32 Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Chapter 2 Analog I/O Module Features
Resolution on Output Module
The module resolution for the 1756-OF8I module is always 16 bits, regardless of
operating mode and operating range.
Table 3
lists the resolution for each module’s input/output range and
corresponding range capability.
Scaling
When scaling, you choose two points along the module’s operating range and
apply low and high values to those points.
For example, if you are using the 1756-IF8I module in Current mode, the module
supports a 0…21 mA actual range capability. But your application uses a 4…20
mA transmitter. Scaling lets you configure the module to return data to the
controller so that a low signal value of 4 mA returns a low engineering value of
0% and a high signal value of 20 mA returns a high engineering value of 100%.
Table 3 - Module Resolution in Various Configuration Selections
Module Mode Available Input/
Output Range
(1)
Actual Input/Output
Range Capability
Number of Bits
Across the
Theoretical
Operating Range
Number of Bits
Across the Actual
Range Capability
Resolution (signal
per count)
1756-IF8I
Voltage
-10…10V
0…10V
0…5V
-10.5…10.5V
0…10.5V
0…5.25V
24 bits
23.75
22.75
21.75
1.49 µV/count
Current
0…20 mA
0…20 mA (sourcing)
0…21 mA
0…21 mA (sourcing)
22.74
2.99 nA/count
1756-IRT8I
1756-IT16
Thermocouple
-100…100 mV -101…101 mV
24 bits
23.98
0.01 µV/count
1756-IRT8I
1756-IR12
RTD
1…500 Ω
2…1000 Ω
4…2000 Ω
8…4000 Ω
0…510 Ω
0…1020 Ω
0…2040 Ω
0…4080 Ω
23.98
0.06 mΩ/count
0.12 mΩ/count
0.25 mΩ/count
0.50 mΩ/count
1756-OF8I
Voltage
-10…10V
0…10V
0…5V
-10.5…10.5V
0…10.5V
0…5.25V
16 bits
16.00
0.32 mV/count
0.16 mV/count
0.08 mV/count
Current 0…20 mA 0…21 mA 16.00 0.32 µA
(1) These ranges represent the range choices available in the Logix Designer application.
Because these modules must allow for possible calibration inaccuracies,
resolution values represent the available Analog-to-Digital or Digital-to-
Analog counts over the specified range.
Additionally, RPI and Notch Filter settings affect module resolution on the
1756-IF8I and 1756-IRT8I modules. For more information, see page 43
and
page 61
, respectively.
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