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Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Chapter 2
Analog I/O Module Features
The Low Signal point equates to the Low Engineering point and the High Signal
point matches the High Engineering point.
By default, module channels that are used in Current mode are scaled such that
4…20 mA equate to 0…100% engineering units. Other module channels scale 1:1
regarding signal units and engineering units by default.
Module Quality Reporting
The modules indicate the quality of channel data returned to the owner-
controller. Data quality represents accuracy. There are levels of data quality
reported via module input tags.
The following input tags indicate the level of data quality. In the tag names,
x
represents the module channel number:
•
I.Ch[x].Fault
tag - This tag indicates that channel data can be completely
inaccurate and cannot be trusted for use in the application. If the tag is set
to 1, you cannot trust the data reported. You must troubleshoot the
module to correct the cause of the inaccuracy.
Common causes of inaccurate data include the following:
–
An overrange or underrange condition exists.
–
A wire off detection condition has occurred.
–
A short circuit detection condition has occurred.
•
I.Ch[x].Uncertain
tag - This tag indicates that channel data can be
inaccurate but it is not known to what degree of inaccuracy. We
recommend that you do not use the data for control.
If the tag is set to 1, you know that the data can be inaccurate but you must
troubleshoot the module to discover what degree of inaccuracy exists.
EXAMPLE
A 1756-IF8I module that is 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 = 4 mA
–
High Signal = 20 mA
–
Low Engineering = 0%
–
High Engineering = 100%