Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 22)

22 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 2 ControlLogix Isolated Analog I/O Module Features
Floating Point Data Format
The modules return channel data to the owner-controller in the IEEE 32-bit
floating point data format. In your Logix Designer application, the data type is
REAL. You can configure the module to scan its channels and return data as
quickly as every 1 ms.
The floating point data format lets you change the data representation of the
selected channel. Although the full range of the module does not change, you can
scale your module to represent I/O data in specific terms for your application.
When you scale a channel, you select two points that represent signal units, that
is, a Low Signal and a High Signal. You also select two points that represent
engineering units, that is, Low Engineering and High Engineering.
The Low Signal point equates to the Low Engineering point and the High Signal
point matches the High Engineering point.
By default, module channels used in Current mode are scaled such at 4…20 mA
equate to 0…100% engineering units. Other module channels scale 1:1 with
respect to signal units and engineering units by default.
Module Resolution
The modules support the following resolutions:
• 1756-IF8I and 1756-IRT8I modules – 24-bit resolution
• 1756-OF8I module – 16-bit resolution
For more information on module resolution, see page 35 .
EXAMPLE A 1756-IF8I module used in current mode maintains 0…21 mA range
capability. Your application uses a 4…20 mA transmitter.
• If you want to receive values in signal units, configure the module
as follows:
– Low Signal = 4 mA
– High Signal = 20 mA
– Low Engineering = 4 EU
– High Engineering = 20 EU
• If you want to receive values in terms of Percent of Full Scale, configure
the module as follows:
– Low Signal = 0 mA
– High Signal = 20 mA
– Low Engineering = 0%
– High Engineering = 100%