Product Overview
When your process demands precise analog output control with HART communication, the Allen-Bradley 1756-OF8H delivers. This ControlLogix module provides eight differential voltage or current output channels with a single Highway Addressable Remote Transducer (HART) modem. It fits seamlessly into any 1756 chassis, occupying a single slot, and operates as a local or remote I/O module.
Each channel on the 1756-OF8H is configurable for 0-20 mA or 4-20 mA current loops, as well as ±10 VDC voltage outputs. The module's 15-16 bit resolution ensures fine-grained control across all signal ranges. With its R-Ladder DAC conversion method, you get monotonicity with no missing codes, guaranteeing reliable performance in demanding applications.
Technical Specifications
| Specification |
Value |
| Part Number |
1756-OF8H |
| Brand |
Allen-Bradley |
| Series |
ControlLogix |
| Module Type |
Analog Output Module with HART capability |
| Number of Outputs |
8 Differential |
| Output Signal |
Current: 0-20 mA; 4-20 mA; Voltage: ±10 VDC |
| Resolution |
15-16 Bits |
| Isolation Voltage |
50 Volts Continuous |
| Overvoltage Protection |
±24 VDC |
| Accuracy |
Voltage: 0.1% of range; Current: 0.5% of range |
| Data Format |
Integer mode (left justified, 2's complement); IEEE 32-bit floating point |
| Output Conversion Method |
R-Ladder DAC, monotonicity with no missing codes |
| Current Draw |
230 mA @ 5.1 VDC and 230 mA @ 24 VDC |
| Removable Terminal Blocks |
1756-TBNH, 1756-TBSH, 1756-TBCH |
Key Features & Benefits
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HART Communication: Integrated HART modem allows digital process data overlay on analog signals, enhancing diagnostics and maintenance.
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Flexible Outputs: Each channel supports both current and voltage signals, reducing inventory and simplifying system design.
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High Resolution: 15-16 bit resolution provides precise control for critical loops.
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Open Circuit Detection: For current outputs set below 0.1 mA, the module detects open circuits, improving fault visibility.
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Field-Replaceable Terminal Blocks: Supports 1756-TBNH, 1756-TBSH, and 1756-TBCH for easy wiring and maintenance.
Industry Applications
In process industries such as oil and gas, chemical, and water treatment, the Allen-Bradley 1756-OF8H excels. Use it to drive valve positioners, variable frequency drives, or chart recorders with 4-20 mA loops. The HART capability lets you retrieve device diagnostics from smart transmitters, reducing downtime. In discrete manufacturing, the module handles ±10 VDC signals for servo drives and analog actuators. Its 50V continuous isolation and ±24V overvoltage protection safeguard the module in harsh electrical environments.
Installation & Setup
Install the 1756-OF8H into any ControlLogix chassis slot. Ensure the chassis power supply can handle the module's current draw of 230 mA @ 5.1 VDC and 230 mA @ 24 VDC. Use the removable terminal block (RTB) that suits your wiring: 1756-TBNH for single or double wires (0.33-2.1 mm² / 22-14 AWG single, 0.33-1.3 mm² / 22-16 AWG double), or 1756-TBSH for single wire only (0.33-1.3 mm² / 22-16 AWG). Configure each channel via the ControlLogix programming software, selecting current or voltage mode and scaling as needed. For HART, connect the modem to the appropriate terminals.
Maintenance & Reliability
Regularly inspect the module for dust buildup and ensure proper airflow. Check that terminal block screws are tight to avoid loose connections. The module's open-style enclosure requires a clean environment; if installed in a dusty area, use a filtered cabinet. Calibration accuracy is 0.1% (voltage) and 0.5% (current) without HART, and Rockwell recommends a 12-month calibration interval. With proper care, the 1756-OF8H provides years of reliable service, minimizing total cost of ownership.
Compatibility & Integration
The 1756-OF8H is part of the ControlLogix family and works with any 1756 chassis and compatible ControlLogix controllers. It supports both local and remote I/O configurations. The module communicates over the backplane, so no external network configuration is needed for basic operation. For HART, the module integrates with Rockwell's FactoryTalk software for device management.
Buying Guide
Before purchasing, verify that the 1756-OF8H matches your required output count and signal types. Confirm your chassis slot availability and power budget. Choose the correct removable terminal block (1756-TBNH, 1756-TBSH, or 1756-TBCH) for your wiring needs. PLC Source PRO offers genuine Allen-Bradley products with fast shipping and competitive pricing. Trust PLC Source PRO as your reliable supplier for industrial automation spares.