User Manual

166 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 9 Troubleshoot Your Module
If the previously listed tasks fail to resolve your issue with incorrect RTD readings
on your module, use the following table.
Table 17 - 1756-IRT8I Module - Troubleshoot Incorrect RTD Readings
Possible Cause of Incorrect
Reading
Description Recommended Action
Wire Off When using a 3-wire RTD
device and any of the following:
• One wire is disconnected
from any of the channel’s
terminals.
• Wires are disconnected from
any combination of
terminals:
– IN_x(+)/A
– IN_x(-)/B
– IN_x/RTD C
• All of the wires are
disconnected from the
channel.
The following occurs:
• Input data for the channel
changes to the highest scaled
temperature value associated
with the selected sensor type.
• The I.Ch[x].Overrange tag is
set to 1.
x represents the channel
number.
• Check the wiring, terminations, and for an open wire.
• Make sure the length of the RTD cable is within module
specifications.
Wire length that is too long has a higher impedance, and can be
interpreted as an open circuit.
When using a 4-wire RTD
device and any of the following:
• A wire is disconnected from
only terminal IN_x(-)/B.
• Wires are disconnected from
any combination of the
channel’s terminals, that is:
– IN_x(+)/A
– IN_x(-)/B
– IN_x/RTD C
– IN_x/RTD D
IMPORTANT: There is one
combination exception that
does not apply.
A wire off condition is not
detected when wires are
simultaneously disconnected
from only IN_x/RTD C and
IN_x/RTD D terminals.
• All wires are disconnected
from the module.
If bullet 1, the following occurs:
• Input data for the channel
changes to the lowest scaled
temperature value associated
with the selected sensor type.
• The I.Ch[x].Underrange tag is
set to 1.
x represents the channel
number.
If bullets 2 or 3, the following
occurs:
• Input data for the channel
changes to the highest scaled
temperature value associated
with the selected sensor type.
• The I.Ch[x].Overrange tag is
set to 1.
x represents the channel
number.