Rockwell Automation T8433 Trusted TMR Isolated 4-20 mA Analogue Input Module - 20 Channel - Manual (Page 13)

Trusted
TM
Module T8433
Issue 11 Apr 10 PD-T8433 13
1.6. Housekeeping
The input module automatically performs local measurements of several on-board signals that can be
used for detailed troubleshooting and verification of module operating characteristics. Measurements
are made within each slice’s HIU and FIU.
1.7. Fault Detection and Testing
From the IMB to the field connector, the input module contains extensive fault detection and integrity
testing. As an input device, all testing is performed in a non-interfering mode. Data received from the
Main Processor via the IMB is stored in redundant error-detecting RAM on each slice of the HIU.
Received data is voted on by each slice. All data transmissions include a confirmation response from
the receiver.
Between each slice of the HIU and the corresponding FIU, there is a bidirectional optically isolated data
link. The data link is synchronised and monitored for variance. Both the FIU and HIU have onboard
temperature sensors to characterise temperature-related problems. Each FIU is also fitted with a
condensation sensor.
The power supplies for both the HIU and FIU boards are redundant, fully instrumented and testable.
Together, these assemblies form a Power Integrity Sub System.
The module field input is redundantly isolated on the FTU and processed by a modulator which
serves as a precision A/D converter. These circuits, two per channel on each slice, produce a digital
output which naturally transitions between on and off. Any failure in the circuit causes the output to
saturate to stuck-on or stuck-off which is automatically detected. As the conversion process is
dynamic and not gated like traditional ADCs, most failures are rapidly diagnosed and located. Each
channel is partnered with an individual D/A converter which non-intrusively injects a unique test signal
into the
front end. The test signal is extracted and analyzed for the correct signature downstream
by the HIU before the signal is presented to the Main Processor.
By using the circuit, the analogue path in the module is short, completely testable, and involves very
few components. This results in most analogue failures being contained to a single channel on a
single slice instead of causing a group of eight or more inputs to fail.
1.8. Sequence of Events Characteristics
The input module automatically measures the field-input voltage, compares the value to the
configurable thresholds, and determines the state of the field input. An event occurs when the input
transitions from one state to another. When an input changes state, the on-board real-time clock value
is recorded. When the TMR Processor next reads data from the input module, the input state and real-
time clock values are retrieved. The TMR Processor uses this data to log the input state change into
the system Sequence of Events (SOE) log. The user may configure each input to be included in the
system SOE log. Full details of SOE are contained in PD-8013 – Trusted
TM SOE And Process
Historian.