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Chapter 1 Introduction
1-5
1.3.2 Current input
When the analog input is current input, the A/D conversion module has only one input
ranges such as 4 ~ 20mA.
With all analog input range, the digital output is varied in the range of 0 ~ 4000. Therefo re,
the resolution of the A/D module is obtained by following equation;
1) 4 ~ 20mA range
When the A/D module operates with 4 ~ 20mA range, the 4mA analog input is converted
to digital 0, and the 20mA analog input is converted into digital output 4000. There fore,
the resolution per 1 digital value is 0.004mA.
Figure 1.6 A/D conversion characteristic ( 4 ~ 20mA )
4000
currentinputMinimumcurrentinputMaximum
moduleA/DofResolution
−
=
2000
2001
2002
1998
1999
12.000mA
12.004mA
11.996mA
12.008mA
11.992mA
4000
2000
0
12mA 20mA
Analog input current
Digital output value
4mA