Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 123)

Publication 1756-UM009C-EN-P - December 2010 123
Temperature-measuring Analog Modules (1756-IR6I, 1756-IT6I, and 1756-IT6I2) Chapter 6
Real Time Sampling
This parameter instructs the module to scan its input channels and obtain all
available data. After the channels are scanned, the module multicasts that data.
During module configuration, you specify a real time sampling (RTS) period
and a requested packet tnterval (RPI) period. These features both instruct the
module to multicast data, but only the RTS feature instructs the module to
scan its channels before multicasting.
For more information on real time sampling, see page 24 . For an example of
how to set the RTS rate, see page 210 .
Underrange/Overrange Detection
This feature detects when a temperature-measuring input module is operating
beyond limits set by the input range. For example, if you are using the
1756-IR6I module in the 2…1000
Ω
input range and the module resistance
increases to 1050
Ω
, the overrange detection detects this condition.
The table lists the input ranges of non-isolated input modules and the
lowest/highest signal available in each range before the module detects an
underrange/overrange condition.
Low and High Signal Limits on Temperature-measuring Input Modules
Input Module Available Range Lowest Signal
in Range Highest Signal
in Range
1756-IR6I 1…487
Ω
0.859068653
Ω
507.862
Ω
2…1000
Ω
2
Ω
1016.502
Ω
4…2000
Ω
4
Ω
2033.780
Ω
8…4020
Ω
8
Ω
4068.392
Ω
1756-IT6I and
1756-IT6I2 -12…30 mV -15.80323 mV 31.396 mV
-12…78 mV -15.15836 mV 79.241 mV
IMPORTANT
Be careful when ‘disabling all alarms’ on the channel because it
also disables the underrange/overrange detection feature. If
alarms are disabled, overrange/underrange is zero and the only
way you can discover a wire-off detection is from the input
value itself. If you need to detect a wire-off status, do not
‘disable all alarms’.
We recommend that you disable only unused channels so
extraneous alarm bits are not set.