Rockwell Automation T8424 Trusted TMR 120Vac Digital Input Module - Manual (Page 10)

Trusted TM Module T8424
Issue 8 Sep 11 PD-T8424 10
Each field input is connected to a single bit sigma-delta analogue to digital converter. These circuits,
one per channel on each slice, produce a digital output signal which is dynamic in nature. Failures in
the circuit components cause the signal to saturate to stuck-on or stuck-off which is automatically
detected. Hence, failures are rapidly diagnosed and located.
Latent faults are detected automatically by monitoring the amplitude and phase of a test signal that is
continuously injected into the front end, and removed from the measurement as part of the digital
signal processing. Each channel utilizes a test signal with a unique phase, so crosstalk faults are
quickly identified.
1.8. Sequence of Events Characteristics
The input module measures the field-input voltage amplitude, compares the value to the pre-
determined thresholds, and determines the state of the field input. The TMR processor syncrhonizes
the real-time clocks for every module slice in the system twice each second using global broadcasts.
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-
T8013 – Trusted
TM SOE and Process Historian.