Product Overview
When a ControlLogix line needs precise analog signals for modulating valves, VFDs, or dampers, the Allen-Bradley 1756-OF4 delivers. This four-channel analog output module produces both voltage and current signals, giving you flexible control over actuators and retransmission devices. As a non-isolated module in the ControlLogix series, it installs directly into any 1756 chassis and supports Removal and Insertion Under Power (RIUP), so you can swap or add modules without shutting down the process.
Technical Specifications
| Specification | Value |
|---|---|
| Outputs | 4 voltage or current |
| Output Voltage Range | ±10 VDC |
| Output Current Range | 4…20 mA |
| Voltage Resolution | 15 bits across 10.5 V, 320 µV/bit |
| Current Resolution | 15 bits across 21 mA, 650 nA/bit |
| Backplane Current (5 V) | 150 mA |
| Backplane Current (24 V) | 120 mA |
| Power Dissipation (Max) | 4.9 W at 60 °C |
| Isolation Voltage | 50 V continuous |
| Removable Terminal Block | 1756-TBNH or 1756-TBSH |
| Module Scan Time | 12 ms floating-point, 8 ms integer |
| Module Error | 0.15% voltage, 0.3% current |
| Settling Time | <2 ms to 95% of final value |
The 15-bit resolution on both signal types means fine control over your process. Voltage resolution reaches 320 µV/bit across 10.5 V, while current resolution hits 650 nA/bit across 21 mA. The module supports IEEE 32-bit floating point or 16-bit integer data formats, and its onboard features include data alarming, scaling to engineering units, and real-time channel sampling.
A Practical Fit for Modulating Control
In oil and gas operations, the 1756-OF4 typically drives modulating control valves, variable frequency drives, dampers, and louvers. The 4-20 mA range suits long cable runs to field devices, while ±10 VDC works well for short-distance signals to recorders, indicators, and data loggers. You can also use the outputs as remote setpoints for advanced strategies like cascade and feedforward control.
Because the module supports producer/consumer communication, it can multicast fault data and status to an owner-listening controller. That makes troubleshooting faster and keeps your control loop responsive.
Installation and Integration Notes
Install the 1756-OF4 into a 1756 ControlLogix chassis after the chassis and power supply are installed and grounded. A 20-pin removable terminal block (1756-TBNH or 1756-TBSH) is required for field wiring. The module supports RIUP, so you can remove or insert it under power without disrupting other modules.
When integrating into a ControlLogix network, remember that fieldbus wiring may require an external gateway or connection module. Confirm cables and gateways with your supplier before commissioning.
Maintenance and Reliability
Plan for calibration every 12 months. Calibration accuracy should be better than 0.05% of range from 4 to 21 mA and -10.4 to 10.4 V. The module includes short-circuit protection limited to 21 mA or less and open-circuit detection for current outputs (set output above 0.1 mA). Overvoltage protection is rated at 24 VDC. With a maximum power dissipation of 3.25 W (4-channel current) and thermal dissipation of 10.91 BTU/hr, the module runs efficiently in typical panel environments.
Selection Checklist
Before ordering, verify your chassis has available slots and that your power supply meets the backplane current draw of 150 mA at 5 V and 120 mA at 24 V. Confirm you have the correct removable terminal block. If you need fast dispatch, worldwide, Oil AutoTech stocks ControlLogix spares and can help with technical selection. Contact Oil AutoTech today for pricing and availability.
Frequently Asked Questions
Q: What is the difference between the 1756-OF4 and a 1756-OF8?
A: The 1756-OF4 provides four output channels; the 1756-OF8 provides eight. Choose based on your loop count and chassis space.
Q: Can I use the 1756-OF4 for both voltage and current outputs simultaneously?
A: Yes. Each channel can be configured for either voltage (±10 VDC) or current (4-20 mA) output.
Q: What terminal block do I need?
A: The module requires a 20-pin removable terminal block: 1756-TBNH or 1756-TBSH.
Q: How often should I calibrate the module?
A: Calibrate every 12 months for best accuracy. Target better than 0.05% of range.
Q: Does the module support hot-swap?
A: Yes, it supports Removal and Insertion Under Power (RIUP) when installed in a compatible ControlLogix chassis.
