Omron NX-OD4121 — NX Output Unit, 8-Point NPN, 24 VDC
SKU: NX-OD4121USD 52.00
NX-series 8-point NPN transistor output unit, 24 VDC 0.5 A per point / 4 A per unit, screwless push-in connector, 12 mm wide. Sync or Free-Run I/O refresh selectable. Standard speed (0.5 ms / 1.0 ms). For NX-ECC201/202/203 EtherCAT coupler.
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Product Overview
The NX-OD4121 is the 8-point NPN (sinking) transistor output unit for Omron's NX-series EtherCAT slice I/O system. The 8 outputs are arranged in one 8-bit I/O word with one shared common, each capable of switching up to 0.5 A at 24 VDC (4 A per unit total). The screwless push-in connector on the bottom accepts 0.2 to 1.5 mm² conductors with ferrules — fast wiring without screws, no re-torquing required after thermal cycling. The 12 mm module width is one of the slimmest in the NX output family, allowing 16 NX-OD4121 units on a 250 mm EtherCAT slice — twice the density of the 24 mm NX-OD5256 (16-point PNP).
Where the NX-OD4121 fits in the NX output family
The NX-OD4xxx output family splits along four axes: point count (4 / 8 / 16 / 32), output polarity (NPN sinking vs PNP sourcing), connector type (screwless push-in vs MIL connector vs high-density), and speed (standard vs high-speed). The NX-OD4121 (this SKU) sits at the 8-point / NPN / screwless-push-in / standard-speed intersection. For higher-density PNP outputs, pick the NX-OD5256 (16-point PNP, screwless push-in, 24 mm wide) — the PNP sibling of this SKU. For 4-point high-speed pulse output (for stepper drive control), pick the NX-OD3257 (4-point NPN, 300 ns minimum pulse width) or NX-OD3268 (4-point NPN, 2 A per point high-current).
Synchronous vs Free-Run I/O refresh
The NX-OD4121 supports two I/O refresh modes selectable in Sysmac Studio under the EtherCAT slave configuration: (1) Synchronous I/O refreshing — the outputs are applied at the same point in each EtherCAT cycle, in lock-step with the EtherCAT distributed clock (DC). This is the default mode and gives deterministic output timing — every output transition is reproducible to within the EtherCAT cycle time (typically 250 µs to 2 ms, set by the EtherCAT master).
Wiring, screwless push-in connector, and NPN sinking output
The screwless push-in connector accepts 0.2 to 1.5 mm² conductors (AWG 24 to 16) with ferrules (Phoenix Contact AI 0.5-10 WH or equivalent) or solid conductors. Insert a flat-blade screwdriver (2.5 mm wide) into the orange rectangular slot above the terminal, push to open the cage clamp, insert the stripped conductor (8 mm strip length), and release — the conductor is held by spring tension at ~5 N contact force. The NPN output sinks current to 0 V when the output is ON — connect the load between +V (24 VDC supply) and the output terminal.
Key Features
- 8-point NPN transistor output unit for NX EtherCAT slice I/O
- 24 VDC rated output voltage
- 0.5 A per point / 4 A per unit maximum load current
- Screwless push-in connector — 0.2 to 1.5 mm² with ferrule
- 12 mm wide
- Standard speed: 0.5 ms ON / 1.0 ms OFF response time
- Synchronous I/O refreshing or Free-Run refreshing
- EtherCAT slave with Distributed Clock synchronization support
- SKU: NX-OD4121
- Series: NX-series NX-OD4 Digital Output Units
- Voltage: 12 TO 24 VDC
- I/O: 8 I/O
Best-Fit Applications
- Solenoid-valve actuation on a packaging machine — 8 × NX-OD4121 outputs driving 24 VDC pneumatic valve solenoids, 0.5 A per.
- LED indicator stack-light control on a machine operator console — 4 × NX-OD4121 outputs driving red / amber / green.
- Relay-driver outputs on a control panel — 8 × NX-OD4121 outputs driving G2R-2-SND or G6B-4BND relays for higher-current AC switching
- Stepper-motor pulse-direction control on a small pick-and-place — 4 × NX-OD4121 outputs providing PULSE/DIR/ENABLE for 2 stepper axes, 4 axes.
Buying Checklist
- Pick NX-OD4121 for 8-point NPN 24 VDC 0.5 A output with screwless push-in connector — the slim 12 mm NX slice
- Pick NX-OD4256 for 8-point PNP sourcing — pick if your PLC's I/O is PNP sourcing
- Pick NX-OD5256 for 16-point PNP sourcing at 24 mm width — pick if you need higher density in PNP sourcing
- Pick NX-OD3257 for 4-point NPN high-speed pulse output — for stepper pulse control
- Pick NX-OD3268 for 4-point NPN 2 A high-current output — for direct solenoid valve drive without intermediate relay
- Pick NX-OD6121-5 for 32-point NPN with MIL connector — pick for highest-density NPN applications
Technical Specifications
| Model | NX-OD4121 |
|---|---|
| Series | NX-series NX-OD4 Digital Output Units |
| Type | 8-point NPN (sinking) transistor output, screwless push-in connector |
| Number of Output Points | 8 points (1 byte, 1 common) |
| Internal I/O Common | NPN (sinking) |
| Rated Output Voltage | 12 to 24 VDC |
| Operating Load Voltage Range | 10.2 to 28.8 VDC |
| Maximum Load Current | 0.5 A per point / 4 A per unit |
| Leakage Current at OFF State | 0.1 mA max |
| Residual Voltage at ON State | 1.5 V max (at 0.5 A load) |
| Output Type | Open collector transistor (NPN sinking) |
| Wire Range | 0.2 to 1.5 mm² (AWG 24 to 16) with ferrule |
| 5 VDC Backplane Current | 80 mA max |
| 24 VDC I/O Current | 4 A max per unit (sum of all 8 outputs) |
| Operating Temperature | 0 to +55 °C |
Resources & Downloads
FAQ for NX-OD4121
What's the difference between NX-OD4121 and NX-OD4256?
The NX-OD4121 (this SKU) is the 8-point NPN sinking version and the NX-OD4256 is the 8-point PNP sourcing version. Both are 12 mm wide, both have screwless push-in connectors, both are rated 0.5 A per point / 4 A per unit, both have 0.5 ms / 1.0 ms response.
What EtherCAT coupler does the NX-OD4121 require?
The NX-OD4121 requires an NX-ECC-series EtherCAT coupler on the left side of the NX slice. Three options are available: (1) NX-ECC201 (4 A I/O, 250 µs minimum cycle time) — standard pick for general-purpose applications where the slice total current is below 4 A.
Can the NX-OD4121 drive 24 VDC relay coils directly?
Yes — the NX-OD4121's 0.5 A per point output can drive any standard 24 VDC relay coil (G2R-2-SND at ~30 mA, G6B-4BND at ~25 mA per coil, LY2N-J at ~36 mA) with plenty of headroom. Wire the relay coil between the +V terminal and the output terminal (NPN sinking — output sources ground when ON).
What happens if an NX-OD4121 output shorts out?
The NX-OD4121 has per-channel overload protection with auto-recovery. When an output detects a short circuit (e.g. load shorted to ground, load current exceeds 0.5 A continuous, load wiring fault), the affected output shuts off within 100 µs, the output's yellow status LED turns OFF, and an error flag is set in the EtherCAT slave's diagnostic register (visible in Sysmac Studio's I/O map view and in the NJ/NX CPU's error log).
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