Allen-Bradley 1756-IH16I ControlLogix 16-Channel Isolated 125V DC Input Module

Technical Functionality

The 1756-IH16I is a high-voltage digital input module engineered for the ControlLogix 1756 chassis. It is designed to interface high-potential DC field signals with the PLC backplane, providing sixteen points of sensing. A critical feature of this module is its individual channel-to-channel isolation, which prevents electrical interference and ground loop issues between different field circuits. Supporting both sink and source wiring configurations, it offers maximum flexibility for electrical designers working with 125V DC control logic, commonly found in power utility and heavy industrial environments.

Core Specifications

• Manufacturer: Allen-Bradley / Rockwell Automation

• Product Line: ControlLogix

• Model Number: 1756-IH16I

• Input Density: 16 Individually Isolated Channels

• Voltage Category: 125V DC

• Operating Range: 90V to 146V DC

• Input Configuration: Sink or Source (Bi-polar)

• Isolation Rating: 250V Continuous (Basic Insulation)

• Isolation Testing: Routine tested at 1350V AC for 2 seconds

• Backplane Power Usage: 0.71 Watts

• Maximum Power Dissipation: 5 Watts @ 60 °C (140 °F)

• Heat Generation: 17.05 BTU/hr

• Required Terminal Block: 1756-TBCH (Cage clamp) or 1756-TBS6H (Spring clamp)

• Module Width: Single Slot

• Shipping Weight: 0.45 kg (Module only); 2.0 kg (Total package)

Application and Reliability

The 1756-IH16I is frequently deployed in substations and large-scale manufacturing facilities where 125V DC is the standard for protective relaying and switchgear control. The individual isolation of every channel ensures that a fault in one field circuit does not compromise the operational integrity of the remaining fifteen inputs. To streamline maintenance, the module utilizes a Removable Terminal Block (RTB), allowing technical staff to replace hardware without disturbing the complex field wiring. Onboard diagnostics and input filtering settings are configurable via Studio 5000 software to ensure signal stability in high-noise environments.

Frequently Asked Questions

What is the benefit of individual isolation in the 1756-IH16I?Unlike group-isolated modules, the 1756-IH16I allows each input to have a different voltage reference or be connected to a different DC power source. This prevents a single ground fault from tripping multiple inputs across the module.

Does this module support Change of State (COS) detection?Yes, the 1756-IH16I can be configured to trigger a system interrupt or update when an input transitions from ON to OFF or OFF to ON, ensuring high-speed response for critical events.