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Chapter 1 Introduction
1.3.2 Current input
W h e n t he anal o g i n p u t i s current input, the A/D conversion m o d u le has only one input
ranges such as 4 ~ 20m A.
W ith all analog input range, the digital output is varied in the range of 0 ~ 4000. Therefo re,
the resolution of the A/D m o d u le is obtained by following equation;
Resolution
of
1) 4 ~ 2 0 m A range
W h e n t h e A / D m o d u le operates with 4 ~ 20m A range, the 4m A a n a log input is converted
to digital 0, and the 20m A analog input is converted into digital output 4000. There fore,
the resolution per 1 digital value is 0.004m A.
4000
2000
0
4 m A
Maximum
A/D
module
1 2 m A
2 0 m A
Analog input current
Figure 1.6 A/D conversion characteristic ( 4 ~ 20mA )
input
current
Minimum
4000
2002
2001
2000
1999
1998
11.992mA
11.996mA
1-5
input
current
12.008mA
12.004mA
12.000mA
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