1756-OB32 — 1756 32-Point 24V DC Sourcing Transistor Output Module

The 1756-OB32 is a 32-point sourcing (PNP) 24V DC transistor output module for the 1756 chassis. Thirty-two solid-state outputs, each rated at 0.5A, in a single backplane slot. For high-density digital output applications — valve manifolds, indicator panels, actuator enable signals across a large machine — 32 points per slot keeps chassis slot count manageable and the I/O card count on the bill of materials short.

The module uses transistor outputs throughout. No relay contacts, no mechanical wear, no contact bounce. The 0.5A per-point rating covers the full range of common 24V DC field loads: standard solenoid valves, 24V coil contactors, relay coils, LED indicators, and 24V proximity sensor lamps. For loads above 0.5A per point, relay output modules or an external relay are needed — but the majority of machine I/O fits under this limit without issue.

Specifications

Parameter	Value
Part Number	1756-OB32
Platform	1756 Logix chassis
Output Points	32
Output Type	Sourcing (PNP) transistor
Output Voltage	24V DC (10–30V)
Output Current per Point	0.5 A continuous
Output Groups	2 × 16 points, separate supply commons
Max Group Current	8 A (16 outputs × 0.5A)
Short-Circuit Protection	Electronic, per group
Leakage Current (OFF state)	1 mA max
ON-State Voltage Drop	1V DC max
Backplane Current (5V)	250 mA
RTB Connector	1756-TBCH or 1756-TBS6H (36-pin)
Operating Temperature	0°C to 60°C
Standards	UL 508, CE, IEC 61131-2

High-Density Outputs in the 1756 Chassis

The 1756 chassis supports modules from 8 to 32 points per slot. The 32-point density of the OB32 maximizes the output count per slot, which matters in large-scale systems where the chassis slot count directly affects panel footprint, backplane cost, and wiring density at the terminal blocks.

A machine with 128 digital outputs needs four 1756-OB32 modules versus eight 1756-OB16 modules. Four slots versus eight, four RTBs to wire versus eight, four line items in the spare parts kit versus eight. At the system level, the density advantage adds up — especially in applications like large packaging lines, multi-station assembly cells, or process control systems where output-heavy automation is the norm.

The two groups of 16 outputs are an important structural feature. Each group has its own V+ supply terminal and its own 0V common terminal on the RTB. Both groups typically connect to the same 24V DC supply, but running them separately lets different output groups be on different supply circuits — useful when some outputs must be on a separate fused or switch-protected supply for fault isolation or when switching both groups off with one contactor isn't appropriate.

FAQ

Q: Can NPN (sinking) sensors or devices be controlled by these outputs?

Output type refers to how the output switches loads — sourcing outputs supply 24V to the load. NPN/PNP classification is a sensor/input distinction. Any 24V DC load that accepts a sourcing current can be switched by the 1756-OB32, regardless of whether the device is described as NPN or PNP in its input specification.

Q: What RTB (removable terminal block) is required?

The 1756-OB32 uses a 36-pin RTB. Compatible options are the 1756-TBCH (cage-clamp wiring) and 1756-TBS6H (screw clamp). The RTB is ordered separately from the module and is not included in the module's packaging.

Q: Does the module support hot-swap — removing and inserting under power?

Yes, in appropriately configured 1756 systems. The 1756 chassis and processor support module insertion and removal under power. The controller software handles the temporary loss of I/O data from the slot being serviced. Verify the controller's I/O configuration and the machine's interlocks allow safe module removal before executing a hot-swap in a running system.

Q: What happens to outputs when the controller faults?

Default behavior is to de-energize all outputs (go to the OFF state). This is configurable in Studio 5000 — outputs can be set to hold last state or go to a user-defined value on controller fault. For most machine safety applications, de-energizing on controller fault is the correct fail-safe default.

Q: Can the 1756-OB32 be used in a remote chassis over EtherNet/IP?

Yes. The module installs in any 1756 chassis, local or remote. In a remote chassis with a 1756-EN4TR or EN2T communication module, the OB32 outputs are addressed and controlled by the primary controller over EtherNet/IP exactly as if they were local — the addressing is transparent in the Studio 5000 I/O tree.

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