Application Scenarios

A bottling plant’s depalletiser was plagued by intermittent solenoid failures that were difficult to diagnose. The outputs were distributed across a mix of modules, and when a solenoid shorted, the maintenance team could not tell from the control room whether the problem was the output card, the wiring, or the valve. During a planned rebuild, the electricians consolidated the 24V DC solenoid bank onto a 1756-OB8​ in the main 1756 chassis. Each of the eight channels now drives a dedicated solenoid circuit, and the module’s per-point diagnostics made a failed or shorted load visible at the point level. Troubleshooting that once took an electrician an hour now takes a few seconds at the HMI.That is the real value of the module. A DC output card is not glamorous, but it is the boundary between the control system and the physical machine. When a valve, contactor coil, indicator, or interlock stops responding, the 1756-OB8​ is the component that has to be checked first — and the one that has to be replaced fastest when it is the cause.

Parameters

Note: the 1756-OB8 has one common for all eight outputs, so the group shares a return path. It does not have wire-off detection. The 2 A per-point rating assumes the total module load stays within 16 A; size the field wiring and protection accordingly.

Technical Principles and Innovative Values

Innovation Point 1 — Eight Independently Switched 24V DC Outputs in One Slot.​ The 1756-OB8​ gives the control program eight discrete on/off channels, each rated at 2 A, through a single chassis slot. For solenoid valves, contactor coils, stack lights, and alarm horns, that density is a clean fit — one module per machine function without burning rack space.Innovation Point 2 — Full Backplane Integration.​ Output state, module health, and fault information travel over the 1756 backplane rather than through hardwired feedback contacts. The controller sees the module as a native I/O device, so diagnostics appear in the program and on the HMI without additional wiring or a separate monitoring device.Innovation Point 3 — Sinking Output Configuration.​ The module switches the low side of the load, which suits the 24V DC sinking wiring convention commonly used in machinery and process installations. Pairing it correctly with the field-device sourcing convention avoids the familiar mistake of ordering a sourcing output for a sinking application, or vice versa.Innovation Point 4 — 16 A Module Capacity with a Single Common.​ The 8-channel, 2 A per-point design yields a 16 A total module rating. The single common for all eight outputs simplifies the return wiring but also means the group return and protection must be calculated against the full 16 A, not per channel in isolation.Innovation Point 5 — Built for the Cabinet Environment.​ With a 0–60 °C operating range, 5–95% non-condensing humidity tolerance, 5 g vibration rating, and 30 g operational shock rating, the 1756-OB8​ is specified for the vibration, shock, and temperature conditions found in machine cabinets on production floors.Innovation Point 6 — Series-A Hardware Requires a Separate Terminal Block.​ The Series A 1756-OB8​ does not ship with an integrated terminal block. A removable terminal block (RTB) — such as the 1756-TBCH or 1756-TBS6H — must be ordered separately. This matters most during replacement: the existing RTB can be transferred to the new module, preserving wiring, but only if the series and terminal-block type match.