Allen-Bradley 1756-OB16D ControlLogix Diagnostic Output Module

1756-OB16D ControlLogix Diagnostic DC Output Module

Product Introduction

The 1756-OB16D module from Allen-Bradley delivers intelligent DC output control with comprehensive diagnostic capabilities for your ControlLogix system. This module offers 16 sourcing outputs arranged in two isolated groups of 8 points each. It operates within a voltage range of 19.2-30V DC with a nominal 24V DC source configuration. What sets the 1756-OB16D apart is its advanced diagnostic feature set, including per-point electronic fusing, no-load detection, output verification, and pulse testing. These capabilities provide you with unprecedented visibility into the health of your field devices and wiring, making troubleshooting faster and more effective.

Technical Specifications

The Allen-Bradley 1756-OB16D operates with a nominal 24V DC source voltage and accepts a range from 19.2V up to 30V DC. This module draws 250 mA from the 5V backplane and 140 mA from the 24V backplane. Its maximum power dissipation reaches 3.3W at 60°C. For output delay, the off-to-on transition takes a nominal 55 µs with a maximum of 1 ms. Meanwhile, the on-to-off transition has a nominal 630 µs delay with a maximum of 5 ms. The module provides a minimum load current of 3 mA per point and maintains off-state leakage current below 1 mA per point. Additionally, the maximum on-state voltage drop measures only 1.2V DC at 2A, ensuring efficient power delivery to your loads. The isolation voltage between groups and from user to system withstands 2546V for 1 second, with a maximum continuous voltage rating of 250V AC.

Diagnostic Features in Detail

The 1756-OB16D truly excels with its comprehensive diagnostic capabilities. Each output point features electronic fusing, protecting individual channels from overcurrent conditions. The module supports no-load detection for off-state conditions, alerting you when a connected device loses power or disconnects. Furthermore, output verification confirms that the field device actually turned on when commanded, providing critical feedback for safety and quality applications. The pulse test function allows you to verify output circuit integrity with a user-configurable maximum pulse width. You can also configure fault states and program mode states independently for each output point. Choose from 'Off' (default), 'On', or 'Hold Last State' to define how the 1756-OB16D behaves during processor faults or program mode transitions. Additionally, the diagnostic latching feature captures fault events and timestamps them for later analysis.

Output Current and Derating

The Allen-Bradley 1756-OB16D delivers robust output current capacity. Per-point, it supports up to 2A maximum at 30°C, derating linearly to 1A at 60°C. For the entire module, the total current capacity reaches 8A at 30°C and 4A at 60°C. This derating curve ensures reliable operation across the full temperature range. The module also handles surge currents of 4A for 10 ms per point, repeatable every second, accommodating inrush loads from solenoids, contactors, and other inductive devices. The short-trip diagnostic function activates at 8A for a minimum of 180 ms and at 10A for a minimum of 120 ms, providing robust protection against short-circuit conditions.

Installation and Compatibility

Installing the 1756-OB16D requires a standard slot in any 1756 ControlLogix chassis. Before installation, ensure you have properly installed and grounded the chassis and power supply. For field wiring, you need a 36-position Removable Terminal Block (RTB). The 1756-OB16D works exclusively with the 1756-TBCH or 1756-TBS6H housings. These RTB models support all diagnostic functions, including no-load detection and output verification. The module also supports removal and insertion under power (RIUP), simplifying maintenance without system shutdown. Its operating temperature ranges from 0°C to 60°C, with storage temperatures from -40°C to 85°C. The module withstands 30g shock and 5g vibration, making it suitable for demanding industrial environments.

Application Scenarios

The Allen-Bradley 1756-OB16D fits a wide range of control applications where output reliability and diagnostics are essential. Common uses include actuator control, valve positioning, solenoid activation, indicator lamp operation, and relay driving. The diagnostic features make it particularly valuable in critical processes where unplanned downtime carries significant cost. For example, the no-load detection alerts you to broken wires or failed field devices before they cause production stoppages. Similarly, output verification confirms that critical safety devices respond correctly to commands. The 1756-OB16D integrates seamlessly into any ControlLogix configuration, from standalone controllers to large distributed control systems (DCS) and the PlantPAx platform.

Packaging and Shipping

Each 1756-OB16D module ships in anti-static protective packaging to prevent electrostatic discharge damage. We thoroughly inspect every unit before shipment to guarantee full functionality. The package contains the module only. Please remember that the RTB housing is not included and requires a separate order. We ship worldwide using FedEx, UPS, or DHL, processing all orders within 24 hours. You will receive a tracking number upon dispatch to monitor your delivery status.

Frequently Asked Questions

Q: What diagnostic features does the 1756-OB16D offer compared to a standard output module?
A: The 1756-OB16D provides per-point electronic fusing, no-load detection for off-state wiring checks, output verification to confirm field device activation, pulse testing for circuit integrity, and configurable fault/program states. Standard output modules lack these advanced diagnostic capabilities.

Q: Which terminal blocks are compatible with the 1756-OB16D?
A: The Allen-Bradley 1756-OB16D requires a 36-position RTB and works with either the 1756-TBCH (screw-type) or the 1756-TBS6H (spring-clamp) housings. These specific RTB models support all diagnostic functions of the module.

Q: What is the maximum current I can draw from each output point?
A: Each output point on the 1756-OB16D supports up to 2A at 30°C. This derates linearly to 1A at 60°C. The total module current capacity is 8A at 30°C and 4A at 60°C. Always consider the temperature derating when designing your system.

Q: How does the electronic fusing work on the 1756-OB16D?
A: The 1756-OB16D features per-point electronic fusing that protects each output channel from overcurrent conditions. Unlike traditional fuses, electronic fusing does not require physical replacement. The module reports the fault to the controller, allowing for software-based diagnostics and reset.

Q: Can I configure how the 1756-OB16D responds during a processor fault?
A: Yes, the Allen-Bradley 1756-OB16D allows you to configure fault states per point. You can set each output to 'Off' (default), 'On', or 'Hold Last State' when the processor enters fault mode. Similarly, you can configure program mode behavior independently for each point.