Overview
The Allen-Bradley 1791-N4C2 is a discontinued analog Block I/O module designed for legacy programmable controllers and distributed I/O networks. This Block I/O module features 6 analog I/O points (4 analog inputs and 2 current outputs), and features an input impedance of 10 Megohms and an absolute accuracy of 0.1% at 25 degrees Celsius. The Allen-Bradley 1791-N4C2 module also contains a 24 Volts DC current-limited voltage source for accommodating the loop-powered current transducer inputs. This proven analog block delivers precise signal conditioning for temperature, pressure, and instrumentation applications across manufacturing, utilities, and process industries.
Key Features
- 6 analog I/O points (4 analog inputs and 2 current outputs)
- Each of the four inputs can be configured for voltage or current analog signals
- Two 0 to 20 milliamps rated current outputs
- Absolute accuracy rating of 0.1% at 25 degrees Celsius and a linearity rating of 0.05%
- Input impedance of 10 Megohms and output impedance at less than 1 ohm
- Update rate per channel of 108 milliseconds
- Connects to the controller via a standard Remote I/O (RIO) network link
Technical Specifications
| Power Supply Voltage | 120 Volts AC |
| I/O Configuration | 4 Analog Inputs (voltage/current configurable) + 2 Current Outputs |
| Input Signal Range | Voltage: single-ended or differential; Current inputs accommodate loop-powered transducers |
| Output Signal Range | 0–20 milliamps DC |
| Auxiliary Power | 24 VDC current-limited (100 mA) for loop-powered transmitters |
| Accuracy | ±0.1% at 25°C |
| Linearity | ±0.05% at 25°C |
| Input Impedance | 10 Megohms |
| Output Impedance | <1 Ohm |
| Channel Update Rate | 108 milliseconds per channel |
| Common-Mode Rejection | −75 dB |
| Dimensions | 6.95 H × 2.71 W × 3.85 D inches (176.5 H × 68.8 W × 98 D mm) |
| Weight | 1.20 lbs (0.54 kg) |
| Operating Temperature | Air gap below module must not exceed 60°C (140°F) |
| Communication Protocol | Remote I/O (RIO); Block Transfer; Discrete Transfer |
| Series | Block I/O 1791 (discontinued) |
| Condition | Used surplus |
Typical Applications
- Analog sensor signal conditioning for temperature and pressure measurement
- Industrial process control with loop-powered 2-wire transmitters
- Distributed I/O networks using legacy PLC platforms
- Equipment retrofits requiring exact model replacement of existing analog blocks
- Manufacturing automation requiring precise 0.1% accuracy analog conversion
- Batch processing and recipe-driven control systems
Compatibility & Replacements
Compatible With
- PLC-2, PLC-3, and the PLC-5/250 programmable controllers
- SLC family controllers through a discrete transfer process
- Standard Remote I/O (RIO) network infrastructure
- Block Transfer and Discrete Transfer communication protocols
Replaces / Drop-In Replacement For
- Alternate Part Numbers: 1791-N4C2/A
- Direct replacement for 1791-N4C2 Series A units
- Verify compatibility with your legacy controller and I/O network before ordering
Works With
- Allen-Bradley programming platforms supporting legacy controllers (RSView, RSLogix, PLC-5 software)
- Remote I/O (RIO) distributed I/O communication networks
- Block Transfer and Discrete Transfer instruction sets in PLC-2, PLC-3, PLC-5, and SLC 500
- Loop-powered 2-wire analog transmitters via 24 VDC auxiliary supply
- Single-ended and differential voltage analog sensors
