DL205 Analog Manual, 7th Edition Rev. D
12-11
Chapter 12: F2-02DAS-1, 4-20mA 2-Channel Analog Current Output
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A
B
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D
Writing the Control Program
Calculating the Digital Value
The control program must calculate the
digital value that is sent to the analog
output. Several methods can be used to
do this, but the best method is to convert
the values to engineering units. This
is accomplished by using the formula
shown.
Adjustments may need to be made to the
formula depending on the scale of the
engineering units.
Consider the following example which controls pressure from 0.0–99.9 PSI. Using the
formula will calculate the digital value to be sent to the analog output. The example shows the
conversion required to yield 49.4 PSI. The multiplier of 10 is because the decimal portion of
49.4 cannot be loaded in the program, so it is shifted right one decimal place to make a usable
value of 494.
Refer to the example on the next page to write the conversion program.
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A = U
65535
H – L
A = Analog Value (0 – 65535)
U = Engineering Units
H = High limit of the engineering
unit range
L = Low limit of the engineering
unit range
A = 10U
65535
A = 494
65535
A = 32374
10 (H – L) 1000 – 0
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