Overview
The Allen-Bradley 1771-IGD is a 16-point TTL input module designed for integration into PLC-5 controller systems. This module provides digital signal acquisition from TTL-compatible devices, with selectable positive or negative logic to accommodate various system architectures without requiring external inverter circuits. Input filtering and fused protection safeguard the module and power supply from voltage transients and accidental overvoltage conditions.
Key Features
- 16 input points: Each accepts 5V DC TTL-compatible signals with ON: 2.0–5.25V DC and OFF: −0.2 to +0.8V DC (positive logic)
- Selectable logic levels: Jumper-configurable positive or negative logic; eliminates need for external inverters
- Input filtering: Integral filtering limits effects of contact bounce and radiated electrical noise
- Fused protection: 0.5A 250V fuse protects against overvoltage (>6.0V DC), reverse DC, or AC voltage application
- LED status indicators: 18 front-panel LEDs: 1 green ACTIVE indicator and 16 red input status LEDs (labeled 00–17 octal)
- Fast signal response: Input signal delay less than 1 millisecond for real-time control applications
Technical Specifications
- Input Voltage (Positive Logic): ON: 2.0–5.25V DC; OFF: −0.2 to +0.8V DC
- Input Voltage (Negative Logic): ON: −0.2 to +0.8V DC; OFF: 2.0–5.25V DC
- Input Current (per point): Max 7mA source, 0.8mA sink
- Backplane Current: 50mA @ 5V DC
- Total Module Current: 380mA @ 5V DC (including external signal current)
- Power Dissipation: 0.4W min, 2.7W max
- Signal Delay: <1 millisecond
- Isolation Voltage: 1500V AC RMS for 1 second
- Operating Temperature: 32 to 131°F (0–60°C)
- Fuse Rating: 0.5A at 250V (Littelfuse 312.250 or equivalent)
- Input Configuration: 16-point TTL, 5V DC nominal
Typical Applications
- PLC-5 controller systems requiring TTL digital input interfacing
- Legacy automation and legacy control systems integration
- Data acquisition from TTL output devices (sensors, switches, logic circuits)
- Real-time monitoring and discrete signal processing in industrial environments
- Systems requiring positive or negative logic signal interpretation
Compatibility & Replacements
The Allen-Bradley 1771-IGD is compatible with Series A and B PLC-5 universal I/O chassis including: 1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, 1771-A4B, 1771-AM1, and 1771-AM2. The module requires a 1771-WH wiring arm (or 1717-WH equivalent) for field signal termination. When used in two-slot addressing mode, the 16-point input module must be inserted in an even-numbered slot (left-hand side of module group). The similar 1771-IG variant exists as an 8-point TTL input module without fuse protection; the 1771-IGD offers extended point count and overvoltage safeguarding. No direct plug-compatible replacements exist; alternative suppliers may offer functionally equivalent TTL input modules from competitors such as Siemens or Omron, though slot and power characteristics may differ.
