Rockwell Automation Publication 1756-UM540E-EN-P - December 2017 33
Analog I/O Module Features Chapter 2
The returned engineering unit’s value is indicated in the I.Ch[x].Data tag as
shown in Tab le 4
.
Figure 3 - Module Resolution Compared to Module Scaling
The module can operate with values beyond the 4…20 mA range. If an input
signal beyond the low and high signals is present at the module, for example,
0 mA, that data is represented in terms of the engineering units set during scaling.
Table 4
shows example values that can appear based on the example mentioned
above.
Calibration
The ControlLogix analog modules are calibrated via the following methods:
• Factory calibration when the modules are built.
• User-executed calibration as described in Chapter 8, Calibrate the
ControlLogix Analog I/O Modules on page 143.
User-executed calibration is optional.
• 1756-IRT8I module only - Channels that are configured for
Thermocouple inputs perform a lead resistance self-calibration when the
module power is cycled.
Module Resolution
5,815,117 counts
0 mA 21 mA
4 mA 20 mA
0% in Engineering
Units
100% in Engineering
Units
Module Scaling
Module scaling represents the data
returned from the module to the controller.
In choosing two points for the low and high value of your application, you
do not limit the range of the module. The module’s range and its resolution
remain constant regardless of how you scale it for your application.
Table 4 - Current Values Represented in Engineering Units
Current Engineering Units Value Value in I.Ch[x].Data Tag
0.0 mA -25.00% -25.00
4.0 mA 0.0% 0.00
12.0 mA 50.0% 50.0
20.0 mA 100.0% 100.0
21.0 mA 106.25% 106.25
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