Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 48)

48 Publication 1756-UM009C-EN-P - December 2010
Chapter 3 ControlLogix Analog I/O Module Features
Relationship Between
Module Resolution,
Scaling, and Data Format The following three concepts listed below are closely related and must be
explained in conjunction with each other.
• Module Resolution
• Scaling
• Data Format as Related to Resolution and Scaling
Module Resolution
Resolution is the smallest amount of change that the module can detect.
Analog input modules are capable of 16-bit resolution. Output modules are
capable of 13…16 bit resolution, depending on the module type.
The 16 bits represent 65,536 counts. This total is fixed but the value of each
count is determined by the operational range you choose for your module.
For example, if you are using the 1756-IF6I module, your module’s available
current range equals 21 mA. Divide your range by the number of counts to
figure out the value of each count. In this case, one count is
approximately 0.34 µA.
Module Resolution
65,536 counts
0 mA 21 mA
21 mA/65,536 counts ~ 0.34
μ
A/count
IMPORTANT
A module’s resolution is fixed. It will not change regardless of
what data format you choose or how you decide to scale your
module in floating point mode.
Resolution is based on the module hardware and the range
selected. If you use a sensor with limited range, you do not
change the module resolution.