
actual data. Although the 12 bit resolution maximum value of 4095 can be stored in one word using either binary or BCD
formats, the 14 and 16 bit resolution maximum values of 16383 and 65535 both exceed the BCD format’s maximum single
word capacity of 9999. Double word math would be required for 14 or 16 bit data in BCD format. Binary data format is
also useful for displaying data on some operator interfaces.
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b
C
D
Analog Value = 12.6 mA; Transmitter = 4–20 mA; Resolution = 16 bit
Result should yield 75.2 PSI
EU =
(
D
− D
offset
)
EU
H
− EU
L
D
max
− D
offset
EU = (41287 − 13107)
140
− 0
65535
− 13107
EU
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