Chapter 1 Introduction
1-5
1.3.2 Current input
W h e n the analo g in p u t is 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;
1) 4 ~ 2 0 m A range
W h e n th 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.
Figure 1.6 A/D conversion characteristic ( 4 ~ 20mA )
4000
current
input
Minimum
current
input
Maximum
module
A/D
of
Resolution
−
=
2000
2001
2002
1998
1999
12.000mA
12.004mA
11.996mA
12.008mA
11.992mA
4000
2000
0
1 2 m A
2 0 m A
Analog input current
D
igital output value
4 m A