1. Introduction

• Purpose: Monitor discrete 120 VAC field devices (switches, contactors, relay contacts)

• Architecture: TMR (3‑2‑0) + 1oo2D per‑channel voting

• Safety: IEC 61508 SIL 3 / SIL 4 certified

• Coating: Standard version (non‑coated); T8424C = acrylic conformal coated

• Temp Range: 0 °C to +60 °C (T8424C: –40 °C to +70 °C)

• Channels: 40 × 120 VAC digital inputs

• Isolation: 2500 V DC optical (channel–channel, channel–system)

• SOE: 1 ms resolution sequence‑of‑events logging

• Hot‑Swap: Yes (online replacement)

2. Product Overview

• 40 × 120 VAC digital input channels (sink/source configurable)

• Fully triplicated (TMR) input processing (three independent measurement lanes)

• Sigma‑delta ADCs for high‑precision voltage sampling

• Per‑channel 1oo2D voting for fault detection

• Optical isolation (2500 V DC) between field and backplane

• Onboard SOE (1 ms) for event time‑stamping

• Independent line monitoring (open/short circuit) per channel

• Front‑panel LEDs for channel status and module health

3. Specifications

3.1 Mechanical

• Form Factor: T8000 chassis module, 56 mm wide, 6U

• Dimensions (H×W×D): 255 mm × 56 mm × 210 mm

• Weight: 1.3 kg (2.87 lbs)

• Mounting: T8100 / T8400 chassis slots 1–16

• Connectors: Front‑panel terminal blocks (TB1–TB5, 8 channels each)

• PCB Protection: Standard (non‑coated); T8424C = acrylic conformal coating

3.2 Electrical

• System Supply: 20–32 V DC (nominal 24 V DC)

• Power Consumption: ≤ 5 W

• Input Channels: 40 × 120 VAC digital inputs

• Input Voltage Thresholds:

  • Logic 1: 90–150 V AC

  • Logic 0: <30 V AC

• Input Current: ~4 mA per channel (at 120 V AC)

• Input Type: Sink (NPN) / Source (PNP) configurable

• Isolation: 2500 V DC optical barrier (channel–channel, channel–system)

• Backplane Interface: Trusted Backplane Bus (TBB), TMR

3.3 Functional

• Voting: 1oo2D per channel (triple measurement + comparison)

• SOE Resolution: 1 ms (per channel state change)

• Diagnostics:

  • Open‑circuit detection (per channel, with line resistor)

  • Short‑circuit detection (per channel)

  • Onboard BIST (Built‑In Self‑Test)

  • Fault logging to system HMI

• Response Time: ≤ 2.0 ms (channel to backplane)

• Data Integrity: BER < 10⁻¹²

3.4 Environmental

• Operating Temperature: 0 °C to +60 °C (standard)

• Storage Temperature: –40 °C to +85 °C

• Humidity: 5–95 % RH, non‑condensing

• Altitude: ≤ 2000 m

• Vibration: IEC 60068‑2‑6 (1 g, 10–150 Hz)

• Shock: IEC 60068‑2‑27 (15 g, 11 ms)

3.5 Safety & Certification

• Safety Standard: IEC 61508 SIL 3 / SIL 4

• Certifications: CE, UL, CSA, ATEX II 3G Ex ec IIC T4 Gc, IECEx

• Fault Tolerance: TMR (3‑2‑0), 1oo2D per channel

• PFHd: < 8.0 × 10⁻¹⁰ / h (SIL 4)

4. Front Panel & Indicators

• PWR (Green): On = Module power OK; Off = No power

• RUN (Green): On = Module active; Flashing = Initialization / BIST

• FAULT (Red): On = Module/channel fault; Flashing = Minor fault

• COM (Green): Flashing = Backplane communication active

• TB1–TB5: 5 × terminal blocks (8 channels each, 120 VAC inputs)

• FG: Functional Ground (chassis earth)

5. Installation & Wiring

• Chassis Mounting: Align with empty slot in T8100/T8400 chassis, insert firmly, tighten front‑panel screws (torque 0.8–1.0 Nm)

• Field Wiring: For each terminal block, connect 120 VAC L to group common terminal, field device output to channel input terminal, device common to 120 VAC N

• Wire Gauge: 16–22 AWG stranded wire; torque terminals to 0.5–0.6 Nm

• Line Resistors: 10 kΩ for open‑circuit monitoring (per channel)

• Hot‑Swap: Supported; system auto‑detects new module without shutdown

6. Operation & Diagnostics

• Power‑up: PWR ON; RUN flashes during self‑test (5–10 s)

• Normal Operation: PWR + RUN steady GREEN; FAULT OFF; COM flashing

• Fault Conditions: FAULT ON = critical fault (channel short/open, TMR mismatch); FAULT Flashing = minor fault (single‑lane mismatch)

• SOE Logging: All state changes time‑stamped (1 ms) and stored in system memory

7. Ordering Information

• T8424: Standard 40‑Ch 120 VAC DI (0 °C … +60 °C)

• T8424C: Conformal coated, –40 °C … +70 °CRockwell Automation

• TC‑8424: Terminal Block Cable Kit (field wiring)