Rockwell Automation T8449 Trusted TMR 24V dc Valve Monitor Module - 40 Channel - Manual (Page 12)

Trusted
TM
Module T8449
Issue 13 Apr 10 PD-T8449 12
Between the HIU and FIU are a series of optically isolated links for data and power. The data link is
synchronised and monitored for variance. Both FIU and HIU have onboard temperature sensors to
characterise temperature-related problems. The power supplies for both the HIU and FIU boards are
redundant, fully instrumented and testable.
1.8. Sequence of Events Characteristics
The module automatically measures the field voltage and current to determine the state of each output
channel, and the field voltage only for the feedback channels. An event occurs when the output
transitions from one state to another, or when the feedback channel voltage crosses a pre-defined
threshold. When a channel (either control or feedback) changes state, the on-board timer value is
recorded. When the TMR Processor next reads data from the output module, the channel state and
real-time clock value are retrieved. The TMR Processor uses this data to log the state change into the
system Sequence of Events (SOE) log.
1.9. Output Switch Structure
The outputs of the Valve Monitor Module provides a TMR switch topology where the load is driven by a
total of three fully monitored, fail-safe (6 element) switch channels, one physically resident on each
OFIU in the module. Any single switch or entire slice failure is designed to leave two of the three fail-
safe switch channels operational to power the load.
Figure 3 Output Switch Structure
The upper switches in shown in Figure 3 are denoted as N.O. (Normally Open), and are controlled by
the OFIU on which they are physically resident.
1 The lower switches are depicted as N.C. (Normally
Closed), and are controlled by the “upstream” neighbouring OFIU. 2
Note:
In this context, N.O. is defined as being in the off state in the absence of control signal power,
and similarly, N.C. is the on state in the absence of control signal power. These switches are
constructed from enhancement mode MOSFETs and are both guaranteed to be off in the
1 Their “home” OFIU.
2 The home OFIU, supplies an independent control signal for the “downstream” OFIU FSS.