Rockwell Automation 61C345 4 Input 4-20mA Analog Rail Module - Manual (Page 23)

4Ć1
4.0 PROGRAMMING
This section describes how the data is organized in the module and
provides examples of how the module is accessed by application
programs.
When creating application programs, the programmer must estimate
the magnitude of input signals because they must be in the
specified range of the Analog Rail module (4Ć20 mA). Input signals
greater than 20 mA will be clamped at 4095. Signals greater than
approximately 22.1 mA will also cause the overĆrange bit (12
decimal; 14 octal) to be set to 1. Input signals less than 4 mA are
clamped at zero (0). Signals less than approximately 2.4 mA will
also cause the underĆrange bit (13 decimal; 15 octal) to be set to 1.
See figure 4.1.
Counts
4095
0 4 20
<2.4 = underĆrange
>22.1 = overĆrange
mA 3 2 1
Figure 4.1 Ć Input Signal Conversion
4.1 Analog Rail Module in AutoMate Systems
This section describes how the Analog Rail is used with AutoMate
systems. Local Head mode allows all four channels on the module
to be updated at the end of the scan (normal I/O update rate in this
configuration), or during the scan using AIN blocks (see section
4.1.4). Rail mode allows only one channel to be updated at the end
of the scan (normal I/O update rate in this configuration), or all four
channels to be updated during the scan if AIN blocks are used.