1794-OV32 — FLEX I/O 32-Point 24V DC Sinking Transistor Output Module

The 1794-OV32 packs 32 sinking (NPN) 24V DC transistor outputs into one FLEX I/O module slot. At 0.5A per point, it's built for high-density switching of 24V DC loads — solenoid valves, indicator lamps, relay coils, and actuator enable signals — in distributed control nodes where output count is high and panel space is constrained.

Sinking outputs pull the load return to 0V when active; the load is wired between the positive supply and the output terminal. This NPN convention is standard in a wide range of industrial equipment, particularly in process and Asian-manufactured machinery. Running a full 32-output module in this configuration means a busy machine — 32 simultaneously switchable loads from one FLEX I/O slot, controlled from whichever network adapter heads the node.

Specifications

Parameter	Value
Part Number	1794-OV32
Platform	FLEX I/O (1794)
Output Points	32
Output Type	Sinking (NPN) transistor
Output Voltage	24V DC (10–30V)
Output Current per Point	0.5 A continuous
Output Groups	2 × 16 points, separate commons
Short-Circuit Protection	Electronic, per group
Leakage Current (OFF state)	1 mA max
ON-State Voltage Drop	1V DC max
Backplane Current (5V)	350 mA
Field Power	24V DC (user-supplied via terminal base)
Operating Temperature	0°C to 55°C
Standards	UL 508, CE, IEC 61131-2

High-Density Outputs in Distributed Architecture

FLEX I/O nodes are typically placed close to the field devices they serve — inside a local junction box, at a machine station, or in a remote enclosure near a process unit. At those locations, panel space is usually at a premium. The 1794-OV32 consolidates 32 output points into the standard FLEX I/O module width, which is substantially more compact than two separate 16-point modules and eliminates one terminal base assembly from the node.

The outputs are split into two groups of 16, each with an independent field power common terminal on the terminal base. Both groups typically connect to the same 24V DC supply, but separating them allows different supply circuits to feed each group — useful when half the outputs control safety-adjacent devices that need supply segregation from standard automation outputs.

Short-circuit protection operates at the group level, not per-point. A short circuit on any output in a group shuts down all 16 outputs in that group until the fault is cleared. Applications that need per-point fault isolation — where one bad output shouldn't kill 15 others — should consider the protected variant (1794-OB32P with sourcing outputs) instead.

Output Fault Behavior on Controller Fault

When the controller loses communication with the FLEX I/O adapter (cable fault, adapter power loss, controller fault), the outputs can be configured to hold their last state, go to a programmed state, or de-energize — depending on the adapter type and output module configuration. For most safety-related applications, de-energizing outputs on communication loss is the correct fail-safe behavior. Verify this is configured correctly before commissioning, especially for outputs controlling actuators or valves that must reach a defined safe position on system fault.

FAQ

Q: Can sinking and sourcing output modules be mixed on the same FLEX I/O node?

Yes. Different output modules on the same node can have different output types. Each module handles its own field wiring independently; they share only the backplane communication bus.

Q: What's the difference between the 1794-OV32 and the 1794-OB32P?

The OV32 is sinking (NPN) with group-level short-circuit protection. The OB32P is sourcing (PNP) with per-point electronic protection and per-point fault reporting. Choose OV32 for NPN load wiring convention; choose OB32P where per-point fault isolation and diagnostics are needed.

Q: Do all 32 outputs update in the same controller scan?

Output data is transferred from the controller to the FLEX I/O adapter in each network scan cycle. All 32 output bits are sent as a single I/O data packet — the outputs update essentially simultaneously from the perspective of the application program.

Q: Is an external fuse required for each output group?

The module has electronic short-circuit protection per group, but external fusing on the field supply to each group is still required for branch circuit protection and code compliance. The electronic protection protects the module's transistors, not the field wiring.

Q: The leakage current is 1 mA — will this keep a relay or solenoid energized when the output is off?

For standard 24V DC relay coils and solenoids, 1 mA is far below the minimum holding current. The load will de-energize reliably when the output turns off. For very sensitive loads with sub-1 mA pick-up currents, verify against the load's datasheet.

1794-OV32 Analog Output Module New In Box 1794OV32