What Is the 1756-OF8H?
The Allen-Bradley 1756-OF8H is an analog output module from the ControlLogix platform. It delivers eight voltage or current output channels plus one HART modem. Each channel handles 0-20 mA or 4-20 mA current signals and +/-10 VDC voltage signals. The module fits a single slot in any 1756 ControlLogix chassis and works as local or remote I/O.
If you run oil, gas, or process automation, you know analog output accuracy drives loop performance. The 1756-OF8H gives you 15-16 bit resolution across all ranges. That means tight control of valves, positioners, and transmitters. And because it carries HART capability, you can configure smart field devices over the same wiring.
Key Specifications That Matter
| Parameter | Value |
|---|---|
| Output Channels | 8 differential |
| Output Signal | Current: 0-20 mA; 4-20 mA. Voltage: +/-10 VDC |
| Resolution | 15-16 bits |
| Accuracy | Voltage: 0.1% of range. Current: 0.5% of range |
| Isolation Voltage | 50 V continuous |
| Overvoltage Protection | +/- 24 VDC |
| Backplane Current | 230 mA @ 5.1 VDC and 230 mA @ 24 VDC |
| Data Format | Integer mode (left justified, 2’s complement) IEEE 32-bit floating point |
| Removable Terminal Block | 1756-TBNH, 1756-TBSH |
| Enclosure | Open |
Accuracy of 0.1% on voltage and 0.5% on current keeps your loops stable. The 50 V continuous isolation separates outputs from the backplane. Note that channels are not individually isolated. Open circuit detection works on current output only, and you must set the output below 0.1 mA for it to trigger.
Where the 1756-OF8H Fits
This module suits continuous and batch processes. In oil and gas, it drives valve positioners and reports back through HART. In water treatment, it controls chemical dosing pumps with 4-20 mA signals. In power generation, it manages actuator commands where +/-10 VDC voltage output is required.
The HART modem is the standout feature. It lets you read transmitter diagnostics and change device parameters without extra wiring. That saves commissioning time and reduces loop downtime.
Installation and Wiring Notes
The 1756-OF8H installs in one slot of a 1756 ControlLogix chassis. Signal wires terminate on a removable terminal block. You can use the 1756-TBNH or 1756-TBSH. The 1756-TBNH accepts 0.33-2.1 mm2 (22-14 AWG) for single-wire connections and 0.33-1.3 mm2 (22-16 AWG) for double-wire connections. The 1756-TBSH supports single-wire connections only at 0.33-1.3 mm2 (22-16 AWG).
Use user-defined mechanical RTB keying to prevent wrong terminal block insertion. Module isolation is between output channels and the backplane only. Plan your grounding accordingly.
Compatibility and Integration
The 1756-OF8H works within the Allen-Bradley ControlLogix platform. It communicates over the backplane to the controller. For HART communication, the module provides one modem shared across channels. When integrating into a plant network, you may need an external gateway or connection module for fieldbus protocols. Confirm cable and gateway requirements with your supplier before commissioning.
Buyer’s Checklist
Before you order, verify these points:
- Confirm your chassis has an open slot and adequate backplane power.
- Check whether your application needs current or voltage output on each channel.
- Decide if you need HART capability for smart device configuration.
- Select the correct terminal block: 1756-TBNH or 1756-TBSH.
- Verify the operating temperature range suits your panel environment.
Please verify current lifecycle status and availability with Oil AutoTech before ordering. Oil AutoTech provides fast-dispatch spares for oil, gas, and industrial automation. Contact Oil AutoTech today for pricing and availability.
