Allen-Bradley 1756-OB16I ControlLogix 16 Point Digital Output Module

The Allen-Bradley 1756-OB16I is a ControlLogix digital output module that provides 16 individually isolated sourcing DC outputs for interfacing field devices with a ControlLogix controller. Designed for applications requiring channel-to-channel isolation, the module supports independent output operation, configurable fault behavior, and scheduled output synchronization within the ControlLogix architecture.

Technical Specifications

Isolated Output Architecture

Each of the 16 output channels is individually isolated, allowing field circuits to operate independently while reducing the possibility of fault propagation between channels. This design is particularly useful when outputs are connected to loads powered from different field circuits or distributed control panels.

The module supports a 10-30 VDC output range and is intended for controlling DC devices such as relays, solenoids, contactors, annunciators, and other field-operated equipment.

Output Performance

Each output channel can deliver up to 2 A at ambient temperatures up to 30 deg C. As operating temperature increases, the permissible current is linearly derated to 1 A per channel at 60 deg C.

At the module level, total output current is limited to 8 A at 30 deg C and 4 A at 60 deg C. Both per-channel and aggregate current limits should be evaluated during system design and load distribution.

Fault Response and Output Behavior

The module supports configurable fault handling on a per-point basis. When a fault condition occurs, each channel can be configured to:

• Hold Last State

• Force ON

• Force OFF

The same configurable behavior is available when the controller enters Program Mode. The default setting for both conditions is OFF.

Output switching performance is suited for discrete control applications, with maximum response times of 1 ms from OFF to ON and 2 ms from ON to OFF.

Wiring and Installation

The 1756-OB16I installs directly into a ControlLogix chassis and uses either a 1756-TBCH or 1756-TBS6H 36-position removable terminal block. Supported field wiring sizes range from #22 AWG to #14 AWG stranded conductors.

Backplane keying is software configurable, while terminal block keying is mechanically user-defined, helping reduce wiring and module replacement errors.

Protection and Isolation Considerations

The module does not include reverse-polarity protection. Incorrect field wiring may permanently damage output circuits, making polarity verification important during installation and maintenance.

The module is also not internally fused. External protection methods may be required depending on the application. Documentation notes that certain fused interface modules may affect product certifications and should be evaluated according to system requirements.

Electromagnetic Compatibility

The module is tested to a range of industrial EMC standards, including:

• CISPR 11 Group 1, Class A emissions

• IEC 61000-4-2 ESD immunity up to 6 kV contact and 8 kV air discharge

• IEC 61000-4-3 radiated RF immunity up to 10 V/m

• IEC 61000-4-4 EFT immunity up to ±4 kV

• IEC 61000-4-5 surge immunity up to ±2 kV common mode

• IEC 61000-4-6 conducted RF immunity up to 10 Vrms

These characteristics support installation in industrial automation environments where electrical noise and transient conditions are present.

Frequently Asked Questions

Q: How many outputs does the 1756-OB16I provide?

A: The module provides 16 individually isolated digital output channels, allowing each field circuit to operate independently.

Q: What is the maximum output current per channel?

A: Each channel can supply up to 2 A at 30 deg C. The rating is linearly derated to 1 A per channel at 60 deg C.

Q: Does the 1756-OB16I include reverse-polarity protection?

A: No. The module does not provide reverse-polarity protection, and incorrect wiring may damage the outputs.

Q: Can fault behavior be configured for individual outputs?

A: Yes. Each point can be configured to hold its last state, turn ON, or turn OFF during fault conditions or when the controller enters Program Mode.