Analog Input
WBPEEUI240751C0 4 - 3
operational. If the backup I/O module has detected a problem
such as an Hnet communication failure, I/O channel failure,
and IFP or LFP field power failure, then no failover will occur.
When a failover occurs due to a non catastrophic failure of the
primary module, the primary will halt with LEDs one and two
on. When a failover occurs due to a catastrophic failure (i.e.,
FAULT lit), an error code will display on LEDs one through
eight of the primary module. Refer to Table 8-3 for a descrip-
tion of the LED status codes.
Analog Input
For analog input capable blocks, channels are directly wired in
parallel to both I/O modules (Figs. 4-1 through 4-7). A short
across an input of one I/O module due to an I/O block fault
will not allow either I/O module to read the input. An open in
an input channel circuit of the base will not allow either I/O
module to read the input.
AIN-120
Failures detectable by an AIN-120 module that cause a failover
to the backup module include:
• Multiplexer failure.
• Amplifier failure.
• A-to-D converter failure.
• Bad voltage reference.
• Channel failure or out of range.
AIN-200/220
Failures detectable by an AIN-200/220 module that cause a
failover to the backup module include:
• Amplifier failure.
• A-to-D converter failure (one per channel).
• Opto-coupler failure.
• Bad voltage reference.
• Bad TC cold junction reference (A-to-D and RTD).
• Channel failure or out of range.
AIN-300
The AIN-300 block has special circuitry to disconnect the RTD
current source on the backup I/O module during normal oper-
ation. This prevents two current sources from being connected
to the RTD at one time. Failures detectable by an AIN-300
module that cause a failover to the backup module include:
• Amplifier failure.
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